Air source heat pump trouble...Help!!!

[Ben Butcher]

Hi Everyone,

I apologise, this is going to be a bit long winded! Any help would be gratefully received though.
I have just finished wiring the supplies for an air source heat pump. By manufacturers spec it needs a 32A supply outside for pump itself, and a 16A supply to the indoor control unit, so that is what I have given it. The existing installation is TT with a 10 way Hager CU and a separate 30mA 100A RCD/Main switch, the CU itself is old school with straight isolator (100A)

Basically the problem is that after installing the two circuits, and prior to connecting them I couldn't get a very good earth reading at the CU. I scratched my head for a bit, and then found that the connection to the earth rod had broken off, the earth rod by the way is only about 2 months old as they had had problems with nuisance tripping.....I dutifully reconnected the earth and continued (got a Ze reading of 232 ohms, a little high I know but given there was nothing before I was keen to carry on a worry about that at the end.)

Anyway, finished wiring everything and switched it all on, after about 5 mins the whole installation switches off at the RCD, and continues to do this randomly untill I switched off the PV to save it from damage. At this point the rest stayed on fine. At the moment the RCD seems happy with either the whole house and PV, or the whole house and Air source, but not both????

Is it possible to overload an RCD and will this make it trip? I am tempted to fit another separate two way CU for the Air source but of course there is very little room in there and the customer is beginning to look at me like a fool on the basis that "it was all OK before...."

Any tips would be very gratefully listened to. Thanks in advance, Ben.

 

[Jdsparky]

Rcds don't protect for over current or over load......probably earth leakage current too high (more than 30ma or 100ma which ever installed), but saying that whoever put the p.v in they should have put t on its own little board with its own Rcd if applicable anyway, as they shouldn't share the Rcd with the house in a perfect world, so the customer may be able to get the p.v company back to change the arrangement they have got at the moment.

 

[Gavin A]

sounds like you've got both PV and heat pump on the same RCD, and the earth leakage current from both combined is tripping the RCD.

is this a whole house RCD ie 100 or 300mA RCD because it's a TT system or just the 30mA RCD for a split board?

if the latter, then you really want to be taking both the PV and heat pump off those circuits onto their own dedicated supply IMO - PV can cause nuisance tripping of RCD, and depending on the inverter can sometimes cause the RCD to stick, and the heat pump will probably have high start up currents, so may well need to be on a more industrial type MCB to allow for this - check manufacturers instructions and I'm sure it will tell you anyway.

 

[Ben Butcher]

Thank you both, having sat here reading for a bit I am beginning to see that generally PV is not installed on a shared RCD, let alone a 30mA one on a whole TT system, I did think this may be asking for trouble! Now of course I have the same old bother, go back to the customer and politely explain that although it is me that has just installed something it is still the PV installers fault...me thinks I might get a frosty response! Probably better for me to move the PV and see if it fixes it. Hey ho!

Thank you both again. Ben.

 

[Jdsparky]

I wouldn't touch the p.v personally as its only started tripping once you've added the heat pump so just put that on its own Rcd board (garage board jobby) and everything should be honky dory, that's if you even need it on an Rcd

 

[Jdsparky]

But make customer aware it should be on its own and for them to query it with the p.v installers if they're still in business.

 

[Ben Butcher]

jdsparky, is that a little sarcasm directed at the PV installer??!!! You may be onto something because on the PV system there are no labels at all and the cable bringing it back to the CU is tw+e across the conservatory roof! I don't profess to be an expert but I do sometimes find myself looking at others work and thinking 'If you can't be bothered to do it right....'

 

[sedgy34]

Do as Gavin says 30ma rcds don't work we'll with DC currents and heat pumps