It never rains - RCBO tripping

Not really a request for help - more of a moan...

*sigh* up to my nose in stressville these few months (work and other stuff), now one RCBO protected ring has tripped *twice* this morning. The one with the freezer+fridge naturally...

I installed the circuit - and Megger tested it 3 years ago and it is/was perfect.

Unless a rat got in and ate something (unlikely), or the RCBO throwing a wobbler[1] I suspect one of the appliances.

I do have an 18 year old freezer and a 15 year old tumble dryer on that circuit, as well as oil heaters, fridge (not that old) and misc electronics.

So I have started the process of isolating non critical devices. We are down to the fridge and freezer now.

[1] Might be a power spike upset it - we do get wobbles on the line, but suspcious it's only hitting one RCBO out of 5 currently active ones

If it happens again - I will test the RCBO with my Megger.

I might try a Megger DC 250V IR test between live-earth and neutral-earth on the appliances. Not sure if that's going to show up a leaky filter - being DC vs AC...

Hmmmm

Reply to
Tim Watts
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If the 'miscellaneous electronics' contains several switched mode power supplies that could be your leakage - high frequency chopping and associated capacitive leakage to earth.

AWEM

Reply to
Andrew Mawson

On Tuesday 22 October 2013 13:31 Andrew Mawson wrote in uk.d-i-y:

Yes..

I just Meggered everything.

1) Unplugged everything and did a full RCD test on the circuit. Results are fine:

Trip times between 17.8mS and 8.1mS at 0 degrees, 180 deg, 30mA test and

150mA (5x) test.

Then I had a good idea - my Megger has a "ramp test" which ups the L-E test current until the RCBO trips.

Empty circuit - 25mA for a 30mA RCBO - within spec.

Long story short, plugging everything in and turning on and repeating the test is still 25mA.

***Until the microwave goes in.

Then it drops to 15mA - indicating the microwave is leaking 10mA all by itself without even being any more "on" than the control electronics.

I suspect that is leaving the circuit sensitive enough to random transients and at the mercy of the frize, freezer and heaters pinging on and off...

What do you think?

The apparant solution is to turn the microwave off when not in use. Odd though - never did it before in 2 years.

It has been very damp of late and the freezer is genering case condensation[1] - that's the only other thing - if a bit of internal condensation is dripping on an electrical part.

[1] It used to have a case heater (which could be disabled by an "economy" switch on the front". That seems to have become ineffective.

I don't much mind taking a punt on a new freezer as the compressor jammed once (freed itself later) so it's on its last legs.

Would like to not have to buy a new microwave/combi though. The final kitchen design will have the microwave sitting on the worktop near the sink, where there is a separate ring - so the freezer/fridge will be on a circuit clear of most of the nasty kitchen appliances - but for now, this is not practical (no worktop).

Tim

Reply to
Tim Watts

On Tuesday 22 October 2013 14:24 Tim Watts wrote in uk.d-i-y:

In summary and for something I *can* usually ask the group:

Is 10mA L-E leakage a bit on the high side for a combi microwave appliance?

I would say so - but I've not actually made a study of leakage currects - except just now, where even an old freezer, tumble dryer and fridge had bugger all (unmeasurable) leakages.

Reply to
Tim Watts

Had a problem with my microwave tripping RCD. Condensation seemed to be getting into the bulb compartment when it was being used to "cook" very wet stuff... Hmmmmmmm.... The problem has since gone though as we've joined the "all microwaves are evil" brigade so it's now only really used as a regular oven than a microwave.

Pete@

Reply to
www.GymRatZ.co.uk

10mA is on the high side. Leaky filter cap?
Reply to
Phil

had that here. I went to a 100mA main breaker. will install RCBOs one day on sensible circuits

Reply to
The Natural Philosopher

might be, might not be. RFI suppression is capacitors across the mains.

10mA is about 138nF capacitance across 230V live/earth if my rusty maths is correct.

well within the bounds of possibility...for a big RFI filter.

(someone else please cross check that)

Reply to
The Natural Philosopher

On Tuesday 22 October 2013 15:38 Phil wrote in uk.d-i-y:

Condensation...

At least I have a simple testing method now... Not a great tip though - not many people have a Megger or similar lying around.

However, it does sound like a little Maplin type box with a rotary switch and a bunch of suitable rated resistors to apply a controlled 1-40mA L-E load/leak in small steps could be a very handy gizmo to have around.

Reply to
Tim Watts

Why not put in a non RCBO cct for teh freezer ? .... I have one for Freezer & Comms Cabinet supply.

Reply to
Rick Hughes

On Tuesday 22 October 2013 16:40 Rick Hughes wrote in uk.d-i-y:

Too much trouble for a single circuit in my house.

To meet the 17th regs, I'd have to have suitable mechanical protection from the ceiling down to the sockets (solid ground floor). Also, whilst the fridge really only has one position it can go, the freezer could go in a number of places so I could not guarantee I could wire every logical position.

It might end up in the conservatory - the kitchen design we have has 3 appliance positions and 4 appliances (plus 6ft fridge that goes the other end of the dining room).

I did consider it - but gave up early on :-|

It's not ever been a problem until today - and now I knwo the cause, might not be again. Just an annoying bugger of an issue though when I was busy...

Reply to
Tim Watts

A ramp test is what I would have suggested:-)

Reply to
ARW

On Tuesday 22 October 2013 17:54 ARW wrote in uk.d-i-y:

Great minds... But you would have thought if it faster :>

Reply to
Tim Watts

And check your email - nothing to do with your post but you never replied to something that is of interest to you.

Reply to
ARW

On Tuesday 22 October 2013 18:31 ARW wrote in uk.d-i-y:

Sorry - Stressville and all that. I will look - promise...

Reply to
Tim Watts

I would have thought so... although the combi bit suggests a mineral insulated heating element as well as the microwave bits (and associated input filtering) - so you potentially get a double whammy.

Do you use the combi bit feature? A test with the heating element disconnected might be interesting.

Reply to
John Rumm

More like 13.8uF

Reply to
John Rumm

X = wC

C = 1/(100.pi.23k)

I also make that 138nF, or 0.138uF.

For once I actually agree with TNP, even if he does call convection assisted conduction, or was it the other way round?

Reply to
Fredxx

yup, me too this time ;-)

Reply to
John Rumm

On Tuesday 22 October 2013 23:22 John Rumm wrote in uk.d-i-y:

Good idea - that is a possibility as the element sits in the steam from something being microwaved.

If it does it again, I can strip (yes, HV capacitors, I know) and megger the element at 1000V (diconnected of course).

Reply to
Tim Watts

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