Tables 430-248 and 430-249

[mshields]

I've got a 5 HP motor that will be on a 240V single phase feeder. This is a phase to phase voltage.

Table 430-248 gives a single phase ampacity for 230V of 28 Amps. I believe this is the correct table to use. Still, Table 430-249, full load current, two phase alternating current motors (4-wire) gives me pause for reconsideration.

Although I'm still pretty sure that the first table and 28 amps is correct, what kind of a motor uses 2 phases and neutral current. Where are these used?

 

[david luchini]

I've got a 5 HP motor that will be on a 240V single phase feeder. This is a phase to phase voltage.

Table 430-248 gives a single phase ampacity for 230V of 28 Amps. I believe this is the correct table to use. Still, Table 430-249, full load current, two phase alternating current motors (4-wire) gives me pause for reconsideration.

Although I'm still pretty sure that the first table and 28 amps is correct, what kind of a motor uses 2 phases and neutral current. Where are these used?

Table 430-249 is for two-phase 4-wire electrical systems. They are not very common anymore. I've only seen it once for some old elevators.

(It is not suggesting 120/240v single phase, 3 wire., ie, 2 phases and neutral.)

 

[GoldDigger]

The two phase system had four phase wires each rotated by 90 degrees from the previous one.
You could also visualize it as two 120/240 systems offset by 90 and sharing a common neutral. Given a two phase supply, you could provide service with only two transformers instead of three.
And it had the same starting torque advantages for motors as a three phase system.

Sent from my XT1080 using Tapatalk

 

[Jraef]

True "Two-phase" distribution systems are extremely rare now, relegated to a few blocks of downtown Philadelphia and some old facilities in Niagara Falls as far as I know. Ignore all that.

But... Be aware that Europeans refer to "two-out-of-three" phases as "two phase". We call that single phase here. It causes a lot of confusion when people come here from overseas, where they do NOT have anything like our legacy "two-phase" systems.