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Discuss RCD device for agricultural location with EV charger & solar in the Electrical Forum area at ElectriciansForums.net

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Hi There!

Background info:
Domestic/agricultural premises.

TT 3 phase supply and main distribution board located inside stables (agricultural location).

Several solar systems, storage battery system + EV charger connected - (lots of DC current's being introduced)

Single phase submain from main distribution board supplying domestic flat (inc. car port with EV charger + rooftop solar installation) does not have RCD protection.
3 Phase 25A solar circuit from main dist board also does not have RCD protection.

Type B RCBO would be perfect but is unavailable.

Looked to see if I could find a Type B RCCB incommer for the Schneider distribution board but unavailable.

2 options:
1) Add RCD protection to Solar and Single phase submain separatly.
2) Fit an upfront 300mA, Type B, 100A, Time delayed RCCB

I figured option 2 would be simplest but the device I found was £1500 DFS 4 100-4/0.30-B NK

It's looking like the independent protection will be cheaper but before I look into that can anyone offer a different angle to approach this, or alternative device that's more affordable?

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Thanks for your response Buzz

100A, 300mA, S, Type B, 4 pole.
Enquired with Schneider technical but they were unable to suggest a part.

I could save the client a little bit of money with 2 independent devices but I think spending a little extra to create a secure - future proof installation is the way to go. Doepke do one for £1500..
I'm surprised type B RCD's aren't more common - seems to be a constant obstacle in my projects.


You might find that using the likes of the Zappi charger deals with the DC fault side there, so it is just a type B for the PV/battery system feed, and a type A overall incomer. But as it is a 3-phase PV setup you will still find few choices for that and maybe not a huge cost saving.
The EV charger is a Zappi but I'm not sure how that helps? Like all chargers, the Zappi is designed to create <6mA DC current which enables a Type A <6mA to be used, but as soon as it's connected in parallel (on the output side of an RCD) with another DC generating device the protection needs to be Type B >6mA (incommer).


I doubt that most electronics has any "normal" DC leakage, it is almost certainly a fault condition, so I would not expect the main incomer RCD to have a significant DC bias to worry about. Also type A will trip on rectified mains, so high DC and high AC component will do, and that really is a TT incomer's job - to cope with faults to earth that the OCPD is unable to clear due to a high Zs.

For additional personnel protection you need fast 30mA trips, though most of these circuits will not be in that category, except perhaps the EV charger. But then as far as I understand it, the likes of the Zappi charger already has that protection built-in, so it should disconnect on a fault that would present a risk to the car user.

Which is why I believe that a couple of "instant" type B RCD on the few DC systems would be the best solution, and have the usual delay RCD as incomer (but type A and not AC, so major faults on the DC side that don't take out the OCPD are still ultimately stopped).
Thanks for your response, you are 'probably' right in the real world, however manufacturer guidance states you cannot cascade RCD Type protection.

Unfortunately there is no requirement that EV chargers etc must not generate DC current under normal conditions, which is where the 'doubt' enters.

RCD type selection is a huge can of worms & I appreciate advice but I do not see how your solution is a benefit?
More time consuming to install.
More complex for the user.
More testing required.
More to go wrong.
You have a small doubt regarding its effectiveness.
Small price saving over Type B incommer.
Not future proof.


My thinking, which could well be wrong, is normally if you did a global IR test on an installation and got under 0.5M you would probably fail it, and proceed to find out what was wrong. If the same installation was running 500V to earth it would leak 1mA (or 0.5mA, if leakage split between L & N equally).

Now you might find cases where significant DC leakage passes through CPC, say just next to a railway line, but that would be very unusual for normal operation.

Still while the type B incomer is expensive, I can't imagine it is much compared to the overall cost of the various DC at-risk systems here, so I agree with you that probably simplest just to go for that!

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