Dogman

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dogman

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Woodward,ok
I have a problem, I would like some help with. We have a 120/240 open delta serving our mechanics shop. Last friday we had winds over 70 mph. The shop kept kicking the main breaker, 200 amp 3 phase. The breaker did not feel hot after it kicked off. It did it 6 times before they left it off.
It has kicked off before in thunderstorms. Why would it kick off the main breaker? Thank you for your help. Bob
 
dogman said:
I have a problem, I would like some help with. We have a 120/240 open delta serving our mechanics shop. Last friday we had winds over 70 mph. The shop kept kicking the main breaker, 200 amp 3 phase. The breaker did not feel hot after it kicked off. It did it 6 times before they left it off.
It has kicked off before in thunderstorms. Why would it kick off the main breaker? Thank you for your help. Bob
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No offense, but resetting a main breaker (or ANY breaker for that matter) 6 times without trying to find the cause of the trip is very poor practice and extremely dangerous.

Most likely there is/was a short circuit caused by the wind making something touch something that should not have been touched. You need a proper electrician to come out and thoroughly investigate the entire system for damage now and most likely the main breaker will need to be replaced.
 
Breaker

Breaker

Before the breaker? First off, I wasn't there. Second I do not need anyone telling me about safety. I wanted some information for me. They changed the 3 phase breaker out. Did it help, we do not know yet. Thank you, Dogman.
 
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Dogman we are here to help. The attitude is not a good way to get help. We have no idea of your experience so we try and cover all the bases.:grin:
 
dogman said:
. . . We have a 120/240 open delta serving our mechanics shop. . . It has kicked off before in thunderstorms. Why would it kick off the main breaker?
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Welcome to the Forum, Bob.

From your profile, I infer that you are describing a mechanics shop that is part of the power company. Am I mistaken? Do you believe the mechanics shop was wired under the guidelines of the National Electrical Code as described in 90.2(A)(4), or was it built as a part of the Utility, outside of the Code?

Supply side disturbances shouldn't interfere with the main breaker for the shop.

The symptoms you describe are strange.
 
hurk27 said:
It could if the shop has some three-phase motor loads, and they are experiencing a single phase condition?

Sounds like maybe a bad phase connection between the transformer and service.
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That's certainly plausible.

Bob, what are the three phase loads in that machine shop?
 
If it trips without even getting warm, that would be magnetic trip activating, like as someone said, something causing a phase wire to brush against another or something grounded and forming a dead short, no?
 
Breaker

Breaker

I apologize for being rude, rough day. Let me give you more information on this. I wasn't there, I was working outages when this was happening. This is a 50 foot by 100 foot mechanics shop. 2 main breakers 1 3 phase the other single phase. Single phase breaker was the one that kicked off 6 times. The 3 phase kicked off once. This has happened before during thunderstorms. The air compresser is single phase. 3 phase, we have exhaust fan and heaters. The building was built in 1992. We had a licensed elect. wire it with help from our meter department. Thanks for the help, I have learned alot from thissite. Bob
 
dogman said:
This is a 50 foot by 100 foot mechanics shop. 2 main breakers 1 3 phase the other single phase. Single phase breaker was the one that kicked off 6 times. The 3 phase kicked off once. This has happened before during thunderstorms. The air compresser is single phase. 3 phase, we have exhaust fan and heaters.
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Curiouser and curiouser.

Your description pretty much rules out single phasing of running 3 phase motor load.

Is the building steel, slab on grade?

Is the supply from pole-mounted transformers?

Are there any simultaneous line events (you are aware of) in the vacinity on the primary circuit supplying the open delta transformer bank?

Did the 3 phase breaker open simultaneously to one of the single phase breaker opens?
 
Are there any exterior aerial runs that can be swinging in the wind and shorting out blowing the breaker? If it happens with winds then it would seem that that has something to do with it. I can't imagine it would be on the line side of the breaker.
 
Breaker

Breaker

It feeds off of a 3 phase overhead line to a 3 phase URD junction box. 3 phase urd goes to our office. 2 phase goes to the shop, open wye- open delta. 120/120/208 240/240/240. The office is not having this problem. I know if anyone can figure it out it will be you guys. Thanks again for your help. Bob
 
If there is a momentary power loss, too many loads may be trying to start at the same time when the power comes back on. If that's the case, maybe add some magnetic starters to avoid auto starting.
 
dogman said:
It feeds off of a 3 phase overhead line to a 3 phase URD junction box. 3 phase urd goes to our office. 2 phase goes to the shop, open wye- open delta. 120/120/208 240/240/240. The office is not having this problem.
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Wait, where are the transformers, how many and what configuration? That is, where does the primary (your high voltage distribution circuit) change to the utilization voltage(s)?

One can't get 208 and 240 out of a single bank of transformers.
 
dogman said:
Yes, you can Al. It's the wild leg, not used. I've built hundreds of them. Thank you, Bob
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:confused: Then I'm being thrown by your claiming the single phase panel in the shop is supplied by a 120/208 open Wye (that is two legs of a three phase configuration with 120? between the 120 Volt legs). Do you mean a center tapped 120/240 Volt single phase transformer, instead (here the two 120 Volt legs are 180? apart and the high leg on the third phase is roughly 208 Volts above the grounded center tap.)?

Again, where are your transformers? What is the transformer bank secondary configuration? Is it open Wye or open Delta or both?
 
Breaker

Breaker

Al, you have a good point, let me explain what we have. The shop feeds from a transclosure, 2- 50 KVA transformers. Voltage on the high side is 14.4. The transformers high side is cut over, so a URD elbow will work. Two other bushings are connected to the neutral, (grounded). Open wye, Open delta, 120-120-208 phase to ground. 240-240-240 phase to phase on the secondary. They go to a CT cabinet, they are split in the CT can. 1 run goes to 3 phase breaker, the other to the 1 phase breaker. (the three wires, a,b, and n produce the 120/240 volt single phase, a,b, and c produce the 240 volt 3 phase. The wire c is called the widleg) I hope I cleared some things up. Thank you, Bob
 
dogman said:
I hope I cleared some things up. Thank you, Bob
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Oh, no. Thank You, Bob. "Heh" ;)

So, the open Wye is on the 14.4 kV side. And the utilization voltage side is a classic four wire three phase 240 Volt open delta with a grounded center tap on one transformer secondary.

Got it.

Here's the first thing I get. The fact that three buildings are supplied off this one transclosure rules out anything on the line side of the junction box where the separate building laterals are spliced.

This turns the focus to the machine shop itself. It sounds like something is being disturbed by the storms, for the correlation of the breaker trips with the storms to be something happening in fact.

The fact that the machine shop main breaker on the single phase panel and the other main breaker in the three phase panel have both tripped is still strange.

If I were able to be present, on site, I would be looking for what could be moved or shaken by the energy of the wind and sound in the storms, and I would be asking questions about the loads that commonly run, and were, in fact, running at the times of main breaker tripping.

I would also be asking if any branch circuit breakers operated at any time, in relationship to the main breaker trips.

The fact that both the three phase main and single phase main tripped is a cause for concern, based on what I understand at the moment.
 
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