Switchboard earthing busbar

This post shows some pictures of the earthing busbar of a main switchboard. Click here to go back to the main post, Switchboard electrical earthing.
Photo 1 - View of the lower part of a main switchboard
You may be wondering why I did not stand back a little bit and take a wider view of the subswitchboard. The would give a nicer picture, right?
I however took this picture when the main switchboard (MSB) has already been located on its actual position in the electrical switchroom (LV Switchroom).
Usually the layout of an electrical LV room is such that the main switchboard is located near the wall of the room. The space behind the board is usually between 600mm to 1000mm between the back of the switchboard and the wall.
In fact 750mm is a more common space clearance for office and residential building. This of from my own personal experience. I do see projects where the architects were more generous.
In those cases you may then find that the clearance is between 1000mm to 1300mm.
Okey, back to the earthing busbar.
Here you see that the switchboard earthing busbar is located at the near bottom towards the rear door of the switchboard. This is a common practise.
The phase busbars are usually at the top part of the 2 meter plus main switchboard.
Here you may also notice the the photo shot was taken at the left end of the long switchboard. "Left" if you look at it from the rear.
So here you can also see how the busbar is mounter to frame or the chasis of the board. This is not how the phase busbars are fixed in place.
You can see the pictures of how they are fixed in future posts. Maybe if you browse around this blog, you may be able to see it already but I cannot be very sure if I have already uploaded a photo that contain this information.
Photo 2 - The earthing busbar of the switchboard
I just zoom in a little onto the busbar so you can see the details better.
Notice how the end of the busbar is fixed to the switchboard structureal frame. This way the structure is automaticalled earthed.
Notice also the green color sticker located on the busbar approximately at the middle of the panel opening.
Photo 3 - The green/yellow submain earthing cables and copper tape
The function of the switchboard earthing busbar is not only to ground the equipment and metal parts loacted on the switchboard.
It also serves as the feeder the grounding facilities that are needed by submain circuits taking supply from the particular main switchboards or cubswitchboard.
So in the above photo you can see four earthing connections: three from grounding cables with green/yellow insulation, and one from a 3mm by 25mm copper tape.
Each of these grounding conductor would be running along its respective phase and neutral conductors.
Photo 4 - The earthing connection to switchboard rear door (metal parts)
The specifications in the original article, Switchboard earthing, requires that all doors of the switchboard be properly connected to the grounding busbar.
So here is how it is done.
Note that it is a common practise to use spring washers to secure the cable ends to the bolt and nut.
It should be noted also that the cable lug should be a ring type.
A fork type of cable lugs should not be accepted.
Photo 5 - Branch earthing connections to the earthing busbar
When the specifications say branch earthing connections, this is what it meant.
The insulated green wires terminated to the switchboard earthing busbar is the earthing branch connections.
The provide proper and reliable connection to all live equipment and components on the panel or inside the switchboard.
Click here to go back to the previous post, Switchboard earthing.
Note: This anchor post, Free electric installation pictures , may contain a summary of the materials you are looking for. It can be faster than clicking through each post title at the Blog Archive. I started it long ago but never actually got around to finish it.
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Temporary electrical switchboards

All electrical switchboards used on temporary electrical installations or building construction sites should be of substantial construction. Where they are installed in outdoor locations, the switchboards should be so constructed that safe operation is not impaired by the weather. This weatherproof criteria usually means an IP rating of not less than IP 65. When the doors are opened, the degree of protection to all live parts should be no less than IP 20.

The method used for installation must have provisions so the cables and flexible extension cords coming in and out of the boards can be properly supported.

The temporary switchboards should also be provided with a door and locking facility that comply to the requirements of the electricity supply authority. Door should be designed and attached in a manner that will not damage any flexible cords connected to the board, and should protect the switches from mechanical damage. The door should be provided with a sign stating ‘KEEP CLOSED’ – ‘LEADS THROUGH BOTTOM’.

The switchboard should have an insulated slot in the bottom for the passage of leads.

