When referring to electrical circuit protection,
there are 2 type of protection: overload and short circuit. With overload
protection the overload protection device can be at either end or anywhere in
between. Since the overload device monitors the current in a conductor
and the current will be the same at either end, it will work anywhere in the
conductor by opening the circuit. Short circuit protection needs to
be closer to the source end of the wire being protected.
An example of placing the overload device near the
'bus' would be the main breaker in a residential electrical service. The
main breaker is located at the distribution bus in the cb panel and serves to
protect both the bus bars in the panel as well as the feed conductors bringing
power from the pole which can be a couple of hundred feet away.
I am not suggesting that anyone not put in
effective short circuit protection if they feel it is necessary, just pointing
out that overload protection does not need to be located at the
source.
Joe
----- Original Message -----
Sent: Friday, December 07, 2007 9:26
AM
Subject: [FlyRotary] Re: circuit
breakers
Bob;
My assumption is
that the circuits coming off the bus are all protected near the bus; so
putting protection on the feed wire near the bus doesn’t protect
anything. But I guess the discussion doesn’t mean much without a larger
context.
Al
G
-----Original
Message-----
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of
bobperk90658@bellsouth.net
Sent: Thursday, December 06, 2007 10:41
PM
To: Rotary motors in
aircraft
Subject: [FlyRotary]
Re: circuit breakers
Sorry that I didn’t make my thoughts
clear. My thinking is that the cable is just an extension of the
positive terminal of the battery.
If there is no possibility of the
wiring shorting out to ground, (This could be what if’this to death) you can
protect for the maximum amount of current your cable can
conduct. If there is any possibility that the cable
could be shorted to ground then, yes protect at the source. I would
think that a plastic plane with the positive cable in an isolated raceway
would present itself as a good candidate for the first scenario. A
switched disconnect could be inserted at the battery and remotely and manually
opened for a fill good safety feature . In any instillation you
have a certain amount of unprotected wiring between the battery and the buss,
this only extends that length.
In my mind the cable is just an extension
of the positive battery terminal, especially if the cable is sized large
enough to carry the entire load plus 100%. This may go contrary to
national wiring code but if you want control of the operation from the pilot
seat then this is what is needed.
Bob Perkinson
Bob Perkinson
-------------- Original message from
"Al Gietzen" <ALVentures@cox.net>: --------------
If
you want to protect the wiring from the battery to the buss place a fuse or
CB close to the buss.
Bob Perkinson
Bob;
Not
sure I understand that. The protection of the wire should be near the
source, not at the far end.
Al