Friday, October 30, 2009

Light fitting specification

The following provides an example specification that can be used in a contract for the installation of the light fittings in a multi-storey office building.

All light fittings shall be designed to prevent ingress of vermin, accidental contact with any live part and to minimize the ingress of dust and dirt. Materials which may be liable to be attacked by termites or other insects shall be avoided.

All outdoor fittings shall be vandal, corrosion, rust-protected and fully weatherproof by means of carefully chosen materials, protective painting and sealing, gasketing and the application of protective compounds.

Each fitting shall be constructed and erected as to be easily accessible for inspection and maintenance.

Each fitting shall be complete with bulbs, tubes, control gears, suspension rods or chain, fixing brackets etc.

Terminals and contacts, as far as possible, shall be shielded as to afford protection from accidental contact. All terminals shall be suitable for connection with metal conduit, to meet with fire regulations.

Sample of each type of fittings must be submitted to the S.O. for approval prior to commencement of manufacture and/or installation.

All fittings, accessories and components in any items supplied shall be uniform of their type, similar parts being interchangeable.

Incandescent lamps
Tungsten filament lamps shall be of bayonet cap general service pattern, internally frosted and shall be suitable for operating on a 240/250 volts A.C. system. The ratings shall be as stated in the drawings.

Fluorescent lamps
All fluorescent tubes shall be of the standard 26mm diameter energy saving type having a color temperature of approximately 6200 degree K (daylight color) if not otherwise stated with, bi-pin lamp cap.

Unless otherwise specified, all fluorescent tubes shall be of switch-start type.

Compact fluorescent lamps
Where SL lamps are specified, they shall be the type of fluorescent lamp integrated with low pressure gas discharge ballast and starter and with Edison screw lamp cap (B22). The wattage of the lamps shall be 9, 13 or 18 as specified in the drawings.

Where PL lamps are specified, they shall be of the type with unique single-ended fluorescent lamps with two pin connection with instant start adapters. The lamp base shall be incorporated with capacitor. The lamp wattage shall be 7, 9, 11, or 13 as specified in the drawings.

Discharge lamps
Where gas discharge lamps are specified, they shall be the type with good color rendering and complete with necessary control gear such as ballasts, capacitors and igniters. The ratings of the lamps shall be as specified in the drawings.

Fluorescent lamp lighting fixtures
All fixtures must be fabricated by manufacturers registered with Director General of Electrical Department, and be approved with The National Testing Department.

The housing, base frame, cover plates and reflector of the fixtures shall be constructed of sheet steel of a thickness not less than 20 SWG.

The sheet steel body shall be designed such that it can be fixed to ceiling or the surface by suspension or on a separate detachable tray.

An adequate mains input terminal block marked “L” and “N” together with a substantial earthing terminal shall be riveted, welded or brazed to the base frame.

Retractable type spring load lamp holders fitted with lamps cap earthing contact housed in a white plastic moulding shall be suitable for direct attachment to the base frame.

All materials liable to corrosion shall be suitably protected and sheet steel surfaces shall be prepared, painted and finished white in stove or vitreous enamel.

Ballasts shall be of the switch start, vacuum/pressure impregnated in polyester resin type comply to B.S. 2818 Part1 or MS. 141: 1973. They shall be compact in design and silent in operation and of the “low loss” type with losses not exceeding 6.5 watts. One ballast shall be used to control one fluorescent tube only.

All capacitors for power factor correction shall be suitable for operating on 250 volts, single phase, 50 Hz at a temperature between -10 degree to 100 degree Centigrade and shall ensure a power factor of not less than 0.85 lagging.

Starter switch shall be of the two pin small metal canister glow type.

All internal wiring shall be heat resistant type and suitably identified by color coding and shall be neatly arranged and adequately supported.

All diffusers, unless otherwise stated, shall be made from tough translucent prismatic plastic of UV-stabilized polystyrene of not less than 2.5mm thick and free from blemishes.

All louvered diffusers, unless otherwise stated, shall be made from UV-stabilized polystyrene material with silver-metallized and parabolic 13mm x 13mm x 11mm cells.

All diffusers and louvered diffusers shall be mounted onto the steel frame which hinged onto the frame work of the fixtures and form a detachable dustproof cover.

Copyright - Light fitting specification

Electrical wiring specification

The following provides a sample specification that can be used in an electrical wiring installation contract for a multi-storey office building.


The scope of this section is to set out the requirements, methods, materials, workmanship, standards and regulations in connection with the electrical equipment and their installation works for this project. 


These specifications shall be read together with the relevant drawings, and schedule of quantities if there is any, that form part of this contract. All the works of wiring and cabling are generally as indicated and specified on these drawings.

