Feeder cable size

[romex jockey]

500kcmil has been a standard for a 400A service for how long?

~RJ~

 

[don_resqcapt19]

500kcmil has been a standard for a 400A service for how long?

~RJ~

Only where the calculated load is 380 amps or less. It has never been permitted for a load higher than its ampacity of 380 amps.

 

[DrSparks]

Actually it is not about the index, if you look at the pages past the index you will find instructions of how to make a proposal or PI.

Roger

Oh I gotcha.

Sent from my SM-A326U using Tapatalk

 

[DrSparks]

Only where the calculated load is 380 amps or less. It has never been permitted for a load higher than its ampacity of 380 amps.

Well for residential 1 fam, it's 400 MCM.

Sent from my SM-A326U using Tapatalk

 

[augie47]

I have feeder breaker 400A that has feeder cable 500kcmil CU feeding 400A MLO panel A.

Panel A demand load comes out to 390A both continuous and non continuous load.

Would the feeder cable size of 500kcmil ok or does it need to be upsized?

Assume 75C

Somehow, we are making a mountain out of a mole hill. According to your post, you are doing plans review and you show a 390 amp load on a 500 kcmil conductor.
Reject it !!!! Send it back ! You have done your job.

 

[James L]

I wonder, since it's a feeder (probably inside)

What's the ambient temperature?

380 amps is at 86 degrees farenheit.
If your ambient temperature is lower than 86 degrees, your 500 kcmil is good for 410 amps

 

[augie47]

I wonder, since it's a feeder (probably inside)

What's the ambient temperature?

380 amps is at 86 degrees farenheit.
If your ambient temperature is lower than 86 degrees, your 500 kcmil is good for 410 amps

You would still have the 110.14 limitations to the 75deg rating

 

[James L]

You would still have the 110.14 limitations to the 75deg rating

I'm not sure what you think you see there that would affect the ampacity of a conductor relative to ambient temperature

 

[romex jockey]

Only where the calculated load is 380 amps or less. It has never been permitted for a load higher than its ampacity of 380 amps.

so somehow a demand load calc is part of this code loop?

~RJ~

 

[augie47]

I'm not sure what you think you see there that would affect the ampacity of a conductor relative to ambient temperature

Doesn't affect the ampacity of the conductor, but he's still limited to terminate at the 75 deg ampacity due to the 110.14 limits.

 

[James L]

Doesn't affect the ampacity of the conductor, but he's still limited to terminate at the 75 deg ampacity due to the 110.14 limits.

75 degrees is not an ampacity, it's a temperature.

If you look at allowable ampacities for conductors, they're based on a particular ambient temperature - 86 degrees farenheit.

There are allowable adjustments if you have a temperature other than 86 degrees.

I was mistaken about the proposed adjusted ampacity (I added by 8% which is the 60 degree column)

75 degree ambient temperature adjustment is 5%

380 x 1.05 = 399

That is, if his ambient temperature is lower than 78 degrees farenheit or 26 degrees celcius

 

[augie47]

(C) Temperature Limitations. The temperature rating associ ated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for termi nations shall be permitted to be used for ampacity adjustment, correction, or both.

 

[James L]

(C) Temperature Limitations. The temperature rating associ ated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for termi nations shall be permitted to be used for ampacity adjustment, correction, or both.

If the ambient temperature is lower than 78 degrees fahrenheit, then 399 amps would be under 75 degrees Celsius.

Like I said, temperature and amperage aren't the same thing.

If the ambient temperature was 50 degrees Fahrenheit, that 500kcmil conductor and all the terminals would be good for 475 amps, and would not exceed 75 degrees Celsius

 

[infinity]

If the ambient temperature is lower than 78 degrees fahrenheit, then 399 amps would be under 75 degrees Celsius.

Like I said, temperature and amperage aren't the same thing.

If the ambient temperature was 50 degrees Fahrenheit, that 500kcmil conductor and all the terminals would be good for 475 amps, and would not exceed 75 degrees Celsius

In 35 years I have never seen an installation where you could use an ambient temperature below 30° C so for me it's not something that will ever have a real world use. Regarding the OP the same thing is probably true.

 

[hhsting]

So one has to look out for number of current carrying conductors in conduit adjustment, ambient temperatures adjustment too?

well I am confused. Does ambient temperature apply to conductors cables only or to the terminations temperature or both?

 

[James L]

So one has to look out for number of current carrying conductors in conduit adjustment, ambient temperatures adjustment too?

well I am confused. Does ambient temperature apply to conductors cables only or to the terminations temperature or both?

Both, because ambient temperature directly affects the operating temperature of conductors and connections.

 

[James L]

In 35 years I have never seen an installation where you could use an ambient temperature below 30° C so for me it's not something that will ever have a real world use.

Why is that? Are you suggesting you've never installed wiring in an atmosphere where temperature is controlled to always be below 86 degrees farenheit?

I sure have.

That's why I asked if it's indoors.
If it's a feeder, most likely never see temps above 75 degrees - which is low enough to add 5% to the ampacity.

OP problem is fixed

 

[wwhitney]

Both, because ambient temperature directly affects the operating temperature of conductors and connections.

That would seem to make sense from physics.

But 110.14(C) is generally understood not to allow or require temperature correction at terminations. I believe the citation is the (2017) portion of 110.14(C)(1) that says ". . . conductor ampacities used in determining equipment termination provisions shall be based on Table 310.15(B)(16) as appropriately modified by 310.15(B)(7)." Since that section references the tables directly, without referencing ampacity correction or adjustment, those do not apply for equipment terminations.

Cheers, Wayne

 

[James L]

That would seem to make sense from physics.

But 110.14(C) is generally understood not to allow or require temperature correction at terminations. I believe the citation is the (2017) portion of 110.14(C)(1) that says ". . . conductor ampacities used in determining equipment termination provisions shall be based on Table 310.15(B)(16) as appropriately modified by 310.15(B)(7)." Since that section references the tables directly, without referencing ampacity correction or adjustment, those do not apply for equipment terminations.

Cheers, Wayne

Yes, but how many amps is a termination rated for? As far as I know, they aren't. They're rated for temperature. It's possible they are rated for amperage. In that case, a larger lug would suffice.

But the amperage required to reach that "max operating" temperature depends partly on ambient temperature

 

[wwhitney]

Yes, but how many amps is a termination rated for? As far as I know, they aren't.

That is an interesting question. I think it has been suggested that an equipment termination rated at 75C accepting a maximum wire size of, say, #3 Cu must be rated for 100A. Not sure about that.

Regardless, the point of the text in 110.14(C)(1) is that the termination ampacity check is a direct table lookup--you don't apply correction or adjustment factors. So at the termination you can't take credit for a lower than typical ambient temperature.

Cheers, Wayne