Advice On Rewire Of Lighting Circuit

[Master Mech]

I have just had some work carried our to rewire a lighting circuit in my house due to it having no earthing.

The lighting circuit is the original lighting circuit that was installed when the house was built in the 50's which was ran in steel conduit.

We now want to fit metal accessories but obviously require earthing for this to be safe so a rewire of this circuit is required & to be honest has been way overdue for replacement anyway.

Like most people I did not fancy chasing all the walls out to install new cables so asked the electrician if the steel conduit already plastered into the walls could be used saving the need to chase the walls out & redecoration.

He said that would not be an issue after looking over the installation as there would be enough room for the new cabling to be fed down the old conduit which was great news.

When he came to install the new cabling here found that he could not install the twin & earth cabling with the sheath attached as there was not enough room inside the conduit.

His solution was to strip the sheath from the twin & earth cabling and then wrap all the individual wires together in electrical insulation tape.

Removing the sheath created the room required to be able to feed the cables down the existing conduit.

Where the conduit ends in the loft space he left the sheath on the cables & the ran them to a junction box.

Here are some pictures of the junction box in the loft space & the tops of where the conduit for the switch drops end.

The same lighting circuit also covers not only the upstairs bedrooms but the landing, hallway & dining room lighting so cables needed to be ran under the landing floor boards & junction boxes installed.

Here are some pictures of the junction boxes under the landing floorboards.

So my question is are there any issues with how this work has been carried out?

I am probably making a mountain out of a mole hill but I would really appreciate your input.

Many thanks

Adam

 

[Master Mech]

Taking into account that the solution that was installed was agreed with the owner, if they do not like the result any alterations now will need to be paid for by the owner.

Whilst I can see where you are coming from he never asked me if this solution was acceptable to me.

I asked him at the time as I had concerns & he told me there was no issues with it & if he thought there was an issue I would expect him to not carry on with the work. I did not feel comfortable pressing the issue further at the time as I did not know how founded my concerns were.

Hence the reason I created this thread to find out if my concerns were founded. I now know there are issues with a work carried out so can with confidence raise them with the electrician.

Also nice to have options to discuss with him on how to resolve the issues that he himself may not be aware of.

 

[Intoelectrics]

Well he had a good think up in the loft & he came up with the solution we have now, the stripped cables.

I thought this was not "correct" so to speak but as I have said this is not my field so I had no way of knowing if this was acceptable or not so I was not in the position to make the call if there was a problem or not at the time.

Hence the creation of this thread, I am not trying to throw the guy under the bus I just wanted other peoples opinions on the work to see if my concerns had any merit.

Fair enough, I wasn't pointing a finger, but I'm sure you can appreciate that sometimes folk only give you half the story.

 

[Master Mech]

If the conduit is big enough would this cable be suitable to use?

https://www.screwfix.com/p/time-3185y-white-5-core-1mm-flexible-cable-5m-coil/68083

 

[Midwest]

I don’t see a problem with that, as long as it’s suitably sized; indeed I did suggest something similar earlier. The only issue I would have, is that this cable is connected to the fixed wiring with a suitable JB with suitable strain relief, and where it exits the split conduit, a suitable grommet is used.

BS7671 reg 521.9.1 (I think) mention use of flexible cable used in fixed wiring. Only caveat is using heavy duty flex. But in your case I can not see it be subject to any mechanical damage.

 

[Pete999]

I don’t see a problem with that, as long as it’s suitably sized; indeed I did suggest something similar earlier. The only issue I would have, is that this cable is connected to the fixed wiring with a suitable JB with suitable strain relief, and where it exits the split conduit, a suitable grommet is used.

BS7671 reg 521.9.1 (I think) mention use of flexible cable used in fixed wiring. Only caveat is using heavy duty flex. But in your case I can not see it be subject to any mechanical damage.

Good thought Mate, I think the answer is to string the So called Electrician up that Decided to strip the Mech Protection from the cables and thread them down a conduit,and chuck his tools away, do every one a favour and rid the world of these cowboys and stop them poncing on the unsuspecting general public, and hear was I thinking that only suspect car dealers were up to this malarkey.

 

[Master Mech]

So I am still waiting for the electrician to come back, I have heard from him & have not gotten a date from him on when he will return.

I do have another question regarding the grouping factor that will be applied to the three cables he has installed in the conduit. The cables/circuits & MCB's are as follows :

4mm2 T&E - 32 amp MCB

2.5mm2 T&E - 20 amp MCB

1.0mm2 T&E - 6 amp MCB

Am I correct in saying that because the conduit contains three circuits the grouping correction factor would be 0.70?

Then I am totally lost on how to apply this correction factor to these these circuits.

 

[Pete999]

Is this a continuous solid conduit system, or an oval conduit for burying in the wall the use of twin and earth suggests the later, can you confirm please?

 

[Mike Johnson]

That must be a very large conduit to accommodate those three cables and keep within the requirements of BS 7671 and not exceed 45% of the net cross-sectional area.

 

[Master Mech]

Is this a continuous solid conduit system, or an oval conduit for burying in the wall the use of twin and earth suggests the later, can you confirm please?

That must be a very large conduit to accommodate those three cables and keep within the requirements of BS 7671 and not exceed 45% of the net cross-sectional area.

He has used 25mm black conduit that is round, it is on the exterior wall of the house.

 

[Pete999]

He has used 25mm black conduit that is round, it is on the exterior wall of the house.

 

[Mike Johnson]

Ok I will bite, 25mm dia conduit has an internal area of 78.5mm sq, 4mm T&E has a nominal dia of 37mm sq so even without the 2.5 & 1 T&E the 45% space requirement is not maintained.

 

[Mike Johnson]

Sorry should have said "with the 2.5 and 1 the 45% space etc:

2.5mm T&E being 32mm sq and 1mm T&E being 24mm sq.

 

[Master Mech]

So in layman's terms there are to many cables for that size of conduit?

If the 4.0mm2 cable was removed would that compile with the regulations?

I presume this regulation is to prevent the cables from over heating?

 

[James]

So in layman's terms there are to many cables for that size of conduit?

If the 4.0mm2 cable was removed would that compile with the regulations?

I presume this regulation is to prevent the cables from over heating?

Also,to allow cables to be rawn in without damaging them

 

[Mike Johnson]

The cross section of T&E is a bit strange, as the cable is deemed to be the diameter of its major axis when in reality its anything but, so most electricians use a bit of common sense where this is concerned.