ECN Forum Forums Code Related Discussion NEC & other Code issues Can you upgrade wire to 90C ?

To me, the 90ºC minimum Conductor rating for supply wires is definitly _cya_ for the Luminare maker and the Luminare installer, along with the local AHJ!
I say this because with a normal Medium Screw-Shell base, one could use a Lamp size of upto 150 Watts. If the Luminare has 4 lampholders, that would allow 600 Watts of lighting power to be used in a relatively small space.
That will raise the ambient temerature at the point of connection to a really high level!
Continuous load time, plus frequent usage (like 4 hours a day, 365 days a year), results in Barbequed Thermoplastic!

Similar may be said for Ballast driven Lamps - especially for surface mounted Luminares.
Heat concentration is greater than the thermal conduction can dissipate, so much heat sinks through the supply Conductors.

To see if this is a valid point, perform a simple experiment.
Take a simple table light fixture (which has an open top shade), and install a 100 Watt A-19 Lamp in it.
Turn on the Lamp, and let it run for a minute or so.
With the Lamp still on, place a Thermometer above the Lamp. Any type of Thermometer will work
(some may prefer to use the ones intended for "back-door" use, but that's another subject and probably another forum! ).
After about 30 seconds, the Thermometer will be upto 80ºC - maybe more!

Advanced Experiment

Cut a 4"Ø hole on a piece of metal, then place it on top of the same table fixture - so all the heat has to flow through the 4" hole.
Now, with the same 100 Watt Lamp running, place the Thermometer across the 4" opening and observe the reaction!

***Be Sure To Shake The Mercury In The Thermometer Back Down Before Beginning Each Experiment!!!***

Simple formulas will describe the resultant heat produced (more like transfered) from an Incandescent Lamp's Filament.

Energy Transmission figure for one Watt would be one Joule per Second. This translates each Watt as heat crossing a surface, divided by time.
Specific heat capacity (heat capacity divided by mass) = Joule per Kelvin Kilogram.
4.184 Joules = 1 Calorie.
1 BTU = 1054 Joules.
105 Watt Lamp running for 10 seconds results in almost 1 BTU.

An example of heat transmitted to an open space:
150fc of light will transmit 8½ Watts per Ft². This would cover transmitted heat into a normal size room, and if the occupants produced 1 Watt per Ft² and the heat losses of the room equal upto 9 Watts per Ft², the room would increase in overall heat concentration by a factor of ½ Watt per Ft² per second.

To answer Thinkgood's question, yes this is referring to the Ambient Temperature of which the Conductors will be operating under. This may result from any source - including the actual Current flowing in the Conductors.
High operating temperatures require proper selection of Conductor Insulation and maximum load Current per instance.

Operating Enviroment constraints must be considered on all installations (which is constantly quoted in NEC Articles - and being the basis of Chapters 1 thru 9!).
The level of heat in which the Conductors will be subjected to in normal operation, is the Ambient Temperature.

Scott35