MCB/RCD on consumer unit tripping

[Jimip]

When we use our microwave the ‘sockets’ RCD trips on the consumer unit.
The microwave starts and runs for about2-3 seconds before it trips. If we use the microwave on medium power all is fine. This has been happening for a couple of years.

Microwave has been into the service centre  in the electrical retailers I work at and had every test he could think of and couldn’t fault it.
Today I’ve moved it to a different socket in the kitchen with same result. Then tried socket in conservatory that goes through its own consumer unit. In there it worked fine on full power but sockets in house had still tripped.

At a bit of a loss as to what to look at next?

Been suggested I could change the RCD to one that gives a slight time lag similar to a slow blow fuse?

any suggestions please?

 

[Andy™]

RCD's are designed to trip within a specific time, so you wont find a 'time lag' one. best thing would be to get someone competant to do some fault finding rather than replacing random parts that you dont know anything about...

 

[boltonsparky]

A time delay RCD isn't suitable for the use you intend. 

I doubt there is much wrong with the microwave itself (proven by the testing done on it) and the problems you are experiencing are due to a build up of earth leakage from various sources, the microwave just tips it over the edge. 

As mentioned by Andy you need to get somebody competent in to test the rest of the installation. They'll be able to measure earth leakage of the installation and I'd bet on it being higher than it should be and the microwave adding just enough to send it over and trip. It may also be that the RCD is over sensitive which a ramp test would eliminate. 

A very basic way of indicating if it is build up of leakage from multiple sources is to unplug everything in the house and just try the microwave on its own but this won't test the installation itself and isn't a substitute for proper testing. 

 

[Murdoch]

Sounds like you have 2 RCD's in series so the one in the main fuseboard will nearly always trip first.

The OP suggests the microwave works properly on a different installation

My suspicion is that your home has a lot of leaky devices and hence the microwave is tipping the RCD over its tripping point. 

If it was me investigating I would use my earth leakage clamp meter first and then do more tests on your installation, starting at the RCD ..........

 

[SPECIAL LOCATION]

Sounds like classic symptoms of a poorly designed electrical installation..

lacking reasonable division of circuits across suitable protective devices as per regs 314..

Probably doesn't help when a further lack of 'what and how RCD's work' is thrown onto the mix..

I would bet both the appliance and the RCD are all working correctly..

and you actually have a problem of cumulative earth leakage across multiple sources/circuits..

Best solution is to start as per Andy's recommendation.

get someone competent to come and do some investigations / tests on your installtion..

:coffee

 

[Jimip]

Thanks everyone for your responses.
 

Looks like it maybe more involved than I hoped!

With having easy access to a new microwave I will try that route first for simplicity but I will certainly get an electrician in to the check the system once the current climate allows.
 

 

[Fly Moose]

For a home owner to test why not turn all your appliances off for the moment. Turn on the microwave. Full power. See what happens. If it works turn on each item one at a time then back off. in sequence. 

The culprit might be a fridge. 

This might guide you to a issue with another appliance....

But as said you may need a proper test on the circuit itself.

 

[SPECIAL LOCATION]

For a home owner to test why not turn all your appliances off for the moment. Turn on the microwave. Full power. See what happens. If it works turn on each item one at a time then back off. in sequence. 

The culprit might be a fridge. 

This might guide you to a issue with another appliance....

But as said you may need a proper test on the circuit itself.

The above method of testing can be a bit hit & miss if there is, as I suspect, multiple circuits sharing the same RCD... 

e.g. traditional split-load or dual RCD board..

compared with a full RCBO board..

As you will have an abundance of parallel, Earth & Neutral connections permanently made at the CU...

And as a lot of devices don't incorporate double-pole switching..

Any current flowing from a perfectly good, appliance on circuit 'A' 'B' or 'C' can make its way to Earth via a dodgy N-E connection on circuit 'D'..

