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Old 12-23-2011, 08:51 AM   #1
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sizing electrical wire for amps


need to run electric to machine . 240 volts 3 phase 100 amps max load. need to know size of wire and size of conduit to use . our power comes from a busduct

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Old 12-23-2011, 09:21 AM   #2
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sizing electrical wire for amps


Here is a good motor calculator http://www.jandlelectric.net/motorcalc.html You did not state horsepower, and using this one http://www.engineeringtoolbox.com/el...tor-d_832.html I am coming up with 43hp. Here is a whole list of different calculators http://www.electrician2.com/calculators/elcal.html which are all really good.

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Old 12-23-2011, 09:45 AM   #3
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sizing electrical wire for amps


100 amp wire ampacity NEC 2011 310.15 (b)(16) CU 90 degree 3 AWG, AL 90 degree shows 2 AWG, 8 AWG CU for equipment ground, 6 AWG AL 2011 NEC 250.122

This is calculated on THWN / THHN

Last edited by CaptainD51; 12-23-2011 at 09:55 AM.
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Old 12-23-2011, 09:53 AM   #4
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Fill capacity for EMT conduit, 3 AWG needs 1 1/4" (6 Max conductors, 3 for 1" so not be enough room), 2 AWG in 1 1/4" EMT show 5 max conductors

2011 NEC Chapter 9 tables 1, 4 and 5
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Old 12-23-2011, 10:39 AM   #5
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sizing electrical wire for amps


Quote:
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need to run electric to machine . 240 volts 3 phase 100 amps max load. need to know size of wire and size of conduit to use . our power comes from a busduct
Hire an electrician!!

This is NOT DIY work and you should NOT be messing with it if you are not a qualified electrician.
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Answers based on the 2008 & 2011 NEC.
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Old 12-23-2011, 11:24 AM   #6
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100 amp wire ampacity NEC 2011 310.15 (b)(16) CU 90 degree 3 AWG, AL 90 degree shows 2 AWG, 8 AWG CU for equipment ground, 6 AWG AL 2011 NEC 250.122

This is calculated on THWN / THHN
Unless the terminals are 90 degree rated you would need to use the lesser ampacities of the 60 or 75 degree columns.
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Old 12-23-2011, 12:45 PM   #7
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sizing electrical wire for amps


Quote:
Originally Posted by CaptainD51 View Post
100 amp wire ampacity NEC 2011 310.15 (b)(16) CU 90 degree 3 AWG, AL 90 degree shows 2 AWG, 8 AWG CU for equipment ground, 6 AWG AL 2011 NEC 250.122

This is calculated on THWN / THHN
CaptainD, you can not use the 90C rating when sizing conductors. You must use the 75C rating and sometimes the 60C rating of conductors.
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Old 12-23-2011, 02:07 PM   #8
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sizing electrical wire for amps


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CaptainD, you can not use the 90C rating when sizing conductors. You must use the 75C rating and sometimes the 60C rating of conductors.
Ummmmm.....
Quote:
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Unless the terminals are 90 degree rated you would need to use the lesser ampacities of the 60 or 75 degree columns.
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Old 12-23-2011, 03:27 PM   #9
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sizing electrical wire for amps


I Think I hear an echo.
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Old 12-23-2011, 03:46 PM   #10
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They do sound similar. Maybe the captain needed a double wham-O.
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Old 12-23-2011, 05:20 PM   #11
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sizing electrical wire for amps


Quote:
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CaptainD, you can not use the 90C rating when sizing conductors. You must use the 75C rating and sometimes the 60C rating of conductors.
Not to argue, I’m learning myself, why is that?

Most THHN/THWN that I’ve seen has 90 degree markings on it. Are terminals not rated to that temp or is there a standard I have not read that indicates 75 degrees?

Note: At 75 degree for 100 amp, CU still shows 3 AWG but it is right at 100 amp, AL drops to 1 AWG

Would that be correct or am I missing something ?

Last edited by CaptainD51; 12-23-2011 at 05:27 PM.
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Old 12-23-2011, 05:24 PM   #12
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sizing electrical wire for amps


Special rules apply to motor circuits' conductors sizing and overcurrent protection.

We need to know the hp and voltage ratings of the motor(s) in order to make a proper calculation.

It's possible that a motor could be supplied with a conductor capable of handling 50 Amps, but can be fused (or circuit breaker) protected at 100 Amps or more. 240.4(D) does not apply when dealing with motors, etc. You have to begin at 240.4(G) ....


More info is needed here ... (and you're right, this is NOT a DIY project!)
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Old 12-23-2011, 05:27 PM   #13
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sizing electrical wire for amps


Quote:
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... am I missing something ?
Yup. Unless marked with a temp rating, all equipment is assumed to be rated for 60C terminations. Most circuit breakers, controllers, etc are marked at 75 C

There is not much out there listed for 90 C terminations (which is pretty hot, and would burn you if you touched it).

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