20 Mar
2011
20 Mar
'11
12:33 p.m.
Ground should never carry any significant current; if
it does, there is
a fault. The allowable current is varies by jurisdiction and type of
Some mains filters have capacitors from the current-carrying conductors
to ground. In this case there may well be an current in the earth wire
even when there is no fault.
equipment. In the US, for Class I (electrically
insulated with
protective earth ground) information technology equipment, the maximum
ground leakage current is 0.75 mA for handheld devices, and 3.5 mA for
other devices.
I made a similar comment a couple of months back, and somebody claimed
that the RCDs (earyh leakage trips, ELCBs, GFIs, whatever you call them)
to their computer room were set to trip at 100A. I queried this at the
time, but was assured such things were not uncommon. I am still a little
worried.
Because the ground conductor is not supposed to carry any significant
current, it should be at nearly the same potential (voltage) everywhere
in the local power network.
Indeed, you have have start (Wye) or delta 3 phase supplies at any
voltage you like.
-tony
Y or D depends on the voltage the equipment needs
per "leg"
Not necessarily. Voltage requirements should be determined by the
specifications for the equipment, which ideally are printed on it somewhere.