Heat Pump Earth Fault/Leakage

[DeeJunFan]

Hi Guys, 

I'm not a spark so forgive the very basic descriptions. 

My Heat pump has been running happily for the last 12 months with no major issues (some wiring issues with startup and shut down signals)

But a week ago it started to trip the 30mA RCD on the board (We have a split board with 2 30mA RCD and a 100A main Switch)

I tracked the problem to the Heat pump unit itself as we had a water issue in the external isolator switch last winter. 

If the supply earth is removed from the board and the unit is started up we can see 130V coming back to the earth terminal on startup of the unit and that bumps up to 230V after about 30/40 seconds with the DC inverter starts to ramp up power (I'm guessing).  Our Spark is unable to go any further with the investigation as he doesn't feel comfortable.  I spoke with a Heat pump guy and he said that he thinks its likely an electrical issue more than a component issue and advised that as the MCB for the Heat pump is going to an RCD with all other fixed appliances and sockets that it may be nuisance tripping given the inverter would generally run around 30mA easily in normal operation and there are no faults appearing on the unit.   He suggested we re-wire the heat pump with a Type C/D MCB and RCD which are better suited to the DC inverter drive.   As we have a TT install the spark isnt prepared to move the Heat pump onto a bigger RCD or to wire it outside of the RCD.   

Basically he said because of the 230V coming down the earth cable he is sure the issue is in the unit itself and nothing to do with the electrical setup.   I dont know enough to know if this is the case or not.    

I'm based in Newry N. Ireland and am having real trouble trying to source someone with the skills to diagnose and fix the issue. 

Any help greatly appreciated. 

Thanks

Damian

 

[NozSpark]

You need to get someone who will test the cabling to the heat pump properly.... disconnecting the earth is neither the correct nor safe way to do this (its actually very dangerous to do this)

Once this is done you will know wether the problem is with the cabling or heat pump... if it's the pump then I'd say that anyone who's competent at testing should be able to figure out which "major" component is at fault 

 

[DeeJunFan]

You need to get someone who will test the cabling to the heat pump properly.... disconnecting the earth is neither the correct nor safe way to do this (its actually very dangerous to do this)

Once this is done you will know wether the problem is with the cabling or heat pump... if it's the pump then I'd say that anyone who's competent at testing should be able to figure out which "major" component is at fault 

This really doesn't fill me with confidence.   So removing the earth isn't very clever then?  I was confused as to how he was testing the unit alright.   He was holding one probe to the live terminal and one to the earth terminal and getting the voltage reading.  

I was thinking he would have been getting the reading from the live voltage but as i said i'm not a spark so dont really know how to use the kit.  

The issue i have then is to find someone who is competent at testing, which seems to be more difficult than you would think. 

 

[Sharpend]

Where was he carrying out this test? At the fuse board or at the unit? 
as Noz has said you need a sparks to test the cable from board to heat pump isolator then depending on results go from there. 

 

[DeeJunFan]

Where was he carrying out this test? At the fuse board or at the unit? 
as Noz has said you need a sparks to test the cable from board to heat pump isolator then depending on results go from there. 

He tested it at the unit with the voltage meter. 

He tested the isolator by removing all wires from the heat pump L/N/E and calling for heat and there was no trip.  Trip only occurs when the heat pump is wired in.   He felt satisfied that this cleared the cabling from the fuse board to the heat pump.  I only spoke to the heat pump guy after this and he mentioned about the potential for issues with the Type B MCB/RCDs when used with a DC inverter.   Also as there are a number of other devices on the 30mA RCD as the heat pump.  But the spark is convinced this isnt' an issue as there is 230v coming from the unit to the earth. 

 

[ProDave]

Hi all.

It was me that suggested @DeeJunFan register on here to pose the question.

The issue appears to be the previous "electrician" knew nothing about earth leakage testing and everyone else tried since refuses to even come and look when they hear the words "heat pump"

So we were hoping there was a competent electrician near Newry that might be willing to come and look at this problem?

 

[DeeJunFan]

Thanks @ProDave  really appreciate the help so far! 

 

[Sharpend]

Do the fan blades spin freely? 
leave isolator switched off, try spinning blades on unit, do they spin freely or is there any sounds such as rubbing, grinding? 
Is there any icing around the unit? 
is there any evidence of water ingress to the electronic PCBS etc? 

 

[DeeJunFan]

Do the fan blades spin freely? 
leave isolator switched off, try spinning blades on unit, do they spin freely or is there any sounds such as rubbing, grinding? 
Is there any icing around the unit? 
is there any evidence of water ingress to the electronic PCBS etc? 

will try and spin the blades and let you know. 

No ice and no signs of water anywhere around the PCBs. 

The isolator had some water/condensation etc but we gave it a good dry out and a few minutes with a hair dryer. 

