Conductor sizing

[smallfish]

To supply a 50 amp load (outdoor spa) a NM cable is run indoors from residential service panel to outdoor disconnect. 2008 NEC 334.80 requires that the NM cable ampacity be in accordance with the 60 degree C conductor temperature rating of 310.15. Therefore a minimum conductor size #6 cu would be required.

However, 2008 NEC 110.14 (C) (1) (a) (3) allows a minimum conductor size #8 cu if the conductor terminations are marked with the maximum temperature rating. All terminations from supply to load in this circuit are marked for 75 degree C wire.

How is the correct size of wire determined if, it is as it appears, either size wire could be used?

Thanks

 

[xformer]

To supply a 50 amp load (outdoor spa) a NM cable is run indoors from residential service panel to outdoor disconnect. 2008 NEC 334.80 requires that the NM cable ampacity be in accordance with the 60 degree C conductor temperature rating of 310.15. Therefore a minimum conductor size #6 cu would be required.

However, 2008 NEC 110.14 (C) (1) (a) (3) allows a minimum conductor size #8 cu if the conductor terminations are marked with the maximum temperature rating. All terminations from supply to load in this circuit are marked for 75 degree C wire.

How is the correct size of wire determined if, it is as it appears, either size wire could be used?

Thanks

Look at 334.80

IMHO, you can only use the 60 degree C rating unless your doing a # of conductors deration. Also, don't forget about ambient temp.

 

[augie47]

THe more stringent rule would apply (60?)
Side note: You might check the spa requirements as far a grounding. Some require a full size equipment ground.