CPC's burning

[petegibbons]

I have been asked to test a property where they are having an ongoing problem with the CPC burning. I went a looked today and the cpc to the central heating has been rewired only recently due to the previous cable burning and it has happened again.

Can anyone shed any light on what may be the cause of this, I am getting a good ZE (TNS 0.21) and getting loop readings you would expect when testing all the circuits although I have found an open circuit on the CPC 's to the ring main and I have also found an old immersion tank which has no CPC at it and is still in use.

All the main bonding conductors are correctly sized and wired to the gas & water, there is also supplementary bonding in place.

Any assistance as to what may be causing this problem and any suggestions as to what we could do to resolve the the fault would be greatly appreciated.

 

[jimsky007]

Hi

Is it a domestic property?? What size of cable feeding boiler?? is it a radial? or is it off the ring??

 

[petegibbons]

Hi

Is it a domestic property?? What size of cable feeding boiler?? is it a radial? or is it off the ring??

It's a domestic property Jimsky, with a 1.5t/e feeding the boiler or a radial circuit.

 

[jimsky007]

Hi

The only thing in the boiler capable of doing this is the high voltage ignition system which might be faulty?? by somehow getting onto the earth cable (cpc)

I suggest you contact the boiler technical helpline and run it past them

 

[petegibbons]

Hi

The only thing in the boiler capable of doing this is the high voltage ignition system which might be faulty?? by somehow getting onto the earth cable (cpc)

I suggest you contact the boiler technical helpline and run it past them

I will do that today, thanks for your help.

 

[Des 56]

No info given about rcd protection or no, or insulation resistance readings, so if no, a possible cause could be the immersion heater having a neutral earth fault and the return current using the local boiler cpc( if ithe immersion tank has no earth path)
Being only 1.0mm and overheating because of that load current

 

[petegibbons]

No info given about rcd protection or no, or insulation resistance readings, so if no, a possible cause could be the immersion heater having a neutral earth fault and the return current using the local boiler cpc( if ithe immersion tank has no earth path)
Being only 1.0mm and overheating because of that load current

Sorry Des, There is no rcd protection to the property and the I.R. readings were all >200.

I am suspecting myself it is a problem with the Immersion heater.

 

[jimsky007]

Hi Peter

Assuming the old immersion circuit was faulty and leaking to earth why would it get a return path via the boiler spur?? if all bonding is in place inc supplementry? Obviously you will have to rewire supply to immerser to incorporate a cpc when you do this the faulty immerser?? should start to trip MCB or RCD
If the immerser is getting a return path via 1mm spur to boiler what route is it taking to get onto CPC??