mikesimpson5
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- Atlantic County, NJ USA
Where in the 2011 NEC does it specifically reference voltage drop for motors?
voltage drop
- Thread starter mikesimpson5
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- Chapel Hill, NC
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- Retired Electrical Contractor
The NEC does not require you to worry about voltage drop except for fire pumps- 695.7 However it is wise to consider it.
I can't remember an NEC reference but isn't there something regarding a percentage voltage drop allow an a branch circuit or feeder which always was intriguing. You would have to know what the actual voltage is in order for whatever it ends up to be to be acceptable. What I do know is that 480v is a nominal voltage but motor used on that system a more likely that not to have a 460v nameplate. The NEMA rated motors normally are designed to operate +-10% of the nameplate voltage.
So, regarding your question it is important for the motor to be within +-10 of its nameplate rating. As such, voltage drop doesn't apply unless the motor is being applied at a voltage which is outside its parameter.
Should you have a voltage drop issue you may have to reconsider adjusting the primary taps of the transformer supplying the system and possible reconsidering the cable side which supplies the motor to allow for voltage drop.
So, regarding your question it is important for the motor to be within +-10 of its nameplate rating. As such, voltage drop doesn't apply unless the motor is being applied at a voltage which is outside its parameter.
Should you have a voltage drop issue you may have to reconsider adjusting the primary taps of the transformer supplying the system and possible reconsidering the cable side which supplies the motor to allow for voltage drop.
broadgage
Senior Member
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- London, England
3% volt drop is suggested in many circumstances as being a reasonable limit of voltage drop, but is not a code requirement.
3% is probably a good figure to aim for, but judgement should be applied.
In the case of a motor used only briefly, and on a long feeder or branch circuit, a larger voltage drop might be reasonable, accepting increased losses and/or reduced motor life rather than spending thousands of dollars on larger wire.
In the case of a large motor with long operating hours, consider the annual cost of energy wasted in voltage drop, larger wire might pay for itself in a year or so.
3% is probably a good figure to aim for, but judgement should be applied.
In the case of a motor used only briefly, and on a long feeder or branch circuit, a larger voltage drop might be reasonable, accepting increased losses and/or reduced motor life rather than spending thousands of dollars on larger wire.
In the case of a large motor with long operating hours, consider the annual cost of energy wasted in voltage drop, larger wire might pay for itself in a year or so.
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