Electrical mystory

We have 208 V coming in. There are transformers in the building and on tools to convert to the needed voltages. European tools usually use 380-400V, US tools 460/480 V. Some that originally required 220/240V will run on the 208 OK. The local utility will no longer supply 240 due to the wild leg problem and unbalanced loading. Lighting is all 120 V. Some of our European tools have two contactors and a timer that switches them between Y & Delta on 6 lead motors. Common in Europe where the electrical systems don't like the high inrush of direct line starting. I should have had 480 V from the utility to begin with but at the time didn't have the need. One of the last things installed on the 208V is a 40 HP vacuum pump. You can hear the wire slap the inside of the conduit when it starts. Should change it to 480!
 
Hmmmmmmm

If you can hear the wires slap the conduit on every start, Are you sure that movement has not worn thru the insulation, or is not getting close to wearing thru, and and causing leakage during the slaps?
 
Good point. I was surprised that it would happen at all. Pretty big wire.
 
The utility should be willing to come out and check the incoming service for free, and/or tell you if there have been any problems at their end recently
-M
 
Larry$ said:
Several different electrical contractors have done work here. The last one just a week ago.
Click to expand...

That alone is interesting........and a good place to start looking!
-brino
 
Late as usual, that's me. Seems most troubleshooting has already been covered. There are a couple of points that need to be stressed though. First and foremost is to check the incoming line for balance. If it's not within 5% or so, scream at the utility. Load balance matters too, but is harder to check. The utility can do it if you don't have an electrician "in house". An "amp-probe" will solve many such problems. But getting into the "entrance" is dangerous. Best electrician is an old timer that shows up with a Simpson 260 and a magnetic Amp-probe. Don't trust the man with a digital anything.

Then you mentioned 460 wye connected with step down or isolation taking place. And a couple other anomolies. Up front was recent work. Is there any way to isolate the "new work" and try the older system? Then there is the compressor(?) slapping the wires when starting. That is a no-no by any measurement. The starting load can be as high as 500% for starting. It doesn't last long, but is a major consideration when sizing wire.

Then the last thing bothering me is the possibility of "delta" distribution from a "wye" source. How old is the original electrical plant? If it is 40-50 years, or more, old, there may be a "grounded delta" system in the mix. Grounded delta was outlawed years ago, but existing systems are "grandfathered" and still allowed. It is seldom (if at all) taught and few are even aware of it. It has a valid reasoning for being used but is highly dangerous. One leg(phase) is intentionally grounded. In a mixed system with wye and delta distribution, strange "electrical phenomena" can occur.

Just remember, you titled the message "Electrical Mystery". That is not so far off the mark, electricity does weird things. When you have solved the problem, the answer is obvious. But finding the answer may well involve standing on one leg, with the opposite eye closed and chanting an Egyptian mantra while holding your mouth "just so".

.
 
Larry$ said:
3 phase doesn't use a neutral! Multiple different grounds. No thunderstorms. Two different service lines from the utility! Multiple different breaker panels. :apologize: @ 8:00am the router was fine, office breaker not tripped two hours later multiple problems! Only one person in the shop, no equipment running.
Click to expand...

3 phase Delta connection doesn’t include a neutral wire but in 3 phase Star connection there is a neutral.
Loss of the neutral changes the voltage at the star point so, because the phase voltages are influenced by an open neutral, the phase current is also out of sync..
 
Last edited:
Problem solved!
The utility had repeating loses of a phase. Nothing appears to be damaged. One older machine had a relay tripped that took us awhile to find.
This sort of thing could be really expensive. I'd like to see how wild the voltage spikes were each time the lost leg was reconnected.
We don't often lose power. Last year it was when a backhoe cut the main power cable. It made a big notch in the bucket.
 
Flyinfool said:
The utility could be having an issue with one leg of the 3PH power
Click to expand...
Valid point. That happened to us a few months ago. It was strange. Having one leg down in a business with lots of lighting and equipment had a strange affect on things.
 
A long time ago I rented a shop space in a 100 year old building. Delta power, one leg center tapped for 120V single phase. Making for the wild leg phenomena. I had an electrician come in to hook up some stuff. He couldn't figure out why there was the wild leg. When I told him he said I was wrong. Same guy wired a 240V single phase compressor. When he got done and turned the breaker on, there was a pop and smoke, breaker tripped. He said there must have been a "wisker" that just needed to be burned off. Next try same result. I watched when he opened the compressor box. He had swapped a hot leg & ground. So much for licensed electricians.
 
You must log in or register to reply here.
Back
Top