elevator motor

[sparky59]

I have the specs on a new 2-story elevator for a church. The motor is a three-phase 208v 15hp. The specs are 155 amps starting current with a max. allowable vd of 10%....76 amps full load current with a max. allowable vd of 5%.....and 51.7 amps rated current with a max. allowable vd of 5%. Am i correct in figuring 76 amps x 125% = 95 amps. So #2 cu for the conductors and overcurrent protection at 155 amps? I don't work with motors very often so any help would be appreciated.

 

[bstoin]

I have the specs on a new 2-story elevator for a church. The motor is a three-phase 208v 15hp. The specs are 155 amps starting current with a max. allowable vd of 10%....76 amps full load current with a max. allowable vd of 5%.....and 51.7 amps rated current with a max. allowable vd of 5%. Am i correct in figuring 76 amps x 125% = 95 amps. So #2 cu for the conductors and overcurrent protection at 155 amps? I don't work with motors very often so any help would be appreciated.

No.
start with 430.6A (use tables such as 430.150, not nameplate values...however, see also exceptions)
see also Table 430.22E (this would be considered an intermittent duty motor) however, in this case you DO use nameplate current rating for your calculation according to 430.22E
see also 215.2for voltage drop. maximum total voltage drop on both feeders and branch circuits to the farthest outlet can't exceed 5%...therefore you would use 51.7 amps to start your calculation if using table 430.22E.
I hope I have been of some help.

 

[Snorks]

You must also take into account distance, insulation type, conductor material, terminal temperature and ambient temperature for sizing a conductor. In addition, power factor must be considered to accurately determine voltage drop.

As far as the 5% device VD...this depends on whether or not you are installing with energy efficient specifications. Also, device nameplate values can be used. But, most use NEC 430 tables as this represent the “worst case” and hopefully establishes a safe conductor size when the motor is replaced with a different manufacture’s motor with different nameplate FLA and power factor ratings.

 

[davidr43229]

Sparky,
That is a small elevator, size your Overcurrent protection device for the max and depending upon your state, don't forget the shunt-trip, which maybe required.

 

[Pierre C Belarge]

You must also take into account distance, insulation type, conductor material, terminal temperature and ambient temperature for sizing a conductor. In addition, power factor must be considered to accurately determine voltage drop.

As far as the 5% device VD...this depends on whether or not you are installing with energy efficient specifications. Also, device nameplate values can be used. But, most use NEC 430 tables as this represent the “worst case” and hopefully establishes a safe conductor size when the motor is replaced with a different manufacture’s motor with different nameplate FLA and power factor ratings.

Where does it state that in Art 430? One other poster posted the correct section numbers in his post.