Quick Blow Vs Time Delay for Resitive Loads

[fifty60]

Does the NEC specifically say that you cannot use inverse time delay C curve breakers on resistive loads like heaters?

I know it is ideal to use the B curve breakers, but is it permitted to use the time delay C curve breakers if they are sized at 125% of the load?

 

[fifty60]

In a bit of a tight spot with this. I took my NEC code book home to study the Intrinsic Safety chapters and did not bring it to the office with me today. I do not think the NEC dictates a specific type of OCPD. The NEC does not specify whether or not it should be current limiting time delay (like the C curve) or that it has to be the quicker blow but still current limiting B curve.

Heaters tend to have higher inrushes, and the C-curves are classified for "medium inrush". I do believe that it is ok to use either sized at 125%. Does the code say otherwise?

 

[templdl]

Does the NEC specifically say that you cannot use inverse time delay C curve breakers on resistive loads like heaters?

I know it is ideal to use the B curve breakers, but is it permitted to use the time delay C curve breakers if they are sized at 125% of the load?

You could if the circuit is first protected with a UL489 OCPD. Them you can use all of the UL1077 OCPDs that you want. Please remember that UL 1077 devices provide supplementary protection and are not intended to replace UL489 OCPDs as required but the NEC.

 

[fifty60]

The breakers themselves are UL489. Thanks for the warning Sir.

 

[templdl]

The breakers themselves are UL489. Thanks for the warning Sir.

Are you saying that the breakers that you are questioning, the 'B' and 'C' curves, are UL489. You did state that "The breakers themselves are UL489."

 

[GoldDigger]

Heaters tend to have higher inrushes,

??? A resistive heater (not including a fan motor) will not have any significant inrush.
A non-PF-corrected switching power supply without a current limiter, a tungsten filament, or a motor will all have much higher inrush than a resistive heating element.
The resistance wire in a heating element has a low temperature coefficient of resistance, and so there will not be a significantly higher initial current, IMHO. Perhaps 20% at the outer limit. Compare this to the factor of ten or more inrush for the other types of loads I mentioned.

Now if you are talking about a heater that uses quartz tube lights or infrared heat lamps as the heating element, you would be right.

 

[fifty60]

The Breakers are UL489 devices. The heaters are Nichrome wire. I have come to the conclusion that it would be ideal to use the B curve, but using the C curve breaker is not a code violation.

 

[templdl]

The Breakers are UL489 devices. The heaters are Nichrome wire. I have come to the conclusion that it would be ideal to use the B curve, but using the C curve breaker is not a code violation.

UL489 OCPDs that have 'B' curves. Interesting. Do you have a reference? I've worked with UL489 MCCBs since 1982 and there was never a reference to a 'B' curve, only UL1077 sopplimentary protective devices.

 

[fifty60]

Please reference Eaton's FAZ series breakers (formerly Moeller). The UL498 are the FAZ-NA breakers. Up until a few months ago Eaton had the WMZT series and not the FAZ, and they only had C and D curves in the UL498. Now, with the FAZ-NA they have the B curves, though the availability is terrible.

 

[petersonra]

i don't think it matters much.

 

[NetNathan]

Automation direct sells the Eaton UL489 breakers in "C" or "D" curve...
http://www.automationdirect.com/adc...ini_Circuit_Breakers_(0.5A-40A,_WMZT3_Series)

 

[templdl]

Automation direct sells the Eaton UL489 breakers in "C" or "D" curve...
http://www.automationdirect.com/adc...ini_Circuit_Breakers_(0.5A-40A,_WMZT3_Series)

Thanks for the reference. I reviewed the UL489 devices and understand their application. The considering the NEC and art 240 Where do these apply there? Could these be used to comply with the branch circuit protection were required by the NEC?
After a brief look at the TC of the UL1077 device oy appears as though the thermalart of the curve is close to if not the same as the UL489 device and there are 3 magnetic calibration available.
Also the UL1077 lacks the stand alone ratings the the UL489 devices have.

 

[NetNathan]

I know the UL489 cb costs more than UL1077, and that UL1077 is sufficient protection if used below a UL489.
However, to prevent confusion when replacing in a control panel, I just always buy UL489.