Electrician detecting why RCD trips

Should a qualified electrician be able to determine why an RCD continually trips " at Random ".

My mothers main downstairs ring (ooh err missus), is contiually triping, even in the middle of the night, or when she leaves the house in the daytime.

The spark says that she should replace all items connected to the ring, as it is one of those that is causing the problem. All attached items, are faily new, ie dishwasher, fridge freezer, microwave, TV.

I don't need to know, how to solve the problem, but whether it's a problem that could be sorted by a qualified electrician.

Jon

Reply to
jon
Loading thread data ...

Perhaps she could unplug the dishwasher and fridge. If that cures the problem, it's the dishwasher or fridge. If it doesn't cure the problem, it's the microwave or TV. Go from there.

Reply to
Chris Bacon

I think this could potentially be a tough one. Certainly try trial and error by removing all plug in appliances to see if the problem goes away is an easy way to start. I recently had RCD trips at random caused by a pipe in the wall leaking onto the back of a socket so it may not be due to anything plugged in at all.

Reply to
mark_yh

The message from "jon" contains these words:

My mother talks a load of tripe, too.

Reply to
Guy King

Difficult one

Determine what the max time between trips is - so you know how long to wait and see whether what you did sorted the problem.

Try and unplug everything from the ring ( run the freezer from an extension cable off another ring) and see if it still trips.

Unplug or plugin 1 item at a time and wait - start with the devices which mix electricity and water !

Good Luck

Robert

Reply to
robert

The message from "jon" contains these words:

Probably.

Does he get commission on all the unnecessary replacements or did he mean disconnected as below?

You can work out which item it is easily if the random events are fairly frequent or over a long period if the random events are infrequent. Just disconnect one item at a time for an extended period until the trips cease. The fridge freezer would have to be connected temporarily to another ring main via an extension lead but the others should only be occasional use (TV perhaps excepted) and the chances are you might get away without a random disconnection with occasional use and then immediately unplugged.

Reply to
Roger

Reply to
Den Corfield

Unfortunately intermittent RCD trips can take ages to find as they never occur when anyone qualified is around (this is true of all intermittent faults!). Even if they do isolating what caused the problem can be difficult.

If it is an appliance insulation tests can be carried out on each appliance. However another common cause is a neutral to earth fault. This may not even be in the circuit where the fault actually shows up. Again it can be tested - but it is time consuming.

Most electricians are unwilling to take this sort of job on as it can't be quoted at fixed price and quite a few lack the ability to fault find methodically.

Short answer is that it is a problem which some electricians can solve but few may be willing to try to. It could also take a long time and hence be expensive.

Reply to
Peter Parry

Do you mean "when she leaves the house" or just when she is not there?

If it is apparently random, it is likely to be caused by something that is self-starting: fridge, freezer, immersion, boiler, PIR...

Reply to
Nigel Molesworth

I've had this problem before once due to a faulty RCD, swapped RCD round in CU and random tripping moved to other ring. Got a new equivalent from TLC problem went away.

Also had an incomplete neutral ring causing spurious RCD trips, looked like the electrician (1974 build house so might have been original wiring, though CU was newish) hadn't tightened a neutral up and it came out on a socket. Just went round and inspected every socket in the house and found that one.

Also had a loose neutral in the meter tails to the CU at a mates house. This caused spurious trips, bugger to find this as we assumed the fault was in the house rewire we had just done (ok 6 months previously), didn't expect the electrician who swapped over the meter tails to not tighten the neutral fully. Tightened neutral feed and problem went away. And this passed proper testing, so I assume the neutral screw must have worked loose ?

Reply to
Ian_m

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "jon" saying something like:

Need to chew over that one for a while.

Reply to
Grimly Curmudgeon

usually yes, but not necessarily. Lack of PAT test equipment, rcd tester and/or unwillingness to spend the time/money may be factors. And in some cases the wirings such a state its pointless fault finding.

senseless advice. Either that tells you what you need to know, or maybe someone misunderstood the advice.

In most cases its solvable without any electrician. But not all.

NT

Reply to
meow2222

A professional will have some good test gear which can be used to eliminate a faulty RCD (unlikely).

I suspect that either there is a neutral-earth short somewhere perhaps on an appliance?

A full test and inspect could be requested this might show up a wiring fault or two.

Although very inconvenient you _might_ be able to track it down by switching off certain circuits or even completely disconnecting them in the CU.

HTH

Reply to
Ed Sirett

not necessarily.

The RCD trips because the current going out through Line to the appliance(s) and coming back through Neutral is not equal and exceeds in total the tolerance of the RCD. Normal RCD tolerance is 30mA (10mA & 100mA also exist). The 'leaked' current returns to the generator via earth.

It is the sum of all 'leaked' current which matters and ALL wiring and appliances 'leak'. Normally it is only a very small amount and so does not trip the RCD. Some types of appliance, especially ones which get hot, tend towards a higher leakage current.

Whilst a gross fault will simply trip the MCB or blow the fuse, minor fault(s) or incipient major fault(s) will allow more mA than designed-for to flow. As it is the total leaked mA which matters it can be that the appliance turned off may be perfectly OK but just happens to be the item which tips the balance - ie the real offender is a different item still plugged in..

