Upgrade RCD

LarpPaul · Post by **LarpPaul** » Fri Jul 12, 2024 10:06 pm

Hi everyone I’m looking at installing an electric shower. However I’ve got a split load board with 2 63A RCDs that are already maxed out and my main cut out fuse is rated at 60A.

My question is can I swap 1 of the 63A RCDs for an 80A RCD as most things on this circuit won’t be running at full capacity continuously and I’ve heard the main fuse can work past 60A for a couple of hours before popping.

TIA

Someone-Else · Post by **Someone-Else** » Sat Jul 13, 2024 12:08 am

That is not how it works.
Where are you going to connect this shower to?
What rating is the shower going to be
Are you (thinking) of doing it or are you going to get an electrician?

LarpPaul · Post by **LarpPaul** » Sat Jul 13, 2024 2:16 am

The shower is 9kw and going on a 40a mcb. There’s space in the board but there is already 2 x 32a and 2 x 16a on one side of the board. That is why I’m wondering if I can just change the rcd for an 80a instead of the already installed 63a to accommodate.

Someone-Else · Post by **Someone-Else** » Sat Jul 13, 2024 10:33 am

Why change it, nothing wrong with what you have, no need to change it. Look up diversity.

OnlyMe · Post by **OnlyMe** » Sat Jul 13, 2024 5:48 pm

S-E is correct. Diversity applies.

ericmark · Post by **ericmark** » Sun Jul 14, 2024 9:04 am

OnlyMe wrote: ↑Sat Jul 13, 2024 5:48 pm S-E is correct. Diversity applies.

It did, years ago, but I believe that is no longer the case? Either the DNO fuse needs to be less than the RCD, or the sum of the MCB's needs to be less than the RCD. Diversity can be used when selecting MCB's, but not RCD's, in the main the move to RCBO's (MCB and RCB combined) has removed the problem.

However, if the DNO fuse is 60 amps, then there is no problem, you can use a 63 amp RCD. The DNO fuse can be 60, 80 or 100 amp. Technically, it could be smaller, but not seen one, the old Wylex fuse box had an isolator rated at 60 amp, so many homes have a DNO fuse that matched the original fuse box, there has been a move to larger supplies to allow the use of heat pumps and EV charging, including three-phase, but never seen a domestic supply over 100 amps.

The RCD is duel marked, 63 amp is the running amps, but the short circuit amps are far higher, 6kA is common, this is selected by measuring the PSCC (prospective short circuit current) and one would need a loop impedance meter to measure this. However, it should be entered onto the insulation certificate, I have two electric showers and a 60 amp DNO supply, so yes you can fit an electric shower even with a 60 amp supply, but the work involved in fitting a new electric heated shower, is in the main the same as fitting a water mixing shower, and the latter is far better. You can get pumped showers, which only need a 3 amp supply, if the shower head it too high, and if you ever get solar, then a water mixing shower allows one to use excess solar to heat the water. If using a combi boiler then no problem with pressure.