Electric Unit Heaters - SCCR

[whiggins]

I have a project with multiple electric unit heaters (3, 5, 7.5, 10 KW). Are they required to have an SCCR rating? I've looked at several catalogues and find no references to SCCR. It is not mentioned or shown as an option.

 

[augie47]

Liklely it's not there as it's not required.
The requirement I believe is covered by UL 1995 is required to include an SCCR on the nameplate with the following exceptions as noted in section 37.3 :
“Equipment intended for use in one-and two-family dwellings, cord-and-attachment plug connected equipment,
or equipment supplied from a branch circuit protected at 60 A or less is not required to be marked with a short-
circuit current rating.”

I would imagine that it is based on the fact that with it is not an issue on circuits with the smaller conductor size.
For an example, a circuit using 25 ft. #6 Cu would reduce a 50,000 available fault to less than 10,000

 

[mayanees]

Augie47, I questioned what you wrote so I ran a calc in SKM, as follows:

 

[augie47]

I ran it on Bussmann' FC2 app... may have made a mistake....

In any event the smaller wire sizes most often reduce available current to a level where SCCR iisn't an issue. Agree ?

 

[whiggins]

Thank you for the prompt replies. If I understand correctly, the 60 A or less rules applies to space heating equipment, but does not apply to compressor/refrigeration units? I know the 60 A exception used to be in 440.4 and was removed.

It seems strange that control panels and refrigeration equipment require adherence to SCCR rules, but electric unit heaters do not. They have contactors, fuse holders, etc. just like other devices.

Thanks again.

 

[Jraef]

SCCR applies to devices that switch or control or protect (by switching). It doesn't apply to end USE devices like motors or heaters.

 

[david luchini]

I ran it on Bussmann' FC2 app... may have made a mistake....

Different voltage. You assumed 208V, mayanees assumed 480V.

 

[whiggins]

SCCR applies to devices that switch or control or protect (by switching). It doesn't apply to end USE devices like motors or heaters.

The larger unit heaters have contactors, fuses, etc. to cycle and protect the heating elements. If I built an industrial control panel to cycle heating elements, I believe it would require an SCCR rating. If these devices are inside the heating unit it doesn't seem to apply. That I don't understand.

 

[mayanees]

Different voltage. You assumed 208V, mayanees assumed 480V.

You're right, and Augie's right!

 

[Jraef]

The larger unit heaters have contactors, fuses, etc. to cycle and protect the heating elements. If I built an industrial control panel to cycle heating elements, I believe it would require an SCCR rating. If these devices are inside the heating unit it doesn't seem to apply. That I don't understand.

Yes, that would be true.