Re: ATM - Kiln Design

["Richard Andersen" <RichardA@island.net>]

On  Thu, 13 Apr 2000  Richard Schwartz <richas@idt.net> wrote:

(snip)

> ......A good starting point is
> to determine how much power your house wiring can supply.   Design the
> kiln around that limitation.

(snip)

> ...... My
> power limit is 30 amps at 220 VAC.

(snip)

The following comments apply to the standard North American household 
power distribution scheme. It won't make sense to Brits.

 Are you sure that is all you can draw? In these times it is very 
rare to find a house with only a 100 Amp service and 200 amp is 
extremely common. Depending on how your house is wired, you may be 
able to get additional power by installing two separate heating 
elements and supplying them from two sources. For example, in this 
part of the world most houses have both stove and electric dryer 
outlets. Using both would preclude cooking for the duration of the 
heat but that can't be too big a problem; eat out for a day or two, 
just for the period that both heat sources are required. Drop back to 
the 'dryer' outlet during cooling and annealing.

Perhaps a bunch of 110 volt circuits might be brought into use as 
additional power sources. Those circuits are usually 15 amps (the 
ones I have here are of that capacity although I used to live in a 
place where the outlets had 20 amp breakers; check yours) so adding 
four small heaters could double what you can get from your 220 
source. The only disadvantage is using 110 volt heaters is that you 
have to use heavier wire for a given quantity of heat.

There are ways to get multiple 220 sources by examining the way your 
110 volt outlets are wired. The power delivered to your house is
220 and the 110 volt plugs are connected between the outside legs of 
the supply line and the center wire (the 'white' wire) which is the 
transformer center tap. With a little experimentation you can get 220 
by connecting to the 'black' wire in each of two different outlets 
that are on opposite sides of the center tap. (if this doesn't make 
sense, write me privately and I'll try to make it clearer.)

Finally, it wouldn't be a very complex task to add another 220 outlet 
to your service. The only limitation is that the total current can 
not exceed the rating of your main breaker. 

Richard Andersen
Victoria, B.C., Canada