One of our customers recently installed a new Main Switchboard at a dairy milking shed. The switchboard had a 100A 3 pole changeover switch for the incoming to allow for the connection of an emergency generator.

The Inspector won't pass ( liven ) the board unless the changeover switch also breaks the Generator Neutral. Our customer contacted the Energy Safety Service who also confirmed this as a requirement.

Is switching the generator neutral required to eliminate the possibility of circulating currents in the E/N conductors if a generator is running at the same time as the mains power is available ? This would be important in areas such as milking sheds where electrical equipment is directly connected to live beasts. ( Or Humans in the case of hospitals ).

My confusion in this case arises from the fact that I have seen plenty of 3 pole changeover switches feeding dairy sheds passed and livened by Inspectors without switching the Neutral.

I'm definitely not disagreeing with the Inspector in this case, in fact I'm sure he's right. ( I'm just ignorant of the theory behind his decision [Linked Image] ) Its just that if this is a valid requirement, then why are other dairy installations not required to be the same ? ?

Can anyone shed some light here ?