Ducts and trenches necessary to accommodate cables and switchgears that are generally shown on the drawings will be provided by Contractor unless otherwise stated. However, it shall be the contractor’s responsibility to ensure during the progress of the work that the various ducts and trenches are constructed in the correct manner and that they are adequate for the electrical works whether such details are specifically mentioned or not.

Wiring methods

All wiring shall be of the “loop-in” system and no joint shall be accepted except at the terminations of the electrical accessories and/or equipment.

No reduction in the number of strands of cables shall be allowed at the terminals. All strands shall be effectively terminated and secured by screws, nuts and washers or other approved means of fixing.

Concealed wiring

All wiring to be concealed shall be neatly run in the concrete or plaster. They shall be secured firmly to the surfaces on which they run by means of lead saddles at interval of not more than 600 mm. 

There shall be a plaster cover of at least 12 mm over all such concealed wires.

It is imperative that all the wiring is completed before surfaces are plastered.

Cables shall be concealed behind cement plaster in the walls and/or ceilings or concealed in roof spaces behind false ceilings. Where cables run over surfaces other than wood behind ceiling, they must be protected by conduit. Chases, not deeper or wider than is necessary to accommodate the cable runs, shall be cut in the concrete/brick walls and ceilings. The cables when fitted shall not protrude beyond the surface of the walls and ceilings. Final rendering and plastering shall be carried out by the Contractor. Cable runs shall always be parallel or perpendicular to walls and shall be adequately secured by non-rusty wiring clips and brass nails at appropriate intervals. Any cutting and chipping of concrete shall be approved by S.O.

Electrical accessories where possible shall be flush fitting housed in open metal or aluminum boxes of appropriate thickness sunk into the walls and fastened by rawl plugs and brass screw. The open side of the metal box shall flush with the plaster wall surface and a hole shall be drilled at the back to permit cable entry. 

Accessories which cannot be fitted flush with wall surface shall be mounted on hard wood blocks of suitable size and thickness which shall be fixed to the walls by means of rawl plugs and brass screws so that the surface of each block shall finish flush with the plastered wall surface.

Surface wiring

Cables shall run on the surface of walls and ceilings or in the roof of spaces and secured by lead alloy saddles of approved design. Saddles shall be fixed by brass nails or screws spaced and not more than 150mm apart and not more than 10 cables shall be clipped together using the same saddles. 

Where cables run over surfaces other than wood, they must be secured on treated hardwood battens firmly fixed in position with rawl plugs and brass screws. Cable run shall always be parallel or perpendicular to walls and earth wires shall be fixed on the outside of the cable runs. All wiring which is installed at less than 1200 mm above floor level or subject to mechanical damage easily shall be protected with a wooden or plastic casing.

Electrical accessories shall be of the surface pattern type fixed on hardwood blocks with brass screws. Where more than one piece of accessory are grouped together, a single wooden block shall be used to accommodate all the accessories. However, it shall not be larger than necessary and it shall be cut at the side of the wooden block to permit cable entry.

PVC insulated cable

PVC insulated cables shall mean Polyvinyl chloride insulated cables. The conductors shall be of high conductivity stranded copper conductors. They shall manufactured in accordance with the specifications of BS 6004 or MS 136 and be of the 600/1000 volts grade.

The colors of the insulation shall be in accordance with Table 51A of the 16th Edition of IEE Wiring Regulations.

Cables to be used for surface and concealed wiring shall be PVC insulated and PVC sheath.

All cables shall be supplied at maximum required lengths and no joints are permitted.

Conduit installation

All conduits, fittings and associated accessories shall be galvanized and shall comply with B.S. 31. Conduits shall be screwed and welded Class “B” and fittings shall be manufactured from steel or malleable cast iron.

Where PVC conduits are specified, they shall be of high quality rigid type with all approved type joints, tee off and jointing materials.

Concealed conduit shall be fixed securely to prevent movement before casting of floor slabs, floating of plaster and casting of columns and beams.

Conduits and associated accessories shall be painted with one coat of red lead whenever the exposed galvanized surface has been cut or otherwise damaged including exposed threads and connections after erection.

Conduits shall be properly and tightly screwed into the full depth of box spouts and butted in sockets between lengths to ensure maximum mechanical strength and electrical continuity so that the wiring is continuously and effectively protected throughout its whole length, is not in anyway under mechanical stress.

The whole of the conduit system shall be continuous throughout. A separate earth continuity conductor shall be provided in all metal conduits. All conduits shall be earthed at terminations.

