Type A RCD upstream,downstream or up the swanny.

NICKYNUNN · Sep 5, 2021

Hi All.
I've got to get a job ready for Pod point to install a car charging unit.
They need the gas bonding to be done,which is quite straight forward.
And they need a type A RCD put in the board.
The point is going in a garage which has a sub board feed from a B40 mcb on the main house board,which has type AC RCDs.
Im finding it difficult to get hold of more specific information from them. But Im guessing they want the AC RCD covering the B40 mcb in the main board swapping out for a type A ?
Should the subboard also have a type A RCD?
I've only briefly visited the job,so I still have to get my bearings with it all.
Any thoughts from those that know more than me on this?

Mikegh · Sep 5, 2021

I think what you're looking at is type A at the main board upstream of a B type rcbo at the sub board for the ev charger

The AC types don't work upstream of the B types

NICKYNUNN · Sep 5, 2021

Mikegh said:
I think what you're looking at is type A at the main board upstream of a B type rcbo at the sub board for the ev charger

The AC types don't work upstream of the B types

Nice one, thanks

pc1966 · Sep 5, 2021

DC-sensitive type B RCDs are quite expensive, check if it is actually needed as some EV chargers only expect type A feeding them as they handle DC leaks themselves.

If the main board has a 30mA RCD feeding the garage then it does not need a local RCD. It won't do any harm, but it is not needed, and means there are two possible devices to reset if tripped.

If the garage feed is SWA then it does not need a RCD feeding it (unless TT so Ze too high) so it would be better to have the RCD at the garage CU and a non-RCD MCB on the supply. Less chance of a garage/EV fault taking out house electrics.

NICKYNUNN · Sep 5, 2021

pc1966 said:
DC-sensitive type B RCDs are quite expensive, check if it is actually needed as some EV chargers only expect type A feeding them as they handle DC leaks themselves.

If the main board has a 30mA RCD feeding the garage then it does not need a local RCD. It won't do any harm, but it is not needed, and means there are two possible devices to reset if tripped.

If the garage feed is SWA then it does not need a RCD feeding it (unless TT so Ze too high) so it would be better to have the RCD at the garage CU and a non-RCD MCB on the supply. Less chance of a garage/EV fault taking out house electrics.

Brilliant thanks , they have stipulated a type A rcd .

pc1966 · Sep 5, 2021

Just to add, if you can change the board RCD to type A it is generally a good thing as better protects other circuits from electronic-style faults.

But see what you find on a closer inspection. You might also find problems in getting new parts for it if the main board is quite old which makes the best solution a more complicated judgment.

If in doubt get some photos, @westward10 is the one to ask for any unusual CU parts, he is a walking encyclopedia!

NICKYNUNN · Sep 5, 2021

pc1966 said:
Just to add, if you can change the board RCD to type A it is generally a good thing as better protects other circuits from electronic-style faults.

But see what you find on a closer inspection. You might also find problems in getting new parts for it if the main board is quite old which makes the best solution a more complicated judgment.

If in doubt get some photos, @westward10 is the one to ask for any unusual CU parts, he is a walking encyclopedia!

Thank you very much for taking the time. Much appreciated ?

Mikegh · Sep 5, 2021

I was assuming it was a TT setup at the main board

I'm not that familiar as we don't have it here

You don't want 2 30mA RCDs in series as pointed out

NICKYNUNN · Sep 5, 2021

Mikegh said:
I was assuming it was a TT setup at the main board

I'm not that familiar as we don't have it here

You don't want 2 30mA RCDs in series as pointed out

Its a tncs system as I recall. They have power networks coming to upgrade the fuse also.Theres actually a three phase head,although only one phase is used.

Mikegh · Sep 5, 2021

Well you'd be looking to do as pc1966 advised

Avoid rcd protection on the sub-main

hasel5 · Sep 6, 2021

If the Sub main is SWA remove from DB and fit in switch fuse sized to cable size etc and feed from Tails with Henry's

Garage end fit a new DB with Separte DP RCBO for each circuit Pod point will fit a CT to garage supply and set the clamp current to the size of the switch fuse or lower to stop any overloads of the sub main

Any questions PM me as quite knowledgeable on there use and installation

And a type A RCBO is fine if you have a AC downstream it will be Blinded by the DC and might not work so essential to get this right

timhoward · Sep 6, 2021

hasel5 said:
If the Sub main is SWA remove from DB and fit in switch fuse sized to cable size etc and feed from Tails with Henry's

Sorry, but can't get this image out of head now...
Like this?

[ElectriciansForums.net] Type A RCD upstream,downstream or up the swanny.

Gavin John Hyde · Sep 6, 2021

Fit an MCB in the garage board and route it through a separate type a rcd?
Typical Pod Point though... get all the hard work done as they cant and dont do it then come fit a charger...
I use the small enclosures with Type A RCD/RCBOs in from WCED you can buy one on amazon for £25-30

NICKYNUNN · Sep 6, 2021

Gavin John Hyde said:
Fit an MCB in the garage board and route it through a separate type a rcd?
Typical Pod Point though... get all the hard work done as they cant and dont do it then come fit a charger...
I use the small enclosures with Type A RCD/RCBOs in from WCED you can buy one on amazon for £25-30

Nice one , thanks