10kw heater wire gauge?

[kwired]

The conductors are sized for the MCA (top line) - that does not include the 2.25 multiplier for the motor.

The data are hard to interpret without the column headings.

My guess is first column is heater amps second column is MCA third column is MOCP. Each with a value for 208/240 volts.

I was right, he posted full view about right when I posted

 

[wwhitney]

Well, the 310.15(B)(2)(a) temperature correction for 60C conductors at 21C - 25C is 1.08. So if you can argue that the heater will never run when the ambient temperature is above 77F (and that the NM cable will be at that ambient or lower), then you could argue for an 8% ampacity increase.

It occurs to me that because of the way 210.19(A) is written, the above never works. Namely 210.19(A)(1) requires a minimum current rating before the application of correction and adjustment factors (and includes a 125% factor for continuous loads), while 210.19(A)(2) requires a minimum ampacity (after application of correction and adjustment factors, no 125% factor for continuous loads).

So you don't get to take advantage of the 1.08 factor when trying to satisfy 210.19(A)(1), and in the scenario above, 210.19(A)(1) would still be violated. Basically the ampacity increase from temperatures below 30C can only be used to counteract ampacity adjustment from more than 3 CCCs.

Cheers, Wayne

 

[kwired]

It occurs to me that because of the way 210.19(A) is written, the above never works. Namely 210.19(A)(1) requires a minimum current rating before the application of correction and adjustment factors (and includes a 125% factor for continuous loads), while 210.19(A)(2) requires a minimum ampacity (after application of correction and adjustment factors, no 125% factor for continuous loads).

So you don't get to take advantage of the 1.08 factor when trying to satisfy 210.19(A)(1), and in the scenario above, 210.19(A)(1) would still be violated. Basically the ampacity increase from temperatures below 30C can only be used to counteract ampacity adjustment from more than 3 CCCs.

Cheers, Wayne

One should still be able to splice a lesser conductor at a point near where the lower ambient begins and likely would need to increase that conductor again if leaving the lower ambient. Probably not worth the effort on a short run, but at same time one needs to consider voltage drop if a long run and still may not want to reduce the conductor.

 

[drcampbell]

The problem is you must use the nameplate even if it is calculated incorrectly.

Is the objective strict compliance with code, or a safe installation that will receive the blessing of the AHJ, possibly with a one-time field variance?

 

[Dennis Alwon]

Is the objective strict compliance with code, or a safe installation that will receive the blessing of the AHJ, possibly with a one-time field variance?

IDK, but if the inspector sees the nameplate how could you argue that it is incorrect. Probably the best option is to contact the manufacturer and see how they got their results.

 

[MackDaddy]

^{The objective is to have a safe installation that the plan reviewer will accept using the existing 6ga. wire.
I contacted the heater manufacturer [Warren] and they were of no help. I did not contact the equipment manufacturer.}

 

[wwhitney]

One should still be able to splice a lesser conductor at a point near where the lower ambient begins

Nope, generally not for ambients under 30C. 210.19(A)(1) is still going to require a minimum wire size based on Table 310.16 without any ampacity increase due to temperature correction.

Cheers, Wayne

 

[kwired]

Nope, generally not for ambients under 30C. 210.19(A)(1) is still going to require a minimum wire size based on Table 310.16 without any ampacity increase due to temperature correction.

Cheers, Wayne

And that base ampacity will depend on temperature rating of splicing devices, which can potentially be 75 or even 90C. A circuit breaker with less than 1000V rating will never be 90 C that I am aware of though.