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Do SP+N RCBO's offer less protection than full double pole RCBO's

Alan B

This is a question that came up in a face book page, someone stated that a double pole RCBO is safer than a SP+N RCBO and personally I couldn't see why one was safer than the other.

My interpretation of the post was 

SP+N  detects L/N imbalance same as any other RCBO but switches L and N

Double pole as above but also detects overload on line or neutral.

Maybe my interpretation/understanding is incorrect?

I can see that there could be a possible advantage in 3 phase environments with 4 pole devices because without thinking too much I assume the neutral current could exceed the line current.

But in single phase circuits from my thinking at least if the line and neutral current are imbalance the imbalance would cause a trip, therefore there is no additional value in monitoring load on the neutral.

Therefore in my mind a SP+N RCD is an acceptable replacement for a double pole RCD, for example for EV charger installs.

Thinking this through further and doing a bit more digging I am coming to the conclusion that a double pole RCBO as I have described above doesn't exist and it's just manufacturers using a different name for the same thing.

Or am I missing something?

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  • 0

    The over current part will only sense on one pole. A truly double pole device, like one for 3 phases has two sets of detection and can be used in split phase (L-0-L) and polarity unknown situations, This is incredibly rarely needed in the UK, and many RCBOS sold as double pole are in fact not - they just have two sets of breaking contacts.

    So, we are not yet ready to declare reverse polarity a non-fault !!
    Mike

  • 0 in reply to mapj1

    I note Wylex were claiming them to be safer in a recent advert in PE. 
    They are useful when downstream of an RCD as once they trip, they won’t leave a detected neutral to earth fault to pull out the upstream RCD. 

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  • 0 in reply to mapj1

    I note Wylex were claiming them to be safer in a recent advert in PE. 
    They are useful when downstream of an RCD as once they trip, they won’t leave a detected neutral to earth fault to pull out the upstream RCD. 

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