460V Motor Connection Leads, sizes

[Isaiah]

Does anyone out there know: Are motor connection leads (pigtails inside motor termination box), sized per NEC requirements of motor FLA x 1.25%? My understanding is motor leads are controlled by NEMA but shouldn't basic sizing requirements still apply according to motor HP, S.F., Insulation type etc?

Thanks in advance.

Isaiah.

 

[jumper]

If you are talking about the factory leads, no , the NEC has nothing to do with sizing them.

NEMA, UL, etc governs them.

 

[Isaiah]

If you are talking about the factory leads, no , the NEC has nothing to do with sizing them.

NEMA, UL, etc governs them.

\

Ok...but where would I find the applicable NEMA info for sizes? Is it contained within MG-1?

 

[jumper]

\

Ok...but where would I find the applicable NEMA info for sizes? Is it contained within MG-1?

IDK, I have never sized or worried about the leads. Why would I?

I simply run my wires per 430 and 310. What are you trying to do? Just curious.

 

[Isaiah]

IDK, I have never sized or worried about the leads. Why would I?

I simply run my wires per 430 and 310. What are you trying to do? Just curious.

Just for info really; subject came up in a meeting yesterday and no one had an answer. I had assumed the pigtails would be sized per 430.22, that is motor FLA x 1.25% - but this may not be the case...Still digging...I may need to go simply go to site and open some peckerheads.

 

[jumper]

You know that the motor leads are high temperature conductors, like 150C, not 90C.

Also the length is so short.

Those and prolly other factors apply.

 

[Isaiah]

You know that the motor leads are high temperature conductors, like 150C, not 90C.

Also the length is so short.

Those and prolly other factors apply.

I think conductor temp needs to correspond to motor insulation, for example:
Class B motor must use 90C pigtails
Class F motor must use 125C pigtails
Class H motor must use 150C pigtails

 

[jumper]

I think conductor temp needs to correspond to motor insulation, for example:
Class B motor must use 90C pigtails
Class F motor must use 125C pigtails
Class H motor must use 150C pigtails

I really do not know, never paid attention. jraef or someone else may. My knowledge of motor design is pretty thin.

 

[Isaiah]

I really do not know, never paid attention. jraef or someone else may. My knowledge of motor design is pretty thin.

I appreciate your feedback. I will physically check a couple motors on site later today.

 

[retirede]

I think conductor temp needs to correspond to motor insulation, for example:
Class B motor must use 90C pigtails
Class F motor must use 125C pigtails
Class H motor must use 150C pigtails

Those ratings are the temperature rise, not operating temperature.

For example, class B is max 90C rise over 40C ambient. The insulation must withstand 130C.

 

[Isaiah]

IDK, I have never sized or worried about the leads. Why would I?

I simply run my wires per 430 and 310. What are you trying to do? Just curious.

I just went out to site and pulled the cover off term box for Baldor-Reliance, 460V 40HP TEFC, squirrel cage, induction motor (nameplate FLA = 44A). The vendor supplied pigtails are #8's; good for 50A per T310.15(B)(16).

FYI.

 

[retirede]

I just went out to site and pulled the cover off term box for Baldor-Reliance, 460V 40HP TEFC, squirrel cage, induction motor (nameplate FLA = 44A). The vendor supplied pigtails are #8's; good for 50A per T310.15(B)(16).

FYI.

That motor is likely 1.15 service factor. SFA would then be 50.6.

FYI

 

[Isaiah]

That motor is likely 1.15 service factor. SFA would then be 50.6.

FYI

True, but motor will rarely, if ever see SFA

 

[retirede]

True, but motor will rarely, if ever see SFA

My point is that the motor design must account for SFA. The design ampacity of the leads is likely greater than 50A.

 

[Isaiah]

My point is that the motor design must account for SFA. The design ampacity of the leads is likely greater than 50A.

Good point. The insulation doesn't state "8 AWG"; but doesn't look big enough to be a #6.

 

[JFletcher]

Good point. The insulation doesn't state "8 AWG"; but doesn't look big enough to be a #6.

7AWG? Metric?

The motors are going to have higher insulation ratings and smaller conductors for the most part.

I did a stator replacement on a Generac generator last year, was somewhat surprised to see the four leads from the stator were only 10 gauge wire, which two of the hots were going to a 80 or 90 amp factory-installed breaker.

Similar small wire surprises can be seen with space heaters and ovens, which use wires that are tiny compared to the branch circuits that supply them. A 2000 watt hair dryer may have an 18 gauge wire cord on it.

as others have mentioned, the motors themselves are largely outside the purview of the NEC.

 

[ActionDave]

Just for info really; subject came up in a meeting yesterday and no one had an answer. I had assumed the pigtails would be sized per 430.22, that is motor FLA x 1.25% - but this may not be the case...Still digging...I may need to go simply go to site and open some peckerheads.

Why stop at the motor leads? What about the windings in the stator? They are seeing the same current.

 

[Jraef]

Wire ampacity given for sizes called for in the NEC have little relationship to conductors used inside of equipment. Ampacities are not finite, they are based on safety factors and temperatures for the expected use. Field wiring, which is what the NEC covers, has to account for all manner of variations that might possibly be encountered so they are purposely extra conservative. Internal conductors in equipment are selected as part of the complete assembly design. The insulation used is part of that design and with different insulation, as well as different thermal limits allowed in the entire assembly, the conductor ampacity is going to be very different. Bottom line, you can’t make comparisons.

 

[winnie]

On top of the 'different ampacity for conductors designed into equipment' that Jraef notes, there is also much larger variability in conductor types.

The lead wires in motors are very likely high temperature conductors with finer stranding than most building wire. Each copper strand has a thick coating of nickel to protect from oxidation, and the stranding itself makes the apparent cross section of the wire larger. The conductor sizes are not limited to 'every other AWG size' such as are common under the NEC, and can even be half or quarter sizes (yes, you can buy 23.5 awg magnet wire for building motors).

Net result is that you can't really look at the wires and even be sure what size they are. They might be 8 AWG, or they might be 9.5 AWG. Or 7.5. Or some 'metric' size that isn't even one of the standard 'preferred' mm^2 values.

-Jon

 

[retirede]

On top of the 'different ampacity for conductors designed into equipment' that Jraef notes, there is also much larger variability in conductor types.

The lead wires in motors are very likely high temperature conductors with finer stranding than most building wire. Each copper strand has a thick coating of nickel to protect from oxidation, and the stranding itself makes the apparent cross section of the wire larger. The conductor sizes are not limited to 'every other AWG size' such as are common under the NEC, and can even be half or quarter sizes (yes, you can buy 23.5 awg magnet wire for building motors).

Net result is that you can't really look at the wires and even be sure what size they are. They might be 8 AWG, or they might be 9.5 AWG. Or 7.5. Or some 'metric' size that isn't even one of the standard 'preferred' mm^2 values.

-Jon

Yep - I’ve always figured the manufacturers knew what they were doing and never worried about the size of the wires.