zog
Senior Member
- Location
- Charlotte, NC
I had the 1st reply to the OP and said test the breaker, most obvious thing to do and 4 pages later no one has even discussed it. Ho wabout testing the breaker?
Circuit Breaker tripping...not sure why...
- Thread starter emahler
- Start date
- Status
zog
Senior Member
- Location
- Charlotte, NC
Well thats tough, no spares?
zog said:
zog....it's a $700 part...i'm not big into troubleshooting by replacing parts, especially expensive parts...should we be able to determine that it's a bad breaker, it'll get replaced ASAP..
we've done some preliminary field testing, but nothing seems out of whack...the only thing that is off is the imbalance of the phases and the fact that Phase A was over 180A...
Heck, I even felt the wires, and none were abnormally warm...they are 4/0 CU THHN for the record...
LHarrington
Senior Member
- Location
- Saginaw Bay area Michigan
Good morning,
This may be reaching but the large retail store, it wouldn't happen to be a home improvement store would it, and if so do they have electric fork trucks that require the voltage sucking chargers that could come along with it. I had encountered and facility such as this while shopping that the same situation had accord a bank of light had gone out and after several minute of watching store employee's scrambling I had to ask if they had found the problem their response was no it wouldn?t come back on. I had asked if I could help by at the least looking. A long story short someone had installed and large SCR charge for the for truck battery off the same supply as the lights. When the charger kicked on breakers didn't like it.
LHarrington
This may be reaching but the large retail store, it wouldn't happen to be a home improvement store would it, and if so do they have electric fork trucks that require the voltage sucking chargers that could come along with it. I had encountered and facility such as this while shopping that the same situation had accord a bank of light had gone out and after several minute of watching store employee's scrambling I had to ask if they had found the problem their response was no it wouldn?t come back on. I had asked if I could help by at the least looking. A long story short someone had installed and large SCR charge for the for truck battery off the same supply as the lights. When the charger kicked on breakers didn't like it.
LHarrington
quogueelectric
Senior Member
- Location
- new york
I think I get it now
I think I get it now
A 225 mdp feeding a 225 panel with a main breaker all 277/480 3 phase correct? Are there other 225 breakers that you could swap out with less load on it? Are there any spares in the mdp that size??Do you have an infared thermometer to see what the temp of that breaker is under full load as opposed to the surrounding breakers. Can you swap the 225 in the mdp with the 225 at the panel. Lastly have you physically checked the breaker screws for tightness and that they are all screwed in to the same depth and or discoloration, melted insulation on the wire? One more that the screws on the bus detail to the breaker are tight sometimes they are missed at the factory.
I think I get it now
A 225 mdp feeding a 225 panel with a main breaker all 277/480 3 phase correct? Are there other 225 breakers that you could swap out with less load on it? Are there any spares in the mdp that size??Do you have an infared thermometer to see what the temp of that breaker is under full load as opposed to the surrounding breakers. Can you swap the 225 in the mdp with the 225 at the panel. Lastly have you physically checked the breaker screws for tightness and that they are all screwed in to the same depth and or discoloration, melted insulation on the wire? One more that the screws on the bus detail to the breaker are tight sometimes they are missed at the factory.
quogueelectric said:
checked the terminals, nothing was loose...no discoloration...I shut off the one 20A cb that was pulling 21.5A...this brought the load on that phase down to 160ish...so we are now within rating on all 3 phases...
this may be the excuse I need to get a little infrared video thermometer...
quogueelectric
Senior Member
- Location
- new york
Fluke laser thermometer
Fluke laser thermometer
Fluke sells a very reasonable laser thermometer less than 100 bucks I have used it a lot in the last year you just have to read the instructions carefuly to use it correctly It has a 10-1 spread on the cone of ir laser. This means 10 inches away gives a 1 inch circle. 20 inches away covers a 2 inch circle and so on. I picked up mine on ebay new for less than 50 bucks. Whenever you need to check out a failing breaker you can do it quickly and acurately with this and know which one is the problem without even taking the cover off. Real high tech I highly recomend it. I used it a couple of months ago when a huge MCC cabinet had caught fire I located the burning switch in seconds and shut it down before the arc blast that was about to occur actually happened putting me and others at minimal risk.
Fluke laser thermometer
Fluke sells a very reasonable laser thermometer less than 100 bucks I have used it a lot in the last year you just have to read the instructions carefuly to use it correctly It has a 10-1 spread on the cone of ir laser. This means 10 inches away gives a 1 inch circle. 20 inches away covers a 2 inch circle and so on. I picked up mine on ebay new for less than 50 bucks. Whenever you need to check out a failing breaker you can do it quickly and acurately with this and know which one is the problem without even taking the cover off. Real high tech I highly recomend it. I used it a couple of months ago when a huge MCC cabinet had caught fire I located the burning switch in seconds and shut it down before the arc blast that was about to occur actually happened putting me and others at minimal risk.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Tossing another theory or two into the ring...
