sizing electrical wire for amps

vmw

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

gregzoll

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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CaptainD51

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

CaptainD51

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

Speedy Petey

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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Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.

Jim Port

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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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.

wareagle

CaptainD, you can not use the 90C rating when sizing conductors. You must use the 75C rating and sometimes the 60C rating of conductors.

Speedy Petey

Ummmmm.....

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Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.

Jim Port

I Think I hear an echo.

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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.

wareagle

They do sound similar. Maybe the captain needed a double wham-O.

CaptainD51

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 ?

kbsparky

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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kbsparky

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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