Tumble Dryer RCD Problem

[davas]

Hi everyone,

Just looking for some guidance on an issue we've got with our new tumble dryer. Since we bought it it has been intermittently tripping our RCD on our CU. We assumed it would be a fault on the dryer itself so had the manufacturer tech service people out. The issue has never happened before and it is certainly the tumble dryer that is causing the trip (happened maybe 15 times in a 6 week period after we got it and every time the dryer was on but not necessarily running a cycle. It has a crease guard function so it continues operating after the program has finished)

In short they put a test meter on the dryer and found no electrical faults etc. with all reading being within spec. He said it was probably just an over-sensitive RCD but since he's not an electrician he can't advise what that could be/mean. That's why I'm here

The user manual point out that the following for the appliance:

"If using a residual current circuit breaker, only use one that bears the following mark:

The presence of this mark is the only way yo be sure that it fulfils all the applicable regulations. "

(the symbol is for a Type A RCD...

)

My CU is a split board with two RCDs 80A 30mA Type AC

So finally my question... if the manufacturers are saying their product should only be added to a type A RCD, would my AC type work in the same way? Would getting an electrician involved to test things be a waste of time since the RCD is clearly doing what it is supposed to?

Any ways to narrow down the issue and identify if it's a dryer fault or electrical fault somewhere?

Many thanks if you attempt to answer

 

[Swwils]

Any dampness or leaks near the plug?

 

[ericmark]

The type AC RCD may not operate if there is a small DC current, so the problem is not tripping when required, not tripping when it should not trip. So where an inverter is used, this can stop a type AC tripping.

Your fault is more likely down to the power the unit uses, and a neutral to earth fault.

As the power uses increases the voltage between neutral and earth also increases, so some thing like a lump of damp bread in a toaster turned off but plugged in could allow a small current to flow neutral to earth, but not enough to trip anything, but switch on the kettle and the current increases so the voltage difference increase and so RCD trips.

So ensure anything with a metal earth pin is unplugged when not in use. Class II equipment like the phone charger and transistor radio not a problem, but kettles, toasters etc, can cause problems even when not in use, but left plugged in.

I also have all type AC RCD's well in my case RCBO's, it was an error, did not realise type AC until after fitted, but I have 14 of them, so any fault is limited to one circuit, I did consider swapping to type A, after being on order for 4 months and not turning up, I cancelled the order. I think the chance of DC current freezing the RCD at the same time as a fault should trip it is remote, and with a TN supply it is secondary protection anyway.

Most countries have banned type AC RCD's but not the UK. But problem is not tripping when they should, not tripping when they should not.

 

[Harry Bloomfield]

Any ways to narrow down the issue and identify if it's a dryer fault or electrical fault somewhere?

As per Eric's comments about the RCD type, not being the issue.

Your drier will undoubtedly have a filter on the electrical input, to limit interference to its electronics. The filters have a small amount of leakage, not enough on there own to trip an RCD. Lots of other equipment with electronics, or motors can include a filter and it might be that their combined leakage on a circuit is enough to trip the RCD. It would be worth your while identifying everything else on the same circuit and trying running the drier with some of them unplugged, at least until you find which item is pushing it over the limit.

The only other way is to have someone come along and measure the actual earth leakage, with a suitable meter.

 

[ericmark]

I would agree with @Harry Bloomfield we should when we install an RCD measure the back ground leakage and insure under 9 mA, I have never done this, my meter will only measure 100 mA or more, I have used an RCD tester which tests it does not trip at 15 mA and does trip at 30 mA, but we were always told to do that with no load, so I have for years it seems been doing it wrong.

If I was still working today I would buy a clamp on meter that will measure 1 mA, but we fitted 100's of type AC RCD's feeding many circuits each for years, and we did not measure the the back ground leakage or test while the system was under load, and still not seen a RCD tester that can simulate a 6 mA DC current to test any RCD, and the early ones did not say type AC, A, F or B.

Today I would not use a single 30 mA RCD to feed many circuits, the cost of RCBO's has dropped, so no longer a need, I did the calculation the other day on a 4 way consumer unit, it was less than £30 more for all RCBO's, but clearly you have an old system, and you need to work with what you have.

As explained since the tumble dryer is a high load, any earth to neutral problem will show itself when it is running, I have a 500 volt insulation tester so for me easy, I test earth to neutral, but for you it is a case of unplugging anything not in use.

 

[Harry Bloomfield]

I would agree with @Harry Bloomfield we should when we install an RCD measure the back ground leakage and insure under 9 mA, I have never done this, my meter will only measure 100 mA or more, I have used an RCD tester which tests it does not trip at 15 mA and does trip at 30 mA, but we were always told to do that with no load, so I have for years it seems been doing it wrong.

Me, for my own test at home, I would disconnect the earth at the consumer unit and put my ordinary meter in series with the earth to the circuit.

So far as tripping mA, if you are not too bothered about knowing the time to trip graph, you could use a high value resistor, in series with a pot. I could even measure the trip time with a storage scope.

 

[ericmark]

Today with what I know now I would test with all connected, if it does not trip with extra 15 mA to earth leakage then clearly OK. Setting tester to 10 mA so test is 5 mA extra to earth without tripping likely also means within the 9 mA recommended, however prices have dropped I did find a clamp-on to measure 0.001 amps for £35 so if I came out of retirement I would buy one.

However my point is for years and years I always tested with all MCB's switched off, as that what I was told to do in collage, and no one talked about less than 9 mA to earth without a fault, so with in some cases 6 MCB's on one RCD some homes must have been very near the limit.

In my last house I had two RCD's feeding two old Wylex fuses boxes with the fuses replaced with MCB's, this was installed around 1992 when getting two RCD's built into a consumer unit was rare. So I have lived with RCD protection for years, and tripping seemed to come in batches, trip 6 times in a month then no more trips for a year, and nothing found, resetting on RCD could cause other one to trip, got in the habit of turning off the MCB's first, and since I had a RCD tester and an insulation tester and a loop impedance tester yes did test except the loop impedance tester always tripped one of the RCD's but not the other one, and both were the same.

So when I moved in here, and found main house not protected, I went all RCBO, no way did I want a repeat of what happened with last house. And only trips I have had were where it should have tripped.

I have no problems telling some one to use one of these,

but home made testers no. Not worth the risk.

 

[Harry Bloomfield]

The OP would be well out of his depth in testing the earth leakage current, so I wasn't suggesting it to him, but in response to you.