3-phase Conversion

March 1, 2003

Do you have a 3-phase 208/240v heating appliance and you don't have 3-phase power? Want to hook it up to 208/240v single-phase household power?

I just found a small steam kettle to augment our herbal products production capacity but it's a 3-phase kettle and at the moment at our present location we only have single-phase 110/220v power.

(this one is similar but not identical)

Follow my instructions at your own risk!

Here's a schematic diagram that I found in the kettle (lucky!):

From the diagram you can see how the 3 wires from 3-phase (dashed lines) hook up to the top of the contactor. You can see that each of the 3 heating elements (shown by round circles with 2 connections below the contactor) is hooked up between each phase of the power wires.

Now, with single phase power you have two power conductors and one ground wire. What you need to do is wire all three elements across the outer contactor terminals just the same way as the middle heater element. Basically all three elements will be connected in parallel to each other and to the outer terminals.

The centre terminals in the contactor would then be unused.

You can't run 3-phase electric motors or any appliances with electric motors in them that require 3-phase power. This is only applicable to resistive heater elements.

The disadvantage is you have 3 x 3kw heaters which will now draw 9kw of power. Everyone knows Ohm's law watts=voltsXamps , so 9000 watts / 220v = 40.9amps current draw, which is much more than on 3-phase. You will have to make sure that your electrical breaker at the fuse panel and the wiring your are using can handle this current load. DO NOT run such an appliance on 12 or 14gauge ordinary wires, you'll burn your place down if you do.

Also note that it shows a 50A contactor (relay) and this is adequate, however the kettle I have has a 40A unit in it so this isn't good enough to handle the higher single-phase current demand, and must be replaced.

Here is the modified wiring for single-phase. Keep in mind from each element you have two wires, so 6 wires come from the heating elements and they all connect on the contactor so the drawing is slightly incorrect, as in having 2 wires service all three heater elements:

That's all there is to it.