T&E In Round Conduit 20mm

[recorder]

Hi All

Would sincerely appreciate some advice please on the following: had an electrician rewire the garage. Installed 2 double metal clad sockets and 2 2-way metal clad light switches all wiring hidden in 20mm conduit.

The electrician used 2.5mm cable for sockets/32A mcb and 1.5mm cable (3 and 4 core) for light switches/3A FCU.

There were 2 electricians and one was an apprentice and I overheard them arguing about placing t&e into conduit and the apprentice suggested the use of single core cable. I don't know anything about wiring, cables or conduits.

They had 1 x 2.5mm cable from the consumer unit to the 1st socket then another 2.5mm cable from the 1st socket to the second socket/there was no return.

For the lighting they used a 2.5mm cable from the 1st socket and into a FCU (3amp) and then a 1.5mm cable to the light.

For the 2 way switches they used 1.5mm 3 and 4 core cable. In some places the 2.5mm and 1.5mm cable run together in conduit. There are 2 bends for socket cabling/3 meters cable length and about 4 bends for lighting cabling/5 meters length.

All I wanted to know was have they wired the garage correctly as their disagreement on the use of t&e has made me think twice and when I asked them they just said everything is fine no need to worry.

Thank you.

 

[DaftPunk]

T&E in conduit is fine, it's just a bit harder to install due to its overall size and that it has solid copper conductors whereas singles are smaller and stranded copper conductors.

The worry for me is that you're describing a 2.5mm² radial circuit for the sockets. This must be supplied by an OCPD with a maximum rating of 20A. It sounds like yours is supplied from a 32A device, which is too large for the size of cable.

 

[securespark]

My only addition to that is possibly that if the sparks used 20mm conduit, on parts of the run where the conduit is heavily populated, there may not be enough space in the conduit, leading to possible overheating and (more likely) damage to cables during installation due to their additional bulkiness.

In this case, maybe the apprentice was right! Certainly the 32A breaker is wrong, unless the cable is 4 milli, not 2.5.

 

[sparkwright]

The thing with using single cores (as the apprentice wanted to do) is that the whole installation has to be in round conduit.

By using twin and earth, you don't need a full conduit system. Just, for example, the drops down the wall; and the wiring up high just cable clipped to the surface.

If EVERYTHING in the garage is complete uninterrupted conduit, singles should have been used really.

If just random conduit drops, has to be twin and earth.

Spacing factor comes into it with conduit.

 

[Lectrician]

My only addition to that is possibly that if the sparks used 20mm conduit, on parts of the run where the conduit is heavily populated, there may not be enough space in the conduit, leading to possible overheating and (more likely) damage to cables during installation due to their additional bulkiness.

In this case, maybe the apprentice was right! Certainly the 32A breaker is wrong, unless the cable is 4 milli, not 2.5.

Overheating is not the reason for "conduit/trunking cable factors", that's what the grouping correction factor is for.

 

[PrenticeBoyofDerry]

The electrician used 2.5mm cable for sockets/32A mcb.......They had 1 x 2.5mm cable from the consumer unit to the 1st socket then another 2.5mm cable from the 1st socket to the second socket/there was no return.

32AMCB is not suitable for this type of socket arrangement, either 20A device should have been used or a return leg to CU to make the circuit a ring final rather than a radial circuit.

and 1.5mm cable (3 and 4 core) for light switches/3A FCU......For the lighting they used a 2.5mm cable from the 1st socket and into a FCU (3amp) and then a 1.5mm cable to the light...........For the 2 way switches they used 1.5mm 3 and 4 core cable. In some places the 2.5mm and 1.5mm cable run together in conduit

That seems fine, other than the sizing of spur cable from socket to FCU, but this is down to original MCB sizing.

There were 2 electricians and one was an apprentice and I overheard them arguing about placing t&e into conduit and the apprentice suggested the use of single core cable. I don't know anything about wiring, cables or conduits.

