oil burner keeps tripping main rcd

pixcil

About a week ago woke up to find the rcd switch in house had tripped. Narrowed it down to boiler which is outside. strange thing is when reset i started the burner again and ran fine for ten minutes then tripped the rcd again. Reset rcd and started burner and this time it only ran for 30 seconds and rcb tripped. have had electrician out and he isolated the power from timer to burner (took power from timer through extension cable to burner and ran fine! So I presume its the cable going from timer, underground and running outside to burner? the burner was re connected to its proper cable and then wouldnt fire at all! Eventually(after the electrician hit reset button a few times) it fired but this morning nothing again. iwas told to keep trying it as this can possibly rectify if the cable has only very small break/short? something about the arc from possible short building up a mini weld and repairing itself? Doesnt sound too viable to me but hey, me simple minded artist. any ideas?

Avns1s

Does the RCD trip regardless of whether the boiler is running?

Has the electrician definitely checked that there is a break? ie no live or neutral at the boiler?

pixcil

Avns1s wrote: »

Does the RCD trip regardless of whether the boiler is running?

Has the electrician definitely checked that there is a break? ie no live or neutral at the boiler?

The trip only goes when the timer is turned on. the burner then starts up and trips after ten(ish) minutes.
The sparks tested the circuit and all the relevant electrics in the burner. No probs. We isolated the timer and ran the burner from different power source and it ran fine. Also took a lead from timer(disconnecting the proper power cable) and ran to burner and that was fine too! But when the timer was reconnected to the burner through the existing cable in the ground the trip goes again. The sparks tested the cable on its own and didnt show any faults!

Avns1s

Maybe I missed this in your last post, but did the electrician run the boiler over the existing cable without the timer?


If he did it's hard to pinpoint exacly where the fault is.

Theres no chance that there is any dampness in the timer or any of the connections on the cable? It takes very little to trip the RCD.

pixcil

Avns1s wrote: »

Maybe I missed this in your last post, but did the electrician run the boiler over the existing cable without the timer?


If he did it's hard to pinpoint exacly where the fault is.

Theres no chance that there is any dampness in the timer or any of the connections on the cable? It takes very little to trip the RCD.

We put in a new timer which seems to work fine and we ran the burner from an extension cable from a socket in kitchen having disconnected the timer and the cable from it to the burner.The burner ran fine. while the burner was disconnected from the timer and cable in the ground i turned on the timer and the trip went! The timer still had the cable attached that runs to the burner but we had disconnected the cable at burner end. Thats why we think it must be the cable running from timer (underground) to burner?Er..does that make sense? Its kind of tricky to explain but hopefully getting there! Thanks

Avns1s

That certainly would seem to indicate that the cable is faulty.

If it is a multicore cable as oposed to a twin and earth, you might be able to use other cores of the cable.

As an alternative, (I'm sure others will disagree with this) but if there is no socket in your boilerhouse that you could plug into, especially powertools that you use outdoors, you could isolate the circuit to the boilerhouse from your RCD. Therefore you'd have the following:

Consumer Board Live connection ===> 10a Circuit Breaker ===> Timer ===> Boiler

rather than

Consumer Board Live connection ===> RCD===> 10a Circuit Breaker ===> Timer ===> Boiler.

It only takes 3 thousandths of an amp leakage to trip the RCD. Provided its a fixed installation like your boiler with no sockets, you could try the above.

pixcil

Haven,t a boiler room, just the burner is out in back garden. The timer is on the same ring as sockets in kitchen! which is not right apparently? Gunna dig up cable and replace. If it still trips gunna emigrate to hot country where they've never heard of central heating! Hah!

Thanks for replies

Avns1s

No bother.

Possibly the best thing to do is to replace the cable if you dont have to cut through the paths etc. It would be better on it's own MCB but it's not a big deal except when you get problems like this!

It would be unusual that the cable would get damaged, provided that is, the proper cable was used, ie Steel Wire Armoured SWA and not just grey T+E stuck in the ground. Good luck with it anyway.