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#16226 - 11/07/02 08:28 PM 120/208 three phase  
Shinkman  Offline
Junior Member
Joined: Nov 2002
Posts: 6
I do some work for a fire protection company, mostly residential. I went to look at and bid on a small commericial job for this company today. Its a very old factory/warehouse in a large old complex. They are switching the current water sprinkler system to a dry system. My job would be to get power to a 1/2 hp air compressor. Install a small electric baseboard heat unit to keep this 4x4x8 foot room at a constant 40 degrees and also install a keyless light/switch. My problem is the old (1940's) electrical equipment. a wall of troughs, disconnects and an old GE 225 amp 120/208 three phase loaded panel. There is a newer 30 amp GE heavy duty fused three phase switch that was once used to control some type of lift that is gone now. Can I replace this switch with a four circuit panel and power my job with this?? I have not seen the specs but I believe the air compressor and heat are 120volts. I just dread opening up this old can of electrcal worms. i just want to safely do my work and go. Any sugestions--thanks If I have the neutral in the disconnect can I tap off of two of the hots to feed my new panel? in other words can I use this three phase disconnect but only use two of the fused hots to get my feed, and leave the third empty? I understand that with this 120/208 I will get 208 measured from hot to any other hot. I will get 120 measured from any hot to neutral or ground. If I bring two of these hots to my new panel I will not be able to get 240v, I will only be able to use single pole breakers...Is this correct?? Can you ever pull 240v from a 120/208 service??

[This message has been edited by Shinkman (edited 11-07-2002).]

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#16227 - 11/07/02 09:16 PM Re: 120/208 three phase  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
If it's currently 208V, what about running a grounded-circuit conductor to the disconnect and installing two suitably rated fuses for the new equipment? It may not be ideal, but for the situation at hand, well...

#16228 - 11/07/02 09:27 PM Re: 120/208 three phase  
Ron  Offline
Joined: Mar 2002
Posts: 582
White Plains, NY
If the fused switch has three hots a neutral and a ground, then yes, you can put in a small laod center connected to the fused disconenct. Be sure to place correctly sized fuses for the disconenct to protect the downstream wire and panel. If no neutral then maybe feed a delta-wye isolation transformer to result in a derived neutral on the secondary for your new panel.


#16229 - 11/10/02 01:25 AM Re: 120/208 three phase  
Surge_in_fl  Offline
Joined: Oct 2002
Posts: 17
Tampa, Florida
Sounds to me like you should sub this part of the project to an electrical contractor to save yourself from some unwanted liability.

#16230 - 11/10/02 05:08 AM Re: 120/208 three phase  
elektrikguy  Offline
Joined: May 2002
Posts: 132
Not being able to see this job is hard but it sounds like you are on the right track with mounting a small load center. In a room that small I am sure that it should not be that difficult for you to get a white(neutral) wire to the load center. Make sure that the neutral is the same size as the hots. I am wondering why you asked about 240 volts? Is the baseboard heater you plan to purchase a 240v model? In any case you indeed can put a two pole breaker in you little load center. Another option could be to make it a single phase load center and "phase" one wire as a neutral. Remember that if you do do this that you must make the wire you choose to use as your neutral white by means of phase tape or some other means as to make it permanantly identifiable. You would also then have to purchase a 2 pole breaker for your 2 hots to put in the existing GE 3 phase panel. This whole situation should be sounding to you like you should be letting someone qualified do this portion of your job huh?

What about taking the 3 pole breaker in the existing panel that isn't doing anything and replacing with 1 single pole for the aircompressor and the light and 1-2 pole for the heater?

Ron: I think you "derived" something completely overkill.

[This message has been edited by elektrikguy (edited 11-10-2002).]

[This message has been edited by elektrikguy (edited 11-10-2002).]

#16231 - 11/10/02 09:18 AM Re: 120/208 three phase  
electure  Offline

Joined: Dec 2000
Posts: 4,262
Fullerton, CA USA
Unless the conductor that's to be used as a neutral is #4 or larger, phase tape cannot be used to identify it per NEC 200-6 (sorry, my '02 book's not here).
Remember, this is a 30 amp disco.

If you really need 240 (or thereabouts) volts, you could use boost transformer. (autotransformer)

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