90C ampacity usable for grounded conductor?

[wwhitney]

Say you have a feeder between panelboards. Typically at least one end of the ungrounded conductors will landed on a breaker which has max 75C rated terminations. But the grounded conductor may run from one neutral bar to another. Are those neutral bar terminations possibly rated 90C?

If so, you could run, e.g. a 125A feeder with 90C insulated conductors using #1 Cu for the ungrounded and #2 Cu for the neutral, and still have 125A ampacity on the neutral.

Related question: how about the ungrounded conductors on a feeder from feed-through lugs to an MLO panel?

Cheers, Wayne

 

[infinity]

I don't think that the standard neutral bar in a panelboard is rated higher than 75° C. I've never seen one so labeled.

 

[wwhitney]

I don't think that the standard neutral bar in a panelboard is rated higher than 75° C. I've never seen one so labeled.

Ah, 110.14(C)(1) tells you that it would have be to "listed and labeled" for 90C conductors. Is there any technical reason to expect it couldn't be so listed and labeled without any actual modifications? Same question for feed-thru lugs and main lugs.

Cheers, Wayne

 

[tom baker]

I seem to recall a code change for allowing the neutral to be sized at 90 deg c, that Mike Holt submitted.

 

[don_resqcapt19]

I seem to recall a code change for allowing the neutral to be sized at 90 deg c, that Mike Holt submitted.

I think it said that you don't have to size the grounded conductor at 125% and can size it at 100%. See Exception #3 to 215.2(A)(1).

 

[Dennis Alwon]

I believe the terminals are 90C but the entire panel must be rated 90C in order to take advantage of it.

 

[infinity]

I believe the terminals are 90C but the entire panel must be rated 90C in order to take advantage of it.

Yes that's correct. The entire assembly would need a 90° C rating.

 

[wwhitney]

Yes that's correct. The entire assembly would need a 90° C rating.

But does assembly in the above mean "neutral bar," or "panelboard including neutral bar," or "panelboard and enclosure"?

Also, suppose you had a panel where the neutral bar was just going to have a few large connections. Could you substitute a Polaris-style connector rated at 90C? And then if a neutral conductor in a feeder had those at both ends, use that conductor at its 90C rating, despite the panelboard's 75C rating?

Cheers, Wayne

 

[LarryFine]

Since temperature ratings are based on avoiding insulation damage, wouldn't the lower-rated conductor require all conductors in a given raceway to be limited to that lower rating?

 

[Dennis Alwon]

But does assembly in the above mean "neutral bar," or "panelboard including neutral bar," or "panelboard and enclosure"?

Also, suppose you had a panel where the neutral bar was just going to have a few large connections. Could you substitute a Polaris-style connector rated at 90C? And then if a neutral conductor in a feeder had those at both ends, use that conductor at its 90C rating, despite the panelboard's 75C rating?

Cheers, Wayne

My understanding was the entire panel must be rated 90C which IMO, doesn't make sense except that they may be trying to limit the heat that could build up inside the panel.

 

[wwhitney]

Since temperature ratings are based on avoiding insulation damage, wouldn't the lower-rated conductor require all conductors in a given raceway to be limited to that lower rating?

I guess I'm assuming all the conductors would have 90C rated insulation, so it wouldn't matter within the conduit. The 75C vs 90C ampacity is based on the termination limits, and so part of the question is whether the termination limits can be independent, or if somehow the 75C ungrounded termination temperature precludes having a 90C termination for the grounded conductor, physically within the same cabinet.

Cheers, Wayne

 

[electrofelon]

I believe if you look at the manufacturer's destructions for the terminations, you will find that no terminal is rated above 75 c,. Even though often the larger lugs are made by a third party and say 90° c on them. I am not sure why this is. Perhaps there is a general restriction in UL 67 the standard for panel boards?