I want to replace a fluorescent ceiling fixture with a line voltage flexible track kit. There is a WARNNG on the box that says.. Risk of Fire, most dwellings built before 1985 have supply wire rated 60 Degrees Centigrade. Consult an electrician before installing. My dwelling was built in the late 40's or early 50's. Is there any dangers here that I should be worried about?

What they are telling you is that there is a risk of fire caused by heat.

There are three temperature grades of wire insulation. 60, 70 and 90 (all Celsius). Residential wire and cables were originally spec-ed out at 60. As the temperature climbs above the rated temp. The insulation can melt or burn. This in turn set up a bare wire arching condition between two conductors and Whoosh, there stands a burnt out shell where a home once was.

Currently, the NM Shielded cable used has wires that are rated at 90 c. (194 F).

It should also be noted that the heat being talked about has a combination of sources, the heat put off by the wire itself as current flows through it and the lighting fixtures being two of them.

My point being, nobody should assume something like this will be OK because "it doesn't get hot in my area". Believe me I've heard it before.

What they are telling you is that there is a risk of fire caused by heat.

There are three temperature grades of wire insulation. 60, 70 and 90 (all Celsius). Residential wire and cables were originally spec-ed out at 60. As the temperature climbs above the rated temp. The insulation can melt or burn. This in turn set up a bare wire arching condition between two conductors and Whoosh, there stands a burnt out shell where a home once was.

Currently, the NM Shielded cable used has wires that are rated at 90 c. (194 F).

Donf, Thought I would let you know, per 334.80 2005 NEC , types NM,NMC, and NMS shall

Use the 60deg. Column for ampacity.

Yes, but the wires are rated at THHN, 90 Celsius.

Currently, the NM Shielded cable used has wires that are rated at 90 c. (194 F). I believe donf was trying to say the conductors inside the Sheathing is rated @ 90 degrees.

Just to add (as mentioned by benaround):The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60°C (140°F) conductor temperature rating. The 90°C (194°F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.