Electrical Wiring Phase Problem - Help

[johnc]

For the second time in three years I've burned up one leg of the three phase power from the meter to the main breaker to my shop. The complex management will make the repair on their nickel but I was just told that there might be a phase problem between the secondary panel that supplies power to my TIG welder and the main power feeds into the shop.

 

Being an electrical idiot I've done the Interent search thing (no, I haven't searched Hybridz ) but haven't come up with much to help me figure out the problem. I plan on hiring an electrician to correct the problem but I want to understand how the three legs can be out of phase with the power coming fro SCE? Seems that SCE has some method of grounding or phasing that prevents people from stealing power and it requires some kind of grounding back through the three main power leads?????

 

Here are the basics:

 

• 208v/100 amp service 3 phase.
  
• 100 amp 3 pole breaker from the meter to the shop.
  
• Secondary panel in the shop gets 100amps 3 phase and has a 70 amp single phase breaker to the TIG welder.
  
• Heavy aluminum welding (200amps AC) over an extended period will burn out one leg on the feed from the meter to the 100amp main shop breaker and then trips the 100amp breaker.
  
• The 70amp breaker does not trip - in fact, no breakers in the shop trip. Just the same leg that goes from the meter to the main shop 100amp breaker and its in a central panel on the building, 50 yards from my shop.
  

 

Any ideas or suggestions on how to determine is something is out of phase?

[proxlamus©]

John I'll ask the electrician at work tomorrow and type up an answer for ya tomorrow =)

[woldson]

Same phase?

[Mikelly]

John, I don't have an answer, but do have a recommendation from my brother inlaw who is a licenses electrician in Virginia... Work with a Commercial Power Electrician on this, and not "just" an electrician. Make sure the person you hire is licensed at that level. Apparently here on the right coast, that is a huge distinct issue and grey area when seeking services from the electrical trades.

 

Subscribed, as I'm curious of the answer myself.

Mike

[johnc]

I spent a lot of time talking with an SCE repair tech and a local IBEW trained contractor and both say there isn't such a thing as a phase issue as I've described it. The SCE tech says that his company does nothing special with the power to prevent power theft other then to make the meters harder to remove and impossible to flip.

 

My recurring problem is lugs that loosen over time due to the expansion and contraction of the different metals involved (copper, brass, steel, and aluminum). About every 6 to 9 months (when I remember) I go out to the main panel and tighten the lugs to try and prevent this problem. I may need to do it more often especially when welding a lot of aluminum.

[woldson]

I talked to Mr. Palmer of avista 15-18 yrs experience. He said I could be a load in-balance at the panel. Heat is a by-product of the in-balance.

He him self right now is at a company that has a 600amp service and smoked there box, fraction away for structure fire.

Load in-balaence is attributed to, too much draw on one phase. Even at home you should have a balance on both buses for this reason.

[johnc]

Unfortunately my welders are all single phase so one leg gets hit harder then the others. I've spread out the other electrical loads (compressor, band saw, lathe, charger, etc.) on the other legs.

[fastzcars]

your right John. it's a load imbalance, your pulling more amps through one leg on the 3 phase circuit. The only way to be sure is to put an amp meter on the panel and reading through all 3 legs and see what your pulling through each and try to shift the load evenly across all 3 legs. Has edison replace the meter? maybe the meter panel has too much carbon buildup from the previous burn outs that it's causing resistance? Just a thought?

[26ounce]

Hi John,

from what you have described you have;

 

a 3 phase 100amp rated submain from meter room to a subboard in your unit (protected by a 100a circuit breaker)

 

On your subboard, you have a 100amp main switch, which isolates the circuit breakers to your subcircuits, (light, power, etc) including a 70amp 3 phase subcircuit for your welder.

 

One phase from the meter room to your unit keeps burning out.

 

Two things spring to mind

 

1/ High resistive joint (loose connection) in submains

 

2/ Submain circuit breaker needs to be upgraded to a higher kVA rating

(Industrial is normally 6kVA with the inductive load from your welders,

you may need a 9kVA rated breaker)

 

+ you really shouldnt need to keep tightening the terminals on your circuit breakers, have your sparky check them for you.

 

Let me know how you go

 

cheers

[garvice]

2/ Submain circuit breaker needs to be upgraded to a higher kVA rating

(Industrial is normally 6kVA with the inductive load from your welders,

you may need a 9kVA rated breaker)

 

26ounce

First off, you mean, 6kA not 6kVA (Breakers are rated by load rating I.E 100A part and breaking capacity, how much current it can break in a short circuit condition, this is the 6kA or 10, 16 25 etc, etc.) If it was 6kVA then in a 208V case you would only be able to break 28A under a short circuit condition.

