Hey guys,
We have a Quality lab where in all the equipments are fed from a 3 phase, 30KVA UPS. All the loads including emergency lighting is single phase and connected to this UPS. Recently a service person reported that one of his equipment failed due to earthing problem. His complaint is that some where in the down stream neutral and earth is getting short because of which there is short circuit in his electronic equipment.
all the body earthing of equipment is connected to dedicated earth pit. I have checked phase to phase, phase to neutral voltages found ok. Neutral to earth voltage is 0.4 volts. His argument is that since earth and neutral are short somewhere voltage between them is so less which in normal case should be between 1 and 3 V
To prove his theory i have checked current flowing throwing each phase, neutra, and earth wire using clamp meter. and found the imbalance current through neutral is matching with difference of currents between all the phases together. current through earth condutor is of few milliamps.
I would like to know is there any thing fishy to have a low potential difference between earth and neutral ( I suppose voltage more than 3-5 between Neutral & earth is what we should be concerned about), I would like to iterate that we have had a heavy rainfall recently which may be the reason for low earth resistance.
Even if there is a short between earth and neutral at downstream is it so dangerous? which is the standard( IEEE,IEC, IE etc) that is directing on this?
Thanks
Neutral Problem
Re: Neutral Problem
