How much heat can cloth wires withstand.

I’m replacing the bad socket in a 300 watt halogen torchiere lamp. The wires are some sort of cloth covering rather than plastic, I assume they’re designed for high temperature. Do I have to be careful running the wires (is it OK of they touch the metal reflector or the ceramic socket) or is it OK as long as they’re not actually touching the bulb?

Cloth coverings tend to be good for higher temperatures than plastic, but not necessarily. Cotton cloth insulation can’t get as hot as solid Kapton plastic can, for example.

I would be careful running the wires, and tie them away from parts that you wouldn’t let sit on your clothing, if that’s a useful guide.

Using Teflon shrink wrap tubing on top of the cloth would give extra insulation if you think the cloth can’t take it.

The one or two inches of wire closest to the bulb will get hot. Not because of I[sup]2[/sup]R in the wire, but because the conductor (copper) is a good thermal conductor, and some of the heat generated by the bulb will be conducted directly into the conductor. So just keep that in mind when routing the wires.

Braided insulation is generally intended for higher temps, though the limit depends on the material. Yours is probably fiberglass insulation, which can take temps you’re not likely to see anywhere in your torchiere lamp. I expect your wiring will be fine even if it’s in contact with the reflector or the socket.

my thought is that it is a fiberglass insulation.

Ah no, its not the heat from the bulb that is important here…
In fact, its misleading to mention that heat is also being conducted through the electric conductors…

The fibreglass insulation actually works to keep the plastic inside below melting point, ONLY because the heat that does get through the fibreglass is conducted away by the copper !

The fibreglass is also resistant to degradation due to light - eg UV , and temperature.
SO the fibre glass must remain close to the bulb, where the bulbs light and heat would otherwise hit the plastic insulation.

If he has to redesign the fitting a little, eg to add a different fastener (to attach to wall or ceiling), is there any rule about what to do with the fibreglass sheath and the wire run ?

  1. Do not touch ANYTHING to bulb ! Ensure it does not move to the bulb. Something touching the bulb can melt, or cause the bulb to break

  2. keep the fibreglass close to where it was before, as in, do not move it and expose the plastic insulation to the light and heat from the buble.

  3. You can touch the fibreglass to the ceramic joiner or to the metal, that won’t matter. (and in fact helps, as the fibreglass will conduct heat to the metal,and the metal then conducts heat to the large surface area …which means lower temperatures … )

  4. Further notes… Don’t add plastic joiners, don’t put any force/tension/pressure on the wire , don’t run the plastic insulation near sharp parts (metal body, screws,etc)

Unless it’s a really old fixture, which would have asbestos fiber insulation. (But that would be much older than any halogen fixture.)