New build

[SUNRAY]

Today a tripping problem in a new build property purchased 8 days ago, I measured ~100KΩ L-E.
It turned out to be rain getting into an outdoor FCU feeding the garage, non sealed back entry T&E from the kitchen socket ring.
The CU:

Note how PV & EV charge point switched off due to not yet fitted despite being part of the property spec.

& meter box

The Neighbour (moved in December 2023) had the same problem (of tripping when it rained), hopefully the liberal quantities of clear silicon sealant added to both FCUs by one of the site staff has sorted the issue.
Neighbours CU:

 

[ericmark]

I thought not allowed to use same RCD for charge point as rest of house? Not sure about solar, but where is the SPD? rather surprised a new build with MCB's would have expected to see all RCBO's today. It this just a temporary board, my problem today is 6 mA DC is very little, with all RCBO's should there be DC it will only affect one circuit, so not that much of a problem, with MCB's and only 2 RCD's how does one ensure DC or high frequency from LED lighting, induction hobs, washing machines, freezers etc does not stop the RCD tripping with faults from other circuits? Am I missing something?

Also with solar how do you ensure the solar supply does not cause overload? I know my DNO supply is only 60 amp, so even with solar it will not exceed the 100 amp total the consumer unit can handle, it seems to be a 17th edition install?

 

[Risteard]

I thought not allowed to use same RCD for charge point as rest of house? Not sure about solar, but where is the SPD? rather surprised a new build with MCB's would have expected to see all RCBO's today. It this just a temporary board, my problem today is 6 mA DC is very little, with all RCBO's should there be DC it will only affect one circuit, so not that much of a problem, with MCB's and only 2 RCD's how does one ensure DC or high frequency from LED lighting, induction hobs, washing machines, freezers etc does not stop the RCD tripping with faults from other circuits? Am I missing something?

Also with solar how do you ensure the solar supply does not cause overload? I know my DNO supply is only 60 amp, so even with solar it will not exceed the 100 amp total the consumer unit can handle, it seems to be a 17th edition install?

You're absolutely correct - it must be a dedicated RCD for each EVSE.

 

[JohnW2]

Today a tripping problem in a new build property purchased 8 days ago, I measured ~100KΩ L-E.

A 100 kΩ L-E fault obviously should not, in itself, get anywhere near tripping anything - were there other faults?

 

[JohnW2]

Also with solar how do you ensure the solar supply does not cause overload?

Overload of what?

 

[Murdochcat]

That’s just a very crappy design and install - from what we can see. Wonder what’s concealed?

 

[Murdochcat]

You're absolutely correct - it must be a dedicated RCD for each EVSE.

And that RCD needs to be double pole too

 

[ericmark]

Overload of what?

The consumer unit, it is designed for 100 amp, which without solar is limited with the DNO fuse, but a 6 kW solar array and 3 kW battery can mean it can be required to handle over 100 amp. So there needs to be a fuse or other overload device to limit the total input to the CU unless the total of DNO + Solar + battery can't exceed 100 amp, i.e. 60 amp DNO fuse, which is unlikely when designed to charge an EV as well.

As to 100kΩ yes 230/100000 = 2.3 mA however only if measured with 250 volt. Since @SUNRAY likely it was, but so many measure using 9 volt, and that is simply not good enough. I know I have measured the leakage

and had some surprising results, picture at 8 mA is just within limits for a single RCD, but seen where the total leakage is for a single RCD exceeds the recommenced 1/3 of RCD rating, remember an insulation tester uses DC so is no good to measure the leakage due to inductive and capacitive linking. The installation shown actually had 14 RCBO's so was well within limits, however it surprises me that there is no box on the installation certificate to enter the leakage in. The installation certificate acts as a check list, it prompts inspectors to test the important things.

The other missing entry is the loop impedance or resistance line - neutral which relates to volt drop. We should test both line - neutral and line earth and enter the worst reading, but worst for tripping the MCB or for volt drop are not the same.

