Does polarity matter for an RCD?

Steve T · Jul 8, 2021

Hi all,
I recently was given an old 2 pole Legrand RCD meant for the European market but it doesn't have any indication of which side is neutral and live, and also doesn't indicate which side the supply and load go into. A picture is attached. I've looked at the data sheet which doesn't provide any info.

Does that mean the polarity is not important nor which side the supply and load go into?

Thanks for any replies!

[ElectriciansForums.net] Does polarity matter for an RCD?

Strima · Jul 8, 2021

It's marked on the device:

1 - supply line
2 - load line
3 - supply neutral
4 - load neutral

Depending on the application you have in mind for this RCD it would need to be installed in a Legrand enclosure with the correct busbar and MCBs etc.

As it is second hand I would also recommend getting it fully tested before use.

Steve T · Jul 8, 2021

Strima said:
It's marked on the device:

View attachment 87491

1 - supply line
2 - load line
3 - supply neutral
4 - load neutral

Depending on the application you have in mind for this RCD it would need to be installed in a Legrand enclosure with the correct busbar and MCBs etc.

As it is second hand I would also recommend getting it fully tested before use.

Brilliant thanks, I wasn't sure how to interpret the diagram but makes sense now.
I'm not actually planning on using it in an installation, I was just given a few European electrical bits including that rcd by a relative who's doing lots of work in their house as they know I'm interested in it.

Mikegh · Jul 8, 2021

Does 1 2 3 4 mean all that though

I was looking at DP MCBs similarly marked and 1 and 2 seemed to be the load side according to the way they're fitted

Obviously they're not denoting L and N on the mcb

westward10 · Jul 8, 2021

The schematic indicates line to 1 and neutral to 3.

Lucien Nunes · Jul 8, 2021

The numbering shows the official assignment of line / load and L / N, you will see from the schematic that this puts the contacts upstream of the transformer and test button. However as far as AC RCD functionality is concerned a conventional non-electronic DP unit will work with either polarity and line and load in either position. All that matters to it is that the current flowing 1-2 is equal to that flowing 4-3.

Mike Johnson · Jul 8, 2021

Normally on Continental MCB's and RCD's the inlet side is staggered to allow neutral and phase bus bars.

Mikegh · Jul 8, 2021

Lucien Nunes said:
The numbering shows the official assignment of line / load and L / N, you will see from the schematic that this puts the contacts upstream of the transformer and test button. However as far as AC RCD functionality is concerned a conventional non-electronic DP unit will work with either polarity and line and load in either position. All that matters to it is that the current flowing 1-2 is equal to that flowing 4-3.

If memory serves Hager explicitly states this

You can supply them any way top bottom right left which is handy to know

I would specifically buy Hager DP for that convenience if buying in bulk

As posters said the way protective devices are gone now you just can't take things for granted anyway

Mike Johnson · Jul 8, 2021

I usually buy my Hager DP from here: Electrical Wholesaler - Search - https://www.electricalwholesaler365.co.uk/search?searchtext=Hager+RCBO&searchmode=anyword

brianmoooore · Jul 10, 2021

What you must not do is to feed power to the top on one side and to the bottom on the other. RCD will still work fine, but the resistor limiting the current flowing when the test button is pressed will be destroyed when you push it.

Mikegh · Jul 10, 2021

brianmoooore said:
What you must not do is to feed power to the top on one side and to the bottom on the other. RCD will still work fine, but the resistor limiting the current flowing when the test button is pressed will be destroyed when you push it.

Can you explain that thanks

I'm not getting what you mean

Mikegh · Jul 10, 2021

Mikegh said:
Can you explain that thanks

I'm not getting what you mean

You mean supply phase on top and supply neutral on bottom ?

That would be a rare occurrence

brianmoooore · Jul 10, 2021

Rare, maybe, but I came across it once. I must have been the first person to push and hold the test button, because a puff of smoke came out of the RCD, and the test button never worked again.

123 · Jul 14, 2021

brianmoooore said:
Rare, maybe, but I came across it once. I must have been the first person to push and hold the test button, because a puff of smoke came out of the RCD, and the test button never worked again.

The older contactum ones did this if my memory serves me correct.

Lucien Nunes · Jul 14, 2021

You mean supply phase on top and supply neutral on bottom ?
That would be a rare occurrence

I don't see how this would work at all. The entire load current would be sensed twice as an imbalance so the RCD would trip at 15mA load.

brianmoooore · Jul 14, 2021

Lucien Nunes said:
I don't see how this would work at all. The entire load current would be sensed twice as an imbalance so the RCD would trip at 15mA load.

Maybe it did, but this was a 100mA RCD IIRC, so 50mA. Wouldn't be a problem with an installation in good order.
I replaced the RCD, and moved the neutral in to the top, as it should have been.

Does polarity matter for an RCD?

Steve T

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Strima

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Steve T

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Mikegh

westward10

Lucien Nunes

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Mike Johnson

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Mikegh

Mike Johnson

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brianmoooore

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Mikegh

Mikegh

brianmoooore

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123

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Lucien Nunes

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brianmoooore

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