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Testing requirements between mains supply and a backup generator.

MS01
Firstly to set the scene, i have an electrical installation with has a mains LV switch panel that is supplied via a DNO supply and has a standby generator. The Generator feeds into a section of the panel which can be isolated via a bus coupler device to ensure only the key services are fed via the Generator. My question is these  circuits will be tested under the characteristics of the mains DNO supply but is there a requirement to do the same exercise with the generator in operation?

I appreciate the difference with the lower fault level contribution with a higher ze from the Generator but …why would you need to undertake the cable tests for the standby Generator scenario as well as the normal mains supply?.   


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    why would you need to undertake the cable tests for the standby Generator scenario as well as the normal mains supply?.   




    In short, You don't .

    If there are bits of the installation that are only live under backup gen operation, yes, do remember they need testing too. Otherwise the main thing is to verify the ADS still works if the genset is a bit short on PSSC compared to the mains, and the other biggy to verify is that Zs  and Ze are going to be OK if the incoming mains is cut off - including loss of all supply side earthing. 

    That can be mostly a paper work exercise, and is normally trivial for things protected by RCBO or a genset incorporating an earth fault relay, and bit more involved if there are parts of the installation where it is protected by fuses and breakers only.

     


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    why would you need to undertake the cable tests for the standby Generator scenario as well as the normal mains supply?.   




    In short, You don't .

    If there are bits of the installation that are only live under backup gen operation, yes, do remember they need testing too. Otherwise the main thing is to verify the ADS still works if the genset is a bit short on PSSC compared to the mains, and the other biggy to verify is that Zs  and Ze are going to be OK if the incoming mains is cut off - including loss of all supply side earthing. 

    That can be mostly a paper work exercise, and is normally trivial for things protected by RCBO or a genset incorporating an earth fault relay, and bit more involved if there are parts of the installation where it is protected by fuses and breakers only.

     


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