Flexible metal conduits shall not be accepted as a means of providing earth continuity. A separate earth continuity-conductor shall be provided with every part of the system formed by such conduit.

Conduit sizes shall be selected carefully for the number and size of cables they are to contain. The conduits shall be arranged with an adequate number of boxes to allow easy draw in and draw out of any one or all of the cables at any time. 

The conduit sizes shall not in any circumstances be less than 20mm and the number of cables drawn in shall not be greater than the appropriate number permitted in the 16th Edition of IEE Wiring Regulations.

Cables for lighting and power circuits shall not be drawn into the same conduit as those for extra low voltage systems. 

Lighting and power final circuits shall not be run in the same conduits, except where an adaptable box is employed as a final distribution point. A number of final circuits may be grouped together in a larger circuit between the distribution board and the adaptable box provided that all sub-circuits are of the same phase. 

In case of three phase circuits, all three phases and neutral if any should be drawn into the same conduit. Where condensation is likely to occur in surface conduits they shall be laid in falls to drain off condensed moisture so it does not gain entry into terminations.

Conduit work and accessories where not concealed shall be fixed effectively by means of heavy patterned spacing saddle and some approved metal or other non-disintegrating plugs of proprietary manufacture.

On straight runs the conduit shall be supported by saddles at intervals not exceeding 900 mm in addition to supports provided by any structure, box or fittings included in the run. For 40 mm conduit saddles maybe spaced at intervals not more than 1220 mm.

Hanging or suspending conduits using wires are not permitted 

Bends must in all cases be supported on each side by two saddles as near thereto as possible and a draw in box shall be provided after two bends and after not more than each 9 m of straight run.

Where conduits cross expansion joints they shall be installed in such a way so as not to resist relative movement of the sections. A suitable crossing shall comprise conduits telescoped one inside the other with the free ends or ends projecting immediately to one side of the crossing. Earth bonding of the telescoped end, which shall be suitable bushed, shall be affected inside the box to maintain earth continuity of the system.

Immediately on the completion of erection of any conduit during building construction all exposed switch, socket and conduit risers shall be plugged effectively against the ingress of water and dirt particularly where concrete shall be poured. Such seals shall be maintained in good order for such times as is necessary to complete wiring and connection of fittings and switches.

All conduits shall be swanned out and free from moisture to the S.O. satisfaction before wiring is commenced. Draw in tapes with absorbent cloth, such as flannel or army pull through cloth shall be used for this purpose.

On completion of the installation all exposed conduits shall be painted with two coats of good quality approved paint and to the satisfaction of the S.O.

Cable trunking installation

Cable trunking may be employed in lieu of conduit where multiple runs would otherwise occur.

All cable trunking shall be manufactured from good quality hot dipped galvanized mild sheet steel of not less than 18 SWG for sizes up to 100mm x 100mm and not less than 16 SWG for sizes up to 150mm x 150mm and not less than 14 SWG for larger sizes.

The trunking shall be installed complete with all necessary accessories such as bolted flanged outlets, blank ends, reducers, outlet bushes, bends, tees, sleeve couplings, intersection four way boxes and fitting adapters. 

Bridge pieces to act as cable retainers shall be readily removable, but positive fixing by machine screws for cover shall be provided. The inner radius of any bend shall not be less than 2.5 times the minor dimension of rectangular section trunking.

A 25mm x 3 mm copper tape shall run throughout the whole length of trunking from main switchboards to sub-switchboards, from main switchboards to distribution boards and from sub-switchboards to distribution boards to provide earth continuity.

All trunking shall be supported adequately by suitable brackets fabricated from galvanized mild steel sheet flat.

Whenever permitted by the S.O., cables for power and lighting circuits and extra low voltage systems shall not be run in the same trunking unless they are segregated effectively by means of rigidly fixed metal barrier or screen. 

The erection work of a trunking must be completed before any cable is drawn in. 

The number of cables run in a trunking shall be such that a minimum space factor of 45 percent is provided.

Cable tray installation

Perforated hot dipped galvanized mild steel cable trays of not less than 16 SWG may be employed in lieu of conduit.

Trays shall be of appropriate width with an up-turned flange both sides 20 mm deep and shall be with all necessary long radius bends and tees and fixing brackets fabricated from mild steel flat.

They shall generally be supported by directly beaming into top side of the concrete rib construction at 1820 mm centers forming the ceiling and in this event only, a simple and efficient approved clamping arrangement to the ribs shall be affected to prevent lateral displacement of the tray. 

Trays may be employed in other situations at the discretion of the contractor in order to carry out multiple runs of the M.I.C.C. and multi core cables as an alternative to fixing by saddles to the structure.