The temporary switchboard should be attached to a permanent wall or other suitable portable structure, which has been designed for the purpose. Pole or post-mounted switchboards should be fixed by means of coach screws or bolted.

If the switchboard is used to supply other sub-boards downstream, every sub-board should be provided with a clearly labeled main isolating switch.

Temporary lighting outlets should be in a separate section on the switchboard and they should be clearly identified as lighting circuits. To protect from electric shock, the supply to the temporary lighting section should be provided with 100 mA residual current device (RCD), while the supply to the temporary socket outlets section should be protected by an RCD or earth leakage circuit breaker (ELCB) of sensitivity not more than 30 mA.

If too many tools are connected at the same that results in frequent tripping of the shock protection device, then the supply should splitted into multiple sections or multiple distribution boards, with each section or DB protected by a 30 mA RCD. This will prevent the shock protection device from being defeated by workers whose works have been most inconvenienced by the frequent tripping.

The electrical contractor or nominated persons should ensure that all power circuits are isolated or made accessible so as to eliminate the risk of fire, electric shock or other injury to persons after completion of the daily work.

All temporary supply mains should be protected by a circuit breaker or H.R.C. fuses.

A clearance of at least 1200 mm should be maintained in front of all switchboards and if the switchboard is located in a room, a clearance of 700 mm minimum should be provided around the other three sides. If the switchboard is also provided with rear access, then the rear of the switchboard must also have a 1200 mm clearance minimum.

Temporary switchboard should be so located that the maximum lengths of the flexible cords do not cause excessive voltage drops and impairs the normal operation of electrical equipment and portable electric tools.

The switchboard should be properly earthed and the color-coding of the protective conductors shall be done in accordance with IEC 60646.

A main earth bar should be provided inside the switchboard and it shall be connected to the temporary electrical grounding using appropriate size earthing conductor. The cross-section of the conductor shall be sufficient to carry the rated short-time withstand current of the switchgear.

All metal parts of the switchboard cubicle, and the metal parts of the components that are mounted on the switchboard including door, relays, instruments, etc shall be earthed through branch connections to the earth bar.

Frames of the draw-out circuit breakers (if they are used) shall be connected to the earth bar through a substantial plug type contact.

All temporary electrical equipment and switchgears including the switchboards should be inspected and labeled regularly by a licensed competent person before their first use and every three months thereafter.

The details of the inspection should be recorded in a logbook for inspection purposes. The details recorded in the logbook should include but not limited to the following:
a) Date of the inspection.
b) Identification no of the equipment or switchboard inspected.
c) License number of the inspecting competent person.
d) Any repair required because of the inspection.

Inspection label or sticker should be attached to the inspected switchboard showing the date of the most recent inspection. This label should carry the verification signature of the endorsing competent person.

Repair works that are required by the inspection should be carried out without delay. If the required repairs are related to safe use of the temporary switchboard, they must be properly carried out before the board is put to further use.

There is also a more detailed article on temporary electrical installation at this post, Temporary Electrical Installations.

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Switchboard electrical earthing

Following is a picture showing the earthing busbar of a main switchboard. Below the picture is a simple performance specifications for the grounding of the switchboard.
The are also two more posts on switchboard installation check and switchboard electrical tests. The latter is a general list of tests and inspections that are usually required of a major switchboard such as main switchboards and large subswitchboards.
Photo 1 - Earthing busbar of a main switchboard (MSB)
The earthing of an electrical switchboard shall be in accordance with BS 7430, and the color coding of protective conductors shall be in accordance with IEC 60646.
Switchboard earthing busbar
The switchboard earthing busbar shall be installed internally along the full length of the switchboard. The material of the busbar shall be the same as the material of the phase busbars. (See more photos: Switchboard earthing busbar.)
Equipment earth bar
Where the substation consists of 11 kV switchgears, transformers and LV switchboards, earthing copper tape shall be installed continuously along the full length of the substation.
It shall be connected to the main system earth bar at both ends using appropriate size earthing bolts with nuts and spring washers.
The earthing copper tape shall be made of hard-drawn high conductivity copper.
The cross-section of the earth bar shall be sufficient to carry the rated short-time withstand current of the switchgear for the allowable temperature rise and the time specified.
Internal branch earth connections
The branch earth connections made from the switchboard earthing busbar to the individual switchboard components shall consist of adequately sized copper strips, or green/ yellow striped PVC sheathed stranded copper conductor.
The termination lugs shall be of the compression type.
Earthing of metal parts
All metal parts of a switchboard where live components (such as relays, instruments, indicating lights etc) are mounted shall be earthed through branch connections to the switchboard earthing busbar.
Doors of the switchboard shall also be similarly earthed.
Frames of the draw-out circuit breakers shall be connected to the earthing busbar through a substantial plug type earthing contact.
Note: This anchor post, Free electric installation pictures , may contain a summary of the materials you are looking for. It can be faster than clicking through each post title at the Blog Archive. I started it long ago but never actually got around to finish it.
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Switchboard electrical tests

