Wiring a 3 phase 208 volt heater
#9
  
I currently don't have a good source of shop heat.
I found a great deal on a used Fostoria 3 phase 208 volt heater.
I am wondering if there is a way to rewire this to run off 240.
I am having a 100 amp service put in the shop in 2 weeks.
I thought that the 3 phase existing wiring would take up too much of my service.
Electrical work is not my strong suite, so any help would be greatly appreciated!

Here is the wiring diagram


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#10
  Re: Wiring a 3 phase 208 volt heater by Dusty Workshop (I currently don't ha...)
Yes, it will run on single phase but you won't be able to run it at its full 3 phase capacity.  You'll have to rewire the elements to the contactors.  Do you know if all the elements are good?
Blackhat
Common decency is as rare as common sense. I figure there was only a finite amount of both made and its getting shared out among too many folks.


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#11
  Re: Wiring a 3 phase 208 volt heater by Dusty Workshop (I currently don't ha...)
You can certainly wire it for 240v 1phase, but your elements are going to run much hotter and probably cycle on the limit and the amps will go up some- the wire size may become incorrect.
The fan motor is single phase, see if it is rated 208/240v.
The contactor may need replacing as well as the limit and fan controls (volt/amp rating)

Otherwise, you might spend less buying the correct heater.

Personally, I would get all the parts in 240v, remove all wiring and controls and just start from scratch.
"There are no strangers- only friends I haven't met.
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#12
  Re: Wiring a 3 phase 208 volt heater by Dusty Workshop (I currently don't ha...)
what daddo said is all true. And usually these things are the victims of "value engineering" to within a gnat's breath of disaster.  However, looking at the circuit, all the elements have 208 across them.  If you could live with half of the heat, you could put two in series and have 3 parallel circuits.

It's possible there is a single phase version of this, have you looked?  That might reveal if it is possible to re-wire.
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#13
  Re: Wiring a 3 phase 208 volt heater by Dusty Workshop (I currently don't ha...)
I assume the elements to be good.
I think that I can get this unit for $150 or less.

Here is a link

http://www.fjevans.com/FES-1520-3A-Heat-....1774.html

Is there a way to check the elements in the field?
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#14
  Re: Wiring a 3 phase 208 volt heater by Dusty Workshop (I currently don't ha...)
Assuming the impedance remains about the same, running 208V elements on 240V will give 33% more heat from I^2R heating. That's almost certain to burn them out fast, if the overtemp element or sensor doesn't open first.

Running a 240V heat on 208V is almost alway OK, and is common on electric ovens and ranges and such. But the other way around is asking for trouble, IMO.

You may be able to rewire the internals to put them in series, configured for single-phase, but that's a pretty big 'may be', and you said in your OP that electrical work is not your strong suit.

And FWIW, I get plenty of heat from four (4) cheap little space heaters with fans, about $15 each from the BORG. Only 4.8kW total or so, but I have to shut some or all off after the garage warms up, which takes about an hour. Electric heat is 100% efficient, including the energy for the fan (even the moving air slows and stops through friction, which turns that energy to heat), so it doesn't matter how you make it other than efficiency of distributing it around (having warm air sit against the ceiling is not 'efficient').
Tom

“This place smells like that odd combo of flop sweat, hopelessness, aaaand feet.”







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#15
  Re: Wiring a 3 phase 208 volt heater by Dusty Workshop (I currently don't ha...)
I didn't realize that there were some lower cost options available.
After some web surfing this morning I found that I can get a 4,800 watt /240 v unit for about $100 and a portable 1,500 watt /120v unit for $30. I would move the smaller unit to wherever I am working.
This seems like a viable low cost option.
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#16
  Re: Wiring a 3 phase 208 volt heater by Dusty Workshop (I currently don't ha...)
I had a 4k or 5k in-wall electric heater on a 30A 240V circuit in my last house, installed by the PO, and it was more than enough for a 2-car insulated garage with wooden doors with glass windows. That was in central NJ, not Bismark ND, so YMMV. After warming my garage shop up, I'd turn it to low. Or off. I work better when it's a little cool, but not cold.

Technically, up to 5760W would be ok on a 30A 240V circuit on 10 gauge copper. Heaters are considered 'continuous loads' (full current draw for 3 hours or more), as is lighting and some other things, so the load is limited by the NEC to 80% of the circuit ampacity. Your electrician will need to know what you're planning on installing so he/she can rough in the right circuit.
Tom

“This place smells like that odd combo of flop sweat, hopelessness, aaaand feet.”







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