Three phase to single phase motor

[axd38]

I have a three phase service coming 120/208V panel. I have a chair lift that requires a 110 Volts, 1 Phase, 15 Amps power supply for the motor. Is it OK to make this connection, can there be any adverse affects from an unbalanced load? I am guess also I do not need a transformer.

 

[hacksaw]

depends on you local codes.

you should be making your connection through a power distribution panel. the only reason you would need a transformer is if your your equipment requires complete isolation from the incomming power.

load balancing is a major issue in industrial plants and is always good, but in homes or like industrial it is not always the case.

the safest thing to do is get a licensed electrician involved so that you have a safe and sound connection with appropriate overload protection, safety disconnets, and grounding.

 

[jbartos]

Suggestion/questions:
1. Is this an industrial, commercial or residential place? 120/208V three phase tend to be commercial and industrial power supply.
2. If the panel 120/208V, 3phase, has a higher main protection than 100A, then the 15 single phase circuit will negligibly impact the panel load balance.
3. NFPA 70-2002 National Electrical Code adherence is recommended. GFCI receptacle might be considered or GFI circuit breaker in the panel. The current leakage 5 mA or less is required.

 

[rbulsara]

Simple answer is "there will NOT be any adverse effect by what you are prosposing, from a technical and practical point of view."


It does not even appear to be violating NEC. This is how all singel phase loads in a residential systems, fed by 208/120V systems, are connected.

Meeting Code is a requirement for anything you do. I don't understand some of the cocerns mentioned by others.

 

[jbartos]

Suggestion: A Meeting electrical safety code requirement within a private property is not everywhere enforceable.

 

[acmotorengineer]

axd38 - you're asking for major problems, I would recommend you replace the motor with a three phase motor. A much more reliable motor.

 

[jOmega]

acmotorengineer

Would you care to share some knowledge that supports your supposition that running single phase motors from a 3-phase supply would cause major problems ?

Much appreciated.

jO

 

[blutfort]

In packaged rooftop units Carrier, Trane, McQuay for Commercial buildings it is common practice to use single phase motors for the condenser fans and 3 phase motors for the compressors and supply fans.

These units are UL listed and installed on lots of buildings in lots of jurisdictions.

 

[PUMPDESIGNER]

One problem you may face regards voltage.
Most single phase motors are designed to operate at 230 volts or so. If those motors are operated at 208 volts the motor will run hotter.
Some motors come dual rated for both 208/230 volts, some do not come rated for 208 volts.

We have seen 230 volt motors overheat and have shortened life because of this.

At 208 volts the capacitors found on single phase motors may also be incorrect.

PUMPDESIGNER

 

[jOmega]

Blutfort:

Are the 1-phase motors in those applications connected across one phase i.e. L1-L2 or L2-L3 or L1-L3 of the 3-phase supply ?.. or is there a separate single-phase power source for them... ?

 

[mvcjr]

I think load unbalance is not much of a concern in your case since most probably your chair lift would be operating intermittently. It can become a major concern when a single-phase load is continuously operated.

Also, make sure your 3-phase service has ample capacity to handle the 15-A load.

God bless!

 

[peebee]

axd38: Most likely, the installation you're proposing is just fine. However, as it sounds like you are not very familiar with such things, I strongly urge you to hire a licensed electrician as previously suggested.

j0mega: The motors mentioned by blutfort can often come in just about any flavor you please (and sometimes, if you're not careful with your specs and shop drawing reviews, they come in surprising new flavors too. . . ). Sometimes you gotta bring a neutral out, sometimes not. Sometimes the 1-phase motors are 120-volt, but they have their own transformer included with the equipment. I think the HVAC equipment vendors made a pact a long time ago to NEVER put any clear electrical requirments into their catalogs or drawings just to keep it surprising and new and fun.

 

[jOmega]

Hi PeeBee,

It would seem that the supply is a 3-phase 208v wye ...so that he gets 120v phase-to-neutral.

A lot of the 208 services I've seen run around 200 - 195 , in which case .. the voltage would be around 115 - 112v

Must be an old motor on chair lift if it's n/p 110v .. ya think?

If motor is n/p for 115... I'd expect that 120v won't hurt it.

 

[jbartos]

Comment: I agree with peebee posting where it calls for an appropriate expertise to implement the project. The ground fault current poses a safety concern. The installation should be properly tested for its safety not to electrocute anyone in the lift chair.

 

[skiier]

Use a 3 phase motor if you can. Less components,more reliable and more efficient.Cheaaper to operate as well. More even tourque. Just plain better. Easier to control than single pphase. You are going to use a drive on your control? Proper safetys too? Imean e-stops and cable snesors, et al. Dont kill someone because of a bad safety. Single phase motors suck- they have to be physically larger than equivalent rated 3 phase motor to do the same work.
Every service should be 3 phase. I guess someone thought once they would save 1/3 in material way back when. But now we are making up for it greater line losses due too innefficient single phase motors.Just think of the trillions of dollars lost over the years because some ass dictated cheapness once.And what about the larger copper sizes neded to feed these current drawing monsters.As well as the extra labour needed for larger wires. No thanks. Go 3 phase or go home.

 

[rogiers]

there be no problem if you have the power (A). This two wired motor will work on 120V.
So intermed. use of the lift will be nescesary .

 

[jbartos]

Suggestion: Three-phase versus single phase motor. If the motor HP size gets smaller, e.g. fractional HP, the single motors are widely used since:
1. They need the three conductor power supply instead of the four conductor power supply.
2. They tend to be less expensive and more readily available.
3. The inrush current may be smaller.
4. The protection is simpler.
5. The practically applicable wire size may be the same as for three-phase motor.
6. The physical size may be approximately the same as for three-phase motor, because of the bigger terminal box for the three phase motors.
7. The efficiency and power factor can be about the same as for the three-phase motors.
8. Etc.