The following electrical tests must be carried to all switchboards, sub-switchboards, main distribution boards and motor starter panels.

A. Full type tests
1) Full type tests shall be carried out in accordance with IEC 60439-1, IEC 60947-1, and IEC 60947-6-1. Certificates issued by approved independent testing laboratories shall be submitted to the Employer’s Representative.

The type tests shall include the following:
a) Verification of temperature-rise limits
b) Verification of the dielectric properties
c) Verification of the short-circuit withstand strength
d) Verification of the effectiveness of the prospective circuit
e) Verification of the clearances and creepage distances
f) Verification of mechanical operations
g) Verification of the degree of protection

B. Routine tests
Before the product leaves the works, the manufacturer shall carry out the relevant routine tests in accordance with IEC 60439-1 on the total assembly, and the IEC 60947-1 and IEC 60947-6-1 parts thereof when delivered with time intervals, and the results shall be recorded in a test report.

C. Special tests
Carry out the special tests recommended in IEC 1641 Guide for Testing Under Conditions of Arcing Due to Internal Fault, the result shall be recorded in a test report.

D. Acceptance Tests at Manufacturer’s Work
a) Acceptance tests shall be carried out on the completely assembled switchboards and motor starter panels. Transportable units can be wired together for the purpose of the tests instead of completing the busbar joints.

b) The tests and checks shall include, but not limited to, the following.

c) All the switchboards and motor starter panels shall be visually inspected for technical execution and conformity with the latest issue of approved drawings and the latest issue of the relevant standards. Spot checks shall be made to verify the following:

1) Dimensions
2) The degree of protection of enclosures
3) The degree of protection within compartments
4) The effectiveness and reliability of safety shutters, partitions and shrouds
5) The effectiveness and reliability of operating mechanisms, locks and interlock systems
6) The insulation of the busbar system
7) The creepage distances and clearances
8) The proper mounting of components
9) The internal wiring and cabling system
10) The correct wiring of main and auxiliary circuits
11) The suitability of clamping, earthing and terminating arrangements
12) The correct labeling of functional units
13) The completeness of the data on the nameplate
14) The availability of the earthing system throughout the switchgears
15) The interchangeability of electrically identical components

d) Dielectric tests shall be carried out in accordance with IEC 60439-1. The test voltage shall be at least:

1) For main circuits, 2500 Vac for 1 minute.
2) For control and auxiliary circuits, 2 x Un + 1000 Vac, with a minimum of 1500 Vac for 1 second.

e) Testing of the mechanical and electrical operation of a number of functional units on random basis, including their control and protective devices.

f) CT polarity, magnetization, ratio and burden measurements

g) Secondary injection tests

h) Primary injection tests

i) Painting and finishing tests:

1) Measurement of paint thickness.
2) Humidity (cyclic condensation) tests to BS 3900 Pt. F2. Painted panel shall withstand 1000 hours under test with no blistering of film and corrosion of base metal.
3) Adhesion test to ASTM D3359-02. Test tape shall not expose more than one 3 mm.sq of bare metal or underlying coating.
4) Impact resistance test to BS 3900 Pt. E7. Paint shall not chip off.

j) The manufacturer test shall be verified and witnessed by the Employer’s Representative or his representatives.