If trunking or cable trays are used in lieu of conduits, care shall be taken to ensure that all trunking, cable trays and cable runs in areas known to contain corrosive vapors are painted with an approved type of anti-corrosive paint and it shall be deemed that the cost of such painting has been included in the contract sum.

A 25 mm x 3 mm copper tape shall run throughout the whole length of the cable tray to provide earth continuity.

Ducts and trenches

Unless otherwise stated, ducts and trenches necessary to accommodate cables and equipment will be provided by the building Contractor in accordance with the drawings. However, it shall be the Contractor’s responsibility to ensure during the progress of work that the various ducts and trenches are constructed in positions as are required by the electrical distribution works and as such, are adequate for these requirements whether specifically mentioned herein or not.

If these ducts are not provided the contractor must advise the S.O.’s as soon as possible.

Copyright - Electrical wiring specification

Thursday, October 29, 2009

Lightning protection specifications

The following provides some example specifications that can be used in a contract for the installation of the lightning protection system in a multi-storey office building.

The installation of the Lightning Protection must comply with the specifications below, and the information given in the accompanying drawings, but in any case must always be in accordance with the British Standard Code of Practice BS 6651: 1985 and to the satisfaction of the S.O.’s representative. All materials should conform to the latest edition of B.S. Specifications.

Air Termination
Materials for the air termination must be medium or hard drawn copper or phosphor bronze rod of at least 15mm in diameter.

The terminations shall project at least 460mm above the highest point of the building.

They shall be firmly and permanently fixed with saddles or brackets and protected from mechanical damage.

Roof conductors
Materials for the roof conductors must be high conductivity annealed copper tape with the dimensions of 25mm x 3mm.

The roof conductors shall interconnect all air terminations to all down conductors and form a conducting air termination network covering the area to be protected with closed metal loops.

All exposed metallic structures shall be bonded in a solid and permanent manner to the roof conductor network.

Care should be exercised to avoid corrosion by the bonding of dissimilar metals.

Ferrous metals should not be used.

All joints and conductors shall be protected against mechanical damage.

Roof conductor runs shall be as direct as possible with spacer bars or tape clips at two meter intervals.

Bends shall be made as large as possible and in any event the bending radius shall not be less than 150mm.

Down conductors
Materials for the down conductors shall be of high conductivity annealed copper tape with the dimensions of 25mm x 3mm.

Down conductors shall interconnect the roof conductor network to the earth termination.

The route shall not interfere with the architecture and shall as direct as possible.

The down conductors shall be firmly and permanently fixed to the outside of the building or structure with spacer bars or tape clips at one meter intervals.

All independent metallic structures and other building structures within 600mm of any down conductor route shall be bonded to the nearest down conductor.

Lift shafts and duct shafts shall not be used as down conductor routes.

There shall not be any “up-turn” for the down conductor routes.

Joints and bonds
All joints shall be tinned and soldered and double riveted.

Clamped, bolted and screwed joints shall not be used, except at testing points and at rod connections.

Joints or bonds shall be as few as possible. All joints shall be coated with bituminous paint and protected against moisture and corrosion.

The maximum resistance of a joint shall not exceed 0.5 miliohms.

Tape to tape bonding clamps shall be “Furse” type having tinned contact surfaces complete with 8mm phosphor bronze fixing screw.

Test and junction clamps
Materials for the clamps should be phosphor bronze.

Test clamps shall be provided on each down conductor in an easily accessible position for testing purposes at a height of 2000mm from finished ground level.

Test clamps shall be protected from unauthorized interference.

Test clamps shall be provided on the roof conductor network in such a way that all parts of the network can be tested independently.

The test clamps shall be of approved type and shall not constitute an electrical resistance within the system.

After installation and testing they shall be painted with bituminous paint to prevent corrosion.

Earth termination
Materials for the earth terminations shall be of hard drawn copper or phosphor bronze rod. The minimum diameter of the rod shall not be less than 16mm.

The diameter of the rod shall be chosen according to the site condition but it shall always be such that it can be driven into the soil without bending or deforming the rod. Proper driving head and coupling similar to “Furse” type shall be employed.

The length of the rods shall be made up from the standard 1200mm lengths with internal screws and socket joints.

Minimum lengths of earth driven electrodes shall be 2400mm.

The length or the number of rods shall be increased if the maximum permissible earth resistance of five ohms cannot be achieved with the standard electrodes as specified.

The distance between two driven electrodes shall be equal to or greater than their driven length.

When more than one down conductors are used and terminated at earth terminations, all earth rods shall be bonded together to form one network.

