Replies

1. 
   Stuart | Dec 03, 2006 05:37am | #1

   Yes, single phase motors can be powered from a three phase system, you just use one of the three phases.  It sounds like this building has a 120/208v three phase system.  There are three hot wires and one neutral wire.  Call the hot wires A, B and C; between any two of them (from A to B, from A to C, or from B to C) you will get 208v.  From any of the hot wires to neutral (from A to N, from B to N or from C to N) you'll get 120v. Of course, for most power tools you won't need the neutral connection.

   One thing to take into account is you spread the loads out as evenly as you can across all three phases, so for instance if you have three tools connect the first one to A and B, the second one to A and C, and the third one to B and C.

   Also, take a good look at the nameplates on the motors - they may actually be rated for use at 230v instead of 220v.  If that's the case, 208v is just barely within the +/- 10% tolerance level, and if the service to the building is on the low side you may be in trouble.  Some motors will specifically be rated for use at either 208v or 230v, so again check the motor nameplates.  If you're still in doubt and your tools are fairly new, you may be able to talk to the manufacturers to see if there's any problem with running them at 208v.

2. 
   Jamie_Buxton | Dec 03, 2006 06:57pm | #2

   Right now, I'm running most of my 230 volt machines from two phases of a 3-phase supply, and they're okay.   The only one which complained is the chip collector.  With the lower supply voltage, it consumes more current.  More current leads to more heating.   Run for an hour or two, it would heat up enough that its thermal cutout would pop.   The solution is a buck-boost transformer.  These are transformers intended to make small changes in power voltages.   In my case, I used one to make 230 volts from 208, and the chip collector has been happy ever since.   I bought mine at a commercial electrical supply house which caters to HVAC guys.  IIRC, a 3-hp one cost less than $100.

3. 
   mudman | Dec 03, 2006 08:49pm | #3

   My recomendation is to get a 110/ 220 3 phase transformer. Many electric companies do not offer this option, but you can buy one for 200 - 300 dollars on Ebay. I was lucky, the electric Co. that suplies my shop offered this as an option. The problem is that you will not have the 440 voltage. The only machines that I have looked at that need 440v. are CNC, widebelt, and production machinery.

   Most of the large shops I know have two panels, a 440/220 3 phase and a 110/220 single phase. They have 2 meters and the electric Co owns both transformers. But this gets expensive.

   Before you get too far find out what the property manager is including. Code around here requires seperate disconects for each panel. A fused 200 amp 3 phase disconnect costs $800 new, and $500 on Ebay. The breaker panels and the breakers anre also very costly. A 20 amp 3 phase breaker costs $40, and a 3 phase panel fills up quick. I found a panel that uses regular Square D breakers. The 3 phase breakers look like 3 regular breakers ganged togather. Everything 3 phase costs a lot more, except used machines. You will have to weigh the cost/benifit carefully. If you are signing a long term lease then you should be able to get all this stuff included, or split and prorated.

   Good luck.

   Pardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

4. 
   dukeone | Dec 04, 2006 12:36pm | #4

   Wally: Watch out for the stinger leg! If it is a delta 4 wire supply there will be a high leg ie; one phase that is 208 volts phase to neutral. It will be taped orange if it is done right. If you connect any 120 volt circuits to it you'll let out the smoke which makes machines work.

   KDM retired electrician

   "... Buy the best and only cry once.........

1. 
   KeithNewton | Dec 04, 2006 05:21pm | #5

   < you'll let out the smoke which makes machines work. >That is a good one, I have never heard that. Ha, I guess it is only logical that once you let it escape, the tool no-longer works. duh!

1. 
   dukeone | Dec 04, 2006 09:56pm | #6

   Keith: It is an old joke among electricians but also is applicable to anyone who uses electrical equipment and that is certainly most woodworkers.

   Merry Christmas, Duke"... Buy the best and only cry once.........

5. 
   RickChristopherson | Dec 05, 2006 03:32am | #7

   I have been watching this thread but didn't enter the discussion because I assumed that everything was on track. However, after seeing some of the newer postings I realize that there may be some confusion passing back to the original poster. Most importantly, no one has asked the OP what type of system he has, and this is critical to answering his question.

   Because of the way the original question was posed, I made the assumption that the OP's system was a balanced 120/208 V 3-phase, but this may not be the case. The 120/208 V system is most common in commercial areas, but the 120/240 V hybrid (tapped delta) system is more common in light commercial areas. The easiest way to identify the two is with a volt meter. If the voltage between phases is 240 volts, then it is the tapped delta. If the voltage is 208 volts, then it is the balanced.

   View Image

   Running single-phase, 240 volt motors on a 120/208 V system will cause the motors to run below their optimal voltage and power. In this situation, a buck/boost transformer is the best solution. This can feed just the specific motor, or can drive a separate load center for running multiple 240 volt tools. (120 volt loads are not affected and should remain in their original load center.)

   If the system is a hybrid (tapped delta) then the single-phase tools will already be receiving their desired 240 volts, so this is a non-issue. As one person noted (Oh, that was Duke), it is the tapped delta system that will have a "stinger leg", so this phase should not be used for 120 volt connections.

   
   

   ---

   Edited 12/4/2006 7:46 pm ET by RickChristopherson

1. 
   mudman | Dec 05, 2006 06:33am | #8

   That is a great explanation. I have never seen those diagrams before. It makes more sense than the ones I have seen before.Pardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

1. 
   RickChristopherson | Dec 05, 2006 08:04am | #9

   Thanks Mike.

   It has been so long since I created the graphic, I suddenly realized that I can’t remember why I originally created it, but I have used it many times to answer single-phase and three-phase questions. If my fading memory is correct, I had an electrical lineman for a utility company adamantly claim that the 120/208 V 3-P system discussed in Electricity

   in the Woodshop didn’t exist because he had never personally seen one.

   Over the years I’ve learned that many electricians are only familiar with the type of system they encounter in their daily work. The worst situation was when a mechanic for the company I was contracting with was rewiring the internal windings of a diesel-electric generator because the customer told him they needed a Delta system, and all of the generators are wye configured. The highly trained mechanic couldn’t understand that the generator didn’t need to be reconfigured, but it cost the company thousands of dollars in labor. (I was reminded of that story because the middle diagram was originally created specifically to explain why the situation wasn't necessary, and I copy/pasted it to create the version shown.)

   Edited 12/5/2006 12:08 am ET by RickChristopherson

1. 
   mudman | Dec 06, 2006 12:25am | #11

   It is funny that you mention that. I found the same thing when I was searching for a shop. The first thing I did was call the local utilities and or the proprerty manager. Almost without fail they would claim that I was wrong and that I would be fine with the 220/ 440 set up. The shop I ended up leasing is in a semi-rural area and serviced by a Co op. The guy I spoke with said "Yea no problem, we have those transformers here in the yard.". I thought I was going to have to buy my own transformer, but that was quickly going to get complicated and expensive.Pardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

2. 
   dukeone | Dec 05, 2006 10:23am | #10

   May I recommend to all wishing to learn more about electricity the book: "Electricity One-Seven". I believe it is no longer published but is available at ABE or other second hand book sellers. There are two versions: all seven books in one or seven separate volumes. It starts off at the most basic level: kind of like explaining woodworking from the rain falls in the forrest on the seedlings............

    Duke

    

   http://www.abebooks.com/servlet/SearchResults?sts=t&y=0&tn=Electricity+One-Seven&x=0

   "... Buy the best and only cry once.........

   Edited 12/5/2006 2:37 am by dukeone