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matthewlai avatar image
matthewlai asked

RCD for input of Multiplus II

Hello!

I have a setup where the Multiplus II 48/5000 is in a garage workshop, fed from the main consumer unit with a 32A supply. It imports from and exports to the grid, and the AC outputs power the garage (I chose this topology instead of grid parallel mostly to provide power assist, but more importantly to limit total input current if I am running stuff in the workshop while the battery is charging).

What I am trying to figure out is the RCD setup.

The output side is easy - 30mA Type A RCD for the load. But what about the input side?

I believe in the UK the code of practice requires an RCD on inverter inputs (may be wrong on that). However, if I put another Type A RCD (even if it's less sensitive) on the input, there would not be discrimination. What are people doing with that? Just no RCD protection for the inverter? Or a time delay (Type S) RCD?

This is in the UK.

Thanks!

Multiplus-IIESS
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ejrossouw avatar image ejrossouw commented ·
Some key requirements are it should be on a 1. dedicated circuit and have a 2. dual pole 3. lockable isolator. You can opt for a 50A dual pole RCBO which covers very much all in one. Consider investing in the lastest BS7671 publication and obtain EREC99 for the factual recommendations and regulatory requirements.
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Alexandra avatar image
Alexandra answered ·

@matthewlai

From what I understand from the regs it will be type b on the input

See hagers basic guide.

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ejrossouw avatar image ejrossouw commented ·

"The inverter does incorporate a mains frequency isolating transformer. This precludes the possibility of DC current at any AC port. Therefore type A RCD’s can be used."

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Alexandra avatar image Alexandra ♦ ejrossouw commented ·
Type B prevents/detects DC components over AC. But as was mentioned there is isolation in the Victron inverters. You can get single phase type B.

Arguing types and what is more appropriate is pretty much moot, what are the regulations? What does your provider expect


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ejrossouw avatar image ejrossouw Alexandra ♦ commented ·

BS7671 712.531.3.5.1 is quite clear in it has to be type B 1. unless the inverter provides some simple seperation or 2. the installation does or 3. the manufacturer stated it does not require type B. If however when in doubt, I suggest type B as DC leaks can compromise the safe operation of an RCD.

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matthewlai avatar image matthewlai commented ·
Why Type B? A Multiplus in this application is a single phase inverter. The datasheet also recommends Type A.

The problem is ideally we don't want two Type A in series (one before and one after the inverter), because then if there's a fault at the output, it's not guaranteed which one will trip first (no discrimination / selectivity). A Type S RCD is designed in this kind of situations with a time delay (to be used on the input side, so a load fault will trip the one on the output).

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daza avatar image
daza answered ·

@matthewlai Type A is fine for small DC leakage in electrical devices smart speakers and cheap stuff that doesn’t have good AC - DC separation. Type A RCD is now the minimum house RCD which replaces the Type AC that is/can be compromised when DC flows through it. Type B is more your EV high voltage DC can flow though it without it being compromised. Get either but price does vary.

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mjs500 avatar image
mjs500 answered ·

Type A rcd with 50amp mcb to use transfer switch rating or down rate the mcb to supply size


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rvicev avatar image
rvicev answered · 
I believe in the UK the code of practice requires an RCD on inverter inputs (may be wrong on that).

Believing is simply not good enough : check local requirements first - they have to be followed.

If UK requirements do NOT require an RCD, then simply don´t (KISS principle: I can´t see the advantage on the MP-II input; so just use a bi-polar breaker).

If on the other hand UK requirements DO require an RCD, than it doesn´t matter whether it is useful or not and which type, and no doubt these requirements will also specify which type, so simply install that ?


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ejrossouw avatar image ejrossouw commented ·

BS7671 712.531.3.5.1 is quite clear in it has to be type B 1. unless the inverter provides some simple seperation or 2. the installation does or 3. the manufacturer stated it does not require type B.

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mjs500 avatar image
mjs500 answered ·
  • found the in the
  • MultiPlus-II GX
  • Installation guide
  • The inverter does incorporate a mains frequency isolating transformer. This precludes the possibility of DC current at any AC port.
  • BS7671 712.531.3.5.1 is quite clear in it has to be type B 1. unless the inverter provides some simple separation so type A RCD for MultiPlus -II
  • MultiPlus-II
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