The lightning protection earthing shall not be used in whole or in part as part of electrical earthing without the approval of the S.O.

Chemical treatment of soil at termination points to decrease the earth resistance shall not be carried out without the approval of the S.O.

Connections to the earth electrodes shall be by means of approved connector clamps adequately tightened. Earth connections shall be protected from damage by means of suitable electrode housing. The actual connection of the rods must be accessible and clearly visible when the housing cover is removed.

Testing of earth resistance and conductor continuity shall be carried as specified in the British Standard Code of Practice BS 6651: 1985.

The test shall be carried out in the presence and to the satisfaction of the S.O.

The resultant earth resistance of the electrodes shall not exceed five ohms and this resistance value shall be determined by an Earth Resistance Megger.

Copyright - Lightning protection specifications

Wednesday, October 28, 2009

Electrical earthing system

Almost all electrical systems need an earthing system in order to operate safely. The following is an example of simple earthing specifications for electrical substations. This is just a simple specification and you may need to expand it longer depending on the type and complexity of the project you are going to use it in.

This section covers the earthing of all equipment and the provision of a complete earthing system including materials, electrodes and connections. The complete installation of the system shall be in accordance with the recommendations of the British Standard Code of Practice CP 1013:1985.

Electrical earthing Drawings
All the quantities of electrical earthing materials that have been detailed in the material schedules shall be treated as estimated quantities for tendering purposes only.

The contractor shall be required to prepare installation shop drawings and accurate schedules of materials shall be submitted as part of the shop drawings. The drawings and schedules shall be submitted to the Engineer for approval.

Electrical earthing System
A grid of hard drawn high conductivity copper tapes of cross-sectional area not less than 150, shall be installed by the contractor at each site in excavated trenches at 300 mm depth or, where permitted, in formed concrete cable trenches.

The frame of all electrical apparatus and structural steelwork shall be connected by branch conductors of the same cross sectional area to the substation main bar or where applicable, to subsidiary bars running to a group of equipment.

All isolator bases, post insulator bases, tension isolator strings, earth terminals and earthing switches, neutral current transformers, power transformers, surge diverter bases and where agreed with the Engineer, fences shall be connected to the grounding earth system.

Isolator and earthing switch operating mechanisms and circuit breaker control kiosks not integral with the circuit breakers shall be connected to the earth system by a branch conductor entirely separate from that employed for grounding the isolator, the grounding switch or the circuit breaker structure.

Electrical earthing points
The earthing point shall be of 16mm diameter copper-jacketed steel rod, supplied in 1500mm length and shall have provision for screw coupling with another standard length.

The copper jacket shall be molecularly bonded to the steel core to ensure that the steel core and the copper jacket are permanently bonded.

All rods shall only be driven into undisturbed soil.

Each electrode shall be provided with a complete set of approved non-ferrous clamps for connecting the earth rod to the earthing conductor.

 The rods shall also be provided with a hardened steel tip and cap for driving by means of a power hammer.

The number of earthing points required shall be determined at site after the letting of the contract.

Earthing link chambers and covers shall be provided and installed under this contract. The drawings showing the proposed arrangement shall be submitted by the Contractor for the approval of the Engineer.

The prices quoted in this contract shall include the driving of all earth rods, installation of link chambers, connection to earthing conductors, testing and commissioning to the satisfaction of the Engineer.

Precise locations for the link chambers and the interconnection arrangement will be decided by the Engineer when the complete test result of the electrical earthing system is known.

The combined resistance of all earth rods shall, if possible, be less than one ohm. The result shall not exceed three ohm under any climatic conditions.

Earthing Conductors

Conductors for interconnection between individual earth rods in any group and between groups shall have a cross-sectional area of 150

There shall be at least two such connections from each electrode group to a link chamber.

Conductors for connection between the link chambers and the substation main bars shall have a cross-sectional area of 150 and at least two such connections shall be provided.

There shall be two separate connections between the neutral points of the high voltage systems and the link chamber of the earthing rods. Each of these connections shall a have a cross-sectional area of not less than 50

The material of the earthing conductors shall be annealed high conductivity copper and shall be stranded. They shall be protected with an extruded PVC sheath of 1000 volts grade.

Earthing conductors shall be directly buried in the ground between the link chambers and buildings. Inside buildings they shall be fixed to walls and ceilings using appropriate copper saddles.

Alternative routes to run the conductors on cable racks or in trenches can also be allowed provided appropriate methods and accessories are to fix the earthing conductors are used.

Jointing and Bonding
Prior to jointing (soldering) of the earthing tapes, the surface of the tapes shall be cleaned and thinned. The area of the joint shall be riveted with copper rivets.

