Roger Korn on fri 19 apr 02
The disconnect box with a 2-pole switch is now a REQUIREMENT in schools,
restaurants, and "...public places" for anything drawing 30 amps or more.
Must be
"...clearly labeled ...accessable and located within 25 feet of the
appliance." And
they are cheap. And it beats having to hunt down the maintenance guy who
usually
locks the breaker box and gets uptight if you are not a licensed
electrician. Done
this dance many times. Usually wind up removing the front panel of the
breaker box,
which still leaves the cover locked up so you can't see the labels and have
to flip
breakers until you find the right one. The Law of Unintended Consequences
strikes
again.
Please don't use aluminum, even in approved applications, even with the
magic
anti-corrosion paste. In AZ, most of the mobile home (oops, "manufactured
home")
residential electrical fires are caused by poor connections to aluminum
wire. The
connection corrodes and develops some resistance over time and gets warm,
causing
faster corrosion, developing more resistance, ... Pretty soon, the
electrical box
where the connection is made is acting like a heater and the wood framing
attached
to the box catches fire.
On the subject of breaker sizing, the breaker must be sized so that the WIRE
is
protected from overcurrent and overheating. That way, even if the wire is
too small
for the kiln amperage, the breaker will trip, protecting you from your
error. In
your case, you could use a 50 amp breaker for a 47 amp load, because "50
amps"
means that the breaker will NEVER trip at 50 amps, but WILL trip at 52 amps
(rating
plus 4%). However the WIRE SIZE must be such that the correct voltage (+/-
5%) is
applied to the kiln, even when the resistance-related voltage drop in the
wire is
considered. There are tables in the NEC book, and available at the electric
supplier that tell you what size wire to use for what amperage at what line
length.
This is too long, but be careful out there,
Roger
Craig Martell wrote:
> Hi:
>
> For a 47 amp kiln with a 60 amp breaker you should use #6 copper
> wire. Don't use aluminum even if an electrician says it's OK. If you
have
> to run the line more than 50 feet from the power panel you'll need to
> increase the size of the wire to #4 copper. If the power cord on the kiln
> is the one supplied by the manufacturer and it's in good shape, you don't
> need to change it.
>
> You can hard wire the power cord to the supply line with split bolt
> connectors if you want to do it that way but make sure they are properly
> insulated and wrapped. You can also get a disconnect box and hard wire
> with that. I like to use a disconnect because you can throw the switch
and
> cut power to the kiln when you make repairs without having to go to the
> power panel and throw the breaker.
>
> regards, Craig Martell in Oregon
>
>
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--
Roger Korn
McKay Creek Ceramics
In AZ: PO Box 463
4215 Culpepper Ranch Rd
Rimrock, AZ 86335
928-567-5699 <-
In OR: PO Box 436
31330 NW Pacific Ave.
North Plains, OR 97133
503-647-5464
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