Light fixture said use only 90 degree supply conductors

[jaylectricity]

Can't dispute that, but I have seen many fixtures with thermal sleeves on the wires.

The thermal sleeve is to protect the insulation, not the copper.

 

[mivey]

The thermal sleeve is to protect the insulation, not the copper.

Protect it from what? External or internal heat?

 

[jaylectricity]

Protect it from what? External or internal heat?

External heat, there should be minimal internal heat if the overcurrent protection is working properly.

 

[iwire]

External heat, there should be minimal internal heat if the overcurrent protection is working properly.

You are mistaken there.

The filament in an incandescent lamp is typically between 2000 K to 3300 K (about 3100?5400?F) that heat 'conducts' down through the lamp socket and down the socket leads back to the supply conductors.

 

[iwire]

Think about this. if you had a wire one foot long and you held it at one end between your fingers then I heated the other end to 5000F how hot do you think your end would be?

 

[peter d]

I don't like incandescent fixtures that totally enclose the lamp, even with 90C conductors supplying them. I much prefer pendants, chandelier style, or or other types with lamps away from the ceiling and premises wiring.

But that's just me.

 

[jaylectricity]

You are mistaken there.

The filament in an incandescent lamp is typically between 2000 K to 3300 K (about 3100?5400?F) that heat 'conducts' down through the lamp socket and down the socket leads back to the supply conductors.

Hmm...OK, I'll conced that, but that proves my first point. The rating on the insulation isn't going to protect the copper. The rating is there to protect the insulation so that it doesn't break down when normal heat is applied to it.

 

[peter d]

Think about this. if you had a wire one foot long and you held it at one end between your fingers then I heated the other end to 5000F how hot do you think your end would be?

I don't know. I could get shocked holding onto it.

 

[iwire]

The rating on the insulation isn't going to protect the copper. The rating is there to protect the insulation so that it doesn't break down when normal heat is applied to it.

I do not think anyone has disagreed with that, copper can carry much higher currents then the NEC allows because of that pesky insulation.

Going back to my question about holding the one foot of wire while I heat one end. Would wrapping the conductor with a heat shield make your end colder, the same or hotter?

 

[LarryFine]

Think about this. if you had a wire one foot long and you held it at one end between your fingers then I heated the other end to 5000F how hot do you think your end would be?

Depends on the time and wire area.

Eventually, heat will get through anything. R-value is a time rating.

 

[iwire]

Depends on the time and wire area.

All I can say is thank you captain obvious. :grin:

 

[jaylectricity]

I do not think anyone has disagreed with that, copper can carry much higher currents then the NEC allows because of that pesky insulation.

Going back to my question about holding the one foot of wire while I heat one end. Would wrapping the conductor with a heat shield make your end colder, the same or hotter?

If your heat source is continuous I would say that eventually it would be the same. Provided the insulation could take more heat than you were applying, it would happen faster than if the heat could radiate off the surface of a bare wire.

/educated guess

 

[LarryFine]

All I can say is thank you captain obvious. :grin:

 

[zappy]

So would installing CFL's or LED's lights lessen the heat? How about j-box the old wire in the attic, and run new wire to the fixture. That wouldn't cost the customer that much more. But then again I can hear it now. " It cost me more money to install it then the fixture costs!":roll:

 

[sameguy]

Yes, CFL and LED lamps will make a vast difference. A watt is a watt. The 90c is due to people over watting a fixture.
What changed at U.L. over 60yrs. ? The manuf. have made the same fixture that pasted with K&T, now due to law suites they put a sticker on to cta..

 

[fishin' electrician]

3100-5400?F at the filament and I'm supposed to believe that enough heat conducts through the conductors that a difference in 54?F in the insulation is going to make it OK?

Until someone can show me 75+ years of millions(billions?) of lighting fixtures where the problems of overheating from a properly lamped fixture are serious enough to cause substantial damage to the supply conductors, I will continue to install the new CYA fixtures on existing wiring.

This is merely the fixture manufacturers passing the 'potential for a problem' off to the installing electrician.

And where exactly do these "supply conductors" begin? 1ft away from the fixture? 3ft? 10ft? 100ft? The entire branch circuit? The service conductors?

 

[iwire]

3100-5400?F at the filament and I'm supposed to believe that enough heat conducts through the conductors that a difference in 54?F in the insulation is going to make it OK?

Did anyone say that?

And where exactly do these "supply conductors" begin? 1ft away from the fixture? 3ft? 10ft? 100ft? The entire branch circuit? The service conductors?

If you cannot figure that part out maybe you should stop wiring fixtures.

 

[fishin' electrician]

Did anyone say that?

No, that's why I asked.

If you cannot figure that part out maybe you should stop wiring fixtures.

Where is it defined? I must be stoopid.

 

[peter d]

Ignoring it.

Yep. ..........

 

[mivey]

Think about this. if you had a wire one foot long and you held it at one end between your fingers then I heated the other end to 5000F how hot do you think your end would be?

Less than 5000F. I would be willing to bet the lamp socket never gets much over a couple hundred degrees at the worst.