RCD problem...nuisance tripping

[xr4x4]

looks like a farm, run like a farm but doesnt have any farmers or crops. just the out buildings.

No crops?

Outbuildings which need 50A supplies?

Are you sure there are no crops in them?

lol.. 50amp yes... you should see the size of the SWA..!!

deffo no crops... !!

 

[xr4x4]

some pics...

Main CU

Sticker inside CU door

Main RCD

hope this helps.

 

[bongos]

our mains supply goes into a stand alone 80amp 30ma RCD then into a industrial fuse box with a TT earth.

this box then feeds us with MCBS to sockets lights etc. there are also several supplys going out via SWA cable to a few out buildings.

The stand alone Wylex RCD in your pics here is only on one phase so I would expect it to be after the 3 phase Merlin Gerin CU not before it. What does it say on the front - the pics a bit blurred for me to read the rating.

Which phase is the Wylex on? If it's on the same as the 30mA Crabtree you highlighted in the first post and is also rated at 30mA and/or is not time delayed then I would think either could trip in certain fault situations.

 

[AndyPRK]

30mA Crabtree you highlighted in the first post

It was 100mA

 

[RF Lighting]

Does the wylex RCD supply the merlin board, or is it supplied from one of the circuits in it?

Can we have some wider shots so we can actually see what is going on, especially one showing the cutout, meter and first DB or switch fuse.

 

[ColJack]

here's how i read it..
the supply feeds the RCD which feeds the MG board.. this then feeds the crabtree board via a 50A breaker ( no 50A shown in crabtree.. ) and SWA..?

just because the MG board is a 3 phase one doesn't mean it's not been fitted with a single phasing kit...

you can absolutely get rcbo's for that MG board.. in fact I've got some type C 32A if you want to buy one ... not much use for your 50A supply though..

 

[xr4x4]

here's how i read it..
the supply feeds the RCD which feeds the MG board.. this then feeds the crabtree board via a 50A breaker ( no 50A shown in crabtree.. ) and SWA..?

just because the MG board is a 3 phase one doesn't mean it's not been fitted with a single phasing kit...

you can absolutely get rcbo's for that MG board.. in fact I've got some type C 32A if you want to buy one ... not much use for your 50A supply though..

bingo...single phase incoming - cutout - meter - 30ma 63 amp WYLEX RCD (in pic) then 50a mcb from the MG board feeds other crabtree (white CU in other pic) via SWA.

i think the best way to go is a RCBO 50a to replace the 50a mcb current, that way we can see when there is a problem.

allthough tbh honest, the problems always seem to be with the 16amp septic tank supply in the crabtree CU, it runs a pump in the tank and trips sometimes.. for no reason. (maybe becasue its a 30ma RCD in here)

can i get a main RCD fitted in the MG board, of the right rating and get the odd RCD removed? then get a 50a RCBO to replace the current 50MCB that i have current?

therefore stoping the whole supply going down for a little problem.

does that make sense?

thanks so far....!

 

[Spark123]

I thought if the supply is TT then the main isolator should be 4 pole on the MG board?
More piccys needed as RF says

 

[xr4x4]

Does the wylex RCD supply the merlin board,

yes

or is it supplied from one of the circuits in it?

no

Can we have some wider shots so we can actually see what is going on, especially one showing the cutout, meter and first DB or switch fuse.

two wires in, 100a main fuse, two cables to meter, two cables out to wylex RCD (pictured) then into the merlin board.

thats it...

hths

 

[ColJack]

no you can't get an RCD fitted as the main switch in the MG board as it would have to be a 3 phase RCD and I don't think they'll work on single phase..

you need to get that wylex RCD changed to a 100mA type S RCD.. ( time delayed.. )
adding a 50A RCBO to the MG board won't help one bit..
the 30mA main RCD will still trip before the 100mA one in the crabtree board..

 

[Spark123]

The markings on the MG board indicate a 3 phase board (L1, L2, L3), ideally these should have been changed.
I take it that it has a single phase kit installed.

 

[xr4x4]

I thought if the supply is TT then the main isolator should be 4 pole on the MG board?
More piccys needed as RF says

whys that?

i can get some more pics, will have to be tomorrow now tho.

 

[Spark123]

In a TT system the main isolator is meant to cut all live conductors, including the neutral.
In a domestic situation even in a TN system the main isolator is meant to cut all live conductors.

 

[ColJack]

the main isolator in this case would be the RCD..

 

[Spark123]

what's the supply being TT got to do with having a 4 pole isolator?

you mean that the neutral should be through the isolator too....?

yes it should..

Yep, that is what I was getting at. All live conductors should be cut when opening the isolator. IIRC where the supply is TN and supplied in accordance with the ESQCR, and where the installation is supervised you can get away with just cutting the phase conductors.
The isolator is provided for isolation purposes and thus imo should cut all lives.