SCCR Rating - fault current 1p or 3p? 4

[eeprom]

Hello,
Another question on SCCR ratings for devices. I am hopeful that this one gets answered. When a device is rated to withstand 14kA fault current, is that a single line fault or 3 phase fault.

thanks
EE

 

[jraef]

Bingo. Better stated than I had done in the beginning.

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[LionelHutz]

Yes, can't get any clearer than DRWeig's answer.

 

[eeprom]

Okay, phase II. The SB4 states that only power circuit components need to be rated with SCCR. Panels which contain only control components need no rating. So, what is the definition of "power" circuit?

Specifically, if I have a control panel with no external loads (motors and such), but I do have a panel heater and a panel light, how do those devices get rated? Are these power components, control components, or neither?

I'd appreciate a reference to documentation if any of you can find it. Thanks.

 

[LionelHutz]

It should be quite obvious when looking at a panel. Devices hooked to the main power feed are power and devices not hooked to the main power feed (after a control power transformer) are control. I'm pretty sure there are some 1-line pictures in the standard illustrating this.

 

[eeprom]

If it is obvious, I wish you would explain it to me. I take for granted that I'm not smart enough to notice the obvious.

Not all panels have main power feeds, nor do they have control transformers. Consider a panel with one PLC, a light, and a heater. There is no external loads to the panel, however the heater and the light are not control devices. I could easily argue that the panel heater is a load.

Where do these devices fit into the SCCR rating?

 

[djs]

UL has sometimes taken the stance that even 120 VAC PLC control panels must have an SCCR. I say sometimes because it really depends on who you talk to at UL. Mostly because most people don't care about SCCR ratings for single phase 120 VAC equipment.

 

[DRWeig]

Hi again eeprom,

Look at the glossary at the front of UL 508A, plus diagrams 6.1, 6.2, and 6.3.

The diagrams are especially helpful.

The standard is also broken up into chapters, two of which are power circuits and control circuits. Basically, if a device's specs are in the power circuits section, treat them as power circuit devices.

Good on ya,

Goober Dave

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[eeprom]

Thanks. I am familiar with those diagrams. In fact the lack of clarity is what led me to this forum. But I hadn't considered the control versus power segregation of the manual. Good idea. Thanks.

 

[LionelHutz]

The components you're talking about would require a CPT if it is not supplied...

Table SA1.1 spells much of it out too.

A PLC would likely have a CCN of NRAQ from under section 45 - control switching devices.

The Pilot light likely has a CCN of NKCR from section 46 - control circuit loads.

The heater likely has a CCN of NITW2 from section 26 - Enclosure Enviromental Controls. This isn't under the control or power sections so you have to decide.

Have you considered taking a UL course on the subject?

 

[eeprom]

LionelHutz,
Thank you very much. I would love to take a course on this. Maybe then I could write up a proper procedure for following this requirement. It's just disappointing that UL could devise such a requirement that nobody seems to fully understand.

 

[DRWeig]

eeprom,

Coincidently, I got an e-mail from UL Academy just now, regarding 508A (link below and discount code). I've taken this course along with our whole panel shop, it's good. Plus, you get to know the instructors -- they're good folks to ask for opinions when strange applications come up.

UL Academy 508A

Register for any UL Knowledge Services workshop with discount code PC412* before May 15th and receive 10% off!

Good on ya,

Goober Dave

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