Does the incoming power vary wildly on your 3ph service?

[ZooCity]

We have a high leg delta 3ph service here.  Our TexAir dryer is a big 3ph monster that we run with the front IR panel off (was inoperable when we got it and we haven't seen a big need to repair it yet since it's really the forced air that we need, not the IR).  So we did size down on the breaker just a hair when it was installed, knowing the unit won't ever be able to draw it's full amperage.  We were careful with this and my electrician didn't see how it would be an issue.  He was correct for the most part, it hasn't been a problem except after 5pm on weekdays, i.e., quittin' time at many large plants.  At this time the breaker will sporadically overheat and trip.  I need to log this somewhere but I don't recall it happening at other times of day.  We run 10-6pm here and sometimes later.

Is this due to a surge of juice on the grid as plants shut down?  Seems logical but I don't know enough about 3ph to say for sure.

[ScreenFoo]

E=I*R  where E is voltage, I is current, and R is resistance.

If the resistance stays the same, and the voltage increases , the amperage increases as well.  The resistance on the panels and coils should stay so consistent it could be considered a non-variable... assuming there's nothing wrong with them or the circuits leading up to them.

If it is voltage fluctuation, a meter with peak hold could verify that pretty easily.  Trick would be keeping people away from the control/shutoff box while you have a meter hooked up to the mains for part of the afternoon...

[ZooCity]

Voltage jump was my suspicion.  The voltage does vary of course but I think it's varying too far at this time of day.  For the exorbitant rates we pay for "commerical/demand" service I think this ought to be better regulated.

[Binkspot]

Check you connections and make sure they are tight on the breaker and dryer. It could be a loose connection or a weak breaker. It might just be a fluke that it trips around 5, it may just be that's how long it takes the breaker to over heat and trip.

Like Foo said the draw should be a constant. Actually the draw should be less with higher voltage.

[ebscreen]

It would take voltage drop to up the amp draw and trip the breaker.

We've had breakers do funny stuff. 3 phase breakers ain't cheap for what they are (a ganged
single and double pole) but it might be worth swapping out.

Our natural gas feed fluctuates a heck of a lot more than our electric.

[ZooCity]

Yeah those 3ph breakers are stupid expensive.  I'm lucky that a local electrical supply gives us contractor rates on SqD (we have a QO panel) or I would probably vomit every time I had to buy one. 

I'm guessing that breaker is sized right on the very edge of being able to handle the load going through it so it takes almost nothing to push it to trip.  We probably just cut it a little bit too close on the install for this. 

This feels like a trashy move but I've noticed that a box fan aimed at the breaker almost eliminates this issue.  I know that's not good form so I'll look into ponying up for a new breaker and have my electrical guy come and check out the run just in case.  I'll tally this one up on the list of reasons I need a gas dryer in here.  Thanks for the thoughts you all.

[whitewater]

Check what Binkspot said...it just happened to me.. the connections in the box were loose... it tool about 9 mos for them to loosen.

[ZooCity]

Check what Binkspot said...it just happened to me.. the connections in the box were loose... it tool about 9 mos for them to loosen.

I checked recently but not the wires at the breaker...on the to do list now.

[whitewater]

yeah, we turned power off to box.. the wores at breaker were hot. we tightened the screws down...thats what the problem was.. no issue since. Maybe thats why the fan was working to cool it just enough.

[Binkspot]

Not that I'm proud of it but when we would make runs the Islands and Central America on the older boats it wasn't unusual to have fans blowing on the electrical panels to keep breakers from popping.

[ebscreen]

Used to have a main breaker that would pop on hot days. It was facing the hottest
sun of the day. Pretty sure they don't take stuff like that into account when rating breakers.

Thought just popped in my head. Check the connections on your other panels. Those are the weakest
link in any IR system, and if they start degrading, your draw goes up.

[screenprintguy]

Might sound goofy, but our panel is in the same room as our compressor, it's really hot in there and used to trip breakers later in the day. We put an attic exhaust fan in the roof of the room, when the room gets above 95 it kicks on, and then a turbo blower blowing fresh air across the panel and the compressor motor/pump. Since we did that, we no longer have the popping breaker issue, it really helps regulate the temp in there.

[ScreenFoo]

Kind of a weird thing there--electromechanicals are VERY sensitive to ambient temp--in fact, they are using the temp of a conductor to sense the current.  If you're planning on running a breaker outside it's normal op temp, your amperage trip rating will change.

Excellent point on the connections though...  should have emphasized the whole 'assuming there's nothing wrong with them or the circuits leading up to them.' part of it--pretty big assumption most of the time.