3-phase vs. single

[bams50]

I'm building a new shop, and 3-phase electric is available. I'm looking at air compressors. I can get a large used compressor from a closed car dealership, one single and one 3-phase (both similar size, about 5 HP motor). Other things being equal, and with 3-phase on site, which compressor would be preferable?

 

[Norcal]

3 phase is preferred.

 

[54stude]

Did you get a quote on the 480V 3 phase installation, step down transformer (to 208v 3 phase), and panel yet? For a building the size you mentioned in your intro, I am assuming you are thinking about a 400 amp service?

If the price of getting the 3 phase power to the building is reasonable for you, the main advantage of 3 phase in your setting would be the ability to buy reasonably priced used equipment. Since most houses cannot get 3 phase power, there is less market for the used 3 phase equipment. There are other advantages in terms of smooth running motors, being able to use smaller wire due to the higher voltage and lower amp draw per phase, and I believe there is a cost savings per KWH also. There are disadvantages also like being charged more if you do not use power evenly on all 3 phases, which is your power factor (PF). Also, you would want to understand if you are liable for repair of the wiring and transformer up to your 480v panel.

 

[Steve from Socal]

Three phase power IS very desirable for all the reasons above. That said; carefully consider what the total cost difference is to use three phase service. Most utilities have a demand charge for three phase service, it could be insignificant or more than double your bill. Kilowatts are kilowatts; IF single phase power is substantially less expensive consider using a phase converter.

I have a shop with three phase service and the KWH charges are reasonable, the 8 dollar per KWH demand charge is a whole nuther story!

Steve

 

[A_Pmech]

If you plan on having an automotive machine shop with numerous machine tools then I would install 3-phase. However, if you're planning a typical auto repair shop I don't think I'd bother with the significant added up-front expense of installing a 3-phase service. Auto shops don't really have any large motor loads and large motor loads are the main reason for installing a 3-phase service. The fact that you're considering a 5HP compressor suggests to me you don't really need 3-phase. 5hp is a small motor load.

If I did install a 3-phase service I certainly wouldn't install a 480V system in an auto shop. You'll be paying $50 or more a month to keep a transformer warm 24/7/365 so you can plug in a hair dryer, which makes no sense at all.

 

[sneezer41]

I have no special metering or anything for my business 3 phase.

it is also 208, I believe from the pole.

 

[Tscott]

Did you get a quote on the 480V 3 phase installation, step down transformer (to 208v 3 phase), and panel yet? For a building the size you mentioned in your intro, I am assuming you are thinking about a 400 amp service?

If the price of getting the 3 phase power to the building is reasonable for you, the main advantage of 3 phase in your setting would be the ability to buy reasonably priced used equipment. Since most houses cannot get 3 phase power, there is less market for the used 3 phase equipment. There are other advantages in terms of smooth running motors, being able to use smaller wire due to the higher voltage and lower amp draw per phase, and I believe there is a cost savings per KWH also. There are disadvantages also like being charged more if you do not use power evenly on all 3 phases, which is your power factor (PF). Also, you would want to understand if you are liable for repair of the wiring and transformer up to your 480v panel.

Um, the OP said nothing about what voltage he was considering. If he has 3Ø available, then he can most likely get either 120/208 or 277/480. The power company will install a transformer to provide what he needs. Based on what we know, I would assume he would be better off with 120/208 so there will be no need for a step down transformer.

If you plan on having an automotive machine shop with numerous machine tools then I would install 3-phase. However, if you're planning a typical auto repair shop I don't think I'd bother with the significant added up-front expense of installing a 3-phase service. Auto shops don't really have any large motor loads and large motor loads are the main reason for installing a 3-phase service. The fact that you're considering a 5HP compressor suggests to me you don't really need 3-phase. 5hp is a small motor load.

If I did install a 3-phase service I certainly wouldn't install a 480V system in an auto shop. You'll be paying $50 or more a month to keep a transformer warm 24/7/365 so you can plug in a hair dryer, which makes no sense at all.

Pmech is correct. If you plan to run large machinery, 3Ø is the way to go, but if you plan on just a simple shop, then you would probably be better off with a standard 1Ø service since it will cost you less up front. Any deals on 3Ø equipment can be easily offset by the extra cost you pay for 3Ø if your not careful. Check with your utility about the rate structure as well. Remember to get 3Ø the power company will need to install 3 pole top transformers or 1 large 3Ø transformer and these can greatly increase the cost of an install depending on how the utility capitalizes their costs and passes them on to you.

Tom

 

[bams50]

Hmm... lots to consider here. No, I haven't made any inquiries or priced anything yet- or made any plans. This is my first foray into this area where I know next to nothing.

Here's my reason for asking:

I bought two of these, running at the time, out of a closed Lincoln dealership for $400 each. That was before I knew anything about Phases.

Info on the motor tag:

10HP
Code H
60 Hertz
Phase 3
1750 RPM
Volts 208-230/480
Amps 26.4-25/12.5
and some other stuff...

They are said to be about three years old.

One of my main goals for the new shop is for once in my life to have more than enough air- both volume and pressure, no excuses. I don't plan on milling machines or the like, but one never knows. And, I'm trying to think of resale value. Maybe I can't use these compressors; maybe it can be solved with a new single-phase motor or that conversion deal; but I don't want something that's cobbled or of questionable durability.

