Sub Boards for heat pump installations

[ScottishGasMan]

Just wanting to run a few things by you to check I've got this right in my head with what is allowed and what is not.

Some heat pumps need Type-B RCD protection, If you have a full or nearly full CU and can't fit it in, or can't get appropriate breakers of the same make you would need a sub board (or full CU replacement with bigger board)

If you split the meter tails to feed 2 boards.

A. Is there not an issue with both boards having say 100A cutouts, meaning you could draw more than the DNO fuse cutout? (obv they should be doing MD calculation to ensure thats not an issue with whats installed in the house, but are you allowed to split incoming supply to 2 boards in this manner?)

If you did split supply into two boards, would they both have to be the same make? Or could one be Hager and another Crabtree for example?





When I'm checking heat pump installs, I often see CUs with mixed branding MCBs/RCDs in them which I know Is not allowed. But unsure when using sub boards if they both have to be same make, or they can be different.

I know (Think I know) If you have main CU, then had say a 40A fuse feeding a 2nd board, which had its own fuses/rcds for feeding heat pump/controls etc then they could be differnt without a problem?

 

[EFLImpudence]

Some heat pumps need Type-B RCD protection, If you have a full or nearly full CU and can't fit it in, or can't get appropriate breakers of the same make you would need a sub board (or full CU replacement with bigger board) If you split the meter tails to feed 2 boards.

Ok.

Is there not an issue with both boards having say 100A cutouts, meaning you could draw more than the DNO fuse cutout?

What do you mean?
They will both be fed from the one existing cut-out - you cannot fit another - so no difference between one board or two.

(obv they should be doing MD calculation to ensure thats not an issue with whats installed in the house, but are you allowed to split incoming supply to 2 boards in this manner?)

Only after the meter.

If you did split supply into two boards, would they both have to be the same make? Or could one be Hager and another Crabtree for example?When I'm checking heat pump installs, I often see CUs with mixed branding MCBs/RCDs in them which I know Is not allowed. But unsure when using sub boards if they both have to be same make, or they can be different.

No. Makes no difference having separate different makes but not mixed.

I know (Think I know) If you have main CU, then had say a 40A fuse feeding a 2nd board, which had its own fuses/rcds for feeding heat pump/controls etc then they could be differnt without a problem?

Correct.

 

[ScottishGasMan]

What do you mean?
They will both be fed from the one existing cut-out - you cannot fit another - so no difference between one board or two.

Sorry, Yes, I meant from a single main cut out.

I had it in my head somewhere that the Main Switch on the CU couldn't be rated higher than the cutout, so following that In my head 2 CUs would always be higher than the cutout and not allowed. But then its just clicked that the main 100Amp switch is just the max rating of the switch and not itself a protective device.

So multiple CUs ok

No. Makes no difference having separate different makes but not mixed.

This is what started my line of questioning off, as I was trying to explain to some engineers that an RCBO with B on the front of it has a circuit breaker characteristic of B, but will still have a Type A Residual protective function. To which I was told Thats why they are often fitting subboards, but you cant mix different brands of equipment.

I know you can't use different brands within the board for the type rating, but never heard of a problem using different makes of board assuming they contain the same equipment.

So Cutout -> meter -> Isolation switch -> Henelys -> Henleys can then feed 2 different makes of board (so long as each only contains their own make of devices)

 

[ScottishGasMan]

but will still have a Type A Residual protective function

Also yes, I realise it could be a type AC on the RCD side. But currently to the best of my knowledge, no one makes an RCBO that has Type B RCD protection, although I did read recently a company was developing one.

 

[EFLImpudence]

This is what started my line of questioning off, as I was trying to explain to some engineers that an RCBO with B on the front of it has a circuit breaker characteristic of B, but will still have a Type A Residual protective function. To which I was told Thats why they are often fitting subboards, but you cant mix different brands of equipment.

Yes, it is a poorly marked system using the same letter for two different characteristics.

I know you can't use different brands within the board for the type rating, but never heard of a problem using different makes of board assuming they contain the same equipment.

You are confusing me again.
As you said, different brands are not supposed to be mixed but two different brand boards presumably do not contain the same equipment.

So Cutout -> meter -> Isolation switch -> Henelys -> Henleys can then feed 2 different makes of board (so long as each only contains their own make of devices)

Yes.
You might be able to fit both sets of tails to the isolation switch or maybe Henleys as well would be more convenient.

 

[ScottishGasMan]

You are confusing me again.
As you said, different brands are not supposed to be mixed but two different brand boards presumably do not contain the same equipment.

Typing on phone at the min so probably trying to shorten it up to much.

When I say same equipment I meant same as board. ie. incoming supply feeds 2 boards, one is hager and the other is BG, The hager board contains only hager breakers, and the BG board only contains BG breakers. Thats not an issue?

 

[ScottishGasMan]

Yes, it is a poorly marked system using the same letter for two different characteristics.

Yea, I can certainly see how so many people get confused with it.

I train folk on heat pumps, more so the installation & plumbing system side of it, but get a lot of electricians coming in now, and many are not well versed in different RCD types to begin with (I suppose domestically if they don't do PV/EV then they would only ever have likely used one type of RCD or RCBO. And as you say the labeling of RCBOs amplifies the confusion.

I'm not there to train electricians in their own trade, but I want to be helpful where I can and just wanted to make sure I've got it right in my head that I don't give out any inappropriate advice.

 

[EFLImpudence]

When I say same equipment I meant same as board. ie. incoming supply feeds 2 boards, one is hager and the other is BG, The hager board contains only hager breakers, and the BG board only contains BG breakers. Thats not an issue?

All good.

I train folk on heat pumps, more so the installation & plumbing system side of it, but get a lot of electricians coming in now, and many are not well versed in different RCD types to begin with (I suppose domestically if they don't do PV/EV then they would only ever have likely used one type of RCD or RCBO. And as you say the labeling of RCBOs amplifies the confusion.

I've been retired nine years so not exactly an expert on the different types so I wouldn't advise on which do what.

The powers that be in the electrical sector do seem to change their minds quite often.

I'm not there to train electricians in their own trade, but I want to be helpful where I can and just wanted to make sure I've got it right in my head that I don't give out any inappropriate advice.

 

[ericmark]

But currently to the best of my knowledge, no one makes an RCBO that has Type B RCD protection, although I did read recently a company was developing one.

Not as a single module width, but they are made.

Heat pumps do interest me, as there is no reason, just like with commercial freezers, why the motor speed can't be adjusted rather than switch on/off, and that could include not only temperatures of the dwelling, but also power availability, so it could reduce what power it used as demands on the home increase. So, like with EV charging, we could have CT coils to tell the heat pump when to reduce what it is using.

However, I have seen it with my immersion heater, that also has a CT coil to tell the iboost+ how much power it can use, so with solar power, EV charging, DWH, and heat pumps we would end up with an array of CT coils, and I know the iboost+ CT coil does not like being too close to other CT coils, so can see in the future a power management system, to decide what can run when.

Already, things like the ivector fan assisted radiator are designed to connect to a building management system, and clearly with the lower temperatures use with heat pumps, fan assisted radiators are going to be a huge advantage when trying to reduce recovery time.

Oh, I am glad I am retired, but it does mean level 3 education is likely in the future not going to be enough, and we will have electricians as well and heating and ventilation engineers with degrees. I assume to be called an engineer, they have a degree? Yes, I did do a degree, but have no wish to do the maths required for a degree on a daily basis.

However, on the original question, there has been news about the use of consumer units outside, and it seems there are moves to alter the regulations about that. And a lot of debate going on.