Consumer Unit Wiring Question

[Wired1]

Hi,

I have a question about wiring a garage consumer unit.

I have a Volex garage 2 way consumer unit IP65 - 6A & 16A (main incoming breaker 32A).

Not sure which size wire to use to connect the main breaker to the neutral bar.

Any advice please?

Thanks.

 

[PrenticeBoyofDerry]

Do you mean isolator or is it an RCCB?
Photo please!

 

[abrocky]

Too many variables not known to advise.

Cable calculations required for volt drop etc..

Wat type of cable is to be used, Distance from where it's weirded from and to, how the cable is run, buried, clipped direct etc? Ambient temperature, are you on rewire able fuses? Ambient temperature?

may be easier, and safer to get an electrician...

 

[ban-all-sheds]

Not sure which size wire to use to connect the main breaker to the neutral bar.

And I am certain that you should not be attempting the installation of a consumer unit.

Are you planning to do it illegally?

What about testing?

 

[AndyPRK]

normally a thick bit of wire is used!

called tri something. Can't see any on ebay.

An off cut of the incomming wire would do.

 

[viewer]

Too little information to know about the installation. OP doesn't even say whether a detached garage. It is on a 32A MCB, but is that protected by a RCCD?
However all those factors and questions raised by posters don't address the simple original question - what to use for the 50mm long link? As the OP will have got so far and will (have to?) continue whatever, I'd suggest that, in the absence of "blue" wire s/he should use a piece of 6mm or 10mm (as available) Y/G and sleeve it with blue.

 

[rjm2k]

A photo always helps

 

[ban-all-sheds]

OP doesn't even say whether a detached garage.

Irrelevant.

It is on a 32A MCB,

Is it? He says the CU has a "main incoming breaker 32A", not what the supply to it has.

The problem is that Volex don't appear to do a CU with a 32A breaker as an incomer, or even a 32A RCD, so what do we have here?

And it's not normal, is it, to buy a CU with a switch or RCD incomer which is not cabled to the N bar, or at least supplied with a length of cable, so what do we have here?

Do we have some cobbled together unit rather than a proper CU?

Do we have someone asking who has mis-described what he has because he doesn't know what he is looking at?

what to use for the 50mm long link?

Why doesn't someone who is competent to install a CU know what size cable to use given the rating of the device protecting it?

As the OP will have got so far and will (have to?) continue whatever

No, he doesn't have to continue whatever, what he has to do is to stop right now and get someone who knows what they are doing to install this.

I'd suggest that, in the absence of "blue" wire s/he should use a piece of 6mm or 10mm (as available) Y/G and sleeve it with blue.

I'd suggest that he engages an electrician.

And I would assert with utter certainty that any advice or assistance which leads to him continuing to grope his way forward is dangerous and irresponsible, and absolutely not in his best interests.

 

[Agile]

You all seem to imagine that this is brand new and internally wired.

Most likely its bought at a car boot sale and can be in any state !

Tony

 

[ban-all-sheds]

You all seem to imagine that this is brand new and internally wired.

Do we have some cobbled together unit rather than a proper CU?

 

[Wired1]

Not sure which size wire to use to connect the main breaker to the neutral bar.

And I am certain that you should not be attempting the installation of a consumer unit.

Are you planning to do it illegally?

What about testing?

It will be Part P tested don't worry.

The incoming mains breaker (RCD) is 40 amp although the current through this is limited as its a spur taken off the main consumer unit and is on a 20 amp MCB. The incoming wire is 2.5mm 2 therefore - nothing to do with me, existing wiring / arrangement which I don't intend to touch.

Technically therefore, I know I could get away with 2.5mm inside the garage unit as its already limited upstream. However, I doubt it would pass an inspection with that as the main breaker is 40 amp.

My feeling therefore is the main breaker to neutral bar needs to be of higher rated cable even though its limited by the feed in. Not sure what diameter should be using though for a 40 amp breaker - 6mm 2, 10mm 2?

 

[Wired1]

OP doesn't even say whether a detached garage.

Irrelevant.

It is on a 32A MCB,

Is it? He says the CU has a "main incoming breaker 32A", not what the supply to it has.

The problem is that Volex don't appear to do a CU with a 32A breaker as an incomer, or even a 32A RCD, so what do we have here?

Sorry should have read 40 amp - One of these:

http://www.toolstation.com/shop/Ele...nits/Volex+Garage+Kit+IP65/d190/sd2917/p27838

 

[securespark]

You need to ensure that the cable supplying the garage CU is meaty enough

a. to take the load you intend putting on that cable AND

b. to exceed the value of the device supplying the cable.

The RCD is not a current limiting device. It will not trip if you exceed 40A. But it must not be used to supply more than 40A.

But it can be used for circuits under 40A.

 

[rjm2k]

I doubt it would pass an inspection with that as the main breaker is 40 amp.

My feeling therefore is the main breaker to neutral bar needs to be of higher rated cable even though its limited by the feed in. Not sure what diameter should be using though for a 40 amp breaker - 6mm 2, 10mm 2?

I'm no expert but I can't see how it can pass an inspection if the cable feeding it is not correct.

On the cable to use in the CU, just looking at T&E online suggests that 10mm will take 52A and 6mm will take 38A, but as you say the 2.5mm is protected by a 20A breaker at the main CU I'd hazard a guess that it's not that relevant. If anyone were to upgrade the 20A breaker the cable would probably melt anyway with a higher load than 27A

I have a similar setup in my garage and it was suggested to me that as long as the cable out of the main CU is RCD protected and also has a suitable fuse (I think it has 16A from memory) then I may as well scrap the garage CU/RCD, feed the garage lights off a 5A FSU and the sockets direct. Indeed recent experience with an angle grinder tripped the main CU fuse but left the garage fuse of the same rating alone, also testing the RCD tripped both the main RCD and the garage RCD at the same time.

How about posting a photo of the main CU and garage CU etc .

 

[securespark]

Valid point about the RCD's: are there two in line?

But my point about the 40A RCD still stands: Just because it is a 40A RCD does not mean it should be supplied with a cable rated at 40A. The cable feeding the garage CU should be rated to the device supplying it and the design current.

Having said that, I believe that there is no discrimination between the breakers.