In a message dated 06/10/00 14:34:45 GMT Daylight Time, [email protected]
writes:
<< I feel that
overcurrent protection should be on all current carrying conductors. With a
230V~ product you never know where in the world the product will be shipped,
if
the AC Main has a grounded neutral, or if the receptacle is polarized. So, I
feel you never know for sure which line or if both lines will be "HOT" in
reference to Earth ground.
Am I being too cautious or do I have a point? >>
Hi Brian.
Not too cautious, and you do have a point.
Overcurrent in the form of a two pole circuit breaker is always preferred as
it definitely breaks BOTH lines whichever line has the overcurrent event.
Overcurrent protection on both lines with fuses is not so useful as one fuse
will blow before the other, invariably leaving one fuse intact while the
power is on,. If the fuse in the Neutral line is blown, then the equipment
is effectively left live, and therefore by implication hazardous!
My preferred outlet protection is to use two pole circuit breakers where I
can, but if I must use fuses to use only one, and that in the Live feed.
Permanently connected equipment on installations with ambiguous live/return
connections should always be protected with a two pole CB.
Portable or fixed installations connected to mains by cables with grounded
plugs into socket outlets can be protected with a single fuse.
Mains connections via reversible non grounded free sockets, e.g. portable
Hi-Fi, TV's etc.., should be double insulated anyway, and can have a single
fuse with no risk.
In the UK, our LV distribution is always STAR (Y), with the centre point
earthed at the transformer/distribution board. We don't ever fuse neutrals,
only the lines.
Dual fusing is only found in industrial fixed installations at the final
outlet, never in the LV distribution system, and then usually in the form of
dual fuseholder/IEC 10A inlets.
Just a tuppence worth...
Chris Dupres
Surrey, UK.
-------------------------------------------
This message is from the IEEE EMC Society Product Safety
Technical Committee emc-pstc discussion list.
To cancel your subscription, send mail to:
[email protected]
with the single line:
unsubscribe emc-pstc
For help, send mail to the list administrators:
Jim Bacher: [email protected]
Michael Garretson: [email protected]
For policy questions, send mail to:
Richard Nute: [email protected]
