Tripping Main

[jerjwillelec]

I have a Square D (LAL26400) 400 amp Main Breaker that has begun inconsistently tripping. It feeds an old Highschool baseball field. With all load on, it shouldn't reach over 350 amps (I say shouldn't because I only tested it with the lights on, which is right around 250 amps...no concessions). One of the days had a heat index of 104? but the other day was considerably cooler. I believe it to be around 10-13 years old.

Anyone had any comparable experiences?

 

[augie47]

Along with checking current I wold suggest an infrared scan.

 

[cadpoint]

IMO, you need to meggar the wires.

Ten years of chemicals on the field, possible watering and possible
water line repairs, who knows where you'll fine the wire faulting.

If you do meggar, meggar the total job.

 

[templdl]

Alomng with checking current I wold suggest an infrared scan.

Ditto.
Also, were you standing there when the breaker tripped? If so you may be able to determine if it tripped because of thermal or instantaneous. If so if the breaker trips thermally the thermal element must be allowed to cool before the breaker will allow you to latch and close it. If it tripped instantaneously you will be able to latch and close the breaker without waiting but reclosing into a short circuit/fault could have catastrophic consequences.
As Augie47 recommended do a thermal scan of the breaker which will detect loose terminations that would cause the breaker to "derate" which results in the breaker to trip prematurely. Load end terminations are much closer the thermal elements than the line end terminals. Also, if you can confirm that it isn't a terminal issue after you have assured that the thermals are secured to the breaker and the wires secured in the terminals don't forget that a 400af breaker does have a separate trip unit comment held in place on its line end with 3 screws which if not torqued properly can also cause heating.

 

[ATSman]

Questions:
Does the main have GF protection?
What time of day is the tripping occurring? During the time of a game with concessions?
Early morning hours? During a heat spell?
When was the last time the breaker was primary or secondary current tested?
Need more information.

 

[cowboyjwc]

Are they using the breaker as a switch? Could be that it's just worn out, but I wouldn't disagree what everyone else has mentioned either. My first thought was a bad wire somewhere too.

When was the last time the lights were changed or upgraded?

 

[templdl]

Are they using the breaker as a switch? Could be that it's just worn out, but I wouldn't disagree what everyone else has mentioned either. My first thought was a bad wire somewhere too.

When was the last time the lights were changed or upgraded?

How many times does it take to turn off and On a breaker to wear it out?
Please note that UL489 requires that a 225-600af breaker must pass an endurance test of 1000 operations at full load and 4000 operations at no load with 4 operations per minute.
Also note that it is good for a breaker to be exercised which helps with distributing the lubrication of the mechanical parts as well as keeping the contacts in good condition. The contacts actually rub together when they are closed which helps to keep and corrosion from degrading the moving and stationary contact connection.

 

[cowboyjwc]

How many times does it take to turn off and On a breaker to wear it out?
Please note that UL489 requires that a 225-600af breaker must pass an endurance test of 1000 operations at full load and 4000 operations at no load with 4 operations per minute.
Also note that it is good for a breaker to be exercised which helps with distributing the lubrication of the mechanical parts as well as keeping the contacts in good condition. The contacts actually rub together when they are closed which helps to keep and corrosion from degrading the moving and stationary contact connection.

Also note that 240.83(D) says.......Circuit breakers used as switches in high-intensity discharge lighting circuits shall be listed and shall be marked as HID.

 

[jim dungar]

Also note that 240.83(D) says.......Circuit breakers used as switches in high-intensity discharge lighting circuits shall be listed and shall be marked as HID.

UL only tests breakers up to 50A for use as a light switch.

?HID? ? A circuit breaker rated 50 A maximum, 480 V or less, and intended to switch high intensity discharge (HID) lighting loads on a regular basis is marked ?HID.?

Note, the time frame for 'regular basis' is not defined.

 

[cowboyjwc]

UL only tests breakers up to 50A for use as a light switch.


Note, the time frame for 'regular basis' is not defined.

That's a good point, but I'll bet the baseball coach doesn't know that. And that's my other point, it's not designed as a light switch, and even at the 1000 operations that it's supposed to be designed for, as noted, we were told that it's a 13+ year old field so if used just half a year that's a thousand operations in 6 years.

BREAKERS WEAR OUT. That being said, it could just be a bad conductor. As I noted earlier.

 

[templdl]

That's a good point, but I'll bet the baseball coach doesn't know that. And that's my other point, it's not designed as a light switch, and even at the 1000 operations that it's supposed to be designed for, as noted, we were told that it's a 13+ year old field so if used just half a year that's a thousand operations in 6 years.

