Question on 3 Phase, 240 Volt

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  #1  
Old 03-23-05, 04:07 PM
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Question on 3 Phase, 240 Volt

As a maintainence man in our expanding small factory, I was instructed to mount and connect the wiring to a 50 Amp, 240V, 3 phase panel. Conduit was already there, just had to add a few feet, and reconnect the wiring (from a previous use by the former occupant). My Fluke meter showed 236 to 240 V between any two of the three legs. PVC was used for the conduit for the new panel, so I pulled a #8 stranded wire for ground, taped it green, etc. The crew from the old factory (we're relocating the operation from CA to IN) came in to install the equipment and finish the wiring. One thing they wanted to do was use part of the new panel for 110 V circuits, (as they had in the old factory,) using one leg and a ground. Had I known this, I would have had a separate 110 V panel ready for them! When they made their connections, their shaker indicated no voltage at the end of the circuits they had installed. My Fluke meter showed 130, 115, and 160 volts respectively between the three legs and the ground lug at the panel... and then my battery went dead. My Ideal tester lit up the 120v indicator and buzzed at each of the three points, as well. A professional was called in, and told them this couldn't be done with this 240 volt circuit since there wasn't a neutral at the transformer. Possible code violations notwithstanding, why didn't this work as they expected? It seems similar to a residential service entrance connection, and this is how they had proceeded in the former operation. The professionals returned to run a new circuit from a 480 panel and installed a transformer, allowing the work to proceed, but I wasn't able to get with them to have the technicalities explained. Was this a result of Delta vs. wye configuration? The company owner appears to feel that I was responsible for the delay, and I'd like to know exactly what the problem was, should I need to defend my position (not in a legal sense, of course). Thank you, once again , for your expert opinions.
Jess
 
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  #2  
Old 03-23-05, 04:55 PM
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Its not so much being Delta vs. Wye as it is 3 wire vs 4 wire three phase service. You were trying to get 120 volts from a three phase 480 service with no neutral (three hot legs only and ground with no neutral bonding) This cant be done. You must have a 4 wire service (3 hot legs a neutral and bonded ground) Second you never use ground as neutral they are not the same. I suspect they ended up using a grounded wye 208/120 transformer to supply the 120 voltages. There are other choices but this I believe is the most common. Take a look at this link for some configurations that will aid your understanding .... http://www.bmillerengineering.com/elecsys.htm
 

Last edited by Roger; 03-23-05 at 05:06 PM.
  #3  
Old 03-23-05, 05:46 PM
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As a maintenance man you should not have been touching this. In a commercial environment this is a job for an electrician only.
 
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Old 03-23-05, 07:20 PM
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Maybe in a perfect world that would be the case. I've found myself disliking my job at times when working WITH a licensed electrician on a job, let alone without one.
 
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Old 03-23-05, 07:35 PM
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i agree with Bob,unless you have a great deal of experience with 3 Ph the owners had no right to make you responsible.I hope they didnt come down on you too hard.
 
  #6  
Old 03-23-05, 08:43 PM
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Rider you and a jillion other maintenance men are in the same position. Anybody who thinks electricians are used in building maintenance outside of union shops is greatly misinformed. This is common place. Rarely are skilled electricians used in situations like yours. The owners simply will not pay the higher costs of using them. I find it almost funny that your owner now has to get skilled electricians to get the job done. What he should be doing is getting you the training you need to be able to perform these tasks. In the future best thing you can do is be up front that your skills need to be "updated" so you can work on these electrical assignments with confidence and more importantly...safely. Gotta know what your looking at with 3 phase or dont touch it. You employer got what he deserved. Yes, I know if you say no to doing these jobs it risks your job. Best advice I can give you is read these forums frequently there is a wealth of information that appears here. John and Racraft and many other professionals on this site share their knowledge freely so take advantage of it. Good luck
 
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Old 03-24-05, 04:21 AM
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Thank you all for your replies and opinions. I was up-front with the plant manager about my limited knowlege in this area, and worked alongside an experienced electrician for the first few projects they wanted, and have done much research and reading on my own since starting there. The difference now is that since the former facility is closed, the owner is on-site, and brought with him his maintainence men from CA to finish the installation of the machinery. If I had my preferences, I would have completed courses began years ago in electricity & electronics. At 54, it's a little late to go back & pick that up now, and I don't expect to be working at this place more than a couple more years anyhow (my income retirement from my "real" profession starts in two months). This job is only paying 1/2 what I made as a CDL driver, and has yet to offer any benefits, so it may be shorter term yet. I shall continue to do what I can in this position, but my formost priority is to be sure that any work that I do is safe for both myself, and any others that may be affected.
 
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Old 03-24-05, 07:41 AM
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It doesnt sound like his maintenance men knew how to deal with this either.
 
  #9  
Old 03-24-05, 10:33 PM
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If the right transformer was used in developing the 240 3ph, 2 120v 1ph circuits could have been pulled off. This would require a 240V delta with a grounded center tapped leg. However, if this is not the style of service you currently have, it is a moot point. If the guys from california and your bosses didn't make it clear what was expected, how can they complain about the results?
 
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