Kiln trips breaker after replacing elements and power plug, but...

[davidh4976]

It's an old Gare 1027 that has been converted to a digital controller.  It had been working well except we were starting to get really uneven firings and the element resistances were starting to vary greatly from element to element.  I replaced the elements and ran a quick "paper test" that showed all elements were firing. Then I ran the oxidation firing (cone 04 with 1.5 hour hold) with no problem.  Then I replaced the plug because it was showing some thermal stress.  Started a cone 6 test firing (empty except for shelves, posts, cones). The circuit breaker tripped at some point. I did a brief look at the new plug and the elements and everything looks OK at a quick glance. It turned back on (without firing) without problem. Then, I just sighed and went home!

I'm going to start troubleshooting this morning.  I'll start by opening the  control box and checking for obvious shorts. The circuit breaker was reused from the time the building had been a machine shop, so there is a possibility that the circuit breaker is going bad. Any thoughts are appreciated.

 

UPDATE: no signs of any problem with the kiln, its wiring, or its plug. But, I checked the circuit breaker and found that the electrician we hired to put in a 60 amp circuit for the 45 amp kiln only installed a 50 amp breaker (when we moved the kiln six months ago)!  It looks like he reused an existing but unused 50 amp breaker.   Moral: double check what your electrician installs!  My current theory is that the old elements were drawing a little less power than the new elements, and now the new elements are drawing just enough to cause the breaker to trip.  Generally, breakers don't like more than 80% of their rated amperage for prolonged periods of time.  I checked the circuit wires and fortunately, the wires are correct for 60 amps and it's just the breaker that needs replacement.  I have a call in to the electrician.  In the meantime, I checked everywhere in town and no one carries the breaker type that we need, which is probably why the electrician did not install the 60 amp in the first place.  We went ahead and ordered a replacement breaker.  To be continued...

Edited October 20, 2023 by davidh4976

[Bill Kielb]

Your problems are not unique. Here is a post I placed in a previous thread to show what can happen when folks don’t follow the requirements.  The whole thread is worth the read as we see this time and time again from owners to electricians and even an inspector on occasion. What I have learned: Get the right size breaker, check all connections carefully, not just a once over.

 

[neilestrick]

@davidh4976 Sounds like you got it figured out.

For future reference, and for others that may read this:

1. When the breaker trips immediately when the elements turn on, then there's a short in the system somewhere. Usually it's in the kiln, like a relay has melted out or a wiring connection has fried and there's a bare wire making contact with the kiln body, or it wasn't wired properly when you repaired it. In rare instances the short could be in the outlet or the wires from the outlet to the breaker.

2. When the breaker trips after the kiln has been on for a few minutes (or longer), then  it's a breaker issue. Either the breaker is the wrong size, or it's old and worn out.

[davidh4976]

I figured out what was causing this, but wanted to allow for a lot of firings to make sure. It turns out that inside the digital controller that I added, the 'wire-end' of the compression terminal on one of the internal wires was a bit too close to the controller's metal housing. I disassembled the controller (which was bought in one preassembled piece), and found signs of arcing. I put a good bend into the terminal, put everything back together, and have had no problems now over many, many firings.