RCD protection for new pool heat pump

AussieP · Jan 12, 2022

Hi there all

I have a quick question. My garden supply CU has a 100A AC RCD as main switch - off that is my greenhouse supply circuit. Then a 63A AC RCD which protects 7 circuits, one of which is a pool heater. I am replacing the old heater and the new one requires residual DC protection. Can I replace the 63A RCD with a Type A ? My gut feel is that I will have to replace the 100A RCD main switch to a Type A as well ??

Could another option be to move the pool heater circuit next to the main RCD switch , then it's own supply to a small sub board with a Type A 30mA RCD protecting the circuit mcb ?

Deleted account · Jan 12, 2022

Can we have a photo. From your description is seems the circiut in question is protected by 2 RCD’s in series. I suspect this isn’t the case, but best make sure with photo.

AussieP · Jan 12, 2022

Paignton pete said:
Can we have a photo. From your description is seems the circiut in question is protected by 2 RCD’s in series. I suspect this isn’t the case, but best make sure with photo.

Sorry I should have worded that slightly better. Main switch is 100Amp 100mA AC RCD. The greenhouse supply is installed but not live yet ( being rejected next week! ). The RCD protecting other circuits is 63Amp 30mA Type AC. Just trying to get photo for you.

AussieP · Jan 12, 2022

Paignton pete said:
Can we have a photo. From your description is seems the circiut in question is protected by 2 RCD’s in series. I suspect this isn’t the case, but best make sure with photo.

Deleted account · Jan 12, 2022

AussieP said:
Sorry I should have worded that slightly better. Main switch is 100Amp 100mA AC RCD. The greenhouse supply is installed but not live yet ( being rejected next week! ). The RCD protecting other circuits is 63Amp 30mA Type AC. Just trying to get photo for you.

thanks. Sounds better. I’d assume a time delayed 100ma. Also I assume you have an earth rod (TT system) for your earth path.

my First instinct is to say replacement of the rcd protecting the new heater i all that should be needed, however as I was typing this reply I thought about it a bit more.

I have read about DC RCD fault current blindness And some articles do say it can interfere up stream. So maybe both do Need changing.

I await an answer from some of our more intelligent members with anticipation.

I have recently installed a circuit in my home for a electriv vehicle charger and fitted a DC RCD however I did not replace any other residual current devices.
my set up is different I have each circuit protected by sepearate RCD’s. And don’t have double rcd protection on the EV circuit.

sorry I couldn’t be more help.

AussieP · Jan 12, 2022

Paignton pete said:
thanks. Sounds better. I’d assume a time delayed 100ma. Also I assume you have an earth rod (TT system) for your earth path.

my First instinct is to say replacement of the rcd protecting the new heater should be needed, however as I was typing this reply I thought about it a bit more.

I have read about DC RCD fault current blindness And some articles do say it can interfere up stream. So maybe both do.

I await an answer from some of our more intelligent members with anticipation.

I have recently installed a circuit in my home for a electriv vehicle charger and fitted a DC RCD however I did not replace any other residual current devices.
my set up is different I have each circuit protected by sepearate RCD’s. And don’t have double rcd protection on the EV circuit.

sorry I couldn’t be more help.

Thanks for replying. My situation is a little convoluted at my property, I installed an earth rod making the garden supply a TT as it shared the PME earthing arrangement with the house supply ! I have two 100Amp supplies coming into the property ( one for the house which is TNCS and the other (supplies garden on it's own) had no direct earthing but connected to MET where the PME arrangement was shared !) I disconnected the old earth conductor from that MET which went to the old CU in garden !

AussieP · Jan 12, 2022

Paignton pete said:
thanks. Sounds better. I’d assume a time delayed 100ma. Also I assume you have an earth rod (TT system) for your earth path.

my First instinct is to say replacement of the rcd protecting the new heater i all that should be needed, however as I was typing this reply I thought about it a bit more.

I have read about DC RCD fault current blindness And some articles do say it can interfere up stream. So maybe both do Need changing.

I await an answer from some of our more intelligent members with anticipation.

I have recently installed a circuit in my home for a electriv vehicle charger and fitted a DC RCD however I did not replace any other residual current devices.
my set up is different I have each circuit protected by sepearate RCD’s. And don’t have double rcd protection on the EV circuit.

sorry I couldn’t be more help.

Just thinking if your EVSE has built in typeA rcd and the supply cable doesn't require additional protection it can be supplied from the non RCD side of the CU yeh ? Just the appropriate sized MCB for the load .

Deleted account · Jan 12, 2022

I’ve just put the circuit in ready for the ev charger. I’ve not actually bought or fitted it yet. But yes most do have built in Rcd‘s.
however In my experience I don’t like to rely on built in protection. especialy where electric vehicles are concerned.

did you say your garden supply is PME and TT?

AussieP · Jan 12, 2022

Paignton pete said:
I’ve just put the circuit in ready for the ev charger. I’ve not actually bought or fitted it yet. But yes most do have built in Rcd‘s.
however In my experience I don’t like to rely on built in protection. especialy where electric vehicles are concerned.

did you say your garden supply is PME and TT?

It shared the PME via the earth conductor connected to the MET in the meter cupboard ! I made it a TT by installing a new earth conductor to an earth rod and disconnecting the old conductor .

brianmoooore · Jan 12, 2022

Right, I'm lost! Are you saying that CU has two independant supplies coming into it; one connected to each of the RCDs?
Surely if a DC sensitive RCD is downstream of a conventional one, in the event of a DC fault, which will 'blind' the conventional one, the DC sensitive RCD will trip, removing the DC component, and the upstream RCD will then be 'unblinded'.

Deleted account · Jan 12, 2022

brianmoooore said:
Right, I'm lost! Are you saying that CU has two independant supplies coming into it; one connected to each of the RCDs?
Surely if a DC sensitive RCD is downstream of a conventional one, in the event of a DC fault, which will 'blind' the conventional one, the DC sensitive RCD will trip, removing the DC component, and the upstream RCD will then be 'unblinded'.

The way I read the opening post and additional replies.

2 100A supplies

one for house cu

one for garden CU.

the garden CU has been turned into a TT.

main switch in garden CU is a100mA RCD.

the heater circuit in garden CU is protected by a 30mA RCD As well.

as for the blinding. Could the heater being installed blind the upfront RCD from conventional faults on other circuits During normal running of appliance without a fault on the heater.
hope that made sense.

AussieP · Jan 12, 2022

Paignton pete said:
The way I read the opening post and additional replies.

2 100A supplies

one for house cu

one for garden CU.

the garden CU has been turned into a TT.

main switch in garden CU is a100mA RCD.

the heater circuit in garden CU is protected by a 30mA RCD As well.

as for the blinding. Could the heater being installed blind the upfront RCD from conventional faults on other circuits During normal running of appliance without a fault on the heater.
hope that made sense.

you got it Pete . two supplies . one does house , other for the garden which is about 15 meters away.
new supply was added when house extended and work done in garden, one supply couldn't handle the total demand. Both supplies shared the same PME earthing arrangement.