Wire Calculation For Motor

[Alwayslearningelec]

Basic wiring question..:ashamed1:

OK, if you have a disconnect feding a motor from a 1p/20a ckt in a 120/208v 3 phase panel how do you know how manywires are needed....hots, neutral/ground?

Do you use the disconnect switch to determine, the panel info etc. In other words do you have enough info listed above to determine that.

If it is a 1p/20a it could only have ONE hot...correct:dunce:.....2pole would be TWO hots etc. etc.?????

 

[Strathead]

Basic wiring question..:ashamed1:

OK, if you have a disconnect feding a motor from a 1p/20a ckt in a 120/208v 3 phase panel how do you know how manywires are needed....hots, neutral/ground?

Do you use the disconnect switch to determine, the panel info etc. In other words do you have enough info listed above to determine that.

If it is a 1p/20a it could only have ONE hot...correct:dunce:.....2pole would be TWO hots etc. etc.?????

There is invariably one more piece of information, the voltage. But either way it is still always just 2 wires for a single phase motor. If it is a motor controller, starter etc. that may not be true.

 

[Alwayslearningelec]

There is invariably one more piece of information, the voltage. But either way it is still always just 2 wires for a single phase motor. If it is a motor controller, starter etc. that may not be true.

So what changes if it is 120/208 or 277/480? Two wire....a hot and neutral???

 

[Strathead]

So what changes if it is 120/208 or 277/480? Two wire....a hot and neutral???

It is not, it is, 120 or 208 or 240 or 277 or 480 or other odder voltages. In all cases it is 2 wires for single phase plus the ground. Voltage tells you whether it is two hots or a hot and neutral. Well not really, on a submarine 120 volts is two hots. That is why they hire electricians not plumbers.

 

[Jraef]

Basic wiring question..:ashamed1:

OK, if you have a disconnect feding a motor from a 1p/20a ckt in a 120/208v 3 phase panel how do you know how manywires are needed....hots, neutral/ground?

Do you use the disconnect switch to determine, the panel info etc. In other words do you have enough info listed above to determine that.

If it is a 1p/20a it could only have ONE hot...correct:dunce:.....2pole would be TWO hots etc. etc.?????

You have your own answer in your question, see the highlighted text above. 1p = "1 pole".

If you feed one pole from a 208Y120V panel, that is 120V. But for the circuit to be complete, the 120V load needs a neutral connection. However, you do NOT switch the neutral circuit, you are not allowed to (except under certain specific conditions). So you will have 3 wires going to the load: a hot, through the switch (black wire), an unbroken neutral (white wire) and a green or bare ground wire.

 

[Alwayslearningelec]

Ok, another side note. So if the same motor was fed from a 277/480V panel with a 3 pole breaker but now the same motor is fed from a 120/208 panel...why is it now a SINGLE POLE breaker. Is it because of the voltage and why??? Sorry for being a PIA

 

[Strathead]

Ok, another side note. So if the same motor was fed from a 277/480V panel with a 3 pole breaker but now the same motor is fed from a 120/208 panel...why is it now a SINGLE POLE breaker. Is it because of the voltage and why??? Sorry for being a PIA

Not a valid scenario or at least it would not have been fed from 3 poles of a 3 pole breaker. A single phase motor always requires two wires from the source regardless of the voltage. A three phase motor always requires 3 wires from the source regardless of voltage. You really need to take a basic electricity course. You have a curious mind and these questions are easily understood with basic theory. Try your local community college, or even a correspondence course.

 

[Alwayslearningelec]

Not a valid scenario or at least it would not have been fed from 3 poles of a 3 pole breaker. A single phase motor always requires two wires from the source regardless of the voltage. A three phase motor always requires 3 wires from the source regardless of voltage. You really need to take a basic electricity course. You have a curious mind and these questions are easily understood with basic theory. Try your local community college, or even a correspondence course.

Thanks...I will persue.

 

[cadpoint]

In your mind Draw a single line diagram left to right; left terminal is hot, middle is a device, the other wire is neutral to terminal point; apply voltage.