Over current device sizing

[vtsoundman]

There is something else going on here...a 20A breaker will often hold 110% (22A) for an hour. I know this from lots of testing of various breakers. Yes, breakers do become weak with multiple trip events - and Res'd breakers don't like being used as swtiches...

The OP needs to put a ammeter on the load that can capture both peak draw and RMS draw....assuming the wire isn't loose, undersized, or the breaker isn't getting hot from some other source, he's got a partial short (few of the heaters coil are done) or the motor is slowing cooking itself.

These things on a GFCI? If so, then you have a leakage issue. Did the blowers always do this? If not, then leakage (GFCI) or high impedance short become lower impedance with heat. Hot air blowers implies water...so to the OP, do screw around - get the repair tech in there and get it fixed right.

The trip curve for a 20A SqD Qo is below... assuming the breaker isn't trashed, @ 3min of running with a trip, my guess is your pulling >30A or more - most likely approaching 40A.

edit: can't post the image...click here instead

 

[JFletcher]

No. Absolutely not. A 20A breaker is not a 16A breaker rounded up.

I think he is treating these as continuous loads thus I took his post to mean that these heaters should only draw a maximum of 16 amps.

I would replace the breakers with new 20 amp ones, and see if they hold. Actually first I would make sure there is nothing else on those circuits... There probably is something, I seriously doubt the two receptacles that these heaters are plugged into are on individual / dedicated Branch circuits.

If replacing the breakers, or removing other loads from those circuits does not do the trick, next cheapest solution is to buy new heaters, it will be the only NEC compliant way to do it without rewiring with #10, which will probably cost more than the heaters.

 

[JFletcher]

A 20 amp breaker should hold less then 20 amp load indefinitely. Should likely hold up to maybe 25 amps for at least your mentioned 3 minutes that it is tripping an 18.7 amp load. You are probably getting extra heat from someplace - maybe poor bus contact?

Check the bus and make sure there isn't bad connection there. Better yet check it before initially replacing the old breaker.

As long as voltage remains the same resistance heat will draw the same current whether the appliance is dirty or not. Only way it draws more is if resistance decreases - which it is more likely to increase then to decrease.

The blower probably isn't much load at all compared to the heat, but if ventilation openings are plugged that fan likely draws less current because it is moving less air. I don't think cleaning the thing is going to change your problem of tripping the breaker, still a good idea to prevent overheating the element though.

If the bearings or bushings on the motors are in the process of seizing up, the motor will turn slower than normal and amps will be higher as it starts to approach locked rotor current, correct?

But yes, great idea to clean them, if they're moving less air, they will have a higher internal temperature and possibly Catch Fire, especially with the likeliness of animal fur getting sucked up here and there and winding up on the elements

 

[kwired]

If the bearings or bushings on the motors are in the process of seizing up, the motor will turn slower than normal and amps will be higher as it starts to approach locked rotor current, correct?

But yes, great idea to clean them, if they're moving less air, they will have a higher internal temperature and possibly Catch Fire, especially with the likeliness of animal fur getting sucked up here and there and winding up on the elements

Yes, but if this is what I think it is, it is basically a hair dryer and the motor isn't much of a load and is likely impedance protected. If it stalls elements get real hot real quick and a high limit thermostat cuts them out.