Strange RCD tripping problem.

[justpassingthrough]

I wonder it anyone has any thoughts on this, I am having problems with the RCD tripping.
It’s a 30mA main RCD on TT installation (overhead cables) (yes I know it should be 100mA but it normally doesn’t trip). It only trips in the morning after 7:00AM and stops at 8:00AM when my E7 switches off (but no faults on the radiators, besides they are on all night)( I think it trips as the loads switch on or off but only after 7)

Doing some more checks I found that the E to N voltage was over 8 volts during the time the tripping happens and also up to about 9:00AM then the E to N voltage drops back down to a more normal 0.8 to 1.2 V but it does vary.

The other thing is it only trips when the weather is cold, as it originally started last March, if you remember the very cold spell we had, then it didn’t trip any more until the first cold weather this winter but as it’s been mostly mild no tripping. As it’s cold again it’s started tripping again, hence more investigating.

I think I have now checked all my equipment for faults but as I don’t use anything different during very cold weather can’t think it’s that.

So is it possible for faulty equipment at another premises on my phase (or other 2 phases) to affect my trip and also cause the higher E to N voltage?

Is there something I have over looked?

Or is this situation normal for a TT install and nothing to worry about, just it’s being picked up by a sensitive RCD, if so should I just change the main RCD to 100mA and forget about it?

By the way, earthing is via 2 stakes and also bonded to the water main.

Many thanks for your thoughts, sorry it was so long.

 

[ELZ4742]

i would say the 30a is just too sensitive, but i would reccomend a test before carrying out any advice given here.

 

[industryspark]

get the rcd changed to a 100Ma main time delayed and have a seperate one for the stuff that needs 30mA rcd protection(sockets,shower ect....)

rcbo's could also be an alternative (expensive one).

 

[IJWS15]

You probably have two small earth faults, neither of which is enough to upset the RCD on its own but together they do.

It would appear that one is in the Economy 7 - and the other ... What else is used between 7 and 8?

When it is cold humidity tends to be higher and it conducts better!

Would suggest you also need to find the cause.

 

[justpassingthrough]

Nothing different is used when it's colder just the same storage rads.

As it was milder this morning no tripping and my rads were at the same settings.

It's seems it is something that is only working when the temp is near to freezing but only comes on about 7AM, but it's not at my property, so could it be a very leaky heater/appliance at another property on the same phase?

I have serveral small busnesses near me on the same overhead span and also a 3 phase sewer pump station at the end of the road (that one has caused me RF problems in the past)

I think it might just be time for a 100mA main RCD, I guess I have been lucky until now not to have had any false tripping for the 8 years that it's been in, I do have a split load board now anyway so changing the main RCD would bring it more up to date. Never bothered as it never random tripped.
Thanks for your thoughts and ideas.

PS

When it is cold humidity tends to be higher and it conducts better!

That's not quite right, cold air is less humid as it holds less mositure so is very dry. so can't be that. Or are you meaning that when it's cold the air holds less mositure and so disposits it on surrounding items making them damp?

 

[bernardgreen]

It's seems it is something that is only working when the temp is near to freezing but only comes on about 7AM, but it's not at my property, so could it be a very leaky heater/appliance at another property on the same phase?

I have serveral small busnesses near me on the same overhead span and also a 3 phase sewer pump station at the end of the road (that one has caused me RF problems in the past)

Sewage pumping stations often start work at around 7 o'clock as people wake up and go the bath room. Small businesses turn on heating around that time to be warm when workers arrive. Phase unbalance and a neutral dragged away from ground potential is likely at the end of a long feeder route.

The pumping station emptying our village ( 200 yards from here ) did play havoc with the domestic neutral before it was upgraded and put on it own 11kV pole route. Anyone with a Neutral to Earth fault on a TT supply was not safe from trips when the pumps kicked in.

That may be relevant to your problem

 

[IJWS15]

What I meant was "relative humidity" is higher rather than "specific humidity" - effectively more risk of earth leakage.

Are you sure there is nothing else used in the house at that time - shower, kettle, cooker? Would not affect the RCD at other times as the heating would not be on!

 

[justpassingthrough]

Thanks for your thoughts I seem to have found part of the problem, one of my storage rads has a leak to earth, hence the tripping until they went off.

But there is obviously an external factor that starts abround 7:00 AM as well, as tripping has stopped now the weather is milder and the leak isn't anywhere near bad enough to trip on it's own.

Strange thing is I checked for leakage the other day and found nothing, maybe it had reduced as the rad is was cooler at that time.

 

[luminaire]

Why do you have two earth electrodes? Where are they connected to?

 

[Jaymack]

A loose connection downstream of an RCD, may cause it to operate due to transient voltages or capacitive effects.

Jaymack

 

[securespark]

If you only have ONE RCD covering your TT install, DON'T change it for a 100mA one, that would then be AT RISK.