Just to be clear, all breakers are sized to deliver 100% of rated current only for short periods, defined as under 3 hours and only under ideal conditions (40deg C, free air flow, properly sized conductors etc.). They are also designed to carry 80% continuously under those same conditions (often referred to as the "80% rule"). But those values are not directly related to the trip curves. What happens when you exceed 80% of rated current for more than the 3 hour limit is that you can expect a higher temperature rise than the breaker was designed for. If your ambient is low, that may not be an issue, but if it is in a distribution panel with a bunch of other warm breakers, it can (and usually is). Thermal trip elements are calibrated to have their trip curve pick up at between 105% and 125% of rated current. But since they are calibrated at 40deg C and those other "ideal" operating conditions, the extra heat rise from a >80% load, even if below the maximum rating of the breaker, can be expected to cause it to pick up at a lower current value and therefore trip with less current than you might expect. How much less is unpredictable because you have taken the breaker out of its design limits. Add to that the fact that the ambient in the MDP would likely be higher than in the LDP, along with the probability of harmonics from the ballasts and you can easily have what you experienced.
Then, after a bi-metal thermal element has tripped once it takes incrementally less heating to make it trip again and gets worse and worse with each successive trip. The phenomenon is called "thermal memory". UL testing and calibration specs for a thermal trip element in a breaker only call for it to trip, reset and trip once more. After that, all bets are off. It's not that they will fail to trip, but rather that they tend to start nuisance tripping. Whenever I see a breaker trip more than twice in a couple of hours and I can't find a reasonable cause (or I've found and corrected it already), I replace the breaker. The user may find that a tough pill to swallow, but they are the ones who were overloading their circuits and "them's the breaks".
Just to be clear, all breakers are sized to deliver 100% of rated current only for short periods, defined as under 3 hours and only under ideal conditions (40deg C, free air flow, properly sized conductors etc.). They are also designed to carry 80% continuously under those same conditions (often referred to as the "80% rule"). But those values are not directly related to the trip curves. What happens when you exceed 80% of rated current for more than the 3 hour limit is that you can expect a higher temperature rise than the breaker was designed for. If your ambient is low, that may not be an issue, but if it is in a distribution panel with a bunch of other warm breakers, it can (and usually is). Thermal trip elements are calibrated to have their trip curve pick up at between 105% and 125% of rated current. But since they are calibrated at 40deg C and those other "ideal" operating conditions, the extra heat rise from a >80% load, even if below the maximum rating of the breaker, can be expected to cause it to pick up at a lower current value and therefore trip with less current than you might expect. How much less is unpredictable because you have taken the breaker out of its design limits. Add to that the fact that the ambient in the MDP would likely be higher than in the LDP, along with the probability of harmonics from the ballasts and you can easily have what you experienced.
Then, after a bi-metal thermal element has tripped once it takes incrementally less heating to make it trip again and gets worse and worse with each successive trip. The phenomenon is called "thermal memory". UL testing and calibration specs for a thermal trip element in a breaker only call for it to trip, reset and trip once more. After that, all bets are off. It's not that they will fail to trip, but rather that they tend to start nuisance tripping. Whenever I see a breaker trip more than twice in a couple of hours and I can't find a reasonable cause (or I've found and corrected it already), I replace the breaker. The user may find that a tough pill to swallow, but they are the ones who were overloading their circuits and "them's the breaks".
pbeasley
Senior Member
- Location
- Orange County, CA (for now)
since no one has addressed this....emahler said:unless MH fixtures draw less after they are on for awhile, i'll stick with my original story
Yes, MH fixtures can draw less after they have been on for a while. They can also draw significanlty more on a hot-restrike than on a cold-strike.
On a related note, MH fixtures can draw more after the units have aged. This is especially noticeable on 120v fixtures as PF capacitors get older. I am not sure how relevant that would be in a 277v fixture.
pbeasley
Senior Member
- Location
- Orange County, CA (for now)
sorry.. my bad :grin:emahler said:
- Location
- Massachusetts
You still playing with this thing?
Come on, step up to the plate, buy a new breaker, if it is not the breaker you will have one to gather dust on the shelf. :grin:
Come on, step up to the plate, buy a new breaker, if it is not the breaker you will have one to gather dust on the shelf. :grin:
iwire said:
i already got a 200A sentron gathering dust...
however, since we lowered the load on phase A - it's been holding...i think it's a load issue...i also believe that we will be replacing the breaker...but it's sunday, and i'm just waiting for the superbowl...
so, i'll play with this as much as I want...
edit to add - knowing the record of the companies you ave worked for, you will have to excuse me for not jumping on your business advice
Last edited:
- Location
- Massachusetts
emahler said:
Is that today?
It's barely been in the news in my area. :wink: :roll: :grin:
(I live about 10 miles from the home of the Pat's.)
- Location
- Massachusetts
emahler said:that seriously explains a lot
Yeah, but which part?
The fact I don't follow sports
The fact it has been in the news a lot
Or that I live in Teddy's State.
- Status