Splitphase (single) 240v or 2 phase 208/240v

[Jpflex]

When trying to find proper conductor and breaker size to a 2 hp continuous duty 230v Air compressor with service factor 1.15 over 1200 rpm we use FLA in nec table

However, my question is that how do you differentiate the service source as single (split) or two phase because both can yield over 200 volts potential. Either system determines FLC and they vary greatly

I’ve worked with y generators and could two legs to get desired voltage which I assume would be 2 phase or 2 phases.

Power going to my compressor in question now I’m confident is standard two hits and neutral single phase or splitphase since neutral splits phases for usable 120v from 240 source. How would you identify a 2 phase source?

Also how do you identify if motor is squirrel cage or wound rotor if not listed on nameplate and windings are internal not visible from outside motor?

Thanks

 

[Jraef]

2-out-of-3 phases is still called “single phase”. It doesn’t matter (from a naming convention) whether there is a neutral involved or not, just that there are only 2 hot wires. Virtually everything you will come across that is not three phase is single phase.

“Two phase” means something different from what you are talking about. It exists only in a few really old areas, like some old parts of Philadelphia and up state New York, around Niagara. In a true two phase system, there are at least 4 hot wires, which is one reason it never became widespread. The chances that you are really coming across two phase power are slim to none. The chances of you coming across a motor made within the past 120 years that was built as two phase are zero.

But part of the confusion that can happen around this issue is that in EUROPE, where they have never seen true two phase like we have here, they sometimes refer to 2-out-of-3 phases as being “2-phase”, which causes confusion when being read by electricians here. You have to learn to recognize that as an anomaly of speech and translation from whatever language their literature was originally written in.

As to how to tell if a motor is wound rotor or squirrel cage, wound rotor motors are rare and special, requiring a special control system that has resistors that must be wired to slip rings on the end of the motor. Nobody makes single phase WR motors and although small three phase WR motors were once popular for things like cranes and winches for their to the ability to control torque, hardly any does that now because VFDs has made that easier to do using standard squirrel cage motors. So 99.9% of motors you encounter 1HP and up will be squirrel cage induction motors (SCIM).

 

[tom baker]

You mentioned the air compressor is continuous duty, it would be very unusual for an air compressor application to be continuous duty, meaning that it runs for more than three hours. If you could attach a picture of the motor nameplate we can help you determine the motor branch circuit conductor size circuit breaker size and if overloads are needed thank you.

 

[retirede]

You mentioned the air compressor is continuous duty, it would be very unusual for an air compressor application to be continuous duty, meaning that it runs for more than three hours. If you could attach a picture of the motor nameplate we can help you determine the motor branch circuit conductor size circuit breaker size and if overloads are needed thank you.

A 2 HP compressor application is not likely continuous duty, but many larger applications are. Most bigger body shops have multiple compressors with at least one of them running fully loaded all day. Most factory plant air systems are designed that way, too.

 

[augie47]

A 2 HP compressor application is not likely continuous duty, but many larger applications are. Most bigger body shops have multiple compressors with at least one of them running fully loaded all day. Most factory plant air systems are designed that way, too.

My experience has been different. The plant compressors I have seen might operate 24/7 but never fully loaded for any 3 hour period.

 

[retirede]

My experience has been different. The plant compressors I have seen might operate 24/7 but never fully loaded for any 3 hour period.

If the plant requires more than one compressor, and they don’t have at least one of them fully loaded, they are not running them in the most efficient manner.

 

[don_resqcapt19]

The "continuous duty" marking on the nameplate just means that the motor is suitable to operate continuously at rated horsepower. Most industrial motor nameplates have that marking.

 

[Jraef]

The "continuous duty" marking on the nameplate just means that the motor is suitable to operate continuously at rated horsepower. Most industrial motor nameplates have that marking.

Yes, the “continuous duty” marking on a motor is not the same as “continuous” as defined in the NEC. But I can relate to the confusion.

 

[garbo]

Side note: While working at a large plant back in the 1970's the air compressor service tech installed unloaders on a few of our 100 HP maybe 10 year old compressors. During production motors ran all the time. When we installed our first 200 HP screw air compressor it had a large label stating not to start & stop the motor more then 3 times a hour so motor ran continuous. After production was done for the day turned all the large air compressors off and let a small 40 HP air compressor take over.

 

[garbo]

2-out-of-3 phases is still called “single phase”. It doesn’t matter (from a naming convention) whether there is a neutral involved or not, just that there are only 2 hot wires. Virtually everything you will come across that is not three phase is single phase.

“Two phase” means something different from what you are talking about. It exists only in a few really old areas, like some old parts of Philadelphia and up state New York, around Niagara. In a true two phase system, there are at least 4 hot wires, which is one reason it never became widespread. The chances that you are really coming across two phase power are slim to none. The chances of you coming across a motor made within the past 120 years that was built as two phase are zero.

But part of the confusion that can happen around this issue is that in EUROPE, where they have never seen true two phase like we have here, they sometimes refer to 2-out-of-3 phases as being “2-phase”, which causes confusion when being read by electricians here. You have to learn to recognize that as an anomaly of speech and translation from whatever language their literature was originally written in.

As to how to tell if a motor is wound rotor or squirrel cage, wound rotor motors are rare and special, requiring a special control system that has resistors that must be wired to slip rings on the end of the motor. Nobody makes single phase WR motors and although small three phase WR motors were once popular for things like cranes and winches for their to the ability to control torque, hardly any does that now because VFDs has made that easier to do using standard squirrel cage motors. So 99.9% of motors you encounter 1HP and up will be squirrel cage induction motors (SCIM).

Back in the Late 1960's can remember helping my dad wire in a brand new Bridgeport milling machine that came brand new from the factory with a two phase motor. Have worked on 4 & 5 wire two phase & even had a 2300 volt two phase 3 wire transformer feed a remote building. A few weeks ago for fun googled 30 amp 4 fuse 4 pole safety switch. Did not receive any replies. Last time I purchased that type of 250 volt safety switch was back in the early 1970's and believe it was twice the price of a 3 pole 3 fuse safety switch here in Philly.

 

[augie47]

Side note: While working at a large plant back in the 1970's the air compressor service tech installed unloaders on a few of our 100 HP maybe 10 year old compressors. During production motors ran all the time. When we installed our first 200 HP screw air compressor it had a large label stating not to start & stop the motor more then 3 times a hour so motor ran continuous. After production was done for the day turned all the large air compressors off and let a small 40 HP air compressor take over.

FWIW: My comment was directed more toward the NEC continuous load definition "A load where the maximum current is expected to continue for 3 hours or more". I may be incorrect but I assume a compressor which "loads and unloads" would reflect that loading on the current draw and thus not be considered a "continuous load" per NEC definition.

 

[garbo]

FWIW: My comment was directed more toward the NEC continuous load definition "A load where the maximum current is expected to continue for 3 hours or more". I may be incorrect but I assume a compressor which "loads and unloads" would reflect that loading on the current draw and thus not be considered a "continuous load" per NEC definition.

Always used wires at least 125% more then what the NEC gave for motor ampere rather then the always lower nameplate Amp. Often wondered if the NEC should lower the ampere in NEC motor table for motors that run on VFD'S ( without bypass option ). We had over 500 VFD'S where I retired from. From 2 to 1,750 HP. Performed PM'S on everyone and seldom did a motor run within 95% of motor nameplate amps while running at 100%. That and long ramp up times never had high or locked rotor current during start ups. Just about all new & replacement motors were ordered as energy efficient types.