# Three phase for a resistance load??

• posted on September 20, 2006, 12:14 pm
Hello,
The engineers in sci.engr.electrical.sys-protection were useless on this question, so I thought I would ask it here where the *real* knowledge is.
The question is regarding the use of 3-phase power. I noticed an electric pottery kiln the other day that used 3-phase power. It was about a 6 or 7 kw model. As I understand it, electric kilns are resistance loads, just like a toaster oven.
I had always thought that 3-phase power was an advantage only for induction loads, and had no advantage over single-phase for resistance loads. Is that correct? If so, what would the advantage be for a 3-phase kiln such as those shown at
http://www.skutt.com/products/elec_req.htm ?
Thanks for any enlightenment.
--
To email me directly, remove CLUTTER.

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• posted on September 20, 2006, 12:43 pm
Vic Dura wrote:

The advantage is lighter gauge supply wire and smaller control contactors since you are dividing the load across three wires instead of two with the resulting lower current per wire. You also balance the load across all three power phases in the building as opposed to concentrating the load on only two phases. No other particular advantages.
Pete C.

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• posted on September 20, 2006, 12:53 pm
wrote:

Exactly.

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• posted on September 20, 2006, 4:59 pm

The advantages Pet mentions are relatively minor in a smallish kiln like this.
The other advantage is much simpler to understand: "because it interfaces with 3 phase power".
Kilns like this are most often situated in light industrial or commercial buildings. Such buildings are usually fed with three phase. Aside from general purpose outlet circuits (and _some_ lighting), the higher power circuits (ones you'd sling 30A at 240V devices on) are virtually all 3 phase (or 2 phase of 3) devices.
Which is why, for example, in large commercial wood working shops, even the smaller tools (eg: a 14" bandsaw with a 1HP motor, which'd normally be on a 15A 120V circuit in a home hobbyist's house) are three phase.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.

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• posted on September 20, 2006, 1:01 pm
Vic Dura wrote:

Looking at the web page you linked to it is obvious to me that the 3-phase kilns are special purpose. They clearly state that they are special order only. I assume they are for use where you only have 3-phase available.
Bill Gill