I am about to sign a contract to rent a 40'x25' garage for my small contracting business. I plan on setting up a small shop for cabinet building, minor vehicle repair and storage.

The building has 3 phase power, which as a residential thumb-smasher, I don't don't know much about. IF I pull one leg of the 3 phase to get 110V (and two to get 220V) do I use ground as the ground and the neutral? OR do I have to convert in the panel some other way? I can't figure out what to do without my white wire!

I am gonna call my electrical sub in the morning but I thought it was easier to embarass myself here first by admitting I don't know diddley about 3 phase.

Thanks,
Ed

 

You are on the right track but it depends on what type of 3-phase you have. Your Electrician is trained to handle this problem.

 

Yeah... Most small building commercial 3-phase is 208Y/120V: three phase legs, neutral and ground. Most household 220 single phase equipment will be fine on 208 single phase (2 legs of 208Y), although the amp-draw will be slightly higher. Have any equipment you are unsure of ready with cleaned off name-plates and/or the user manuals and your electrician should be able to easily answer your questions.

 

you need to use a transformer to pull single phase power the three phase i have been around was 480 volt so each leg is 480 I dont know what you have but its probably 220 what ever it is the voltage on each leg and between each leg is whatever the rated voltage is so one leg and a neutral wont give you 110 like single phase

 

Light commercial 3 phase is usually 208 Wye. It is designed for a mix of single phase and three phase loads. Your electrician should be able to pull your 120 volt lighting and receptacle loads right off the main panel without any conversion being required. He has the option of re-wiring any of the three-phase 208 volt outlets to 208 volt single phase by changing out the receptacle at the box. No new wires need to be pulled.

Somewhat less likely is that you have 240 volt open delta. In this case, you have two legs at 120 volts line-to-neutral, and one "wild leg" at 208 volts line-to-neutral. Your 120 volt loads have to come off only two of the three legs of the three phase. Commonly, the "wild leg" uses a smaller transformer and should only be used for actual 3 phase loads. Your single phase 240 volt loads get supplied by the "main" center tapped transformer. But this is just a question of tapping the correct two of the three wires at each load.

If you plan to buy industrial woodworking or machine tools, you will find that used three phase equipment sells at a considerable discount compared to single phase equipment, because most home users buying this stuff at auction don't have access to three phase service.

For that reason, I would suggest keeping your existing 3 phase service, and have your electrician put new receptacles into enough 3-phase outlets to service your existing single phase equipment. You shouldn't need to change out the main panel or to pull new wires.

Equipment that uses a mix of 240 volt and 120 volt power (such as an electric clothes dryer) is somewhat of a special case. In that circumstance, an existing 3-phase receptacle might not be supplied with a neutral at all, and the neutral would have to be pulled from the panel.

 

Before the invetion of soft start motor controls, Does anyone remember the Wyy->Delta start timed relay. My ex-boss blew up a complete setup including the cabinet it was in. And it was plc controled. wired them both without offsetting leg connections. Sounded like a claymore going off in a concrete bunker! This was also on a 400amp 350hp AC motor with a 6000# + grinding wheel used to grind foam scraps up to make carpet padding.

 

350hp - I woulda paid admission to watch that blowup, from a distance.

 

480v 3 phase = 3 legs of 240v

 

If it is 4W 480V each leg to neutral is 277V and phase to phase is 480. If it is 3W 480V there is no neutral and it is 480V phase to phase.

Ed W. very few people know anything about 3 phase so I wouldn't let your lack of knowlege concern you. You will know a lot more after the electrician reviews the system.

 

midlf is correct on his conversion of 480-3ph. To calculate 1 leg to ground on a delta transformer, you take the square root of pie and times it by 480 = 277.
On a 480 Wyy transformer, One leg is 240 to ground. That is how your house is fed. Using a transformer, one 240V 3Ph leg into split phase transformer = 2 120V "split phase" legs to your house.

 

 

as an electrican i agree talk to one,some of the advice in this thread is good other is pure bs and the posters should not give advice when they dont know what they are talking abouit.

consult a professional it is not a big deal and will most likely save you time and money over poor advice.
pete

 

I agree with what icecold said. I am an electrical engineer and no offense to anyone who has already responded to this thread already, but it is safer to work with an electrician when dealing with 3-phase power systems. It is alot more complicated that just a couple of wires. It also hurts alot more when it decides to fight back.

 

Thanks to everyone who posted and a lot of good info of the educational variety was posted.

I am a bit nuts and will often take on projects that are one level above my ability, but sometime you gotta know when to holdem, know when to foldem!

My electricain will sort this one out for me!