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

Its been awhile but I rarely read directions after all its just a light on a canopy. But yes I believe its says to slide the mesh sleeves over the feeders before connecting. I don't believe it said how long to have the feeders though and generally the sleeves don't cover the whole length of the feeder so what good are they?? In these same lights I've seen many wires with cracked insulation due to heat from fixture(400 watt metal halide). Some installers used them some didn't, some insulation failed(cracked) with them some without hasn't. Not sure why.

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

OK,

In an existing situation with older 60C or 75C wiring, (take your pick) I go out to buy a new builders' grade ceiling fixture that's identical to the one I have (but mine has years of paint splatter on it). I notice the warning label on it says must connect to 90C wiring. It seems I can't legally put this fixture up without doing something to the wiring system (and no one will officially commit to any remedy other than replacement). Does this mean I should be worried about the fixture that is already there? (identical to new one).

If this existing fixture is a hazard, is it because someone may have added insulation over the years or situation involving free air space or dissapation of heat may have somehow changed? Or has it been discovered in recent years that this fixture (and most others) is, or was not suitable for connection to the older wiring types in the first place?

Bill

Very good points, Bill!

Seems to me that the legacy fixtures have the same heat problems as the new ones, just that the new ones have the disclaimer label attached now (probably due to Manufacturers being sued for house fires!).

The potential hazard is, and always has been present, when a fixture incorporates a Medium Based Screw Shell.

150 Watt lamps can be easily installed to them, and even some 250 Watt "sun lamps".

120-130 VAC Medium Based Incandescent Lamps rated 0-150 Watts (some upto 250 Watts) come in commonly used Lamp packages, such as "A", "R", "ER", "PAR" and "T".
Some reflect heat away better than others.

Nevertheless, with so many various power ratings and packages available to the consumer, replacing a failed lamp with "Anything That Fits" becomes normal operating procedure.

There have been disclaimer notes on older fixtures - circa mid 1970's - which state lamp wattage maximum and package type. That may have been their "Transition" period into the 90°C minimum wire rating disclaimers.

Any one else got some input?

Scott35

Scott,

I'm thinking the recent warnings are more than an over-lamping issue, but with the amount of information we are privy to ... who knows?

I haven't noticed in awhile, but I swear that some of these warning labels said something similar to the following : (paraphrasing)

'WARNING: RISK OF FIRE' most wiring installed before 19XX is rated for ..C 'consult a qualified Electrician'.

Now, this doesn't really give much information or any instructions one way or the other, but it does state the possibility of a real danger (without giving any details) and effectively sheds responsibility to the purchaser/installer. It also infers that an installing Electrician should or must have some wealth of information on the subject.

Is there a way to get a report on how fixtures are/were tested and what the results were?

Bill

[This message has been edited by Bill Addiss (edited 08-02-2003).]

What About Heat Shrink Tubinng? Can You Put that over the wires?

Bill:

I would guess that somebody at the UL has the answer.

Relative to heat-shrink tubing, maybe a test would be to slide the tubing onto the conductors, and if it shrinks, that means the lamp is too hot?

A_Sparky,

Some things shouldn't be for us to decide. We don't have the ability and resources to test and evaluate things we think might work. For the benefit of the customer, and our own liability we have to be sure.

I'd like to hear that there is an acceptable fix, or that the problem, in most cases is not severe, but so far I've come up blank.

TG,

Yes, I'd expect that UL does have the answer.
... I wonder if they take requests?

Bill

Short lengths of fiberglass sleeving have been supplied with some light fixtures in England for years.

They don't always allow enough if the cable enters from the far end of the fixture though, and you can bet that on DIY installations nobody will go out and buy a longer length.

I am confused here, (not unusual) no matter how much heat shielding/insulation around the conductor, given enough time the conductor will reach the temperature of the surrounding environment, perhaps short a few degrees from the heat that travels back the conductor towards a cooler environment.

The only thing I would think that would work is the silicone sleeves as they could actually replace the existing insulation.

How would you handle the transition from the old to the silicone?