Megger testing [pat testing]

[dave friday]

Morning all,i/we have a problem with the RCCB tripping at odd times..anyone know what the procedure is for testing domestic appliances?
Ta.

[Jeff J]

Unplug them or change them onto a different circuit, you don't want to be attaching appliances to a merger, unless you want a large repair bill.
Have you managed to narrow it down to anything as appliances with heating elements tend to be worst culprits for this problem.

[ghost123uk]

In the absence of a proper PAT tester, I would get my meter out and go around any appliances that have a 3 wire lead and measure the resistance between the live and earth, with the meter set to it's highest Ohms setting.

Keep you fingers off any metal when doing so, NOT because you can get a shock, but because it will affect the readings.

Between live and earth ideally you should get no reading at all, but on some equipment you may get a very high reading, like 10 M Ohms. Whichever bit of equipment gives a reading is likely to be the culprit.

p.s. = I take it you know which circuit is tripping? (i.e. no need to test the cooker if it's the upstairs ring main (wall sockets) that are tripping.

[dave friday]

Thanks both,Jeff I think you maybe right,the water heater is my guess too.
We only have two circuit breakers fed by the rccb (Spanish/English wiring)
We have two washing machines and the water heater plus TVs .
Why shouldn't I Megger test anything with an earthed plug?.
Ghost ta I was hoping you would have some ideas.
We/I did safety checks on amplifiers using a Megger (in the mid 70 ties)
I can't remember if we had the amps on or off!!
I don't know which circuit is tripping the rccb(I think we have a bit of leakage on both circuits) plus it only trips at night! ( when the mains is a bit higher?)

Why won't G.H.O.S.T. stay as G.H.O.S.T. .!? Auto changes in message to Ghoolie but shows as G.H.O.S.T. in E D I T?!?

[tonytech]

Meggers can produce very high voltages, 500 to 1000dc.
They can terminally damage equipment that contain micro electronics (just about anything these days)
Even some of the older PAT machines warn against using them on PCs.
Have you tried leaving the TV, washing machines unplugged overnight?
My washing machine was leaking onto a mains outlet, The RCD tripped seemingly randomly.

T

[ghost123uk]

I was sent on a PAT testing course a few years ago. The machines we used (at work and on the course) were pretty complicated and had settings for stuff that had metal chassis that were earthed (like washing machines etc). You simply plugged the 13A plug into a socket on the tester and selected the tests appropriate to the piece of equipment on test. It measured stuff like current leakage from live to earth, which iirc is the important one, hence my suggesting the meter approach. Sadly I cannot remember much of the technical details we were taught (it was about 15 years ago).

Why won't G.H.O.S.T. stay as G.H.O.S.T. .!? Auto changes in message to Ghoolie but shows as G.H.O.S.T. in E D I T?!?

It's just the Mods having fun with the swear filter. Not sure at all why they picked on my user name to play about with, it's just a bit of fun I guess

[Jeff J]

If you definitely suspect one of the elements is intermittently breaking down then disconnect & insulate the wires to the one in each appliance one appliance at a time & reconnect the machine to the supply or just megger the elements themselves. Doing that is ok but not the whole appliance as, has already been explained, the high voltages would damage electronic components. As it is an intermittent fault I doubt you would have any joy using a multimeter on any resistance scale
Now that you have mentioned that the problem only arises at night any rise in supply volts will have no effect whatsoever & if is not necessarily when one of the appliance is being used perhaps you should be aware that rod's can trip for a host of reasons from a faulty r c d itself to a fault in a neighbouring property or the supply to your property & they can be a real bi**h to sort out. You may end up having to get a local electrician who is familiar with Spanish distribution to sort it, but you are probably starting in the right place though.

[dave friday]

Checked the water heater 500meg.going to have a go on the wiring tomorrow .
I am aware of the complications with other households tripping (possibly ) our rccb.
I had to fit a couple of earth rods (2 years ago).
We have two overhead cables supplying us,the transformer is about 300yards away!
Thanks for your help/suggestions.

[Smiffo]

Done any decorating lately?
It might not be an appliance, but an earth fault on a ring main, perhaps?

[dave friday]

Thanks Smiffo,no but we do have 6 cats that have a habit of pissing on things including power sockets!! Had to change a few sockets (cats pi$$ reads about 200k!)

[Smiffo]

I presume then, that you have 1 circuit breaker for lights, and one for sockets?
it is all guess work from my end really, but it could be a lighting circuit issue.

You mention it only happens at night - presumably when the lights are on?

You will definitely need to test with a meter.
it's a shame the fault doesn't stay on when it trips the RCCB. If it did, you could take one of the breakers out to at least isolate which circuit is causing it to trip.

[dave friday]

The rccb trips at 5am to 7am! ,if I reset it it might not trip again.there are two circuit breakers,the lighting and the sockets are wired together,a bit of a mess!

[Smiffo]

The rccb trips at 5 to 7am! ,if I reset it it might not trip again.there are two circuit breakers,the lighting and the sockets are wired together,a bit of a mess!

5 Minutes to 7am every morning?
Or do you mean anytime after 5 until 7am?

[dave friday]

yes!,ta,have edited my post.

[Smiffo]

yes!,ta,have edited my post.

I could speculate or guess, but do you have anything on a timer to come on early morning?
Central heating?
Coffee perculator?
Even an outside light that is motion activated...

That sounds really quite a specific time slot - I used to have a toaster that tripped my RCCB - well, one half did anyway.
Get up in the morning, pop toast in, pop the RCCB.
Think about things on a timer if it is that regular though, or something you only use in that time period.

Other than that - it's tester time.