[TheForge] OT - fuses in a 230V (US) circuit

[dann at wctatel.net]

Bruce,

Probably close to 30 years ago now, on my farm place, we had a loose
ground connection where the main wires came to the Rural Electric pole
transformer. We found out about the defective ground, while trying to
resolve why we had an unbalanced "230V" circuit.

Electric potential from one leg to ground yielded a voltage potential of
75 volts, and I remember, that the other leg ran an electric potential of 
165 volts.  In the barn,  I had initially noticed that lights hooked to
one leg were dim, and the other burned bright, but bulbs were very short
lived.

The main transformer pole itself had a substantial looking ground rod.
Also there were ground rods wired to the fuse boxes at various
outbuildings, but grounding was still an issue.
Sounds wierd, but after learning of that,  I know of several intances
where the ground connection had degraded and voltage issues resulted that
damaged circuit boards.

Even though the theoretical potential between the two legs of a "230V"
circuit are zero, I'd want a quality ground rod, plus a wired ground
running to the power company's line.

On the farm, I've changed out most of the old fuse boxes for circuit
breaker boxes.  Property Insurance companies,at least those that I deal
with,  basically require an upgrade to circuit breakers whenever a new
home owner's policy is written.

Dann



> I have a question regarding proper fusing of a 230V circuit.  Now,
> assuming this is two hot lines with no common (earthed at fuse box)
> line, then having a fuse on each line makes sense for fire safety, if
> nothing else.  (A dead short to ground, with corresponding safety
> hazards, could occur on EITHER line, so fusing one line is not
> sufficient.)  No problem there.
>
> (I think circuit breakers are a better choice.  If either leg shorts,
> it throws the breaker, shutting off both legs.  Fuses don't offer that
> protection.  But that's neither here nor there for the question at
> hand.)
>
> In my case, in addition to the two normal fuses, I need an extra
> fast-blow fuse in the circuit to protect sensitive electronics (a
> solid-state relay).  However, I see no reason to use two of these
> expensive and difficult-to-find fast-blow fuses.  If a current spike
> occurred that didn't blow the normal fuses, then the fast-blow fuse
> would blow.  Once it blew, power is off, SSR is protected.  AOK.  Why
> could I possibly need a second fast-blow fuse on the other leg of the
> same circuit?
>
> This is a real headache to me right now, and I can't seem to find an
> on-line text to explain fusing such circuits.
>
> --
> Bruce
> NJ
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