# Adjusting a 600 volt 800 ampere breaker?



## jza (Oct 31, 2009)

I have a client with a Horizon breaker that trips after a power outage. Grid power returns, and the breaker trips. This happens somewhat consistently. I've never dealt with this before and Schneider is asking big bucks to come out and verify the breaker. Can anyone suggest any adjustments that could be made to the set screws?

Images attached.


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## Dennis Alwon (May 9, 2009)

You can turn up the settings but that should only be done by someone who knows what to do. I believe selective coordination needs to be done.


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## jza (Oct 31, 2009)

Dennis Alwon said:


> You can turn up the settings but that should only be done by someone who knows what to do. I believe selective coordination needs to be done.


Please elaborate. I don't mind involving Schneider or a third party, but it needs to be justified.


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## ponyboy (Nov 18, 2012)

It matters what is upstream/downstream of that breaker, that is the essence of coordination; the whole system is taken into consideration. Without a portrait of the whole picture I don't know if it's even possible to guess how to adjust those trims. Zig would know for sure


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## Big John (May 23, 2010)

You run the risk of causing inadequate protection for the circuit and the load.
You run the risk of increasing outages and downtime by messing up circuit coordination.
You run the risk of invalidating any arc-flash study data and exposing workers to increased hazard.
 Simply cranking up trip settings is the rough equivalent of a homeowner putting in a 30A fuse because the 20A keeps blowing. Our policy is to never adjust anyone's protection unless we get engineered settings in writing from the customer. Way, way too much liability there.

What load is downstream from this? Has this always happened or is it new? Have you looked into getting a PQ meter to see if the breaker is responding to real overcurrent?


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## jza (Oct 31, 2009)

Big John said:


> You run the risk of causing inadequate protection for the circuit and the load.
> You run the risk of increasing outages and downtime by messing up circuit coordination.
> You run the risk of invalidating any arc-flash study data and exposing workers to increased hazard.
> Simply cranking up trip settings is the large-scale equivalent of putting in a 30A fuse because the 20A keeps blowing.
> ...


I understand this, which is why I'm not going to go in there and crank up the settings.

I haven't put a PQA on it, because I don't have one and wouldn't know how to interpret the readings. Also, the problem is rather hard to duplicate. It would require involving the utility after hours to simulate an outage. This would be very costly, a cost I'm sure the client isn't willing to incur at this time.

I was just hoping someone could provide a small amount of guidance so I could troubleshoot this on my own, before offering to involve costly sub contractors.

The load downstream isn't anything crazy. Maybe one or two RTU's and other loads you would find in a school. Probably a few ductless A/C's.


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## Big John (May 23, 2010)

Two possible causes, problem with the breaker or legitimate overcurrent. Schneider is gonna do a secondary test on the breaker to eliminate that, there's really nothing you can do there. So that leaves examining the load.

How many breakers are directly downstream of this, is there any way to cycle the majority of the large loads at the same time while a good PQ meter is in place and actually capture the starting current?


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## jza (Oct 31, 2009)

Big John said:


> Two possible causes, problem with the breaker or legitimate overcurrent. Schneider is gonna do a secondary test on the breaker to eliminate that, there's really nothing you can do there. So that leaves examining the load.
> 
> How many breakers are directly downstream of this, is there any way to cycle the majority of the large loads at the same time while a good PQ meter is in place and actually capture the starting current?


I'll look into the downstream loads. There's probably about 8-10 breakers in this switchgear alone. Most of them will directly feed an RTU or HVAC equipment. Maybe 2 or 3 more 600 volt services. 

What I don't understand is, the breaker doesn't instantly trip when it's reset. The maintenance guy is not doing any load shedding, he's simply closing the breaker after it initially trips on return of grid supply.


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## EB Electric (Feb 8, 2013)

The only advice I could give you is find out what it's tripping on: do you know for certain it is actually tripping on over current and not on under/over voltage or single phasing. If it is actually going on over current are you able to determine from the trip unit if it's going on instantaneous, long time, short time, gnd? Also what was the actual load current before this problem started, and what is it now? Regardless, if you find it is going on over current you need to get in another party with a power quality meter for more investigation. If in the end the trip unit settings need to be adjusted you need a co-ordination study from an engineer. There is A LOT of liability changing the co-ordination study settings and even though it only takes 2 seconds to max the dials out, it will be a lifetime of regret if something goes wrong down the road after you adjusted the settings. Don't take this liability on if your company does not do this kind of thing day to day, it's a school full of kids after all, get a company in that is equipped and deals with this sort of thing on a regular basis. There is no real quick answer or getting around having another party that specializes in this work come in.


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## EB Electric (Feb 8, 2013)

jza said:


> I'll look into the downstream loads. There's probably about 8-10 breakers in this switchgear alone. Most of them will directly feed an RTU or HVAC equipment. Maybe 2 or 3 more 600 volt services.
> 
> What I don't understand is, the breaker doesn't instantly trip when it's reset. The maintenance guy is not doing any load shedding, he's simply closing the breaker after it initially trips on return of grid supply.


Keep in mind if the trip unit has thermal memory and is tripping on over current, it is going to trip at a lesser value each time. Have you tried turning off all your loads, closing the main and then powering each load up one at a time. Inrush on all your equipment all starting up at once after loosing utility could very well be tripping the main on overcurrent.


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## Big John (May 23, 2010)

Only thing I can think of off-hand is that there is a utility voltage problem that coincides with the outage and when they get you back online you're getting severe current imbalances. 

When the breaker is reclosed afterwards, the utility voltage has stabilized so there's no trip.


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## Arc'n'Spark (Jul 21, 2011)

Does this happen every time there's an outage or only sometimes? The reason I ask is, if the utility was switching the customer back on at a point where there were only cutouts instead of a gang-operated switch, the breaker could be tripping due to the large three phase motor loads trying to start single phase.

ETA: If the breaker has phase loss protection, it could be tripping due to the same circumstances.


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