There shall not be less than four 3mm rivets used for each joint.

Only non-corrosive flux shall be used in all soldered joints.

Alternative methods employing chemical welding or high compression joints or clamps, may be permitted subject to the approval of the Engineer.

Any alternative method of joints shall only be considered after full details are officially submitted and no work employing them shall commence prior to the official approval from the Engineer.

Tests at Site
The contractor shall carry out all necessary tests to determine the soil resistivity at each area of the sites.

The contractor shall also be fully responsible for proving that the electrical earthing systems comply with the specifications.

It is the contractor’s responsibility to measure the resistance of each electrode installation and the resistance of each complete electrical earthing system without additional charge.

A complete method statement covering the installation procedures, the inspection checklists and the full testing procedures shall be submitted to the Engineer for approval prior to the commence of the actual installation work.

No work shall commence prior to the official approval of the method statement.

Copyright - Electrical earthing system

Tuesday, October 27, 2009

Home electrical earth installation

This post is about home electrical earth installation or home electrical grounding. Some people call it electrical ground, or earth grounding, electrical earth, or just grounding or ground. In fact, I have come into some really funny names for the electrical earth.


That is because the earth has no mass, and it has no quantity. It is actually a function. An electrical current has no mass, but it has a quantity. Your house switched socket outlet is rated 13A, for example. That is 13 Amperes, a quantity that is definite and measurable. The more enlightened ones will say that is the quantity of electrons that is measured.

Unlike current, many people seem to have given up trying to understand this electrical earth, never mind those who never care in the first place.

Whatever the real reasons are, this situation has resulted in a very serious problem: many people are not able to use electricity safely. They allow their loved ones be exposed to unnecessary risks and dangers.

Look at the nice diagrams that I quickly prepared for you below. Picture No 1 is how the small house looks like at the cross section view from the right side of the house. Note that the main entrance is on the left side of the drawing. Picture No 2 is the house electrical layout. I used the same picture (plus a little additional information which I hope you can figure out on your own – this is the kind of materials that nowadays they put inside the books on urban survival skills) in the earlier post to explain on how to read the house electrical wiring, the electrical symbols used, and a simple guide on how to check your house electrical installation from safety view point.

Picture No 3 is something I cooked up to show you an overall view of the electrical system involved in the flow of electricity from the substation to your house. This diagram is very important for those who do not have the time to think about technical stuff on electrical system, but have been very concerned about the risk of electrical shock that may be present in their house. Take your time to study this diagram. It is actually nothing more than a flow chart actually.

While Picture No 4 contains some additional details about “the earth” for your house wiring. This is the earth chamber. This is the part that help the wiring discharge the current to where it belongs when some malfunction occurs to the wiring or the appliances so your house occupants can stay safe. You may have seen this at your house, but only the top part on the surface is visible. So now you can know how it looks inside and underneath.

Please note also that the lightning protection also use the same thing to discharge the lightning current during the lightning strikes. Sometimes it is called the lightning rod. So your house usually has at least two of these earth chambers: one for the electrical and one for the lightning protection system.

That is the short brief about the pictures that I have uploaded to help you to understand what the electrical earth is.

Now let us start the main lesson. I put all the four images first and the explanation after them.

Picture No 1 – Incoming supply and earth chambers

Picture No 2 – Electrical layout drawing

Picture No 3 – Fault current path

Picture No 4 – Details of the earth chamber

1. Home electrical basics

We need the earth installation because we have electricity in our house. So we must understand the home electrics first before we can really understand the earth. You can visit this post, Home electrical wiring, symbols and checking, to read more details of this subject.

Picture 1 shows how the electric supply is brought to the house. It came from a substation somewhere and transported through cables to your house. Here it came through the overhead cables tied to the top of electric poles along the street of the residential area. I am sure most of us have seen this and how the cables are brought to the energy meter at the front wall of the house. Anyone who haven’t seen it can see the pictures of them somewhere else in this blog.

Now look at Picture 3. The source of the electricity is at the substation on the far left of the picture while location where it is being utilized is on the far right. If you see the pretty girl then you can see that she was being electrocuted. That what we all don’t want and that is why you need to watch the diagram carefully. I will not write too long today because it’s already 1.00 AM and I have to go to work tomorrow. However I will update this post and write some more details. By the time I am finished with this post (after a few updates probably) you will understand enough to take the necessary care and precautions at home with regards to electricity and electrical appliances.