BREAKERS WEAR OUT. That being said, it could just be a bad conductor. As I noted earlier.

1000 at full load, 4000 at no load because it may be between 1000-4000. But that's really irrelevant. Breakers don't have counters built into them. But it is something that can be ruled out. With the breaker energized and under load a simple voltage drop check tasked from the line to load terminals of each phase can indicate if there is any contact resistance. You can compare the readings for each phase and you would anticipate that the would be about the same. One phase being significantly different than the others would cause you to consider a potential issue with that pole. Should you exercise the breaker the readings most likely will change. In any event measuring contact resistance is not a valid way to check contacts.
Sometimes using an infrared temperature probe used to measure the surface temperature just above the toggle and to the right and left may indicate heating that may be taking place from the contacts of a give pole.
I've taken many breakers apart and they are not that mystery black box as some may think they are.

 

[BAHTAH]

Breaker Tripping

Breaker Tripping

I have a Square D (LAL26400) 400 amp Main Breaker that has begun inconsistently tripping. It feeds an old Highschool baseball field. With all load on, it shouldn't reach over 350 amps (I say shouldn't because I only tested it with the lights on, which is right around 250 amps...no concessions). One of the days had a heat index of 104? but the other day was considerably cooler. I believe it to be around 10-13 years old.

Anyone had any comparable experiences?

Since you mentioned concessions I assume the breaker supplies both lighting and concessions and what ever else at the baseball field. If you see no physical evidence at the
panel and terminations I would suggest putting a recorder (high speed) on the breaker to see at what ampacity the breaker trips. If the breaker is being used to control the
ballpark lighting, along with everything else, I would suggest a new breaker (0nce reason for trip is determined) and a lighting contactor control for the lighting.

 

[meternerd]

Tripping and turning off a breaker wear different parts. When tripping, there is a small latch that operates from a trip coil. The latch holds the breaker shut. When the trip coil operates, the latch pulls off of the "holding" part and the spring trips the breaker open. The more times it trips, the more the latch wears and becomes rounded, until if finally won't stay latched at all. Replacing the breaker is the best solution. If you have a recording ammeter, or can borrow one, see what the current is when it trips. I'm betting it's within normal range. At least that's been my experience.

 

[templdl]

Tripping and turning off a breaker wear different parts. When tripping, there is a small latch that operates from a trip coil. The latch holds the breaker shut. When the trip coil operates, the latch pulls off of the "holding" part and the spring trips the breaker open. The more times it trips, the more the latch wears and becomes rounded, until if finally won't stay latched at all. Replacing the breaker is the best solution. If you have a recording ammeter, or can borrow one, see what the current is when it trips. I'm betting it's within normal range. At least that's been my experience.

With a molded case thermal magnetic circuit breaker I have never seen one with a "trip coil" only mag only breakers up to 150a. There is a bimetallic thermal element which bends and a extremely simple clapper type mag element consisting of a flat piece of metal which is pulled against a horse shoe shaped piece of steel..
In my 18 years experience direct with the sales and support of breakers to a major breaker manufacturer I am aware of the latch ware issue but never was made aware of it as being an issue. As I recall there may have been a quality issue when the latch component material was not hardened properly and was prone to premature ware.Should there be a latch issue there may be a problem with getting a breaker to latch but it does not cause nuisance tripping as it appears as the OP is complaint about.
Also, you omitted the number of trips a breaker is tested for per UL489 testing requirements. Do you have that number before a breaker may not be able to be latched and closed?
For a breakers to be worn out because of tripping someone ought to seriously review how the breaker is being applied.

 

[meternerd]

I was referring to a thermal-magnetic MCP breaker with a combination instantaneous and thermal element. Sorry. Used to motor circuits. I agree that breakers properly sized should seldom trip. I've just seen a lot of residential main breakers that will not reset after our meter readers turn 'em off to change a meter. So they call me. When I dissect 'em (just for fun) I find worn and dirty latches and hardened grease are usually the reason.

 

[cowboyjwc]

I guess, part of the problem with my responses is that I try to get you guys to quit being so technical and look at what could be a simple problem.

Trying to show each other how smart we are by explaining how a breaker works, probably really doesn't help the OP with his question.

My best guess would be bad conduit and conductors that are going bad. Breaker probably trips most often after a rain or a heavy watering. Used to have the same problem at a mobile home park that I did service work for. Breaker really didn't have anything to do with it.

 

[templdl]

I guess, part of the problem with my responses is that I try to get you guys to quit being so technical and look at what could be a simple problem.

Trying to show each other how smart we are by explaining how a breaker works, probably really doesn't help the OP with his question.