 

[binky]

OK, I'm not familiar with heat pumps but work a lot with Solar Inverters. These put some quite big voltages down earths as they contain 'smoothing circuitry' designed to protect sensitive electronic components, so I'm not too surprised at getting high voltages on the earth.  As others have said, insulation test the cable, but I would also be suspicious of the isolator. If damp has allowed short circuiting of the internal workings of the switch, it will take an awful lot more drying out than 10 mins with a hairdrier, and may have permanent damage caused by arcing across electrical parts. 

 

[DeeJunFan]

Thanks binky

So do you think a good option would also be to replace the isolator and retest? 

Its very hard for me to know what is the best way forward as i dont really know what i'm doing.    I'll pick up a new isolator and check the fins.  But any time we had it running it was running well with no fault codes and the fan was turning as normal. 

Thanks

 

[binky]

an isolator is a lot cheaper than a heat pump unit!

If you disconnect all cables from the switch and leave switch in off position, you can test for continuity between the terminals - there shouldn't be any continuity between terminals.

It may also be worth fitting a separate mini-board for the heat pump alone, I do this for Solar Inverters to avoid RCD tripping issues from shared RCDs. 

 

[DeeJunFan]

an isolator is a lot cheaper than a heat pump unit!

If you disconnect all cables from the switch and leave switch in off position, you can test for continuity between the terminals - there shouldn't be any continuity between terminals.

It may also be worth fitting a separate mini-board for the heat pump alone, I do this for Solar Inverters to avoid RCD tripping issues from shared RCDs. 

Yes i have been advised that fitting an separate RCD (Type A) for the Heat pump.  The type A are supposed to be better suited to DC and avoid tripping. 

Do the fan blades spin freely? 
leave isolator switched off, try spinning blades on unit, do they spin freely or is there any sounds such as rubbing, grinding? 
Is there any icing around the unit? 
is there any evidence of water ingress to the electronic PCBS etc? 

Fan blades spin freely and very easily. 

No Ice or signs of any water in or around the unit. 

Thanks

 

[Sharpend]

I would now follow @binky advice above to test isolator before proceeding with anything else. 
you will need an rcd Ramp test carried out to see how sensitive the rcd is.  
then a measurement of earth leakage on that rcd to see if it’s bordering it’s limit. 

 

[DeeJunFan]

Thanks guys,  

So the main area of dispute between the people i have spoken to is 

A) 130V ramping up to 230V of earth leakage is definately an appliance problem

B)  DC inverters can run dirty and that level of earth leakage can be expected. 

Option A points to a heat pump compressor fault or similar Option B points towards insufficient wiring setup (Spearate RCD required/Isolator issue)

What are your thoughts on that? 

 

[binky]

I would always recommend a separate RCD for something like a heat pump, or ideally arrange circuit so it needs no RCD at all where possible.

I have had to fit some solar inverters on 300mA RCDs - stopped using that make. They would be fine initially on 30mA but after a few years seemed to develope rather high earth leakages.

 

[DeeJunFan]

I would always recommend a separate RCD for something like a heat pump, or ideally arrange circuit so it needs no RCD at all where possible.

I have had to fit some solar inverters on 300mA RCDs - stopped using that make. They would be fine initially on 30mA but after a few years seemed to develope rather high earth leakages.

Thanks @binky This is what the Heat pump guy i spoke to said that the RCD can become somewhat sensitised to the earth leakage.   I spoke to my electrician about it and he said as i was a TT install there is no way he could wire up the heat pump with no RCD?  I'm not sure if thats correct as per regs. 

He also claimed that with that sort of voltage coming back across the earth cable over a month or two the cable would melt and i would have to re-wire everything.  

Appreciate the information. 

Thanks

Damian

 

[ProDave]

The nub is you still need a competent electrician to do the testing, test the wiring and isolator for leakage, test the rcd that's in use, rewire so the heat pump is on it's own rcd, and (probably first) insulation test the compressor and fan motor.

In pointing you here, I had hoped by now someone close to you would have stepped up to the mark.

He also claimed that with that sort of voltage coming back across the earth cable over a month or two the cable would melt and i would have to re-wire everything.  

I think that is in the BS category.

 

[DeeJunFan]

The nub is you still need a competent electrician to do the testing, test the wiring and isolator for leakage, test the rcd that's in use, rewire so the heat pump is on it's own rcd, and (probably first) insulation test the compressor and fan motor.

In pointing you here, I had hoped by now someone close to you would have stepped up to the mark.

I think that is in the BS category.

Thanks @ProDave I really appreciate all the help so far.   David from BiuldHub is hopefully calling out at some stage this evening to do some testing.  

I also spoke to another Electrician locally about 1 hour ago who confirmed that yes the Heat Pump should be on its own Circuit with a Type C "Motor Rated" RCD.  The only problem is he is totally booked up for another week or more but failing that i'll just have to wait.  Its a nightmare given we have Zero heat in the house at the moment. 

 

[DeeJunFan]

I think that is in the BS category.

I thought you were talking British Standard there for a minute.