200 amp breaker tripping

Status
Not open for further replies.
M

milemaker13

Senior Member
Location
Suburbs of Chicago
200 amp, 480 volt, 3 phase breaker feeding subpanel. The sub panel has two, 100 amp breakers feeding large dust collectors.
Maintenance guys say they can run either machine separately with no problem. But if they run both together, the 200 amp breaker feeding the panel will trip. Some times it takes an hour, sometimes it's after lunch.
Each machine is drawing 40- 50 amps, for a total of about 90. ( the motors on these dust collectors should be drawing about 90 amps each, so i assume they are running basically no- load). These machines have been running for several years now ( not newly installed).
I put 3 meters on the incoming power, and never got anything more than about 90 amps total when it tripped the 200 amp breaker.
I'm going to check connections and such when i can shut them both down but I'm wondering if anyone has any ideas. Thanks.
 
milemaker13 said:
200 amp, 480 volt, 3 phase breaker feeding subpanel. The sub panel has two, 100 amp breakers feeding large dust collectors.
Maintenance guys say they can run either machine separately with no problem. But if they run both together, the 200 amp breaker feeding the panel will trip. Some times it takes an hour, sometimes it's after lunch.
Each machine is drawing 40- 50 amps, for a total of about 90. ( the motors on these dust collectors should be drawing about 90 amps each, so i assume they are running basically no- load). These machines have been running for several years now ( not newly installed).
I put 3 meters on the incoming power, and never got anything more than about 90 amps total when it tripped the 200 amp breaker.
I'm going to check connections and such when i can shut them both down but I'm wondering if anyone has any ideas. Thanks.
Click to expand...

Do you have an IR thermometer? Bet something is heating up from poor connection, either a terminal, bus connection, or an internal component of the breaker in question.
 
After ruling out excessive heat with IR..consider having a third party testing outfit test operation of the breaker.

Alternatively harmonics. Has anything (non-linear) new been installed recently, even if upstream of the 200A breaker?
 
Another possibility I've encountered on dust collection blowers; mechanical and/or operational issues. Sometimes they are tied to a system where they turn on when a machine turns on, such as a saw. Then they are supposed to have a "minimum run timer" on them to prevent them from being short-cycled, meaning run for only a short time where the motor doesn't have time to cool off. If you can't find anything else, watch the operators of the machinery and see if, for example, they turn off during lunch because nobody is using the machine, but the timer kicks it off at almost the exact moment that the operator is returning, so it is in fact short cycling.

Or the blower turns off automatically and someone panics and immediately turns it back on, thinking there is something wrong. Usually there is also a "back spin timer" to prevent that from happening, someone may have not understood its purpose and disabled it (I have seen that a LOT for all kinds of machinery...)

Or it has been OFF all the time during lunch, and another one on the same system is turned on first, but the back-flow damper is not closing properly so the pressure from the other blower spins this one backward and when it is called to run, it has to overcome that backward inertia and it's too much.
 
What type of current metering device did you use, many basic models don't measure rms of harmonies. This current harmonies heat the thermo element of breaker therefore it can trip.

Sent from my Nexus 5X using Tapatalk
 
These dust collectors serve the whole shop so they are never turned off during the day.
I have tried running each unit individually and the breaker does not trip (each has run several days). When i ran both the breaker tripped in about an hour and 15 min. They tell me it can take several hours or 1/2 day sometimes but always trips when running both.
Total draw 90 amps on 200 amp breaker.

I have not had an opportunity to check connections yet. They purchased a new breaker already and want me to change it next. That will be the same opportunity to check connections and such (shop must be closed in order to shut down main panel)
I'm still looking for an IR thermometer.
 
victor.cherkashi said:
What type of current metering device did you use, many basic models don't measure rms of harmonies. This current harmonies heat the thermo element of breaker therefore it can trip.
Click to expand...

Just used 3 regular clamp type meters. I know at least one is labled "true rms" . I think the others are as well, not positive. Two of them have "max" features, and I was watching the other closely... nothing like standing there watching a meter for over an hour:blink:
 
Finally able to open panel for a look. The center phase breaker lug is loose, causing overheating. The place is shut down today so we're gong to pull the breaker, clean and tighten up the lug and see how it goes.

The lug, not the wire, is loose. The "new" breaker these guys purchased is not correct. Way too wide, not able to make it fit. If this doesn't correct the problem, ill probably reroute the line to another, newer panel that i can still get breakers for.
 
milemaker13 said:
Finally able to open panel for a look. The center phase breaker lug is loose, causing overheating. The place is shut down today so we're gong to pull the breaker, clean and tighten up the lug and see how it goes.

The lug, not the wire, is loose. The "new" breaker these guys purchased is not correct. Way too wide, not able to make it fit. If this doesn't correct the problem, ill probably reroute the line to another, newer panel that i can still get breakers for.
Click to expand...

I usually change the breaker to play it safe. My thoughts are that loose connection has transmitted lots of heat down inside the breaker and the only way to know it's 100% again is to replace it. I just had the same problem 2 weeks ago on a critical HVAC system and I didn't want to take any chances that it'd trip again.

On a sidenote, we have a few surplus breaker dealers we go through for older obsolete breakers. You may have someone in your area.
 
Status
Not open for further replies.
Top