Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss

Minimum earth fault current

3 views
Skip to first unread message

ubuntu2

unread,
Nov 11, 2009, 3:39:26 PM11/11/09
to
Please could someone help me with working out the minimum earth fault
current for the following.

A 3 phase 4 wire 400V 250A supply to a building is to be provided from
a substation. A moulded case circuit breaker is to be used in the
substation to protect the circuit. The designer wishes to provide the
circuit with current balance earth fault protection since it is
possible that the earth fault loop impedance of the circuit will be
high (maximum 0.8 ohms).

The open circuit phase voltage at the substation is 240V

I now need to know how to work out the minimum earth fault current at
the load end of the circuit.

jk

unread,
Nov 13, 2009, 8:32:07 PM11/13/09
to
ohms law


It should be something you have down pat, since this appears to be a
homework question

ubuntu2 <pgi...@googlemail.com> wrote:

jk

Peter Dettmann

unread,
Nov 12, 2009, 4:32:38 PM11/12/09
to
On Fri, 13 Nov 2009 17:32:07 -0800, jk <kle...@suddenlink.net> wrote:

>ohms law
>
>
>It should be something you have down pat, since this appears to be a
>homework question

You are probably right, but if it is a real question, then there is
not sufficient data provided for calculation, as no mention is made of
the HV bus impedance, nor of the impedance of the transformer
supplying the 400volts. So the minimum fault will certainly be
lower than the simple ohms law value if based only on the figures
supplied.

Peter

0 new messages