Motor starting wire sizing for voltage drop

[kenaslan]

I have a 1HP motor 115V with a 151 foot distance. #10AWG XHHW wire 3C type MC-HL cable. What is the motor starting formula taking into account voltage drop?

Will the motor start or will there be locked rotor issues?

Thanks

 

[ramsy]

I have a 1HP motor 115V with a 151 foot distance. #10AWG XHHW wire 3C type MC-HL cable. What is the motor starting formula taking into account voltage drop? Will the motor start or will there be locked rotor issues?

1HP disposers & pool pumps on #12 wire start fine with 96A locked rotor per Tbl 430.31(A).

If breaker trips during start, Tbl 430.52 permits a Non-HVAC motor OCP oversize up to 250%, but 20A trip curves may be fine.

Unless local energy codes, or special circumstances prohibit 4.5% branch voltage drops, per Tbl 430.248 a 16A load on #10 for 151ft is virtually at Motor's rated 115vac, which is fine w/ 120v at the source.

 

[drktmplr12]

Unless local energy codes, or special circumstances prohibit 4.5% branch voltage drops, per Tbl 430.248 a 16A load on #10 for 151ft is virtually at Motor's rated 115vac, which is fine w/ 120v at the source.

As ramsy has stated, the motor should start, even with 10% voltage drop. Most electric motors have a pretty wide tolerance for voltage. Keep in mind that the amp draw will be higher, but still within the capability of #10 wire. I would use a 30 amp breaker just in case the motor does run a bit higher than 16 amps.

Energy codes that discuss voltage drop in the states are based on ASHRAE 90.1, titled Energy Standard for Buildings Except Low-Rise Residential Building. You would need to determine if Colorado adopted it (it looks like they have) and whether or not it applies to the building you are working on.

The easy way to comply, without doing additional research, is to size the conductors to #8 and call it a day. You are going to spend more time figuring it out then just running the #8 and moving to the next project. My math shows voltage drop of 4% with: PVC conduit, 150 ft run, 120VAC, 0.8 pf, 16 Amps, #10 AWG. Increase conductor to #8 and VD becomes 2.6%.

The United States Dept of Energy maintains a registry of energy codes adopted on a per state basis and information related to them.

 

[kenaslan]

As ramsy has stated, the motor should start, even with 10% voltage drop. Most electric motors have a pretty wide tolerance for voltage. Keep in mind that the amp draw will be higher, but still within the capability of #10 wire. I would use a 30 amp breaker just in case the motor does run a bit higher than 16 amps.

Energy codes that discuss voltage drop in the states are based on ASHRAE 90.1, titled Energy Standard for Buildings Except Low-Rise Residential Building. You would need to determine if Colorado adopted it (it looks like they have) and whether or not it applies to the building you are working on.

The easy way to comply, without doing additional research, is to size the conductors to #8 and call it a day. You are going to spend more time figuring it out then just running the #8 and moving to the next project. My math shows voltage drop of 4% with: PVC conduit, 150 ft run, 120VAC, 0.8 pf, 16 Amps, #10 AWG. Increase conductor to #8 and VD becomes 2.6%.

The United States Dept of Energy maintains a registry of energy codes adopted on a per state basis and information related to them.

a C1D1 junction box would be required at the pump disconnect as the motor term will only accept a #10 max and this is MC-HL, so no conduit. Also there are 5 of these nasty buggers per site (oil well site in ND). So figuring it out could save 10s of 1000s of $

 

[ActionDave]

a C1D1 junction box would be required at the pump disconnect as the motor term will only accept a #10 max and this is MC-HL, so no conduit. Also there are 5 of these nasty buggers per site (oil well site in ND). So figuring it out could save 10s of 1000s of $

From a straight cowboy engineering look at it with no slide rule you should be fine with 10AWG on a motor that size at that distance. It's a single phase motor so your inrush at starting only lasts a second and then your down to 16A max, it wouldn't matter if you pulled 1/0.

 

[drktmplr12]

If you want to prove it, calculate the expected voltage drop and show it is within the specified tolerance of the installed motor. Protect the #10's with 30 A breaker to avoid nuisance tripping and make sure there is motor thermal overload protection

a C1D1 junction box would be required at the pump disconnect as the motor term will only accept a #10 max and this is MC-HL, so no conduit. Also there are 5 of these nasty buggers per site (oil well site in ND). So figuring it out could save 10s of 1000s of $

MC-HL is technically aluminum conduit which imparts the same amount of reactance on the conductors as PVC pipe, because it is non-ferrous. RGS would increase the voltage drop slightly. A moot point because according to the DoE, North Dakota has not adopted any form of energy conservation code.