80% breaker rating - what is at issue?

[Strathead]

So what about breakers that don't have thermal elements, why are they subject to this 80% limitation? Like hydraulic breakers and breakers with electronic trip units. Or do I misunderstand, and their behavior will still be dependent on the ambient temperature?

Cheers, Wayne

Yes. I have set the trip on hydraulic trip units, pnuematic trip units, geared escapement trip units, electronic either worked or they didn't back in the 80's, so we did no adjusting on them, just tested to the dial setting.

 

[Strathead]

As has been stated above, breakers listed to UL489 must carry 133% of rated current.
The tolerances would be based at this point.

133% for a period of time, then they can trip. so that has nothing to do with their ability to trip period.

 

[electrofelon]

Not true. The standard tolerance of a breaker is 20%, period. 100%-20%=80%

Can you provide a source for this?

 

[don_resqcapt19]

40C isn't really that hot, 104F...how hot can a breaker get at 80% current?

UL 489 permits a 50°C temperature rise at the terminations and permits the operating handle to be at 60°C.

How hot can circuit breakers get? What is the temperature of

How hot can circuit breakers get? What is the temperature of a molded case breaker?

www.clipsal.com

 

[don_resqcapt19]

Not true. The standard tolerance of a breaker is 20%, period. 100%-20%=80%

The testing requirements in UL 489 say that at 40°C, the breaker must carry its rated current forever without tripping. This is in an open enclosure at 40°C. The 80% is simply to allow for the mutual heating from the other breakers.

 

[kwired]

UL 489 permits a 50°C temperature rise at the terminations and permits the operating handle to be at 60°C.

How hot can circuit breakers get? What is the temperature of

How hot can circuit breakers get? What is the temperature of a molded case breaker?

www.clipsal.com

and 60C is 140F. Maybe still not so hot you can't touch it, but for someone that doesn't do much rough work with their hands can be pretty hot instantly. Is hot enough to burn most anyone if subjected to it for long enough.

50C rise at terminations can get you close to 90C at terminations pretty easily in a ~90 F ambient.

 

[don_resqcapt19]

and 60C is 140F. Maybe still not so hot you can't touch it, but for someone that doesn't do much rough work with their hands can be pretty hot instantly. Is hot enough to burn most anyone if subjected to it for long enough.

50C rise at terminations can get you close to 90C at terminations pretty easily in a ~90 F ambient.

Yes, if you have an exposed pipe or other piece of equipment less than 7 feed above the floor that is operating at 140°F or above, OSHA requires protective insulation.

 

[electrofelon]

Yes, if you have an exposed pipe or other piece of equipment less than 7 feed above the floor that is operating at 140°F or above, OSHA requires protective insulation.

I did a job with "plant lighting" and had some EMT runs maxed out with 3 full boats of 16A/#12 actual load lighting. It was a bit alarming how hot that conduit was. I never actually measured the temperature but I'm sure it was way below 194 even though it was too hot to touch.

 

[GeorgeB]

Yes, if you have an exposed pipe or other piece of equipment less than 7 feet above the floor that is operating at 140°F or above, OSHA requires protective insulation.

I believe you mean installation. Many (most) hydraulic solenoids are 100% rated at 100°C and are never (thermally) insulated. Systems are designed that only appropriate persons can access them easily.

They shouldn't be on all the time you might say; loss of power vents accumulators to remove stored energy. The accumulator "vent" valve (which I prefer to term "not vent" valve, may be on for weeks at a time. There are others. I'd wildly guess that I can get to these valves standing on the floor by a machine between at between 0.1 ft and 5 ft in over half of all installations.

 

[don_resqcapt19]

I believe you mean installation. Many (most) hydraulic solenoids are 100% rated at 100°C and are never (thermally) insulated. Systems are designed that only appropriate persons can access them easily.

They shouldn't be on all the time you might say; loss of power vents accumulators to remove stored energy. The accumulator "vent" valve (which I prefer to term "not vent" valve, may be on for weeks at a time. There are others. I'd wildly guess that I can get to these valves standing on the floor by a machine between at between 0.1 ft and 5 ft in over half of all installations.

No the hot pipe or equipment, if within 7' of the walking surface must be protected from contact by the use of thermal insulation. or physical isolation, so that the surface a person may come into contact with is less than 140°F.