Friday, April 15, 2011

13A sockets inside underfloor box

These are just pictures of two units of under floor service boxes with 13A switched socket outlets installed.

Photo 1 – 13A switched socket outlets inside underfloor junction boxes

Is there any problem here?

I took this picture some two or three years ago. Shown in the picture are two service boxes for an underfloor trunking system.

For the benefit of readers who are not very familiar with the term underfloor trunking, underfloor junction boxes, and underfloor service boxes and how they relate to each other, please refer to the layout drawing below.

Drawing 2 – Layout drawing of an underfloor trunking system for a high-rise office building

This is an example of an under trunking system layout drawing for an office building.

It was part of a whole set of tender drawings that was being used by the electrical sub-contractors to price their tenders during the bidding process of trade sub-contracts. The main contract was a negotiated-price design-and-build contract. All specialist trades were tendered out in an open tender process.

Many readers can probable make out the underfloor trunking system by just looking at the layout drawing. If you are not sure, below I extracted out some of the relevant symbols.

Image 3 – Junction box symbol

Image 4 – Service box symbol (Type 1)

Image 5 – Service box symbol (Type 2)

Image 6 –Symbol for cast-in-situ three-way underfloor uPVC trunking

Image 7 – Symbol for above ceiling 50 mm x 50 mm G.I. trunking

Image 8 – Two symbols of 13A switched socket outlets

As you can see, the underfloor service boxes are always located somewhere under a worktable (many architects prefer to call them “workstations”).

On the other hand, the junction boxes are always located at the junctions of the underfloor trunking system. It functions just like the conduit draw boxes at a wiring conduit system.

With the junction boxes at a certain maximum intervals along the underfloor ducting and at every corners and junctions (or intersections), the wiring cables can be easily drawn in during the wiring works.

This also helps during maintenance works.

In this design the underfloor ducting is a three-way uPVC type. That means there were three uPVC ducts along from one junction box or service box to another.

The three ducts were meant one each for 240V socket outlet wiring, telephone wiring and computer network wiring.

I am not going to go into many details about the whole underfloor ducting in this post. I just want to explain it in overall perspective to give a background to the issue of the 13A socket outlets as in Photo 1 above.

The 13A switched socket outlets

If you look closely at the above photograph, the power socket in the service box on the right is similar to the type normally used on walls.

While sockets installed inside the left service box is a fully flushed type.

The ones on the right are also called a flushed type, but in reality they are not 100 percent flushed into the surface they are mounted on.

The result of both these two types of socket outlets can be seen in Photo 8 below.

Photo 9 – The underfloor service boxes with the lid covers in closed positions

You can clearly see here that the lid cover of the right service box did not get  into a fully closed position.

Both lids were already pushed all the way down.

The service box on the right would be damaged together with the sockets in it after duration of use.

I believe that readers who have worked with junction boxes before might be asking: What the big deal about it? Either the choice is the left or the right one, either one would be able to work because the service box itself is adjustable vertically.

And both types of socket outlets are not that much different in terms of costs.

That is very true.

The problem here was contract management, not the technical or the implementation part of it.

During the proposal stage three brands of the socket outlets were submitted for approval to the client project managers.

This was a government contract and by the established procedures, in a design-and-build direct-negotiation contract, a main contractor was required to submit three brands of each equipment and material for approval by the government.

Whatever three brands were approved, all three were to included in the signed contract after the price was agreed on negotiation.

It was a good strategy. With three different manufacturers competing for each equipment, the main contractor would logically get a reasonable price during the tendering of trade sub-contracts.

At times, however, the government project managers at the last minutes decided to insist that only one brand for each equipment would be included in the signed contract. During those last minutes, without much time for the engineers to do enough study, one brand was chosen to be bound into the contract.

The main contractor therefore went to the negotiation table with this requirement and committed to the agreed price.

Later, things happened.

In this case, as it happened, the brand that was chosen did not have the fully flushed type of socket outlets.

To make things worse, nobody (including me who looked after the installation works at site) noticed until all the underfloor trunking system were cast into the concrete floor.

If it was realized earlier, the service box height could have been adjusted vertically during prior to the floor screeding works.

The thickness of the reinforced concrete floors could have been adjusted also.

However, once all the concrete floor works have been completed with the service boxes cast in, then there was no more choice.

The make of the socket outlets have to be changed.

Being a government contract, approving the change of brands after the main contract has been signed can have serious consequences on the government officials involved.

In a private project, this is not an issue at all.

A public project has a much higher political factors involved.

On many occasions, change of brands of the equipments and materials was totally forbidden.

Then that small problem above would become a really huge problem.

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.

Copyright . All rights reserved - 13A sockets inside underfloor box

No comments: