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#180713 - 09/07/08 08:38 AM S/O cable in parrallel  
Helectric  Offline
Member
Joined: Jan 2005
Posts: 90
Brandon, SD
I have a large breaker (1,600 amp, 600v) that is tripping intermitantly. This breaker has all of the usual electronic sensing. It's tripping every 18 - 140 hours. Power analyzer isn't picking up anything. Load is a constant 200 amps. I'm not sure if its the breaker or some type of ground fault. A replacement breaker is $10,000.
There is another panel nearby that I can use to temporarily re-feed the load with a smaller, spare, thermal magnetic breaker. The customer has some salvaged 4/4 type s/o cord on hand. To save them some money I'm thinking of using this to jumper over to the other panel approximately 20' away and see what happens. Both panels are in the same locked electrical room with access limited to qualified persons only.
Any thoughts on this? Also I'm thinking of using a separate 4/4 cord to feed each phase leg v.s. splitting them among all three cords i.e., all four wires in each cord will be connected in parallel to the same phase leg. Do you see any problems with doing this>


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#180715 - 09/07/08 08:59 AM Re: S/O cable in parrallel [Re: Helectric]  
renosteinke  Offline
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Posts: 5,316
Blue Collar Country
None at all .... especially with a truly temporary arrangement, to diagnose the problem.

Let's face it ... a $10K breaker is not something to casually replace. Perhaps you can send it to the manufacturer for testing? Dare I suggest .... it might even be possible to repair the thing, should it prove to not meet specs.


#180718 - 09/07/08 10:13 AM Re: S/O cable in parrallel [Re: renosteinke]  
JoeTestingEngr  Offline
Member
Joined: Nov 2005
Posts: 791
Chicago, Il.
I'm sorry but I have to strongly disagree on this one, especially the way "temporary" can get to be a pretty long time. You wouldn't be doing a valid test because the substituted breaker wouldn't have the same sensing as the suspect breaker. I would check to see if they got an Amptector or other test unit when they got their switchgear. Get someone in to do the prescribed maintenance for the breaker. You can verify the long time, short time, instantaneous, and ground fault trip settings. Sometimes the switches on a trip unit getting exercised will end up fixing the problem. We switch between the different sensing circuits (A,B,C) for the different tests so we make sure we use each one at least once. In your case, I would go through each test, 3 times. If nothing else, note all the multiplier and delay settings, exercise the pots & switches, and put them back to where you found them.
Joe


#180721 - 09/07/08 11:25 AM Re: S/O cable in parrallel [Re: JoeTestingEngr]  
LK  Offline
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Joined: Jan 2003
Posts: 1,429
New Jersey
How far is the nearest hospital with a burn unit?

Good your going to save money, you may need it for the long recovery period.

When someone has this type of switchgear, they should also have the ability to do proper maint and repairs, I my opinion proper testing is the only may, there are plenty of qualified testing companies out there.


#180722 - 09/07/08 11:33 AM Re: S/O cable in parrallel [Re: JoeTestingEngr]  
renosteinke  Offline
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Joe, I can't disagree with your approach ... whatever this "amptector" is!

Yes, "temporary" is very often abused. Helectric is describing a tightly controlled use, in a protected location. Using another breaker to verify that the problem is within a breaker, or in the circuit, is a valid procedure.

The problem is, nobody is going to tie up $10K just on a 'maybe.' He stated he has already tried monitoring the circuit, and has not found any transients. Does he continue looking at the circuit - or does he first eliminate the breaker from the list of possibilities.

That brings us to testing the breaker. My tool belt certainly has no means of testing a breaker ... that has been something left to the manufacturer. Even then, many of the tests are performed on a sampling basis, as the test itself destroys the breaker.

If this "amptector" is some sort of way to field test the breaker, and identify any problems with the breaker .... I think it's a great idea.

In the meantime, things need to be kept running. If the reliability of the breaker is itself the question, then I maintain that poses a greater hazard than the risk posed by the temporary bypass for trouble-shooting purposes.

Naturally, the dishonest use of 'temporary' makes this judgment invalid.


#180725 - 09/07/08 01:49 PM Re: S/O cable in parrallel [Re: Helectric]  
Helectric  Offline
Member
Joined: Jan 2005
Posts: 90
Brandon, SD
All of the customers equipment is periodically tested by a testing company. The cost to have someone travel here to test just one breaker would make up a significant portion of the cost to just replace it.
The cable will be protected by a breaker that is properly sized for both the cable and the load served so I don't see any problems with doing this. True, it will be a different style breaker with different sensing/trip characterstics and will not be a true test of the suspect breaker but if it holds then it will allow me to keep the customer's operation going while the original breaker is shipped, tested, and return shipped.


#180726 - 09/07/08 02:01 PM Re: S/O cable in parrallel [Re: renosteinke]  
JoeTestingEngr  Offline
Member
Joined: Nov 2005
Posts: 791
Chicago, Il.
http://www.eaton.com/ecm/idcplg?Idc...on=Primary&&dDocName=TB01900002E

I'm sorry Reno. "Amptector" was just the name of an older trip unit. Page 10 of this pdf shows an example of a breaker tester that I use. You plug it into 120VAC and the front or side of a breaker. It is not destructive at all because you use it to send signals to the trip unit. You can't trust your trip settings unless you verify them with something like this. The procedure is a little confusing at first but with practice, you could probably get through all the tests in under 15 minutes.

He didn't tell us the particulars of the suspect breaker but the one he wanted to use for his test doesn't seem to have any ground fault sensing. My gut is telling me that a 200A constant load on 1600 AT breaker is most likely tripping out on ground fault. That's why a good first step is to log all the settings and exercise them. Then, try easing out on the GF settings if necessary. But still, settings should checked at least every couple of years to avoid nuisance trips or a breaker that won't trip when it should.
Joe


#180727 - 09/07/08 03:07 PM Re: S/O cable in parrallel [Re: JoeTestingEngr]  
Helectric  Offline
Member
Joined: Jan 2005
Posts: 90
Brandon, SD
Joe, although I didn't mention it I have already excersized all of the settings and have been gradually increasing the GF setting. If the breaker is tripping due to ground fault then I would expect the power analyzer to show some increase in current at the time of trip. I'm not seeing this and I am using a very high end analyzer. The current is flat line to trip. This is a Square D breaker and it will likely become the fifth one of this type that I've replaced in the last three years. Two of these were 3,000 amp and cost $27,000 each. All behaved exactly as this one is acting now. All factory post mortems stated failure of the electronic trip portion of the breaker. They were all more cost effective to replace v.s. rebuild. All breakers are 10 years old and are in a clean, temperature comtrolled environment.


#180728 - 09/07/08 03:58 PM Re: S/O cable in parrallel [Re: Helectric]  
renosteinke  Offline
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Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Thanks for the link, Joe. Might be a useful thing to have in a production environment ....

HE ... when you said 'electronic trip' and "Square D" together, I had this 'deja vu' feeling ... but, in my instance, it turned out to be a PoCo issue that was causing problems. Since you've been monitoring things, I'm sure that cause has been ruled out.

Given the history .... well, looks like the Sq D units have a definite lifespan. Again, considering the costs of the equipment ... I might start looking into another make of gear - while, at the same time, expressing your displeasure, with documentation, to Sq D. Amazing things just might happen ....


#180747 - 09/08/08 11:40 AM Re: S/O cable in parrallel [Re: renosteinke]  
mikesh  Offline
Member
Joined: Jun 2006
Posts: 613
Victoria, BC, Canada
I'd wanted to just address the temporary connections. What is the available fault current? If it is high enough then the single cables are potential for broken arms and legs too. A big heavy cable can remove a head if the fault current is high enough the forces to move a big heavy cable can be substantial.
I suspect the problem is in the trip unit and that probably can be changed. Nevermind the potential hazard of open gear and Arc Faults


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