So you can end up leading yourself up a wild goose chase thinking it is the appliance you have just turned on that caused the trip!

 

[Fly Moose]

The only reason I mention this was My fridge was on the way out and it did a similar thing when our lass used the oven. 

I concur with the assessment, but I was explaining as a trial and error for now. Leakage is getting rare in most properties with new technology, Most leakage is Kitchen based. A combination of items also trigger a trip as said. Yes a wild goose chase indeed. 

The other option I would have tried as a house holder(Not an electrician) turn off the other circuits on the side of the RCD leaving the kitchen circuit on. Then try again with full power on Microwave. Then do each circuit at a time see what happens. 

 

[Murdoch]

Single or dual RCD boards are the work of the devil

RCBO boards are a must

 

[Fly Moose]

Yes, and Hagar, are what we install, make a nice breaker sized one you can now do IR tests with them connected. No more removing from the board. 

 

[roys]

I used SBS Daves RCBO’s, compact and double pole, no fly leads to deal with, they are nice and neat.

 

[boltonsparky]

I used SBS Daves RCBO’s, compact and double pole, no fly leads to deal with, they are nice and neat.

I've had a look at their stuff, it looks a really smart set up. They do the fire seal panel for the rear entry knockouts too which I was impressed with. Never had my hands on any of it though, it's always worked out more than locally sourced gear by quite a bit although they're fair priced I think compared to some. 

 

[Murdoch]

I've had a look at their stuff, it looks a really smart set up. They do the fire seal panel for the rear entry knockouts too which I was impressed with. Never had my hands on any of it though, it's always worked out more than locally sourced gear by quite a bit although they're fair priced I think compared to some. 

since the 18th was implemented using single sourced fuseboard s is too much of a risk. 
 

the ones I fit , can be sourced from at least 3 vendors within 10 miles ....

 

[Andy™]

since the 18th was implemented using single sourced fuseboard s is too much of a risk. 
 

the ones I fit , can be sourced from at least 3 vendors within 10 miles ....

exactly, main reason why i wont install anything from a manufacturer/supplier that parts are not easily available

 

[Sidewinder]

...

Leakage is getting rare in most properties with new technology, Most leakage is Kitchen based...

I disagree, with a lot of modern technology comprising of switched mode power supplies, leakage is increasing, thus, the requirement for this not to exceed 30% of the RCD rating, 531.3.2.

 

[kerching]

I disagree, with a lot of modern technology comprising of switched mode power supplies, leakage is increasing, thus, the requirement for this not to exceed 30% of the RCD rating, 531.3.2.

EXACTLY! So,why would anyone ever fit a dual RCD board!

in my humble and  , some would say , bigoted opinion they have never complied. Others may disagree, they are wrong, but are entitled to their opinion

individual RCBOs all the way

 

[boltonsparky]

EXACTLY! So,why would anyone ever fit a dual RCD board!

in my humble and  , some would say , bigoted opinion they have never complied. Others may disagree, they are wrong, but are entitled to their opinion

individual RCBOs all the way

I'm all for RCBO boards now. Type A RCDs and scrap the previous versions 

Trouble is whilst the likes of screwfix and all are knocking out dual RCD boards with AC type RCDs for less that £70 that's what the majority of people will go for as price is king.

 

[Murdoch]

I disagree, with a lot of modern technology comprising of switched mode power supplies, leakage is increasing, thus, the requirement for this not to exceed 30% of the RCD rating, 531.3.2.

agree 110%

Most leakage comes from the plethora of electronic goods around the home including modern kitchen appliances

AMD 2 , rather than faffing around with AFDD's and changing the distance a socket can be from a bath from 3m to 2.5m (I mean WTGrape) should mandate RCBO's for socket circuits IMHO

 

[Sidewinder]

Instead, they have removed the allowance for risk assessment for socket circuits.

So for industrial (mainly) and commercial where you have loads such as machinery with designed in leakage then you are going to have an issue.