3 phase

jonny1982

Member
Location
CA
I have a heater that can operate at single phase or 3 phase. What is the best choice? The amperage of the breaker would be the same for each, correct?

Thanks!
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Definitetly go with 3Ø. A 10kw heater at 3Ø, 208 volts draws 27.8 amps. For 1Ø, 208 it draws 48 amps. I would rather run smaller conductors with one extra conductor.
 

jonny1982

Member
Location
CA
So the specs on the heater I'm looking at says amps per phase is 31.3/27.0 for 240/208 volts. Then it says could be wired for single phase or 3 phase. The way I see it is the amperage stays the same whether or not it's 3 phase or single phase. So the wire size would be the same either way. Am I missing something here?

Thanks!
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
So the specs on the heater I'm looking at says amps per phase is 31.3/27.0 for 240/208 volts. Then it says could be wired for single phase or 3 phase. The way I see it is the amperage stays the same whether or not it's 3 phase or single phase. So the wire size would be the same either way. Am I missing something here?

Thanks!
Yes, you are. What is the KW rating of the heater
?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
So the specs on the heater I'm looking at says amps per phase is 31.3/27.0 for 240/208 volts. Then it says could be wired for single phase or 3 phase. The way I see it is the amperage stays the same whether or not it's 3 phase or single phase. So the wire size would be the same either way. Am I missing something here?

Thanks!
The current draw is not the same when wired 3 phase versus single phase. (See the example in post #5) Also if used at 208 volts instead of 240 volts the lower voltage will cause the heater to have lower current and lower heat output.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Most likely the current draw is not the same when wired 3 phase vs single phase.

It is possible to have the same current draw in different configurations, but in such case the power rating will be different.

Single phase 240V 10A delivers 2400W (2 conductors, each carrying 10A). 3 phase 240V 10A delivers 4160W (3 conductors, each carrying 10A)

Jon
 
Most likely the current draw is not the same when wired 3 phase vs single phase.

It is possible to have the same current draw in different configurations, but in such case the power rating will be different.

Single phase 240V 10A delivers 2400W (2 conductors, each carrying 10A). 3 phase 240V 10A delivers 4160W (3 conductors, each carrying 10A)

Jon
Typically 3-phase heaters, or heaters that can be run on single or three phase, would have three elements wired in delta, and you would have to change connections in the terminal box to rewire it for single and three phase. for the single phase configuration, all three elements would be connected in parallel to the 240 source. You would get the same KW on single and three-phase. You could just hook up single phase to two of the three connections without doing any rearranging, but the wattage would be different.
 
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