You will be lucky to get two sets of T&E through 20mm conduit, so if conduct was being used, the wise option would be to use single cores.
When cables are used within conduit there are a number of de-rating factors of the cables current carrying capacity that need to be worked out, this would include the grouping of cables and the use of containment, I would suggest, in this case that the 32A MCB is replaced by a 20A MCB or the circuit is redesigned in to a ring final circuit.

 

[securespark]

My only addition to that is possibly that if the sparks used 20mm conduit, on parts of the run where the conduit is heavily populated, there may not be enough space in the conduit, leading to possible overheating and (more likely) damage to cables during installation due to their additional bulkiness.

In this case, maybe the apprentice was right! Certainly the 32A breaker is wrong, unless the cable is 4 milli, not 2.5.

Overheating is not the reason for "conduit/trunking cable factors", that's what the grouping correction factor is for.

Not well explained, maybe, but I wasn't implying the spacing factor was there to deal with overheating, just that the cables being grouped together closely may cause overheating.

 

[recorder]

Thank you all for your sincere advice.

I have managed to call out another electrician who changed the mcb from 32a to 20a.

The t&e in conduit he stated is not normal practice but everything seems to be ok and there is no need to start all over again. He further suggested an RCD FCU be fitted onto the main cable coming from the consumer unit into the garage for safety.

He confirmed that the 20mm conduit does have 2.5mm and 1.5mm cable fed into together.

I'm not sure if all these electricians are seeing me as an old fool they can rob.

Can anyone confirm if this is necessary?

Thank you.

 

[Lectrician]

If there is no RCD protection already, then it is absolutely required. Not just for safety, but to comply with the regs.

 

[ban-all-sheds]

had an electrician rewire the garage.

Apparently not.

 

[PrenticeBoyofDerry]

I'm not sure if all these electricians are seeing me as an old fool they can rob.
Can anyone confirm if this is necessary?

I could not comment on whether you are an old fool or not, but it seems you have been wise to post the topic on this forum, for informed replies, opinions and options.

The last electrician (possible the only electrician, ref to BAS post)
Was correct by reducing MCB rating for this circuit, also if there was not any RCD protection offered to the sockets then this should have been installed, as that is a requirement. Using a 13A RCD/FCU is one method to do this, but would restrict the garage load to 13A.
It could be possible to, have the socket plates with RCD protection, as the cable is mechanically protected and not buried or have a 20A RCBO fitted instead of the 20A MCB that has just been installed (if the board allows for this)
RCD sockets are about £20 each and RCBO depending on the board generally around the £30-£35 mark.
Did you receive any documents/certificates for this installation?

 

[mfarrow]

Strictly speaking the second electrician is now in the wrong as he has replaced the MCB with a smaller one but still left you with no RCD protection on the sockets, potentially.

I know the regs now allow you not to fit an RCD when making amendments in all circumstances but this is basically a new circuit now that the CPD has changed and it wouldn't have cost much to fit an RCBO there and then.

Some photos please.

 

[ban-all-sheds]

I know the regs now allow you not to fit an RCD when making amendments in all circumstances.

But thosw were never the circumstances here, from the start:

had an electrician rewire the garage. Installed 2 double metal clad sockets

Of course there may be RCD protection upstream of the garage CU.

 

[JohnW2]

Of course there may be RCD protection upstream of the garage CU.

Possibly - but it seems fairly unlikely, given that the new electrician has advised putting an RCD FCU in the feed to the garage.

Kind Regards, John

 

[JohnW2]

Strictly speaking the second electrician is now in the wrong as he has replaced the MCB with a smaller one but still left you with no RCD protection on the sockets, potentially.

As you say, given that the electrician was obviously awareof the issue, and therefore advised adding an RCD FCU to the garage feed, it does seem a little odd that he didn't simply replace the 32A MCB with a 20A RCBO - the cost of which wouldn't be much different from an RCD FCU + new MCB. One wonders whether there was perhaps a practical issue in fitting an RCBO into the CU?

Kind Regards, John