Information About Magnetic Trip Breakers

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David40

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Don't see them very often but today I came a cross a 600 Amp 3 phase Main Breaker in a church that is one of those magnetic trip type breakers with an adjusting screw on each leg. Where can I get a crash course on the operation of one of these, and learn what the adjusting screws are actually changing. The adjusting screws are labeled with numbers from 2 to 10. What do the numbers represent? Does raising or lowing the adjustment make the breaker easier or harder to trip?
Thanks for any information.
 
don_resqcapt19

don_resqcapt19

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retired electrician
Those settings only change the instantaneous trip setting of the breaker. There should be a label on the breaker that tells you what the settings mean. If not you should be able to find that info on the manufacturer's website.
Note you need to verify that this is not a magnetic only breaker as those are only permitted to be used as part of a listed combination starter. They are never permitted to be used in a panel.
 
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David40

Member
That does not surprise me because it's a real hack job anyway. I was called in because the breaker is tripping when the church is at it's max operation. The breaker is set on "2" so I'm not sure raising the number would prevent this. I had them turn on everything in the place and I got no reading over 100 Amps on each leg.
At some point they added on to the building and put in a separate main disconnect for that area, but took it off the panel bus instead of the entrance conductors. They labeled the new panel as a Main Disconnect but it's feed through the main breaker so it's not a main disconnect. I was going to add a set of lugs to the entrance to pull that extra load off the main breaker and make the second panel Main Disconnect #2 as they originally intended.
But now I'm thinking all it may need is to raise the value on those adjusting screws. Opinions?
 
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nakulak

Senior Member
You should be very careful adjusting the trip settings of the breaker. If the church burns down after you play with them you won't be a happy camper. Just because they can be adjusted does not mean that it is safe to raise the trip setting on the breakers (for any number of reasons, not the least of which is the obvious one - ampacity of the feeders).
 
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jim dungar

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LarryFine said:
If I'm not mistaken, 20% to 100% of the breaker's max rating.

Lower number, "easier" trip.
Click to expand...
No,

They mean 2 to 10 times the breaker handle rating. This is for the Instantaneous (magnetic) pickup point of the breaker.

Just about every breaker above 600A has this type of adjustment.

Many of these breakers go through their life set at the minimum (which is the default for most manufacturers), especially if they are mains and feeders.
 
R

rcwilson

Senior Member
Location
Redmond, WA
The adjusting screws only change the instantaneous trip setting. A breaker should only trip on instantaneous if there is a ground fault or a short circuit. Overloads only trip the thermal trip unit.

Mechanically, a breaker can be reset almost immediately after an instantaneous trip (not that it is a good thing to do.) After an overload (thermal) trip, the breaker needs to cool down before it can be reset.

If the CB is tripping and they are able to reset it, it probably is not a fault, just an overload. It is possible that the trip occurs when some motors or other loads have an inrush current that bumps the load current up to the instantaneous setting for 1/2 second. You would need to connect up a recorder to determine if that is happening.

Moving the loads sounds like the best approach.

On some breakers the 2-10X indicates an instantaneous trip setting of 2-10X the breaker rating, 1200-6,000 Amps in this case. Is there a load that could have a 1000A inrush?

But don't adjust the instantaneous unless you really, really know what you are doing.

The adjusting screw is part of the live parts on older breakers. We investigated a fatality where the insulating cover on the adjusting screw cracked or broke off. The electrician put his screwdriver in the hole and contacted the slotted screw mounted directly on the trip unit. The shaft was also touching the panel cover. The arc killed him and injured his helper. (25 years ago before arc flash awareness.) We found similar panels in other facilities with the same problem.
 
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David40

Member
That second panel feeds 4 large 3 phase A/C units so it's possible it punches up the start amps pretty good if they happen to start at the same time.
I too believe moving the load is the best way to go, it would reduce the inrush current considerably, and if the problem is overload it would take care of that as well. I'll need to monitor the entrance wires to make sure they can handle the total load. If it's high I can always up the wire size as needed.

Thanks to everyone for the advice. :)
 
H

hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
David40 said:
That does not surprise me because it's a real hack job anyway. I was called in because the breaker is tripping when the church is at it's max operation. The breaker is set on "2" so I'm not sure raising the number would prevent this. I had them turn on everything in the place and I got no reading over 100 Amps on each leg.
At some point they added on to the building and put in a separate main disconnect for that area, but took it off the panel bus instead of the entrance conductors. They labeled the new panel as a Main Disconnect but it's feed through the main breaker so it's not a main disconnect. I was going to add a set of lugs to the entrance to pull that extra load off the main breaker and make the second panel Main Disconnect #2 as they originally intended. But now I'm thinking all it may need is to raise the value on those adjusting screws. Opinions?
Click to expand...


Keep in mind 230.72
If this other panel is remote from the first, a disconnect will be needed to be located by the first main.
 
D

David40

Member
No, they are right along side of each other connected with a short nipple. This second panel is just a large fused disconnect that feeds another remote panel where the individual breakers are located for the A/C units.
Someone went to a lot of unnecessary trouble putting that disconnect in because the way it's wired all they really needed to do was add a 3 pole breaker to the existing panel. Of course their mistake now makes it easy for me to fix the problem. Funny how tings work out some times.
 
Pierre C Belarge

Pierre C Belarge

Senior Member
Location
Westchester County, New York
don_resqcapt19 said:
Those settings only change the instantaneous trip setting of the breaker. There should be a label on the breaker that tells you what the settings mean. If not you should be able to find that info on the manufacturer's website.
Note you need to verify that this is not a magnetic only breaker as those are only permitted to be used as part of a listed combination starter. They are never permitted to be used in a panel.
Click to expand...


2 things to remember about this type of circuit breaker.


1. What Don posted above, it is very important.

2. A qualified person should be the only person adjusting the dials!!!!!!!!!!
 
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David40

Member
Not to worry, I'm not going to mess with it. I thought I might be able to give them a quick fix but at this point moving the load is a good compromise. It will be a week and a half before they have a morning available to shut down the entire building, so I have that time to research that breaker. I'll get the numbers off the breaker and check it out. I don't even know if Westinghouse is still in business?
 
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