E. Site Tests
At the completion of the installation at site, each switchboard and motor starter panels shall be field tested by a representative of the manufacturer. A report recording each item of the tests shall be certified by the manufacturer and submitted to the Employer’s Representative.
a) Visual inspection
1) Correctness of location and mounting
2) Labeling, nameplates and markings.
3) Verification of torque for all nuts and bolts on busway.
4) Observation of cable bracing, both incoming and outgoing, certifying that it is in accordance with the manufacturer’s recommendations.
5) Safety shutters, partitions and shrouds.
6) Functional units, operating mechanisms, locks and interlock systems.
7) Mounting of components.
8) Internal wiring and cabling system.
9) Clamping, earthing and terminating arrangement.
10) Earthing system.

b) Dielectric tests shall be carried out in accordance with IEC 60439-1. The test voltages shall be at least:
1) For main circuits, 2500 Vac for 1 minute.
2) For control and auxiliary circuits, 2 x Un + 1000 Vac with a minimum of 1500V for 1 second.

c) Power frequency withstand voltage test.

d) CT polarity, magnetization, ratio and burden measurements.

e) Secondary injection test

f) Primary injection test

g) Functional / sequence test
i) Operation of each disconnecting means under load
ii) Operation of each automatic transfer switch
iii) Operation of all alarm devices

h) Mechanical operation test
i) Operation of each disconnecting means under load
ii) Operation of each auto transfer switch
iii) Operation of all interlocks

i) Calibration and setting of protection devices


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Electrical MCB installation

MCB installation (miniature circuit breakers) in the distribution boards shall comply with IEC 60898-1. They shall be incorporated with overcurrent protection. Their selection for use shall match their operating characteristics.

1. Type test certificates shall be produced for the MCB selected from international recognized testing laboratories.

2. Performance criteria
a) Breaking capacity
The rated short-circuit capacity, Icn, shall be higher or at least equal ot the maximum prospective short-circuit current at the points of installation as stated in the single-line drawings.

The rated service short-circuit capacity, Ics, of 6 kA and 10 kA breakers shall be 100 % Icn and 75 % Icn respectively.

b) Coordination
All MCB in the distribution boards shall be from the same manufacturer and total discrimination with the upstream breakers under over-current conditions shall be guaranteed. Details of the operating characteristics and the coordination with other protective devices shall be submitted to the Engineer for approval. The details shall include the manufacturer’s full current discrimination tables showing the over-current discrimination levels.

Back-up protection is permitted when a current limiting circuit breaker is installed in the upstream. Details of this coordination shall be submitted to the Engineer for approval. The details shall include the manufacturer’s back-up protection tables showing the upstream/ downstream devices and the coordinated level of protection.

c) Installation
The electrical MCB shall be fully rated for uninterrupted continuous service based on an ambient temperature of 30 degree Centigrade.

The MCB shall be of 35 mm DIN symmetrical rail type and available in one, two, three and four pole version.

The MCB shall be suitable for mounting in any positions with no derating.

3. Construction
a) Trip characteristics
The trip characteristics of the MCB shall be Type B, C or D as indicated in the drawings.

b) Operating mechanism
The operating mechanism shall be of the quick-make, quick-break type with the speed of operation independent of the operator. In addition, the breaker mechanism shall mechanically trip free from the operating handle so as to prevent the contacts from being held closed against short circuit and other abnormal conditions.

The operating mechanism shall be designed to operate all poles simultaneously during opening, closing and trip conditions. The individual operating mechanism of each pole of a multi-pole MCB shall be directly linked within the MCB and not only by the operating handles alone.

All MCB shall be tested for isolating function as stipulated in IEC 60898. The isolation function shall guarantee that the breakers when in open position, should have isolation distance in accordance with the requirements necessary to satisfy the need for users safety.

