3 phase

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I have baxter oven, 208/60/3 146.4 amps 51.3 kw, I need to know what size Shunt breaker to install. I was trying to calculate amp on each leg, to get the correct breaker size.
 
Why not use the nameplate amperage of 146 amps which is close to the calculated amps of the oven? {51300/208/1.73=143 amps}

Welcome to the Forum. :)
 
infinity said:
Why not use the nameplate amperage of 146 amps which is close to the calculated amps of the oven? {51300/208/1.73=143 amps}

Welcome to the Forum. :)
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146 amps is on the oven, i wanted to make sure what each phase pulled or does it pull 146 amps per phase?
 
infinity said:
Tom, just curious why the 125%? Couldn't he just use 150 amp circuit?
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I know nothing about the oven and would be inclined to oversize. I just cringe at the thought of putting a 146 amp load on a 150 amp breaker. Continuous or not. 175 would be better but IDK what the breaker sizes are for his system or even know why a shunt trip is needed, unless under a hood.
 
I hope someday the electrical industry will be able to once and for all exterminate the notion of "amps per phase." It means nothing.

If a three phase oven is drawing 146 amps, and let us assume that the phases are balanced, then you will have 146 amps on Phase A, 146 amps on Phase B, 146 amps on Phase C, and if there is a neutral involved it will have 0 amps. The amps on Phases A, B, and C are the same amps. When for example we look at one instant in time, and observe that Phase A is experiencing its maximum positive current, then at that same moment both Phases B and C will be experiencing negative current and not at their maximum values. Current leaves the source on Phase A and returns to the source on the other two phases. This type of thing is happening at every instant in time. There is no "total current," and there is no "amps per phase."
 
charlie b said:
I hope someday the electrical industry will be able to once and for all exterminate the notion of "amps per phase." It means nothing.
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While I agree in principal. Ii think electricians will continue to use this partly due to the practice of calculating amps/phase for load balancing as shown on consulting engineer's panel schedules.
 
If I put an ammeter on Phase A, B and C wouldn't that tell m
jim dungar said:
While I agree in principal. Ii think electricians will continue to use this partly due to the practice of calculating amps/phase for load balancing as shown on consulting engineer's panel schedules.
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Yup, we take per phase amperage readings quite often for various reasons.
 
My objection to the use of the phrase "amps per phase" has to do with the word "per." Here's why: If I were to buy three cartons of eggs at a price of $2.00 "per" dozen, I would multiply 3 times 2 to get a total price of $6.00. Through the past nearly two decades of my participation in this forum, I have seen dozens of posts that, for example, talk about a three phase system that has a current of 300 amps, and ask whether that means 100 amps "per phase." I have also seen the opposite version, the one that mentions a phase current of 100 amps and asks whether that means the "total amps" is 300. That is the nonsense that I would like to see obliterated. So whenever I see the use of either phrase ("amps per phase" or "total amps"), I cringe, and seek to clarify the situation.
 
charlie b said:
Through the past nearly two decades of my participation in this forum, I have seen dozens of posts that, for example, talk about a three phase system that has a current of 300 amps, and ask whether that means 100 amps "per phase." I have also seen the opposite version, the one that mentions a phase current of 100 amps and asks whether that means the "total amps" is 300. That is the nonsense that I would like to see obliterated. So whenever I see the use of either phrase ("amps per phase" or "total amps"), I cringe, and seek to clarify the situation.
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If the panel is 208Y/120 and all of the loads are 120 volts isn't the total amperage at 120 volts 300 amps?
For example I have a panel with only (15) 120 volt, 20 amp heaters (5 per phase) what is the total amps of those heaters? Same 15 heaters but all on the same phase what is the total amps of those heaters is it not the same 300 amps?
 
infinity said:
If the panel is 208Y/120 and all of the loads are 120 volts isn't the total amperage at 120 volts 300 amps?
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There is no single TOTALITY, there is the amount of current/phase. If you have three phases you have three totals.
Once you rewire them so there is a single voltage (2 wires), then you can have a single total.
 
charlie b said:
....
Here's why: If I were to buy three cartons of eggs at a price of $2.00 "per" dozen, I would multiply 3 times 2 to get a total price of $6.00.
....
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In the spirit of this thread, I have to point out that eggs also come in 6 egg and 18 egg cartons, as well as in larger "flats".
 
Rob, please don't think I am picking on you. But I will use one of your statements as my starting point.
infinity said:
If the panel is 208Y/120 and all of the loads are 120 volts isn't the total amperage at 120 volts 300 amps?
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This is not an easy concept to grasp. I will start by saying that if John has 5 heaters, each 120 volts and 20 amps, installed throughout his house, and if Jane has 5 identical heaters installed in the repair garage she owns, and if there are 5 more identical heaters in a nearby restaurant, then indeed we have a total of 300 amps of single phase, 120 volt load. If we instead have a 120/208V panel that has 5 of these types of heaters on each of its three phases, we can (IF WE ARE CAREFUL) say again that we have a total of 300 amps of single phase, 120 volt load. Why do I say “careful”? Because that is not, Not, NOT the same thing as saying the panel has a “total” of 300 amps of current.

If I were to ask you to add 100 forks plus 100 paper clips plus 100 flower pots, and then ask you to give me the total in units of cows, you would call that absurd and suspect that I had gone mad. But then if you were to add 100 amps plus 100 amps plus 100 amps, and try to give the result in units of amps, that would be equally absurd. I would not think you had gone mad, and I know you would be in good company, but you would all be wrong. You look at the word, “amps,” and then look at the word, “amps,” and say to yourself, “Hey, that’s the same word.” Here again, you would be wrong.

The problem is that the single, lonely word, “amps,” does not tell the whole story. It needs more words. Specifically, on a three phase panel you would need to add the following:
  • 100 amps at a phase angle of 0 degrees, plus
  • 100 amps at a phase angle of 120 degrees, plus
  • 100 amps at a phase angle of 240 degrees.
Having different phase angles basically means that the A, B, and C currents reach their instantaneous peak values at different times. That also means, as I said earlier, that current leaving the source on Phase A will return to the source on phases B and C. It is the same current.

Bottom line: If you have 100 amps flowing on each of the three phases, the panel will be experiencing a load of 100 amps, not 300 amps.
 
infinity said:
Tom, just curious why the 125%? Couldn't he just use 150 amp circuit?
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The conductor needs to be 125% anyway and you would have to use a circuit breaker rated for 100%, which at 150A is hard to find and it would have to be stand-alone, not in a panel. Using the 125% loading accounts for the circuit being 80% of the breaker rating and rated to protect the conductors anyway.
 
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