My best guess would be bad conduit and conductors that are going bad. Breaker probably trips most often after a rain or a heavy watering. Used to have the same problem at a mobile home park that I did service work for. Breaker really didn't have anything to do with it.

I have found more often than no that the OP leaves out too many details in the original post and then the respondents have to "guess" what the actual details are.
Also, I'm very interested in the manufacturer of the thermal magnetic MCP that meternerd is referring to as I was always been of the understanding that MCPs were mag. only devices as I'm not familiar with that design. If there is no such product then it is miss information.
In addition, none of the responses that I have provided should be too "technical" for professionals in the electrical trade. I have could that all too may don't have a clue about the product that they are supposed to be familiar with. Is the statement that meternerd correct in that their are thermal magnetic MCPs?
Yes, the possibility that bad conduit that is going bad by leaking after heavy rain could be a cause but if water got into the conduit I don't think that it would dry out. Your comment regarding heavy watering may also lead to water leaking into failed conduit.
These possible causes should be explored along with the other possible caused that have been discussed.
But it is important to find out how the breaker is tripping the sort out what is causing the breaker to trip.

 

[meternerd]

I have found more often than no that the OP leaves out too many details in the original post and then the respondents have to "guess" what the actual details are.
Also, I'm very interested in the manufacturer of the thermal magnetic MCP that meternerd is referring to as I was always been of the understanding that MCPs were mag. only devices as I'm not familiar with that design. If there is no such product then it is miss information.
In addition, none of the responses that I have provided should be too "technical" for professionals in the electrical trade. I have could that all too may don't have a clue about the product that they are supposed to be familiar with. Is the statement that meternerd correct in that their are thermal magnetic MCPs?
Yes, the possibility that bad conduit that is going bad by leaking after heavy rain could be a cause but if water got into the conduit I don't think that it would dry out. Your comment regarding heavy watering may also lead to water leaking into failed conduit.
These possible causes should be explored along with the other possible caused that have been discussed.
But it is important to find out how the breaker is tripping the sort out what is causing the breaker to trip.

Thanks for helping me with my hurt feelings, but I got over that kind of stuff a long time ago. Work with linemen long enough, and abuse just rolls off. As to MCP's, you can get them magnetic only or combo. In our case, we order combo because we have more than just motors in the circuit (control valve solenoids, heaters, etc.) Bottom line is, whatever the trip type, a latching mechanism trips and pushing the breaker to OFF then ON resets the latch. I'd say 80% of the time, nuisance tripping is due to a defective breaker rather than a circuit overcurrent issue. But that's just my experience. Your's may be different. Without some sort of power logger or peak recording ammeter like we use, it's just a guess.

 

[templdl]

Thanks for helping me with my hurt feelings, but I got over that kind of stuff a long time ago. Work with linemen long enough, and abuse just rolls off. As to MCP's, you can get them magnetic only or combo. In our case, we order combo because we have more than just motors in the circuit (control valve solenoids, heaters, etc.) Bottom line is, whatever the trip type, a latching mechanism trips and pushing the breaker to OFF then ON resets the latch. I'd say 80% of the time, nuisance tripping is due to a defective breaker rather than a circuit overcurrent issue. But that's just my experience. Your's may be different. Without some sort of power logger or peak recording ammeter like we use, it's just a guess.

This has been a great discussion meternerd. I may of missed your reply but please advise the manufacturer of a TM MCP as I am only aware that there a mag only devices. Having worked as a sales and applications engineer for the company who invented the MCP we never had a TM MCP. I have also had the distinct privilege of sitting at a test bench with specialized test equipment that test the calibration of TM breakers as a well as MCPs. It is interest I on to note that of the breakers that had been returned a significant proportion were not defective. It was easier for the sales engineers and distributors to not question the customer but to simply provide a replacement for a perfectly good breaker. I've supported these produces in the past for 18 years and believe me there is no room for a thermal element to be included with a Magnetic element of an MCP up to 150a. Trip units 250a and above have MCPs that are basically identical to a TM trip minus the thermal element as I have taken them apart. I have pictures of both a TM breaker and MCP trip elements of breakers that I have cut away for training purposes. Most don't have a clue as to how a breaker works. I have taken most apart.
But I would still be interesting in knowing who manufactures a TM MCP. I may learn something of it may be just some misinformation.
But this has deviated quite a bit from what the OP was asking about which is often very confusing to the poster because it doesn't address his issue.

 

[meternerd]

Probably my bad! We order our MCC's as an assembly, and the breakers that are installed are combination thermal and adjustable magnetic. I think I just assumed they'd be MCP's. I think you're right. MCP's are magnetic only. You're also right.....this is WAY OFF the subject. I'll shut up!:ashamed1: