LCD TV tripping the RCD - any ideas

TeeKay · 15 Apr 2009

This morning my daughter turned on the TV (took it out of standby) and it tripped the RCD. I isolated the TV and managed to reset the RCD but whenever I plug in the TV, which is a 37" Toshiba LCD TV, after about 5 seconds it trips the RCD again.

The TV is 16 months old and still under warranty. The wiring is about 8 years old and this is one of 4 ring mains in the house which covers the lounge, and two bedrooms. It is quite a long ring and the furthest from the consumer box.

The TV is double insulated even in so far as the plug has a plastic earth pin, so I thought the leakage current would be through the aerial or via one of the scart leads through the PVR or the DVD but even with everything disconnected it still trips the RCD. I even put the TV on a wooden table in the middle of the room and plugged it in to a different socket on the same circuit and still it trips the RCD.

I then put the TV in the kitchen which is on a different ring and it was fine

. This ring is nearer the consumer box and so is slightly shorter.

One thing that is interesting is that when it trips the RCD, even after unplugging the TV and walking into the garage (20 secs say) , I can't reset the RCD until I isolate the ring it was plugged into by switching off the MCB.
If I wait about a minute I can then re-enable the MCB and the RCD stays on, until of course I plug in the TV again.

I can only assume that the TV power supply is injecting some harmonic or may be DC (if thats possible) back into the ring which is upsetting the RCD.

Anyone any thoughts?

wundaboy · 15 Apr 2009

My instinctive reply is to say that its that particular ring circuit which is causing the problem, not the TV set.

It sounds to me as if there is already earth leakage on that circuit which is not quite enough to trip the RCD on its own, but which is tipped over the 30mA threshold (or whatever the threshold of that particular RCD is - it may be lower than 30mA, by design or defect) by the inrush surge when the TV is switched on.

What else is on that particular circuit? Any computers, servers, fridges, freezers?

Is this an RCBO circuit (ie circuit breaker with its own individual earth leakage trip test button)? If so, it may be the case that the breaker is faulty.

Taylortwocities · 15 Apr 2009

I have seen this before. It is almost certainly the TV - they have filter components on the mains input and this creates an amount of earth leakage.

The TV, on its own, shouldnt be enough to trip the RCD but you've probably got other 'leaky' devices on the same RCD and it all adds up - the TV has pushed it over the top.

The RCD may too be at the lower end of its operating range, which won't help.
Can you post a pic of your consumer unit? May be able to advise further.

Its may be possible to re-arrange some of the circuits but you'll need an electrician who has dealt with this sort of thing before.

Diyisfun · 15 Apr 2009

If you have another RCD you could just try swapping that over.

TeeKay · 15 Apr 2009

Thanks to all for the replies.

I have a split MK consumer unit. It has a number of non-RCD protected circuits including a circuit for the fridge and freeezer.

The RCD is an MK LN5760s two pole RCD 63A/30ma with its own test button. This covers four 32A rings each on an MK 32A MCB.

On the circuit that trips, it trips the RCD even with nothing else plugged in.

Taylortwocities · 15 Apr 2009

But the RCD will be monitoring all four rings.
You'd need to isolate all of the devices on those rings (includes central heating etc) to make a true test.

I would get an electrician in to test out what is going on. I would move that socket ring onto its own RCBO, that may solve the problem but it needs testing first!

securespark · 15 Apr 2009

Try plugging the TV into a portable RCD & then into a non-RCD-protected socket. Does it still trip?

sm1thson · 15 Apr 2009

and try plugging a high power appliance (fan heater, vacuum cleaner, kettle (although these often cause trips anyway) etc) in to the TV's original socket and see if they make it trip.

bongos · 15 Apr 2009

TeeKay said:
The TV is double insulated even in so far as the plug has a plastic earth pin, so I thought the leakage current would be through the aerial or via one of the scart leads through the PVR or the DVD but even with everything disconnected it still trips the RCD. I even put the TV on a wooden table in the middle of the room and plugged it in to a different socket on the same circuit and still it trips the RCD.

Im confused how you get earth leakage in this scenario if there is no earth connection and all scart/aerial connections etc are disconnected.

bernardgreen · 15 Apr 2009

It is possible that a combination of switched mode power supply in the TV and the capacity in the cable between Live and Earth conductors is generating enough "earth fault" current to trip the RCD.

At 50Hz ( mains frequency ) the capacity is not going to pass much energy from live to earth but if there are high frequency variations in the Live wire from the TV power supply then the capacitive coupling at these high frequencies may be enough to trip the RCD.

Taylortwocities · 15 Apr 2009

May be enough energy to pass from live to neutral.
If installation is TNC-S then neutral = Earth so maybe RCD spots imbalance that way.

sparkyspike · 15 Apr 2009

That doesn't sound right to me. I prefer the earlier answer that the TV is merely adding to the total current drawn and the fault is elsewhere on the ring circuit.

TeeKay · 15 Apr 2009

So here's an update.

I've now tried the TV on all 4 ring circuits. 3 are OK the other always trips the RCD.

I disconnected everything from the bad ring. I then disconnected the ring at the MCB and measured the ring (DC) resistance. Its < 1 Ohm on my Fluke.
I did the same with Neutral and Earth. Again < 1 Ohm.

I then just reconnected one side of the ring in the consumer box and chose a socket about midway round the circuit and similarly split the circuit.

Tried the TV - RCD tripped

I then swapped to the other side of the ring and tried the TV. RCD still tripped.

The only thing that is different on this Ring is it is further (about 15 metres) from the consumer box.

Has this ruled anything out or in ?

Taylortwocities · 15 Apr 2009

So there's something else on that fourth ring that is leaky. The TV is just putting it over the edge.

What else is on that ring? Outside lights, pond pump, computers, etc etc???

securespark · 15 Apr 2009

Are all the rings protected by that RCD?

If your Fluke has an IR tester, use it (having isolated everything on that circuit) to test IR. Start with L/E & N/E so as not to fry anything you may have forgotten.

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LCD TV tripping the RCD - any ideas

sparkyspike

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