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Old 09-19-2012, 05:56 PM   #1
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3 phase power help


In my barn I have a type of 3 phase that I am not familiar with and I am trying to find more info. It is a 60a service and when I go from hot to ground I get 645v from one, 363 from the next and 285 from the last one. From hot to hot I always get around 500v. I am planning on gettigg a transformer to make the power more usable but I would like to know more about what exactly it is. I have been collecting machining and welding equipment and I would like to know a little more before I start plugging stuff in. I am used to standard 277/480 power. Thanks for any help you can give me.

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Old 09-19-2012, 06:05 PM   #2
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3 phase power help


#1 Go back and add your location to your profile. Sure sounds like your not in the US where most of us here from.
First things your going to hear is call an electrition when it comes to working with 3 ph.

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Old 09-19-2012, 06:06 PM   #3
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#1 Go back and add your location to your profile. Sure sounds like your not in the US where most of us here from.
First things your going to hear is call an electrition when it comes to working with 3 ph.
I am in Michigan. I have spoke with multiple electritians and they all give me different answers.
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Old 09-19-2012, 06:54 PM   #4
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I am in Michigan. I have spoke with multiple electritians and they all give me different answers.
Troubleshooting over the internet with 3 phase and those crazy voltages will get you hurt.
You don't need to talk to one, you need one to come out and check themselves.
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Old 09-19-2012, 07:14 PM   #5
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Troubleshooting over the internet with 3 phase and those crazy voltages will get you hurt.
You don't need to talk to one, you need one to come out and check themselves.
I deal with high voltage a lot. I am not a complete newbie. I have encountered this power before. It is an old style 3 phase. I just don't know any more info.
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Old 09-19-2012, 07:23 PM   #6
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3 phase power help


suggest you call the electrical supplier for specifications and application procedures..they may be very helpful
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Old 09-19-2012, 08:21 PM   #7
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In my barn I have a type of 3 phase that I am not familiar with and I am trying to find more info. It is a 60a service and when I go from hot to ground I get 645v from one, 363 from the next and 285 from the last one. From hot to hot I always get around 500v. I am planning on gettigg a transformer to make the power more usable but I would like to know more about what exactly it is. I have been collecting machining and welding equipment and I would like to know a little more before I start plugging stuff in. I am used to standard 277/480 power. Thanks for any help you can give me.
Could be a high leg delta supply !

Or you are really across two phases,
rather then across neutral and one hot !

Ask your poco to check it out for you !

Be really carefull,
I dont have to tell you,
that voltages like that,
will destroy anything imediately.
Including you !
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Old 09-19-2012, 08:36 PM   #8
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Ask your poco to check it out for you !
+1 They will certainly be your best source of information!
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Old 09-19-2012, 08:38 PM   #9
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3 phase power help


I suspect this is an ungrounded 480V delta service that is running a bit high of a voltage. 500V on a 480V service is only 4% above nominal, so while it is uncommon, it isn't necessarily a big problem. The unpredictable voltages between each phase and ground suggest that this service is not ground-referenced. In other words, it's ungrounded. That is uncommon, and is only appropriate in specific types of industrial installations where there is monitoring equipment in place to detect ground faults. You should not have an ungrounded service in a typical barn or shop - they are only for industrial plants with proper monitoring. If the service drop has ONLY three conductors, and all three are insulated, then you probably have an ungrounded delta service. The definitive test for this is to apply a load (like a string of 5 100W light bulbs) between each phase and a good actual ground (like a rod), while measuring the voltage. If it drops much at all, then the service is ungrounded. This test is a bit dangerous because the reference ground rod will be electrified during the test.

It is also possible that the service was originally grounded, but the grounding connection has failed over time. This could create a very dangerous condition, electrifying metal parts on the failed grounding system. If there is evidence of a neutral conductor anywhere in the system, then it was probably grounded originally. It may have been center-grounded like a normal 3-phase service, so the phase-to-ground voltage should be 277V. Or it may have been corner grounded, where one phase was bonded to ground and the other two are 480V with respect to ground. That is a common configuration for agricultural installations like irrigation well pumps. If your service drop has four conductors, or three insulated conductors plus a bare one, then you almost certainly have a 277/480V service with a bad ground. If the service drop has only two insulated conductors and one bare, then it was definitely a corner-grounded delta service that now has a bad ground. In either case, watch out! Metal equipment may be electrified.

Pictures of the panel and the service entrance would be very helpful.

Last edited by mpoulton; 09-19-2012 at 08:41 PM.
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Old 09-19-2012, 09:01 PM   #10
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Old 09-19-2012, 09:24 PM   #11
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I deal with high voltage a lot. I am not a complete newbie. I have encountered this power before. It is an old style 3 phase. I just don't know any more info.
Contact the power company. From what you are saying you are in over your head.

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