Where can I buy an 18th edition consumer unit?

[ProDave]

From a recent Voltium post:

Regulation 536.4.202 – current rating of devices


The issue where there are split load consumer units with a 100A switch and an 80A or 63A RCD providing RCD protection for groups of circuits. Also, if you’ve got a 100A service fuse that doesn’t provide protection for your 63A RCD.


If you’ve a 100A service fuse that doesn’t provide protection for your 63A RCD. Previously, diversity took into account that if you’re the designer you could allow for your 63A not pulling any more than your 63A, and hence no need for protection. But the regulations say there is no diversity. Now, if you have a 100A service fuse or 80A your RCDs in split load boards should match the rating of those devices.

So now the RCD in a split load CU should match the rating of the service fuse, which up here is usually 100A

So looking for a small CU today, looking at Electricfix, not one appears to have a 100A rated RCD.

So are we all quietly ignoring this?  Or does someone know a magic source of CU's with 100A RCD's?

Oh and now there is the need to pull the main fuse to actually see it's rating?  Or do we assume 100A as even though it might not be now, the DNO could fit a 100A fuse at any time?

 

[Evans Electric]

Interesting points there .      Most split load  RCDs ,  without double checking , are 80A  usually , are  they not ?       Does anyone bother or care anymore ?  Do I ?   No . TBH

Oh and now there is the need to pull the main fuse to actually see it's rating?  Or do we assume 100A as even though it might not be now, the DNO could fit a 100A fuse at any time?

We've had this " Need to pull the main fuse "   for a while now ,   certainly  with   the ELECSA  certs  which ask for the rating  / type /  BS number .   

Down here they could be  a mixture of  BS 3036  ..BS1361...60A / 80A / 100A      I used to use my Xray specs  to look  but these days I ignore it  ...not allowed to look so I don't look .   Its an NV  .   If someone needs that info they can turn up and look for themselves. 

 

[ProDave]

The point is, the new interpretation of the regs says we must design the distribution based on the supply fuse rating,  Sure we can put NV, but on the basis it could be anything up to 100A in there, then we must design for 100A?

So 80A or 63A rcd's are no longer okay.  Someone needs to tell the manufacturers.

Or we fit an 80A switch fuse in front of every CU just so we know it has an 80A fuse?

Or (as I suspect is the case) we ignore it as a load of old tosh.  It has been safe like that for the last 10 years, so why is it not safe today?

Who will be the first to get pulled on this at your assesment?

 

[Murdoch]

Clutching at straws springs to mind .....

Going to ignore this tosh

Next

 

[binky]

Never seen a melted RCD in  aboard from overloading - ruddy twaddle imho, so will be duly ignored. Would mean all RCBOs would need to be 100A as well - should make wiring lights entertaining...

 

[Murdoch]

Have the people who write this carp never heard of diversity?

 

[Rutts35]

Diversity? They probably think it's a dance group from Britains Got Talent.  :coat

 

[Tony S]

About the only way around this is a 100A DP MCB as the main isolation point.

Unfortunately it is an expensive option.

 

[ProDave]

About the only way around this is a 100A DP MCB as the main isolation point.

Unfortunately it is an expensive option.

No, you mean an 80A DP mcb as the incomer.

 

[Tony S]

A 100A MCB will operate much faster than a DNO fuse on a short circuit.

 

[ProDave]

Yes but the new interpretation of the regs says 80A rcd must have an 80A OCPD in front of it, not 100A

 

[NozSpark]

The new Hager twin RCD boards have 100A/30mA RCD's and a SPD

Cost around £150+ with 8 MCB's around here

.......however you then run into the reg about leakage on RCD protected circuits being <1/3 mA rating of the RCD

 

[Sidney]

So in domestic you could get away with using a 63 amp MCB with a 100 amp rating as a main switch, then you could use 2x 63 amp rated RCDs or RCBOs etc.

 

[binky]

OCPD can be at either end of a cct, so if you had a 63A RCD that would allow 1off 32A MCBs and say a 20A and a 6A cct attached to it or 3 off 20A MCBs etc etc.

I would argue RCBOs protect themselves in the same way, ie if you try to overload a 32A RCBO it trips out, so doesn't need an OCPD upstream of it.