operating temperature tables

[Wire-Smith]

does anyone know of tables that show conductor(copper-thhn, xhhw,..)operating temperatures at specific currents.




*i know ambient temp and thermal transfer plays a role, i'm just looking for tables for a general reference, any tables


thanks

 

[ramsy]

does anyone know of tables that show conductor(copper-thhn, xhhw,..)operating temperatures at specific currents..

Table 310.15(B)(16) (formerly Table 310.16)
2nd Row of table shows operating Temperature at Max Ampacity of each conductor size, without adjustments, nor inductive loads per 220.18(A)

For other than Max Ampacity, a formula is offered in NEC Tbl-8, Note #2

 

[Wire-Smith]

Table 310.15(B)(16) (formerly Table 310.16)
2nd Row of table shows operating Temperature at Max Ampacity of each conductor size, without adjustments, nor inductive loads per 220.18(A)

For other than Max Ampacity, a formula is offered in NEC Tbl-8, Note #2

thanks



by second row are you referring to 75 degree c column?



i think i'm looking for something different, i didn't explain very well in my first post. are you familiar with 310.15(B)(7) allowing residential service conductors to be rated over table 310.15(B)(16). what i'm looking for is to see at what current does say THHN insulation say for 4/0 aluminum hit a temperature where it starts to degrade at rate that would be of concern. (the point where table 310.15(B)(16) dictates for other than residential service conductors)

 

[ramsy]

..at what current does say THHN insulation say for 4/0 aluminum hit a temperature where it starts to degrade..

Anything over 75°C is prohibited due to equipment limits. See NEC 110.14(C)

 

[Wire-Smith]

Anything over 75°C is prohibited due to equipment limits. See NEC 110.14(C)

i agree, unless you have connections rated higher. what is your interpretation of 310.15(B)(7)? does it allow you to rate your conductors higher than table 310.15(B)(16)? say 4/0 al75c with 190amp calculated service load

 

[ramsy]

i agree, unless you have connections rated higher. what is your interpretation of 310.15(B)(7)? does it allow you to rate your conductors higher than table 310.15(B)(16)? say 4/0 al75c with 190amp calculated service load

See Annex D. Example D7 Sizing of Service Conductors for Dwelling(s)

With no other adjustments, loading 4/0 aluminum to 190A appears to burn at 81°C continuously, but 310.15(B)(7) assumes an 83% demand factor for dwellings not expected to run all loads continuously, much less near Service Ratings.

If 83% demand is expected with 190A Breaker, then 158A is 66°C on 4/0 Al. 83% of 200A Breaker = 166A @ 69°C on 4/0 Al.

 

[Wire-Smith]

See Annex D. Example D7 Sizing of Service Conductors for Dwelling(s)

With no other adjustments, loading 4/0 aluminum to 190A appears to burn at 81°C continuously, but 310.15(B)(7) assumes an 83% demand factor for dwellings not expected to run all loads continuously, much less near Service Ratings.

If 83% demand is expected with 190A Breaker, then 158A is 66°C on 4/0 Al. 83% of 200A Breaker = 166A @ 69°C on 4/0 Al.

thanks


my original post in this thread was related to this so since your going there i'll ask you.

so whats your thoughts on allowing that 4/0al on 200amp breaker with a calculated service load of 190 amps


why wouldn't the code read instead, to allow a reduction of the calculated to 83% for dwellings with up to 400amp services?


why not reduce the calculated load to 83% because of diversification and then the calculated load is within 4/0 75c table 310.15(B)(16) ampacity

and 220.4(B) will let you still round up for ocpd. the way it is seems backwards to me

 

[Wire-Smith]

loading 4/0 aluminum to 190A appears to burn at 81°C continuously,

where/how did you get this? thats what my OP is directly about


thanks

 

[ramsy]

so whats your thoughts on allowing that 4/0al on 200amp breaker with a calculated service load of 190 amps..

If you have knowledge that a dwelling service will frequently or continuously demand 190A, exceeding the 75°C temperature rating described in 2017 NEC 310.15(B)(7)(4) bottom paragraph, you should use a larger wire from table 310.15(B)(16), such as 250 Al, or 3/0 cu.

 

[ramsy]

where/how did you get this?

