What happened here?

[Dave Plowman (News)]

Old car needed the battery charged.

Plugged that in via an extension lead from an outside socket - which has an historical RCD just inside the house - from before when I fitted a modern split load CU with RCD.

Charger was working and showing a charge, so left it to get on.

About an hour later, the house RDC tripped.

Unplugging the charger got things back to normal.

5 amp fuse in the charger plug had blown. Charger is an all plastic type with a two core mains lead.

What sort of fault inside the charger could have caused the RCD to trip?

[Andy Burns]

Does charger work again after replacing fuse, or could its dying act have been to short mains to earth via various cables/car/puddles etc?

[Clive Arthur]

Leakage from live or neutral to earth via the battery charging side through the car body to ground? If it's an old charger, then transformer breakdown could be the issue.

Cheers

[Dave Plowman (News)]

It's an SMPS type - no large transformer.

Of course the negative side of the DC output goes to the car bodywork. Could enough current flow through the tyres?

[Richard]

Some illegal event on the bus bar? ;>

[Archibald Tarquin Blenkinsopp]

If you unplugged only the charger to get things back to normal, it,s the only explanation.

An SMPS invariably uses a fully wound transformer though, they are pretty cheap when running at kHz.

If the charger was blowing the RCD with the plug fuse blown, it limits the possibilities a bit.

A damp plug/ extension, miswiring and damp or an event elsewhere and sheer coincidence that the fuse blew at some point during the charge.

Repeat the scenario and observe.

Of course if the car is very old it might only be suitable for charging via ELCB's :-)

AB

[Peter Parry]

Anything on the AC side which caused a short. RCD's have a habit of tripping on L to N faults which involve high currents. Most commonly seen when GU10 bulbs fail the RCD will often trip even though there is no leakage to earth.

[John Rumm]

Could just be it introduced a significant transient back into the mains... If the RCD was already sensitised, then the just dissipating the transient to earth through connected devices input filters could be enough.

[Brian Gaff]

Where is this plug? Is it in a so called waterproof box outside. I was just wondering if water got into the plug at some point? Obviously it was not the old fried spider thing that often happens to 13 amp plugs to cause this! I think the crucial question is, did the charger actually did? Brian

[Dave Plowman (News)]

Interesting. Got lots of GU 10 here, but never had the RCD trip when one blew. Just the circuit MCB.

[tabbypurr]

- the correct answer.

NT