Means of positive contact identification to mimic the exact position of the contacts shall be provided. The indication of the open and closed position of the main contacts shall preferably be provided by the position of the actuator. Color-coded bands and lettering on the actuator shall be incorporated to aid identification.

The operating handle shall be of the toggle type with facility for installation of padlock device.

All MCB shall have optional field installable accessories like shunt-trip coil, under-voltage release, ON/ OFF indications, alarm switch, etc. The installation shall be flexible such that to allow for fitting of accessories to either the left or right side of the MCB.

All MCB must be suitable for remote controlled ON/ OFF operation via an electrical motor operator.

c) Terminals
The MCB shall have double function terminals to allow for correct termination of busbars and cables. The top terminal shall be suitable for PIN busbar, the bottom terminals shall be suitable for both PIN and FORK busbars.

The cable terminals shall be equipped with safety guards to protect against misconnection. The safety guards shall function in a manner such that there is only one possibility of cable insertion into the MCB terminals. This will eliminate all possibilities of loose cable terminations due to wrong insertions.


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Switchboard installation check

Switchboards are the switching centers of  the low voltage distribution sytem. They are also the places where the control and protection system is located.

Photo 1 - A switchboard being unloaded from the transport at a construction site of a building project

Because of the importance of these equipment, all aspects of a switchboard installation need to be closely monitored. Even the loading and unloading of them to and from the transport need to be monitored.

The following general guide started out as a sample performance specifications for switchboard installations. However, as I tried to make it more detailed, it became more difficult to keep it in a specifications format.

So I decided to just expand it into something like a general guide. I say "general" because I do not want to develop it into a long manual in one go. It will be quite general at this stage, but I will develop it into details using separate short posts for each sub-headings.

As I said, this guide is actually a general checklist of what to monitor and what to inspect. Not everything here need to be followed strictly.

Installation conditions, sequence of work at a particular construction site, and specific arrangement of the  specialist subcontracts etc may make it impractical to follow some of the details in these guide.

It is however the responsibility the supervision personnel to make sure the intention and objectives of the guide are fulfilled, whichever way they are achieved.

Switchboard installation checklist:

A. Preparation of the switchboard room
1) Coordinate with other trade contractors to ensure that the floor of the switchboard room is sufficiently level.

2) The electricity supply for lighting, small power and mechanical ventilation shall be provided as provided for in the construction drawings. Prior to commissioning of the switchboard, the lighting and (if required) the mechanical ventilation works should be completed and tested.

3) If an active fire protection system is required in the
switchroom, the installation should be completed and properly tested before the switchboard can be commissioned.

4) The foundation channels for the switchboard should be installed flushed with the floor.

5) Once the switchboard is located in the room, all entrances should be secured by padlocking all the doors. This should be done regardless whether the installation of the switchboard is completed or not. This measure need to be taken not just for the security of the equipment, but also to prevent any possibility of unathorized tampering of the equipment and components of the switchboard.

B. Cleanliness of the room

1) Prior to the commencement of a switchboard installation work, check to make sure that the room where the switchboard will be installed is free from construction debris.

2) If further "dirty works" (such as hacking of concrete walls to relocate a mechanical ventilation fan) need to be carried out after the switchboard is in place, sufficient precaution should be taken to protect the board from dusts and falling debris.

C. Readiness of the switchboard and other equipment

1) Preferably at this point of time all cable ladders,  HV cables, LV cables and control cables should have been properly installed in the switchboard room and ready for connection to the switchboards, the motor starter panels and the auto transfer switches.

2) Install the switchboard, the motor starter panels and the automatic transfer switches in accordance with the contract specifications, the manufacturer’s instructions and within the designated switchroom as shown in the design drawings.

3) Position and secure the mounting bolts for each of the switchboard and motor starter panels on the foundation channel according to manufacturer’s recommendations. All panels shall be installed level and plumb. The front of all panels shall be lined up and present a neat and orderly appearance.

4) During installation of main busbars and the earthing busbar, make sure that the joint surfaces are clean before tightening the bolts. All bolts used shall be of appropriate size.