For now just observe that the electric current from the power transformer at the substation flows along the path indicated by the direction of the red arrows pointing to the right side of the diagram. When it arrives at the four circuit breakers on the electrical panel, it travels through the lowest circuit breaker because that is the circuit that is supplying the socket out where the washing is connected. Normally the current travel back to the star point of the transformer through the second wire which is the lower black line from the washing machine. I did not put any arrow to indicate the return path of the current. But that path will go to the neutral busbar (the one with the label “E” inside the electrical panel). If you trace the connection, it will go back to the neutral point of the power transformer.

But the diagram shows that there is another two alternative paths the current can take to go back to the transformer star point. The first (or the second because the first is through the neutral wire) is shown by the red arrow right below the washing machine. You can see the black line connecting to the machine’s metal body. The connection is shown here by the black dot at the intersection point.

So the current can travel through the earth wire shown by the red lines as I said above. This is actually the third wire in your house wiring, which is the green wire. If your house wiring is concealed inside the wall, you may have seen the green wire inside the extension cord or at a damaged plug where the cover has been broke. That is the third wire shown by the red line below the washing machine. This path will follow the wire and arrive at the earth busbar (with the label “E”) inside the electrical panel or distribution board. This earth busbar is located near the neutral busbar (label N).

If the neutral busbar is connected to the transformer star point through the neutral return wire, the earth busbar is connected to the earth camber that I mention at the beginning of this post (see Picture 4). The black wire labeled “Electrical panel earthing” is what we called a grounding conductor or the earth conductor. With this earth conductor the machine is solidly connected to earth. Yes, connected to the real earth mass. The earth chamber is just an enclosure and a cover to protect the components inside and underneath it which are a long copper rod with some very important connection accessories inside.

Back to the ground wire path. Under normal situation the electric current inside the washing machine does not flow through this path (the third path). It will just flow through the neutral wire to flow back to the transformer star point. However like everything else in life, nothing last forever. The most expensive machine that you can buy may have a five year warranty sticker on it and the vendor’s office guaranteed that you will have their best technician knocking your house door within 15 minutes of your call.

However the girl in the diagram may not be alive long enough to make the call. The line from the black dot below the machine to the earth busbar follows such a zigzag route. I could have made it straight and direct, but I didn’t. Some of you may have a pretty good idea why. I may need one whole post just to explain the “why”.

Okay, so nothing last forever. One day one of the components and parts inside the machine will fail. If the failure leads to poor insulation of live parts, then a small amount of electric current may leak to one of the exposed metal parts of the machine. That metal part will get energized or “live”. This is why we need the earth wire connection there. The exposed metal parts are not supposed to get “live”. That’s why they are exposed to touch. So the voltage they carry due to the leaked current cannot go back to the neutral star point through the earth wire. With the earth wire, that voltage has a path to escape to which is straight to earth.

So what? The metal part gets energized and it has the current flowing through it and to earth. People will still be touching a live metal, right? Right! But that metal and the designed live metal inside the machine have a very big difference. The bonded exposed metal is at the same potential as the earth which is 0 volt (that is “zero volts”). And the girl there is also at zero volt, the potential of the earth. Since both the girl and the exposed metal are at same potential, the current will not flow through the girl, or the flow will extremely small. (That is in theory. Many other factors are also involved in real situation).

The above is point no 1. Another point is the solid connection will minimize the resistance between the exposed metal to earth. Since the current is inversely proportional to resistance, a minimum resistance will give maximum current. This aspect is utilized by our ancestors to create a protection device that can protect the girl. The leaked current will be detected by the devise and it trips the connection of the supply to the machine. Therefore the will be saved before the voltage rise up high enough to cause serious injuries. The established setting of this current has been 30 mili-Amperes. This is what the experts in this field have come to follow, and this is the label that you can see near the earth leakage protection devise in Picture No 3.

Which devise? That is the ELCB (earth leakage circuit breaker). It’s in side the electrical panel. On the diagram also it is labeled “ELCB”, with “60A DP” and “(30 mA)” label just below it.

The ELCB itself is a long topic so I will save it for another time. But if you cannot wait, my earlier posts have already some information on how it works. I will explain more in future posts. (UPDATE: Visit ELCB - Home Electrical Shock Protection and also ELCB circuit for a much more detailed information about the ELCB circuit breakers.)

So now do you understand why we need the electrical earth there? Why having it properly working is an absolute necessity? A matter of life and death? Good.

I have not forgotten that I titled the post “Electrical earth installation”. And I have not even started the installation part of it. I was absorbed in the why. The how part of it will have to wait for another time. I will continue on this topic as an update to this post. There will be other posts on the earth installations, but I also need to make this post complete as what the title says. Some readers may not have the time or desire to click to another post to get to what they hope to find.

