Wire size
- Thread starter kfenn
- Start date
- Status
- Location
- Massachusetts
Re: Wire size
That motor draws about 27 amps, as you said the 10 AWG is rated 35 amps.
The 60 amp circuit breaker is not for overload in this case.
The only purpose of the 60 amp breaker is Short-Circuit and Ground-Fault Protection, if either of these faults occur the 10 AWG will be sufficient to operate the breaker.
The overload protection of these conductors is provided by the motor overloads in the motor starter.
Take a look at 240.4(G) and sections III, IV and V of Article 430.
[ January 08, 2004, 02:28 PM: Message edited by: iwire ]
That motor draws about 27 amps, as you said the 10 AWG is rated 35 amps.
The 60 amp circuit breaker is not for overload in this case.
The only purpose of the 60 amp breaker is Short-Circuit and Ground-Fault Protection, if either of these faults occur the 10 AWG will be sufficient to operate the breaker.
The overload protection of these conductors is provided by the motor overloads in the motor starter.
Take a look at 240.4(G) and sections III, IV and V of Article 430.
[ January 08, 2004, 02:28 PM: Message edited by: iwire ]
- Location
- Massachusetts
Re: Wire size
Something to consider is the length of the run and motor start up current.
You are on the money as to the minimum allowed by code, but there is no reason you can not exceed code.
Something to consider is the length of the run and motor start up current.
You are on the money as to the minimum allowed by code, but there is no reason you can not exceed code.
- Location
- Massachusetts
Re: Wire size
Well considering a run of 10' and a VFD the 10 AWG will be adequate.
Use 6 AWG if you feel better, but from a code perspective the 10 AWG is fine.
Look at this way, how would the 10 AWG become overloaded?
The motor overloads will shut the motor down if it started to draw above it's design.
If the conductors where to fault to ground the 10 AWG can take the high amps for the short period of time it takes for the breaker to open.
This is no different then using a 8 AWG grounding conductor on a 100 amp feeder, 100 amps is clearly above the rating of the 8 AWG but the conductor will sustain that overcurrent long enough to trip the circuit out.
Well considering a run of 10' and a VFD the 10 AWG will be adequate.
Use 6 AWG if you feel better, but from a code perspective the 10 AWG is fine.
Look at this way, how would the 10 AWG become overloaded?
The motor overloads will shut the motor down if it started to draw above it's design.
If the conductors where to fault to ground the 10 AWG can take the high amps for the short period of time it takes for the breaker to open.
This is no different then using a 8 AWG grounding conductor on a 100 amp feeder, 100 amps is clearly above the rating of the 8 AWG but the conductor will sustain that overcurrent long enough to trip the circuit out.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Wire size
A motor circuit is an exception to the rule of 240.3(D) small conductor ampacity, as stated in table 240.4(D)
With the VFD the motor branch circuit is based on the input power to the VFD.
A motor circuit is an exception to the rule of 240.3(D) small conductor ampacity, as stated in table 240.4(D)
With the VFD the motor branch circuit is based on the input power to the VFD.
Re: Wire size
This could probably be another topic but how did you come up with #10 @ 35 amps. I've always thought the asterisk stated no more than 30 amps for #10 no matter what.All the places I have worked that seemed to be the rule.One thing that I have never been clear on is dual rating on conductors.THWN/THHN. which temp. rating do you use, does it depend on the location? What size cu for a 100 amp feed does everybody use?
This could probably be another topic but how did you come up with #10 @ 35 amps. I've always thought the asterisk stated no more than 30 amps for #10 no matter what.All the places I have worked that seemed to be the rule.One thing that I have never been clear on is dual rating on conductors.THWN/THHN. which temp. rating do you use, does it depend on the location? What size cu for a 100 amp feed does everybody use?
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Wire size
The asterisk (oblisk, actually) for table 310.16 was deleted with the 1999 NEC as the ampacity notes had nothing to do with table 310.16. The ampacity of 10 AWG THHN is 40 amps. unless otherwise modified. The information from the oblisk was moved to 240.3(D)
The asterisk (oblisk, actually) for table 310.16 was deleted with the 1999 NEC as the ampacity notes had nothing to do with table 310.16. The ampacity of 10 AWG THHN is 40 amps. unless otherwise modified. The information from the oblisk was moved to 240.3(D)
electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
Re: Wire size
240.4(D) gives conditions under which #14,#12and #10 can be protected at greater than 15A, 20A and 30A. These conditions are in 240.4(E)..(G)and in table 240.4(G). Also the higher ampacity given in table 310.16 can be used when derating is required.
240.4(D) gives conditions under which #14,#12and #10 can be protected at greater than 15A, 20A and 30A. These conditions are in 240.4(E)..(G)and in table 240.4(G). Also the higher ampacity given in table 310.16 can be used when derating is required.
pierre
Senior Member
- Location
- Westchester County, New York
Re: Wire size
Tom
I am not sure if I understand your post, and I see the oblisk in the 2002 version of the NEC.
Pierre
Tom
I am not sure if I understand your post, and I see the oblisk in the 2002 version of the NEC.
Pierre
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