Circuit breakersRe: control panel

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

A bit of looking at the Square D web site.. http://www.squared-dot-com/
will turn up a handy 800K circuitbreaker data sheet...

Follow the links through circuit protective devices, etc.
The link you wind up with looks like a session specific one, so I won't
bother giving it here.

In any case, the bulletin for Class 601 gives some thermal derating data for
type LA breakers...   the "handle rating" (i.e. the number on the breaker)
might be 125A.. at 40C.. At 10C, the rating is 150A, at -10C, the rating is
180A.... so, that 32A breaker might really be a 50A breaker, if it's not
running at 40C

They also have correction factors for use at 400 Hz (skin effect)

Looking at the triptime charts for some 30-50A breakers (Type FA/FH/FC).. it
looks like a 200% overcurrent will trip in 30-150 seconds (yep, the range is
that big...).  a 150% overcurrent takes from 100 to 800 seconds to trip.
a 130% overcurrent may never trip..., but, in any case will take at least
300 seconds (5 minutes) to trip.



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, October 13, 2002 7:26 AM
Subject: Re: control panel


> Original poster: "Gregory Peters by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>
>
>
>
> > 1.  Fuses (or heavy duty circuit breakers) for input power.
>
>
> I would NEVER rely solely on circuit breakers for a large coil.
> Circuit breakers are prone to not tripping reliably. I have a 32A
> breaker in my box that easily holds off 50A for over a minute. Also,
> circuit breakers can weld shut.
>
> I DO have breakers in my cabinet, but these are also protected by a
> fuse. The system is designed to trip the breakers under a "normal"
> fault (me just removing a bit too much ballast inductance), but a
> large sudden unexpected fault (say a short in the ballast) will trip
> the fuses ~instanty. I have the breakers set at what the wires can
> handle continuously. The fuses are set at nearly twice this rating.
> This way I should bever blow a fuse unless something really goes
> wrong and the breakers don't trip first. But the fuses offer that
> final bit of protection.
>
> Use good quality HRC (high rupture capacity) fuses. These use a
> silver wire in a silica powder. When they trigger, the silica powder
> makes arcing almost impossible. Some other types of fuses can arc
> across if the current is high enough (kind of like a welding arc -
> the wire melts at one end, a small arc forms and spreads across the
> fuse when the rest of the wire melts).
>
> It is quite scary how fast the house wiring heats up with a dead
> short :)
>
>
>
> Cheers,
>
> Greg.
>
>
>