Old Gare occassionally tripping breaker

[davidh4976]

I'm puzzled. One of the kilns in our pottery is tripping the breaker every once in a while part way through it's firing. So, it fires for several (unknown exactly) hours and then the breaker trips. It usually fires for about 8 hours. This kiln has been converted from a kiln sitter to a digital controller so the controller's relays turn all of the heating elements 100% on and off during the firing to gradually increases the kiln's temperature. Most of the time, it fires correctly to completion. This occasional tripping of the breaker started happening after I replaced all of the heating elements. I checked the elements before installing and they were all the correct resistance (29.2-to-30.7 ohms each across six total elements wired in parallel). The resistance of the old elements were 28.5, 29.8, 29.6, 30.1, 30.9, and 31.0 ohms and the breaker never tripped. The run from the circuit breaker panel is about 12 feet. The breaker is a 60amp Type BQ HACR (Label in photo). The kiln is an old Gare 2327, 240 volt, single phase, 45 amp. I've disassembled the kiln to see if I can visually see any place where there might have been arcing or any other possible sign of a problem. The plug was also newly replaced due to corrosion on the old plug, but there is no arcing sign internal to that either. Any ideas of what I should be checking or trying? Is there a Type BQ breaker that may be better suited for the 8 hour firing? Thanks in advance for any suggestions!

[Bill Kielb]

1 hour ago, davidh4976 said:

Any ideas of what I should be checking or trying? I

Since most of your numbers look fine, my most likely guess would be a worn main breaker. For kilns in North America breaker sizing is usually no less than 125% of the connected load to no greater than 150%. This means prox 56 amps to 67 amps so 60 amps is a nice size. Resistance loads tend to heat up breakers so the rule is really to make sure the breaker is protected against overheating by oversizing them appropriately. Often  breakers will wear and overheat more, a simple non contact thermometer is a nice way to check if it’s significantly hotter than similar like loaded breakers in the panel. A final confirmation would be to measure the amperage draw to confirm its in the range of 45 amps and then confirm the connections at the breaker are secure and not overheating the breaker themselves. Once you are confident it is not overloaded and the excess heating is coming from the internal connections within the breaker, time for replacement.

Breakers for normal residential and commercial loads are generally limited by code to operating continuously  at no more than 80% of their rating which is the reciprocal of 1.25. So it all makes sense really and the actual short circuit rating of a breaker is something other than the gross value of the breaker itself. These days you will see machinery with a minimum circuit amps (mca) and a maximum circuit breaker size specified.

Anyway, my guess check the main circuit breaker to see if it is warm or hot after a few hours use. BTW 40c (104f):is the expected max ambient temperature. 104f feels slightly warm to the touch, not much above body temperature.

Edited December 26, 2023 by Bill Kielb

[Dick White]

Agree with @Bill Kielb about the possible worn breaker. Note that element resistance and watts/amps are inversely proportional. Worn elements with higher resistance pull lower amps (and generate less heat, hence the drawn out firing times until it just can't finish), so when you replace them, the amperage pulled suddenly increases again to kiln spec. And just as suddenly, a worn breaker begins causing trouble.

Breakers are specific to the particular brand and type of the panel, usually not interchangeable with any universal substitute, so you will have to look around to find that Siemens brand and type breaker, perhaps even needing to go to an electric supply house instead of the usual orange or blue big boxes.

[neilestrick]

Yep. Whenever I see the correct size breaker tripping after the kiln's been running for a while, it's a worn breaker. It happens.

[davidh4976]

I was working on the kiln this morning and found that the bolts holding the power cable to the controller were a bit loose and the insulation at the end of the cable next to the lugs were a bit charred.  Does not appear to be shorting out to anything. Would that loose connection, at the kiln end of the power cord, cause intermittent tripping of the breaker? 

Edited January 1 by davidh4976

[neilestrick]

26 minutes ago, davidh4976 said:

I was working on the kiln this morning and found that the bolts holding the power cable to the controller were a bit loose and the insulation at the end of the cable next to the lugs were a bit charred.  Does not appear to be shorting out to anything. Would that loose connection, at the kiln end of the power cord, cause intermittent tripping of the breaker? 

Usually when connections overheat like that it reduces the power draw, however if it it arcing then it's possible that it could cause the breaker to blow. I would cut back the power cord to fresh wire and reinstall it and see if that solves the problem. If not then replace the breaker.

[Bill Kielb]

3 hours ago, davidh4976 said:

Does not appear to be shorting out to anything. Would that loose connection, at the kiln end of the power cord, cause intermittent tripping of the breaker? 

Just curious after several hours of operation is the breaker cool, warm or hot to the touch compared to the other breakers in the panel?

[davidh4976]

26 minutes ago, Bill Kielb said:

Just curious after several hours of operation is the breaker cool, warm or hot to the touch compared to the other breakers in the panel?

The breaker seemed slightly warm after running for a while. Not at all hot.  I will measure the breaker temp with a IR temperature gauge later this week.

Also later this week, I will be double checking the torque on the breaker and measuring the current on full load.

[davidh4976]

My thought was also that a loose connection at the kiln would typically not trip a breaker. But, I closely inspected and found no signs of arcing to ground/case or to neutral or to anything else. I did a little internet searching and some sites say that a loose connection at an appliance or outlet can cause the breaker to trip. In any event, I will be replacing the power cord.

[Bill Kielb]

51 minutes ago, davidh4976 said:

warm after running for a while

Check this after several hours or at least four to five hours of operation. Compare with others for perspective

[davidh4976]

5 minutes ago, Bill Kielb said:

Check this after several hours or at least four to five hours of operation. Compare with others for perspective

yep, that's what I did. It just felt slightly warm. I've felt them much, much hotter! But, I will measure the actual temp later this week after 5 hours of firing.

[Bill Kielb]

3 hours ago, davidh4976 said:

yep, that's what I did. It just felt slightly warm. I've felt them much, much hotter! But, I will measure the actual temp later this week after 5 hours of firing.

Hmm, has happened but usually shows a decent amount of heating. If you can measure the amperage and it truly in the 45 amp range, I think it’s realistic to replace that breaker for tripping early. The typical overloaded breaker I see on occasion below, which at prox 130f definitely made it early trip and definitely feels hot to the touch.. That yours is not heating is interesting but I think reasonable to replace if you confirm your kiln is drawing approximate 45 amps when measured. The breaker pictured below was not sized correctly (125% minimum) and is not old but it is loaded near 100% of its rating.

 

Edited January 2 by Bill Kielb