RCD trips with all load breakers open

[santoli3]

If the neutral and earth conductors have a potential difference between them where they enter your property, and this pd could depend on network neutral current then even in absence of line current through the rcd there may well be a neutral current flowing ‘forwards’ through the rcd and then via an rcd load side n-e fault and then all the way back via e conductor or terra firma to the supply transformer star point which is where the network earthed neutral originates. Thus an unbalance of current through the rcd happens. A loop circuit with an emf in it causes a current to flow through the loop.

Shows us a picture of your supply intake so we can work out your home’s earthing system please.

OK. Based on that discussion, I took measurements of neutral bus to earth on each side, and I think I've sorted it. I opened the panel, and opened the main, both RCDs and all load breakers. The attached picture was taken just prior to opening all breakers. Then I measured neutral bus to earth bus resistance on both sides. The left side was overload. The right side was 20 Ohms. I then disconnected individual neutrals one at a time on the right neutral bus until the right side went to overload. It turns out the immersion heater is the culprit. I left disconnected the immersion heater neutral and insulated it. I also disconnected the immersion heater load side from its breaker and insulated it. I labeled both as “Immersion Heater – Faulted”. Now with both sides OL to earth, I buttoned it up and shut all the breakers. So far so good. Thanks all!

 

[Avo Mk8]

OK. Based on that discussion, I took measurements of neutral bus to earth on each side, and I think I've sorted it. I opened the panel, and opened the main, both RCDs and all load breakers. The attached picture was taken just prior to opening all breakers. Then I measured neutral bus to earth bus resistance on both sides. The left side was overload. The right side was 20 Ohms. I then disconnected individual neutrals one at a time on the right neutral bus until the right side went to overload. It turns out the immersion heater is the culprit. I left disconnected the immersion heater neutral and insulated it. I also disconnected the immersion heater load side from its breaker and insulated it. I labeled both as “Immersion Heater – Faulted”. Now with both sides OL to earth, I buttoned it up and shut all the breakers. So far so good. Thanks all!

Well done! Worth checking at the immersion heater (preferably with the local switch 'off') the resistance between the element connections and ground. Sounds like you need a new one!

 

[santoli3]

Well done! Worth checking at the immersion heater (preferably with the local switch 'off') the resistance between the element connections and ground. Sounds like you need a new one!

Thanks. Need is a strong word. The immersion heater breaker hasn't been shut since we moved in (maybe the previous knew something). So I certainly don't need it. But I did rethink my solution, and disconnected the immesion heater loacaly, insulated the leads, and labeled the cover "Immersion heater disconnected due to earth fault". I then reconnected everything in the breaker panel, checked that neutral to earth was still good, then labeled the breaker "immerion heater faulted". This way, the next person to live here, if they "need" the immersion heater, can sort it without having to enter the breaker panel.