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LSI"G" - Electronic Trip Units / Releases and Earth fault protection

Nick Parker

When do I use LSI “G” breakers? I have a TN-S system. The fault current would be high enough that for earth fault, over current protection also operates. Except where the code requires RCD (like sockets & heat tracing), I plan to use just thermal/ magnetic overcurrent protection for all the breakers in the switchboard.

Also would like to know, What's in vogue?

 

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    I'd agree you'd usually just need simple overcurrent protection on conventional TN-S systems.

    You're likely to need additional earth leakage units where the earth fault current might be too small to trip and overcurrent protective device quickly enough - TT systems obviously, but also TN systems where the supply might not be able to deliver sufficient energy (even occasionally) - e.g. parts of a system that might have to run off a backup generator or downstream of a UPS.

       - Andy.

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    I'd agree you'd usually just need simple overcurrent protection on conventional TN-S systems.

    You're likely to need additional earth leakage units where the earth fault current might be too small to trip and overcurrent protective device quickly enough - TT systems obviously, but also TN systems where the supply might not be able to deliver sufficient energy (even occasionally) - e.g. parts of a system that might have to run off a backup generator or downstream of a UPS.

       - Andy.

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