What do you guys think of this? I was hoping to get my air and save good money; but maybe these aren't for me. I'm sure I can sell them if I can't use them. I guess the first step is to talk to the utility company- armed with your advice and info, of course!

 

[Martha39]

I have no special metering or anything for my business 3 phase.

 

[Norcal]

You need to inquire at your PoCo about which voltages are avail., locally PG&E offers 120/240V 1Ø, 120/240V 3Ø delta, 208Y/120V, & 480Y/277V. which ones they (PG&E) give you will depend on the load, but for small 3Ø services they give 120/240V delta. 480V is not a good idea for untrained people IMO, & as said a transformer will cost money to run every month... But if not familiar w/ the quirks of 240V 3Ø it's EZ to let the magic smoke out.

 

[bams50]

But if not familiar w/ the quirks of 240V 3Ø it's EZ to let the magic smoke out.

Not for me, I don't mess with wiring. I don't want to have any worry; nor do I want to risk getting electrocuted

 

[FreddiFiche]

But if not familiar w/ the quirks of 240V 3Ø it's EZ to let the magic smoke out.

Yes, that 'magic' wild leg is VERY good at letting the smoke out. I've seen several Canadian equipment suppliers think they got a 120/240 Y, only to find that a third of their equipment lasted only 16ms....heh. Apparently a delta 120/240 doesn't exist to our north.....

 

[KenC]

I was really fortunate. Wanted 3 phase in my shop behind the house for an air compressor, table say, disk sander etc, that I already owned. The shop has it's own service, about a 300' run from the main line on the street. My main breaker failed, so before replacing it, I contacted the local electric utility, owned by my city.

The crew chief looked at the service and my needs and said, sure I'll provide it for you. I installed a used 3 phase fused disconnect and used panel.
The city electriic guys hung me a new transformer, and pulled another conductor from the street, overhead service so that was'nt a big deal. Now I've got 120/240V 3phase. It looks weird though, 2 transformers, the original center tapped + another. I have 2 phases 125v to neutral (240 phase to phase, one 208 to neutral.

Runs my 5, 3 and 2 hp loads fine.

 

[KenC]

Forgot the best part: NO Charge by the utility!!!!

I was really fortunate. Wanted 3 phase in my shop behind the house for an air compressor, table say, disk sander etc, that I already owned. The shop has it's own service, about a 300' run from the main line on the street. My main breaker failed, so before replacing it, I contacted the local electric utility, owned by my city.

The crew chief looked at the service and my needs and said, sure I'll provide it for you. I installed a used 3 phase fused disconnect and used panel.
The city electriic guys hung me a new transformer, and pulled another conductor from the street, overhead service so that was'nt a big deal. Now I've got 120/240V 3phase. It looks weird though, 2 transformers, the original center tapped + another. I have 2 phases 125v to neutral (240 phase to phase, one 208 to neutral.

Runs my 5, 3 and 2 hp loads fine.

 

[bams50]

What's the opinions on the compressor? Worth seeeking out 3-phase for, or better to just sell or look for single-phase motor?

 

[A_Pmech]

In light of the compressors, I would say it depends on the cost to install 3-phase in your location.

Single-phase 10HP motors area bout $1500 to $1900 new. 1/3rd to 1/2 that NOS on Ebay.

 

[930dreamer]

What's the opinions on the compressor? Worth seeeking out 3-phase for, or better to just sell or look for single-phase motor?

Build a large rotary phase converter, I looked into running the three phase from the pole to my shop, price wasn't too bad except for the 300+ feet of wire and the trench work.

 

[bams50]

In light of the compressors, I would say it depends on the cost to install 3-phase in your location.

Single-phase 10HP motors area bout $1500 to $1900 new. 1/3rd to 1/2 that NOS on Ebay.

Yeesh. For that kind of money it's probably not worth messing with. Before I did that I'd probably do better to sell these for whatever and put the money toward a new compressor with single-phase, right?

Build a large rotary phase converter, I looked into running the three phase from the pole to my shop, price wasn't too bad except for the 300+ feet of wire and the trench work.

I've heard of this, but I know nothing about it, nor do I know the first thing about building anything like it. So then it would come to what I'd have to pay to get it done... after I figure out who in my area even does it

Food for thought...

 

[930dreamer]

Yeesh. For that kind of money it's probably not worth messing with. Before I did that I'd probably do better to sell these for whatever and put the money toward a new compressor with single-phase, right?



I've heard of this, but I know nothing about it, nor do I know the first thing about building anything like it. So then it would come to what I'd have to pay to get it done... after I figure out who in my area even does it

Food for thought...

I like the two compressors, I wish you were closer.

 

[bams50]

LOL. Heard the same thing from a guy in FL. I'll make you the same deal, pay my round-trip expenses and I'll deliver. I'm overdue for a road trip!

 

[Tscott]

If all you want is air, then you might as well sell them and get a 1Ø unit. I got a 7.5HP unit from Eaton and I have yet to run out of air. I painted a boat with it and have been running my blast cabinet and it probably only kicked on once every couple of minutes. 3Ø is good for getting cheap industrial equipment, and that is about all.

Tom

 

[bams50]

I hear you, Tom. I thought eventually I might come across a good deal on maybe a lathe or milling machine, or other equipment. My experience is, any equipment that's three-phase equipment is much cheaper since most people can't use it.

And then there's those cheap compressors I've got. And love...