derating - T310.16

[dana1028]

Got into a discussion with someone -
In T310.16 'Correction Factors' - you would adjust a THHN conductor using a correction factor of 1.04 when you had an ambient temperature of 70F....then apply any other derating factors for conduit fill, etc.

However, it was argued, since there is no correction factor given for temperatures below 70F, then you would not [could not] arbitrarily use a correction factor of 1.04 for an ambient temperature of 68F; thus, you would make no adjustments.

It was argued that if the 1.04 correction factor was valid for temps below 70F then the table would so indicate.

I argued that the correction factor of 1.04 was valid for an ambient temp of 68F. That said, I don't know what you would use for very cold ambients.

Could someone provide some insight? Is there a code section?

 

[Dennis Alwon]

Well I would agree with you but if that were true you would think the table would state 77F and below. It does not but logic would say 1.04 could be used.

I should have been a politician. It makes sense to use 1.04 but what do I know. Let's see what others say.

 

[charlie b]

For less than 70F, I use a correction factor of 1.00. For temperatures between 70F and 77F, I use a correction factor of 1.00. For temperatures between 78F and 86F, I use a correction factor of 1.00.

I just find it easier to decline to take advantage of an increase in ampacity due to lower ambient temperatures. I don't usually need it anyway, and I wouldn't have to prove to anyone that it is acceptable to use it.

Now if someone pushed me into the application of Charlie's Rule here, I would have to say that the code words, as written, do not allow us to use the 1.04 factor for ambient temperatures below 70F.

 

[George Stolz]

Now if someone pushed me into the application of Charlie's Rule here, I would have to say that the code words, as written, do not allow us to use the 1.04 factor for ambient temperatures below 70F.

It's just a fact, Charlie. Since you came up with it, we'll beat you over the head with it every chance we get, akin to a 40,000-strong chorus of nagging wives.