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Old 05-26-2012, 11:05 PM   #16
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What size wire to use


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Originally Posted by stickboy1375 View Post
I dont understand this reasoning at all.... you'll never compensate for voltage drop of that magnitude because the power company is usually at fault for it to begin with.... but increased wire size compensates for voltage drop, not smaller.
Smaller wire has more resistance. A motor at a standstill is more of a resistor than an inductor. Therefore its current draw will depend almost entirely on the voltage at its terminals.

Since there's more resistance in a smaller wire, there will be less voltage at the motors terminals, therefore less current.

Less current will result in less voltage drop at the panel.

The difference between #12s and #10s on a 75' run is pretty small, but it could easily make the lights dim noticeably less.

If you'd like, I can run some numbers and see what comes up, but without the locked-rotor current curve, I'd be guessing to some degree.

Rob

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Old 05-26-2012, 11:13 PM   #17
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What size wire to use


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Smaller wire has more resistance. A motor at a standstill is more of a resistor than an inductor. Therefore its current draw will depend almost entirely on the voltage at its terminals.

Since there's more resistance in a smaller wire, there will be less voltage at the motors terminals, therefore less current.

Less current will result in less voltage drop at the panel.

The difference between #12s and #10s on a 75' run is pretty small, but it could easily make the lights dim noticeably less.

If you'd like, I can run some numbers and see what comes up, but without the locked-rotor current curve, I'd be guessing to some degree.

Rob
LOL, don't worry about it, the lights are going to dim no matter what.
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Old 05-26-2012, 11:19 PM   #18
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What size wire to use


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LOL, don't worry about it, the lights are going to dim no matter what.
Yep, they sure will!!

Lol.
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Old 05-27-2012, 09:47 AM   #19
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What size wire to use


Mark, you might want to re-think that 12-2 set-up. The nameplate says when the unit is running it has a total draw of 20 amps. Are you going to use a 20 amp breaker or a 30, 40 ? If you run 12 ga you must use a 20 amp breaker.Everyone here is looking at voltage drop not to be rude but you would violate the NEC, you can resize the wire and breaker as needed for voltage drop but you first have to figure out how your going to start this unit up and once it's started what it's going to draw as it runs. This unit is going to surge maybe 50 amps or so until the compressor gets to it's running amps. The nameplate tells you a lot. Use 8 ga copper with 40 amp double pole breaker. If you have 240 volts not 208 don't worry about the voltage drop. I know it can seem complicated what makes it so is that it has a compresor in it, it's not a light bulb or a water heater. It has a huge surge everytime it starts. I should'nt do this but I'm trying to help everyone who looks at this question. What would you do if the unit were 1000 feet away from the panel ?
Some of you already know the answer. Talk about voltage drop......
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Old 05-27-2012, 09:51 AM   #20
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What size wire to use


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Mark, you might want to re-think that 12-2 set-up. The nameplate says when the unit is running it has a total draw of 20 amps. Are you going to use a 20 amp breaker or a 30, 40 ? If you run 12 ga you must use a 20 amp breaker.Everyone here is looking at voltage drop not to be rude but you would violate the NEC, you can resize the wire and breaker as needed for voltage drop but you first have to figure out how your going to start this unit up and once it's started what it's going to draw as it runs. This unit is going to surge maybe 50 amps or so until the compressor gets to it's running amps. The nameplate tells you a lot. Use 8 ga copper with 40 amp double pole breaker. If you have 240 volts not 208 don't worry about the voltage drop. I know it can seem complicated what makes it so is that it has a compresor in it, it's not a light bulb or a water heater. It has a huge surge everytime it starts. I should'nt do this but I'm trying to help everyone who looks at this question. What would you do if the unit were 1000 feet away from the panel ?
Some of you already know the answer. Talk about voltage drop......
You obviously are misunderstood, #12awg, 40 amp breaker, and it meets code, so relax. And no, everyone here is not looking at voltage drop, it did come into play, but was never my design issue with the original post.

Last edited by stickboy1375; 05-27-2012 at 09:55 AM.
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Old 05-27-2012, 09:56 AM   #21
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What size wire to use


I don't understand.
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Old 05-27-2012, 09:58 AM   #22
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What size wire to use


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I don't understand.
I know. Not trying to be rude, mind you... I just dislike when people think you can't do something because of lack of knowledge.

Last edited by stickboy1375; 05-27-2012 at 10:00 AM.
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Old 05-27-2012, 10:00 AM   #23
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What size wire to use


Help me out here please.
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Old 05-27-2012, 10:01 AM   #24
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What size wire to use


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Help me out here please.
What part don't you get?
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Old 05-27-2012, 10:04 AM   #25
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What size wire to use


I might be mistaken, but I thought Mark was going to run 12/2 to this unit using a 20 amp breaker.
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Old 05-27-2012, 10:06 AM   #26
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What size wire to use


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I might be mistaken, but I thought Mark was going to run 12/2 to this unit using a 20 amp breaker.
I hope not, that probably wouldn't work, the wire size is fine, but the breaker needs to be 40 amp breaker...
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Old 05-27-2012, 10:10 AM   #27
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What size wire to use


Bear with me please I'm old. So 40 amp breaker on 12 ga wire ?
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Old 05-27-2012, 10:12 AM   #28
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What size wire to use


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Bear with me please I'm old. So 40 amp breaker on 12 ga wire ?
Yes... It's a motor, they have different rules, but to help simplify the problem you're having, the breaker is only providing ground fault and short circuit protection, the overload protection is built into the motor, so the motor is protecting the wire, not the breaker.
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Old 05-27-2012, 10:25 AM   #29
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What size wire to use


I thought the breaker was to protect the branch circuit.

Manufacturers of motors have a special rating for their internal motor wiring in and around the appliance or unit. This applies to them only.
The electrician still has to use 310-16 and adjust for anything else such as voltage drop, conduit fill, breakers, time delay fuses, etc.

Just my 2 cents nothing more..
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Old 05-27-2012, 10:30 AM   #30
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What size wire to use


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I thought the breaker was to protect the branch circuit.

Manufacturers of motors have a special rating for their internal motor wiring in and around the appliance or unit. This applies to them only.
The electrician still has to use 310-16 and adjust for anything else such as voltage drop, conduit fill, breakers, time delay fuses, etc.

Just my 2 cents nothing more..

I used 310-16, #12 AWG is good for 25 amps, 240.4(G) allows this, everything else you can find under article 440 of the NEC... give it a read.

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