Wye-delta starter
- Thread starter jociha
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john m. caloggero
Senior Member
Re: Wye-delta starter
Hi John,
See 2005 NEC Section 430.22(C) Wye start Delta-run motor. The branch circuit conductor to the motor controller are sized at the motor full-load current rating. The conductors from the controller to the motor are based on 58 percent of the motor full-load current rating. Check in one of the NFPA NEC Handbooks in Article 430, I drew a diagram of the Wye start Delta run configuration. o.58 x 992A = 575 amps for the conductors between the motor and controller.
Hi John,
See 2005 NEC Section 430.22(C) Wye start Delta-run motor. The branch circuit conductor to the motor controller are sized at the motor full-load current rating. The conductors from the controller to the motor are based on 58 percent of the motor full-load current rating. Check in one of the NFPA NEC Handbooks in Article 430, I drew a diagram of the Wye start Delta run configuration. o.58 x 992A = 575 amps for the conductors between the motor and controller.
thunder15j
Member
- Location
- Cali
Re: Wye-delta starter
Wouldn't you have to add 25% more to the calculated load if you had a continuous running motor? FLA x .58 x 1.25 = ampacity of conductor from wye-delta starter to motor. (six wires plus egc)
Wouldn't you have to add 25% more to the calculated load if you had a continuous running motor? FLA x .58 x 1.25 = ampacity of conductor from wye-delta starter to motor. (six wires plus egc)
thunder15j
Member
- Location
- Cali
Re: Wye-delta starter
Upon further thought.... when the motor is running in the delta mode, the motor is basically fed in a parallel manner ....MCC to motor conductor sizing would be: FLA / 2 then multiplied x 1.25. This calculates out to 62.5% x FLA for run mode verses 58% x FLA for starting mode(wye connection which only occurs briefly)
Upon further thought.... when the motor is running in the delta mode, the motor is basically fed in a parallel manner ....MCC to motor conductor sizing would be: FLA / 2 then multiplied x 1.25. This calculates out to 62.5% x FLA for run mode verses 58% x FLA for starting mode(wye connection which only occurs briefly)
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Wye-delta starter
I understand the concept of the reduced starting voltage in the Wye configuration but could someone explain how this reduces the starting current? And once the starter shifts to the Delta run configuration how is the running current only 58% of the FLA? And as Thunder mentioned, where does the 125% factor in to this equation?
I understand the concept of the reduced starting voltage in the Wye configuration but could someone explain how this reduces the starting current? And once the starter shifts to the Delta run configuration how is the running current only 58% of the FLA? And as Thunder mentioned, where does the 125% factor in to this equation?
ramsy
NoFixNoPay Electric
- Location
- LA basin, CA
- Occupation
- Service Electrician 2020 NEC
Re: Wye-delta starter
infinity, I'm learning too, but we might wait a while for such expertese to be volunteered in public domains.
This generic description by a private Orig. Equip. mfg. (OEM) describes the wye-delta starting at lower voltage, lower torque, & lower motor starting current, before the starter changes the motor coils from wye to delta full voltage.
infinity, I'm learning too, but we might wait a while for such expertese to be volunteered in public domains.
This generic description by a private Orig. Equip. mfg. (OEM) describes the wye-delta starting at lower voltage, lower torque, & lower motor starting current, before the starter changes the motor coils from wye to delta full voltage.
thunder15j
Member
- Location
- Cali
Re: Wye-delta starter
A wye-delta motor runs like a normal motor and will draw nameplate amps if the load is at the horsepower rating of the motor, when it is connected in the delta run mode. In the wye connected mode for starting, the windings are connected in a series manner, thus limiting the amperage to about 58% of nameplate.
I have also encountered 2 speed wye delta motors that are specifically made for that purpose.
I haven't had the opportunity to work with this kind of starting means on very many occasions, but I think they are a thing of the past. When you add the costs of all those contactors and the extra wires to the motor from the Y-D starter, you are close to an electronic soft starter. You would have to look at torque limits of an electronic unit.
On the two speed units, especially the larger motors, a VFD becomes more feasible.
A wye-delta motor runs like a normal motor and will draw nameplate amps if the load is at the horsepower rating of the motor, when it is connected in the delta run mode. In the wye connected mode for starting, the windings are connected in a series manner, thus limiting the amperage to about 58% of nameplate.
I have also encountered 2 speed wye delta motors that are specifically made for that purpose.
I haven't had the opportunity to work with this kind of starting means on very many occasions, but I think they are a thing of the past. When you add the costs of all those contactors and the extra wires to the motor from the Y-D starter, you are close to an electronic soft starter. You would have to look at torque limits of an electronic unit.
On the two speed units, especially the larger motors, a VFD becomes more feasible.
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