ELectrical System

[ron pfeiffer]

One of the buildings I service was built in 1972 and it has a ungrounded B-phase, (A & C to ground you read voltage B you do not). Does anyone have information on this system or a web site to visit. I am mostly wondering if this system needs to be posted or gain more knowledge on it. Thanks

 

[bphgravity]

Re: ELectrical System

The system you are describing sonds like a corner-grounded delta.

These systems are about absolete and are extremely hard to troubleshoot.

There is a good section on this type of system in the American Electrician Handbook, or just run a search engine for the term "corner-grounded delta", and you will find all the information you need.

 

[tom baker]

Re: ELectrical System

Not only are they hard to troubleshoot, they are much more dangerous than a 277/480, as the voltage to ground is 480, not 277. A ground fault will be very destructive.

 

[bennie]

Re: ELectrical System

I think you mean "grounded B phase". Make sure this is an intentional B phase grounded system. It may be an ungrounded delta system, with one phase inadvertentely grounded.

 

[don_resqcapt19]

Re: ELectrical System

Why are they hard to trouble shoot? There should be no problem trouble shooting a corner grounded system if you understand the system.
Don

 

[bphgravity]

Re: ELectrical System

Originally posted by don_resqcapt19:
...if you understand the system...
Don

This is the key issue to your comment.

I am guessing that if you were to post a poll on how many persons on this forum know what and how a corner-grounded system works, well over half would have no idea.

 

[don_resqcapt19]

Re: ELectrical System

Bryan,
If they don't understand the system, they are not qualified to work on it. Is it an OSHA violation to work on a system that you are not qualified to work on?
Don

 

[bphgravity]

Re: ELectrical System

Don,
Mike Holt says 97% of electricians dont understanding grounding, but 100% are doing it. Does this mean that only 3% of the grounding systems in the world are correct?

OSHA doesn't mean anything to most contractors that are not involved in large projects. This constitutes 2/3 of all contractors in Florida alone. These are the mom and pop shops that hardly pull permits unless they have to.

Many facilities and manufacturing plants slip throught the cracks and never truely train or comply with OSHA regulations. I absolutely agree that unqualified persons should not perform work on systems or equipment thay are not familiar with, but I know it is happening right now as I type and will ocntinue to do so forever.

I contracted some work at a large aricultural facilty that had one corner-grounded service of a few dozen faciltiy-wide systems. The company had three enigineers and an electrical crew of 9. None of them knew how this system worked and how to make proper installations on it. They just used conventional three-phase equipment and were even fusing the grounded leg. This was just one of a million things this place was doing wrong.

So, the problem wasn't troubleshooting a proper operating and installed corner-grounded system. The problem is that many of these systems have been altered and now incorporate improper methods and connections. It makes for quite a mess.

Bryan

[ July 10, 2003, 03:35 PM: Message edited by: bphgravity ]

 

[hurk27]

Re: ELectrical System

I had a newbee heating and air tech that was at a American Legeon here before he called me he had replaced 3 compressors and two condenser motors then called me to tell me the panel was wired wrong as it only has two-pole breakers. He had no clue that it was a grounded B 240v service and it cost him a lot. when he found out the hardway the compressors didn't need replaceing.