30 deg or 40 deg ambient

[cvirgil467]

If NEC ampacity tables are based on an ambient temperature of 30 deg C and most manufacturers terminations are rated for 40 deg C, what do you tell the mechanical engineers the max temeptaure they need to keep the room at?

If it's 40 deg c, do you then need to derate the conductor for 40 deg c ambient temp?

Thanks

 

[haskindm]

You are correct. If the ambient temperature is 40 degrees C then the conductors will need to be derated. See the correction factors at the bottom of table 310.16.

 

[cvirgil467]

or tell the mechnical engineers to design for no more than 30 deg c ambient temperature which could increase project cost and increase electrcial load.

 

[weressl]

or tell the mechnical engineers to design for no more than 30 deg c ambient temperature which could increase project cost and increase electrcial load.

If it is a working environment, it is most likely to be driven by people comfort that is probably around 24Centigrade.
If it is only an unoccupied electrical equipment room then the equipment rating will determine the desired temperature.
Don't forget to tell the mechanical engineers about the heat contribution from the electrical equipment itself.
But consider this; if your wiring leaves the room and most if the wiring is in areas where there IS air-conditioning, e.g. a lower temperature, it may be more cost effective to air-condition the room itself so that the wiring does not have to be oversized. Lower temerature, regardless what the electrical equipment is rated for, will prolong the life of the equipment and reduce the potential and frequency of heat related failures.