5) Permanent phase identification shall be provided on the exterior of the enclosures, and they shall match the busbar phase identification inside the enclosures.

6) Connect the signal cables from each lift motor room to the auxiliary signal contacts of the automatic transfer switch (closed before switch returns to normal power). The termination work shall be done by the lift vendor under the supervision of the electrical sub-contractor.

7)  Connect the signal cables from engine start contacts of the standby generator panel to the auxiliary signal contacts of the automatic transfer switch.

8) Test the racking in and racking out of all withdrawable circuit breakers. Check and adjust the alignment. Check the alignment of all auxiliary contacts.

9) After re-assembling all switchboard panels, check all inter-panel wiring, power and control wiring prior to commencement of the pre-commissioning tests. Unless prohibited by the arrangement of the sub-contract packages, re-assembly of the switchboard panels and inter-panel wiring at the construction site shall be carried out by the switchboard manufacturer.

10) Upon completion of the installation, terminate all control cables, power cables and busducts to the respective terminals.

11) Replace all switchboard and starter panel covers and prepare for pre-commissioning checks.

12) Perform all inspections and tests as prescribed in the the pre-commissioning tests section.

13) Certify that all the required tests have been performed and that the switchboards and the motor starter panels are performing in accordance with the contract specifications.

14) Seal all the rear and top panels of the switchboards, the motor starter panels and the automatic transfer switch units using methods prescribed in the specifications or approved by the Electrical Inspector.

15) All installation procedures shall follow manufacturer’s recommendation wherever applicable.

16) Test all protection relays. This task shall be carried out by a Licensed Testing Contractor approved by the appropriate authority. The testing results, certificates and  all relay coordination curves shall be filed for incorporation into the Operation and Maintenance Manual.

17) Records of the installation works shall be properly kept and submitted to the Employer’s Representative.

18) During termination of cables, ensure that all surfaces are clean before tightening the bolts and cable lugs.

19) Padlock all circuit breakers in the OFF position and keep keys in the lockable cabinet.

20) Carry out the touch-up work on all damaged paintwork of the switchboard and motor starter panels. All surfaces shall be properly cleaned prior to commissioning.

D. Cable installation and termination

1) All power cable installation works shall be carried out after studying and coordinating the recommendations of the cable manufacturer, and the manufacturers of the switchboard, the motor starter panels and the automatic transfer switch unit.

2) Busbar cable termination and units shall be installed on the switchboards at the manufacturer’s works, with busbar connection to the termination and the unit.

E. Packing, transport and handling

1) All switchboards, motor starter panels and automatic transfer switches shall be packed and delivered with appropriate labels as recommended by the manufacturer.

2) The  labels shall be as shown in the contract drawings for easy identification at site.

3) All interconnecting busbars, earth bars, and insulation material or components, etc shall be packed separately. The packing shall be properly secured to prevent any movement or damage during transportation.

4) Measures should also be taken to prevent damage or deterioration of the components and equipment due to tropical climatic conditions or other weather related effects encountered during shipment.

5) Lifting eyes shall be provided to facilitate lifting. The manufacturer shall provide all necessary information for unpacking and lifting safely, including details of any special lifting and positioning devices, whenever necessary.

6) Each switchboard, motor starter panels and automatic transfer switch shall be supplied complete with:

Foundation channels
Foundation bolts
Interconnecting busbars and insulation materials, etc
Accessories

F.  Storage at the construction site
1) On arrival at site, the consignments shall be checked against the delivery notes. (Note: There are cases where a shipmet for one project are sent to a different project due to error by the delivery truck, especially if there are a number of different construction projects running concurrently near to each other.)

2) Upon arrival at site, the switchboards and motor starter panels shall be stored indoor in a clean, dry and appropriately ventilated place. For prolonged storage, the panel anti-condensation heaters may have to be switched on to prevent moisture condensation and consequent damage and mal-operation.

Note: This anchor post, Free electric installation pictures , may contain a summary of the materials you are looking for. It can be faster than clicking through each post title at the Blog Archive. I started it long ago but never actually got around to finish it.


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