 

John,

It sounds to me like you have either a loading issue or a short in the phase that keeps frying (could be some equipment that you are connecting to it).

But before I jump to any conclusions, just a few questions.

1/ You mention that you have a 3Phase 70A feed to your welder, then in the second post you mention that all your welders are single phase. Which one is it?

2/ When welding heavy aluminium (you stated 200A) is this on a single phase? You mention that your 100A CB does not trip. If this is the case, then as your breaker is not seeing the current through all three phases then it may not be enough to trip a thermal CB element, however it may be enough to kill the cable.

 

One suggestion, always have single phase loads protected by single phase breakers. Also, you will need to upgrade your 3Phase supply (100A) to be larger than your largest single phase load (it appears - 200A welder) or by a 3 phase welder (sorry not trying to be your pusher, my wife does say i'm a bad influence on people thinking about upgrading their gear)

 

Brad

[26ounce]

Quite true Brad, kA not kVA, my bad.

[woldson]

Also, you will need to upgrade your 3Phase supply (100A) to be larger than your largest single phase load

 

 

I believe the wire needs to be 80% of total load capable. Basically your max load can not exceed 80% of all things running at one time. This will help heat at bay and you will not get so much expansion and contraction.

 

You will save a bit on power consumption due to less resistive wire. Also you electrical gear will last much, much longer.

I personally under size my breakers in my house, 15amp on 20amp capable circuits, 12awg wire, six or so outlets.

 

Personally I would be butt puckering if I was burning a phase. Having to tighten those lugs is a waring sign, not routine maintenance. This truly is a safety concern.

[johnc]

1/ You mention that you have a 3Phase 70A feed to your welder, then in the second post you mention that all your welders are single phase. Which one is it?

 

I goofed the original post (I'll edit it). The welder requires single phase so its got a sub panel with a 70amp single phase breaker.

 

Also, you will need to upgrade your 3Phase supply (100A) to be larger than your largest single phase load

 

Can't. I rent a shop in a light duty industrial complex. What's worse is that the place is wired with Aluminum. I have replaced all the wiring I can (and some I'm not supposed to) with copper.

 

1/ High resistive joint (loose connection) in submains

 

This is ultimately the problem and tends to recur. The last time it did it the 100amp 3 phase breaker got taken out (it was about 30+ years old) along with the wire. This time the aluminum lug bracket got smoked along with the wire. After fixing yesterday the electrician measured the amps through each leg while I was welding and the one that fails was seeing 66 amps, which he said was below the 100amp rating for the wire.

 

The power for this complex sucks. The best I can get is 208 and it sometimes sags below 200. I know of a HAAS three axis mill in this complex that loses its power supply every couple years. Landlord says, "SCE is the problem." SCE says "Not our problem."

[woldson]

Bummer.

[garvice]

I believe the wire needs to be 80% of total load capable. Basically your max load can not exceed 80% of all things running at one time. This will help heat at bay and you will not get so much expansion and contraction.

Not quite sure what your getting at there mate? Your max load is all things running at once. Or are you saying your largest load (I.E. the largest single piece of equipment)? If so, it can be as large as it wants, as long as its not larger than the breaker (because then it will trip out on overload all the time).

 

WOLDSON

You will save a bit on power consumption due to less resistive wire. Also you electrical gear will last much, much longer.

JOHNC

What's worse is that the place is wired with Aluminum. I have replaced all the wiring I can (and some I'm not supposed to) with copper.

Nothing wrong with aluminium cable guys. It just requires larger cable for the same amperage/volt drop. Copper is better for the same size wire though.

 

WOLDSON

I personally under size my breakers in my house, 15amp on 20amp capable circuits, 12awg wire, six or so outlets.

Good practice. When sizing cable, your CB min pickup setting (1.05xCB rating) must be larger than your Load demand, your Cables derated capacity needs to be more than the CB max pickup setting (worst case 1.3xCB rating). We have a really good and easy to understand standard in Australia. If anyone is interested P.M me.

 

Can't. I rent a shop in a light duty industrial complex.

Sounds like it is time to build that ultimate garage we all dream about.

 

Just one final thing, the problem does sound like it isn't on your side of things. However when you do tighten that aluminium lug, make sure you don't over torque it. I have seen this reduce the contact area that the lug has with the CB tab (doesn't sound logical I know) and actually create more resistance in the join, which then ultimately fails.

[woldson]

Not quite sure what your getting at there mate? Your max load is all things running at once. Or are you saying your largest load (I.E. the largest single piece of equipment)? If so, it can be as large as it wants, as long as its not larger than the breaker (because then it will trip out on overload all the time).

 

 

I'll reconfirm or correct after making inquires, thanks.