In checking pull plugs to disconnect appliances as normal 13A sockets only switch on Line - leaving a possible earth leakage path between N and E.

A meter which measures earth leakage as aoppliances are added is possibly the best starting point. Otherwise failing a meter, you could try

  1. pulling all plugs & see if anything happens after a few hours - a trip then would indicate fixed wiring (wiring & cabling but including cooker, immersion heater, CH)

  1. If it works A binary search for the appliance could be the quickest

- pull half the plugs, see which half causes the trip & repeat with the faulty half etc.. until you find the dud item.

Neither try will prove an item is OK, but it could find the dud one.

Reply to
jim_in_sussex

As the best result per pound and hour, I'd start by getting a multimeter and checking the appliances for leakage. Anyone can do that. If theyre all good, and you're not upto working on the mains, then you'd need an electrician

NT

Reply to
meow2222

Initially I would test all the relevant appliances on the RCD circuit, using a portable appliance tester (PAT), for earth leakage. The circuits from the RCD section of the Distribution Board, then require to be tested for earth leakage; and the tripping values of the RCD, these tests are basic for a competent electrician. If the above tests are not conclusive, I would swap the RCD unit. Socket outlets; which could potentially be used to supply outside equipment are rated for 30mA! do not exceed this value, if replacing the unit.

Reply to
John McLean

As others have said, it could be the RCD or the fixed wiring, but more likely an intermittent neutral-earth fault in an appliance.

If it's intermittent, a simple multimeter test between the N and E plug pins may not find the low resistance at the moment you test it. However, the fault just might leave a more permanent higher resistance track as well, so it's worth checking on a high range too.

To literally "replace" all the appliances is nonsense, of course. If the problem is due to an appliance, it will be just one of them. Since it's tripping fairly frequently, you can take advantage of that to find the problem quite quickly. All it needs is a bit of logic.

If it's a neutral-earth fault, as seems likely, that immediately eliminates all two-wire appliances (ie the TV... unless - but no, let's not go there yet).

Unplug half the appliances, and see whether it's still tripping. You now know which group the problem appliance is in. Now unplug half the appliances in the problem group - keep written notes - and keep narrowing it down until you've found it. Unless you're unlucky, you will have found it in a day or three.

If you can't find it by this method, at least you'll have eliminated the appliances. Then it would be time to call the electrician back again to look at the wiring.

Or maybe there's a short-cut: the other bit of information you haven't yet used is that it's tripping both day and night. Hellooo fridge-freezer... or what about the CH boiler?

Reply to
Ian White

Sods law says it will only occur half way through the wash cycle and it will be an electronic controller so you can't manually step through the cycle!

The problem with many N/E faults is that this won't help. If the current flowing in a circuit with a N/E short somewhere is just insufficient to trip the RCD then almost anything will cause a trip. I first came across this in a house where plugging an extension lead (with nothing connected to it) in a downstairs socket caused the RCD to trip. Plugging it in upstairs didn't. Or at least not until you turned the kitchen light on - whereupon it did! Obviously faulty extension lead - except it wasn't. Leakage at 1000V was in the order of a micro amp or two. Then discovered that if the extension lead was run out it tripped, if it was coiled it didn't. I put a variable resistor and meter between Line and Earth and discovered the RCD trip current was about 0.5mA instead of 30mA (the RCD itself was fine). Eventually the fault was traced to a nail through the upstairs ring cable where a floorboard had been nailed down. The nail was shorting neutral to earth.

The only certain way to find N/E cable faults is to disconnect both ends of the N at the distribution box so it is isolated and then test between N and E (and also continuity of N while you are at it).

Reply to
Peter Parry

Unfortunately IME a 30MA house trip can go even when there is nothing individually connected to it that is faulty and no fault in the wiring.

About 3 or for TVs, computes and other 'permanently on' electronic equipment is enough to set up a few mA of current..then all it takes is a switch on spike to divert via all those filter capacitors to earth and hey presto, out she goes.

I gave up looking on mine..and whacked a 100mA RCD in the whole house. One day I'll get round to splitting the rings with outside sockets off onto a 30mA RCD, but since the last tome I left an extension cable in the rain it tripped the 100mA I am not sure its really worth it.

I hasten to add this was all new installation stuff. we checked for neutral earth shorts and all that bollocks.

If however the installation you have there has been going for years OK, then a fault may have developed. Damp wiring is pone possibility, as is a faulty appliance..but usually its hard to find the latter until and unless it goes 'more faulty'

Unplugging everything and checking each circuit with a meter for earth leakage is what the electrician should start by doing.

Beyond that he should check every appliance for at least an earth to neutral short..

Beyond that, its a game of 'binary chop'..disconnect half the appliances and run for a day. Then take the half in which the fault is presumed to apply, put the good half, and half of the bad half back on, and repeat until you have the faulty appliance.

Reply to
The Natural Philosopher

Unless you are familiar with BS 7671: - (the IEE regulations), I wouldn't offer advice here, 30mA is the maximum for the rating of an RCD for a 13A socket outlet circuit. 50mA is recognised as a lethal current!

A 100mA RCD would be used in the case of a TT installation, as the protection for the total installation; including lighting and power. However, a 30 mA RCD is still required for the socket outlet circuit.

Reply to
John McLean

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.