 

[Fred Blogs]

That’s just a very crappy design and install - from what we can see. Wonder what’s concealed?

I thought "crappy design and install" along with very very poor build quality was the norm these days for new builds.

 

[bernardgreen]

Meauring insulation with a DC voltage will only show leakage due to resistive paths from Live to Earth,

It will not take into account any capacitive paths from Live to Earth

EDIT just noticed that Eric has already mentioned this

 

[SUNRAY]

A 100 kΩ L-E fault obviously should not, in itself, get anywhere near tripping anything - were there other faults?

Correct.
It had rained hard the day before and tripped, when I was there all RCD's were on. Not much work with a hose spray soon tripped it again.

 

[Murdochcat]

You're absolutely correct - it must be a dedicated RCD for each EVSE.

And also for the PV

 

[ericmark]

I have had the ring final in my flat under main house trip due to water ingress, the flat roof was leaking, now all repaired, but having seen the state of the socket, glad it did trip. But this was one circuit of 14 in all. And I was able to wait 4 months to get the roof repaired without any real problem.

One always hopes that any leaks can be fixed quick, but we had a succession of builders before we found one who could actually stop the leak for more than a couple of weeks, and it did need good weather to do the work. Until fixed it was a nightmare, so lucky it only took out one circuit.

Outside supplies are all plugged in so easy to isolate, but having had a house with two RCD's once bitten twice shy, OK they were fitted around 1995 and at that time RCBO's cost an arm and a leg. But in 2008 we got

Every installation shall be divided into circuits, as necessary, to:
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced
by equipment in normal operation

So ground floor lighting and kitchen sockets should not be on same RCD, neither should upper floor lights and ring final. This was the problem with my house, since sockets split front to back and lights split up/down no way could the house be supplied from just two RCD's, it would require some RCBO's so lights and sockets in any area not supplied from the same RCD, and a RCD add two modules so using all RCBO results in the consumer unit being 4 modules less, so got away with 18 module width, 2 for isolator, 2 for SPD so 14 RCBO's.

I simply can't see how a new built can comply with that consumer unit.

 

[JohnW2]

And that RCD needs to be double pole too

Are there any RCDs which are not DP?

 

[JohnW2]

The consumer unit, it is designed for 100 amp, ...

OK - but,in reality the only parts of a CU which would/could ever carry the total load would be the main switch and bits of bus bar(s).

.... which without solar is limited with the DNO fuse, but a 6 kW solar array and 3 kW battery can mean it can be required to handle over 100 amp.

I'm not sure that I understand the thinking/logic behind that arithmetic,

Under what circumstances would any component(s)/part(s) of the CU [and which component(s)/parts(s)? ] find themselves simultaneously carrying 9 kW (say about 39A) from solar + battery PLUS more than about 61 A (around 14 kW) from the grid supply?

So there needs to be a fuse or other overload device to limit the total input to the CU unless the total of DNO + Solar + battery can't exceed 100 amp, i.e. 60 amp DNO fuse, ...

Again, where would you put such a fuse, in a path which could at one time be carrying large amounts of solar, battery and 'DNO' current? One cannot import and export simultaneously.

As to 100kΩ yes 230/100000 = 2.3 mA however only if measured with 250 volt. Since @SUNRAY likely it was ...

Quite so - but, as you say, I imagine that Sunray will have measured at 250V, if not 500V

.... remember an insulation tester uses DC so is no good to measure the leakage due to inductive and capacitive linking.

Very true. However, I very much doubt that any credible amount of inductive or capacitive coupling' would have any significant effect on measured insulation impedance, even if one measured with 50V AC. At 50 Hz, even 1,000 pF (1 nF), a lot more than one would normally expect from any incidental capacitive coupling, would have an impedance of about 3.2 M.

The installation shown actually had 14 RCBO's ...

Which 'installation shown? The only two CUs we've been shown in this thread are both dual-RCD ones.