See Post #2

 

[Wire-Smith]

when i bring this 310.15(B)(7) discussion with others they say " it will likely never get up to 190 amps and if it does it will only be a very short duration"


to me this is more reason for the code to read the other way when you take into consideration trip curves

http://download.schneider-electric.c...ame=736-06.pdf
QOM FAMILY MOLDED CASE CIRCUIT BREAKERS CHARACTERISTIC TRIP CURVE NO. 736-6
175A breaker at 180 amps will take 16 minutes to 2.7 hours to trip at 40*c ambient temp cold start

218 amps(175 x 1.25) is 5.8 minutes to 2.7 hours

 

[ramsy]

why wouldn't the code read instead, to allow a reduction of the calculated to 83% for dwellings with up to 400amp services?

why not reduce the calculated load to 83% because of diversification and then the calculated load is within 4/0 75c table 310.15(B)(16) ampacity

and 220.4(B) will let you still round up for ocpd. the way it is seems backwards to me

An idiot proof temperature calculator is described by the formula in NEC Tbl-8, Note #2, using math to avoid language barriers when matching wire with temperatures, per 110.14(C), and 310.15(B)(7)(4) bottom paragraph of 2017 NEC.

However, there is understandable reluctance to making such tools freely available for idiots in the public domain.

 

[ramsy]

when i bring this 310.15(B)(7) discussion with others they say " it will likely never get up to 190 amps and if it does it will only be a very short duration"..

You need to show substantiation why a dwelling is subject to frequent or continuous loads.

Are pumps running continuously?

Would a Utility History, or Clamp meter reading prove your point?

Without substantiation there is no cause to disqualify the dwelling from 310.15(B)(7)

 

[Wire-Smith]

You need to show substantiation why a dwelling is subject to frequent or continuous loads.

Are pumps running continuously?

Would a Utility History, or Clamp meter reading prove your point?

Without substantiation there is no cause to disqualify the dwelling from 310.15(B)(7)

i'm not saying it is going to get that high if that's how your taking what i'm saying.

my point is that the calculation is that high.

 

[Wire-Smith]

if you interpret 310.15(B)(7) to say you can run 4/0al on 200amp ocpd with a service load calc of 190

what substantiation is there that if you actually have 190 amps running often and for any periods of time, that then you are not code compliant?


i think you might say 110.14(C) and table 310.15(16)


but then go back to my first sentence in this post, the service load calc was 190 and you were allowed 4/0 right?



i appreciate your input, thank you
i'm trying to figure out what i'm missing

 

[Wire-Smith]

You need to show substantiation why a dwelling is subject to frequent or continuous loads.

Are pumps running continuously?

Would a Utility History, or Clamp meter reading prove your point?

Without substantiation there is no cause to disqualify the dwelling from 310.15(B)(7)

if i did do those and it showed it ran 190, would it disqualify it from 310.15(B)(7)? i assume you might say yes because of 110.14(C) and table 310.15(B)(16)



what doesn't make since to me is we did a load calc and it's 190 shouldn't that also disqualify it then?

 

[Wire-Smith]

i don't see where it says the service load calc is only for the service rating and not the conductors, i see how you might get to that because of (B)(7) but to me that seems like a stretch

 

[ramsy]

..my point is that the calculation is that high.

NEC 310.15(B)(7) is intended for dwelling service sized per NEC 220 Load calcs.

If you dont like it, look for any required table adjustments, or load calc errors.

Any conduit on roof, >10% of raceway outdoors - subject to ambient > 30c, more than 3 ccc in raceway, or any pump/fan/motor loads they forgot to factor @ 1.25%. Any continuous loads not factored at 1.25% ?

 

[Wire-Smith]

to me the way (B)(7) is interpreted by everyone i talk to it would make more sense that it would instead be somewhere with demand factors in 220

 

[Wire-Smith]

NEC 310.15(B)(7) is intended for dwelling service sized per NEC 220 Load calcs.

If you dont like it, look for any required table adjustments, or load calc errors.

Any conduit on roof, >10% of raceway outdoors - subject to ambient > 30c, more than 3 ccc in raceway, or any pump/fan/motor loads they forgot to factor @ 1.25%. Any continuous loads not factored at 1.25% ?

the only thing i don't like is i cannot find where the NEC says what most people interpret (B)(7) to say.



i do not read it to allow 4/0 al on a calculated service load of 190, i only read it as providing only another minimum standard you must comply with, not as an exception allowing you to run wire over table 310.15(B)(16) when load calc is above the rating

i see it as adding a restriction to the code not an exeption or demand factor


i see it saying if you have a 200 amp service and a 50 amp calculated load you still can't run less than 4/0 al even if you only have a 5 space panel with 10 amp breakers


i'll keep looking in my spare time though, thanks for your time