Temperature Rating Needed For Heat Resistant Sleeving

[englandjeff]

I need to acquire some heat resistant sleeving to cover cables in our church's light fittings. We have had some problems with cable sheath becoming brittle and breaking down after about 10 years because of the heat from the bulbs. This has caused the circuit breaker to trip. The cable is being replaced and heat resistant sleeving is being used on the live and neutral wires as an added precaution. The bulbs used are 200 watt. I have seen heat resistant braided (glass fibre and resin) sleeving on sale rated to an operating temperature of +150C. Is this likely to be adequate? I have also seen some with an operating temperature of +500C but it looks as if this is used in extreme environments. I want to buy the most appropriate product and cannot find any advice.

 

[Sidewinder]

Are the "fixed wiring" "supply" cable cores suffering the damage or cores within the fittings themselves?

 

[Marvo]

It might be worth checking that the wiring deterioration isn't due to electrical overloading of the cable causing the conductors to get hot or even poor terminations which can also generate heat. You'll get better advice if you can give an answer to sidewinder's question.

3M do an adhesive fiberglass tape in at least three different temperature ratings, it might make your life easier depending where the wiring is.

 

[Technician]

There is something in the BGB about T2 rating of light fittings.

IIRC this refers to a temperature of 210 deg Cel.

Looking at the above posts and thinking about what type of

lights be fitted, I think you may need to post a bit more information.

You never know IF new fittings were placed onto an older

installation which might be drawing more current.

 

[englandjeff]

Hi All,

Thanks for your attention everybody.

The fittings are old but the wiring was completely renewed by a competent firm 10 years or so ago. After a 5 year health check we discovered that earthing relied on a metal conduit containing the live and neutral wires. So, live neutral and earth were re-done. Just recently the circuit breaker turned off two lights which work from one switch. I have just had an electrician look at the problem and it was the sheathing on the wire just as it joins the lampholder proper that had gone brittle. So it is a relatively short length (1cm to 2cm, max) that is a problem. He assures me that the firm who installed the new wiring had done the correct job and the correct wires. The wires in the old fitting have little room and they can easily touch if they become damaged. He has renewed the wires in the two light fittings and used the last of his Heat Resistant Sleeving close by the lampholder as an added precaution. Nevertheless he says there is a strong possibility that the remaining 12 lights will eventually suffer the same fate. I have undertaken to acquire some heat resistant sleeving so that we have some definitely in stock should other lights need attending to in due course. I just want to get the right stuff for the wattage involved.

GENERAL: The supply wires go to a terminal block adjacent to each light fitting. Then there are live neutral and earth wires from the terminal block which travel down metal tubing (the tubing being part of the light fitting) to the lampholder which is screwed to the end of the tubing. There is a reflective shade which is part of the fitting but there are no wires involved.

 

[Marvo]

Here's a link to the 3M fibreglass tape. This one is rated 600v and 200 Celsius so it will be more than adequate. You could also use heatshrink over the top to identify the live and neutral. The tape isn't cheap but I assume you'll get your electrician back and I'm guessing he'll know a cheaper supplier. He may prefer to use silicone insulated singles as well if they can be pulled through the tube going to the lamp holders, to be honest any experienced electrician would be able to design a solution based on the exact layout of the lights in front of him. 

 

[Sidewinder]

OK so it's the wiring inside the fitting then.

Pics would be helpful also if you have them.

When you say that the earth relied on the metal conduit, was this just within the light fitting or throughout the installation?

Not that this would necessarily make any difference to the overheating, just trying to get a mental picture of what is there.

What lamps are in the fittings, is the wiring directly above the lamp, i.e. vertically above?

The 200W lamps what type are they?

Would it be possible to change the lamp specification?

How often do these lamps get used, and for how long at a time?

You can get wire which will withstand up to 450 Deg C easily.

In small quantities too.

What size are the circuit breakers, you say there are 2 lamps per breaker, is this across the whole 10/12 fittings?

How many fittings are there and how many breakers, and how many fittings on each breaker as it were?

As I said pics of even the exterior of the fittings and the lamp itself would help.

 

[englandjeff]

Hi Everyone,

I have decided to get sleeving that can be used up to 500C. That should be sufficient. I have been trying to upload or attach a picture of the fitting which is some 20 feet from the ground but don't know how to do it. Out of interest I have done a tweet with a picture but this site won't let me include a link until I have had 10 posts. My user name on Twitter is @Jeff1uk but I don't know whether you will be able to see the picture as I don't really know how twitter functions!

My registered electrician is happy that the 200 watt bulbs are, over time, causing the problem and a little extra precaution is needed at the lamp holder terminals which are close to the bulbs.

Thanks to all for helping.