See you soon.

Note: Visit this post, Free electric installation picture, to see more pictures, diagrams and drawings of electrical installations. I started it some time back as an anchor post, but got around to really finish it. It can be much faster than searching through the BLOG ARCHIVE folder.

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Monday, October 26, 2009

ELCB circuit

The diagram below shows how a single phase ELCB circuit looks like. However, before I get down to explain more, please take note that I am using the name ELCB as a generic name, just like a circuit breaker.

1. ELCB is a short for Earth leakage Circuit Breaker. When it first came to be used, the devise is actually a voltage-operated device that was designed to detect a current leaking through the earth path of electrical equipment and appliances. I used to see the actual circuit during my college days, but I have to dig it up and redraw it for uploading. You will see it in one of my future posts.
2. The circuit that you see here is actually an RCD (residual current devise), or RCCB (residual current circuit breaker). It is based on the principle of magnetic core balance and the trigger core is current operated instead of voltage operated as in the earth leakage circuit breaker.
3. In terms of performance, the residual current circuit breaker is definitely better. The performance of the old ELCB did not have any problem, but the residual current device can do the same and more.
4. I cannot remember when the residual current circuit breaker actually took over the whole wiring scene, but I cannot find the earth leakage circuit breaker in actual installation anymore. Everywhere that I know is unsung the RCD, but in the field the terminology used have not changed at all. Everywhere and in all design drawings the name ELCB has not been changed. Only some textbook and in the academic classes the RCD or RCCB terms has been used. Therefore, the convention has not been changed. That why throughout this blog I will keep on using the ELCB for this earth leakage device.
5. Originally ELCB was designed to detect earth leakage current and to disconnect the circuit immediately when a certain limit was crossed. Now RCD does the same. Therefore, the general practice to still call the residual devise an earth leakage circuit breaker is still correct. It is still an ELCB by purpose and function even though the internal circuit design has actually changed.
6. However, in certain scenarios both ELCB and RCD names need to be used for clarity. The discussion on internal circuit design of the device like now is one of the scenarios. That is why I will use the two names interchangeable in the following part of this post.
The picture below shows a typical single-phase double pole ELCB circuit. I think it is better to first explain the components of the circuit one by one and explain the how the circuit works afterward.

Diagram 1 – Typical ELCB circuit

a. The supply coil, the neutral coil and the search coil all wound on a common transformer core. On a healthy circuit the same current passes through the phase coil, the load and return back through the neutral coil. Both the phase and the neutral coils are wound in such a way that they will produce an opposing magnetic flux. With the same current passing through both coils, their magnetic effect will cancel out under a healthy circuit condition.
b. In a situation when there is fault or a leakage to earth in the load circuit, or anywhere between the load circuit and the output connection of the ELCB circuit, the current returning through the neutral coil has been reduced. Then the magnetic flux inside the transformer core is not balanced anymore. This unbalanced flux is what we call a residual flux.
c. The residual flux will be detected by the will cross the winding of the search coil and produce a voltage that drives a current inside the wiring of the trip circuit. It is this current that operates the trip coil of the circuit breaker. Since the current has been driven by the residual magnetic flux (the resulting flux, the net effect between both fluxes) between the phase and the neutral coils, it is called the residual current devise. With a circuit breaker incorporated as part of full circuit, it is called residual current circuit breaker (RCCB) or residual current devise (RCD).
d. The incoming current will come through the circuit breaker first before going to the phase coil. The return neutral path passes through the second circuit breaker pole. During tripping when a fault is detected, both the phase and neutral connection is isolated. The circuit breaker can also be used to manually ON or OFF the circuit.
e. The load circuit is not part of the ELCB circuit. However, notice the earthing symbol at the load circuit. That is the earthing connection from the exposed metal parts of the electrical equipment or appliance to the electrical earth. This earthing connection will allow the ELCB fulfill its purpose of being in the electrical circuit. You can have a good operational ELCB unit properly installed and wire at the electrical panel, but if the earthing connection is broken or missing, the ELCB will not trip during an actual earth leakage situation.
f. The test pushbutton and the test resistor are arranged to provide a test function for the ELCB circuit. This part of the circuit bleeds away a fraction of the running current from the phase coil. So the neutral coil current will be higher the phase coil current. Therefore, a residual current will be generated in the trip circuit and trips the circuit breaker.

The above trip simulation tries to check the health of the ELCB circuit. In it works. However, it does not test the complete operation of the protection system that the ELCB is supposed to serve.

Read how you can get electric shocks here. Other related articles: a) Home electrical wiring, symbols and checking;

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