What gauge wire to use in rewiring antique light fixtures?

Don’t forget that you are limited by the structure of the fixture as to how large a gauge you can use. I would use the absolute largest gauge that will work with any particular fixture to reduce the chances of resistance-built heat.

The standard wiring used in modern light fixtures is 16 gauge stranded copper. If the same in 14 gauge will fit, so much the better. The smaller the gauge number, the larger the wire diameter.

See how snugly the old wire fits in the fixture. Take a piece of that wire to the hardware store. They should be able to measure with a wire gauge what size it is. If the old wire fits loosely, you should be able to get the next larger size.

Some of the very old wires have a cloth insulation that is thicker than the modern rubber/plastic, so use the outside diameter of the insulated wire as your guide. For the same outside diameter of the old cloth-covered wire, you should be able to go one wire size larger with modern insulated wire.

Modern “lamp cord” has both conductors molded together, but you can split them into individual conductors if needed; Just nick between them with a knife at the end and you can pull them apart.

If they will possibly fit, you should use compact fluorescent lamps. They reduce power consumption by at least 75% while giving the same amount of light. A 13W CF gives the same light as a 60W standard bulb. They’re now available in physical sizes to fit almost anywhere a standard bulb will. The CFs cost more, but have an operating life at least 5 times longer than the standard bulbs. They fit the same base sizes as standard bulbs, but you should take an old bulb to the store to make sure they match. With CFs, you’ll only be using 104W instead of 480W in the 8 bulb fixture for the same amount of light. At least 75% of the old style bulbs energy consumption is wasted as heat (they are actually better heaters than light sources).

I know a guy that rewires old fixtures for his business. I’ll call him in the next few days and post what he says.

You will be pulling about .5 amps for each 60 watt bulb on 120 volts. Your 8 light fixtures will be pulling about 4 amps. There may be some slight amperage differences since bulbs aren’t a straight resistant load.

Keeping this simple, the wire inside the lighting fixtures is considered to be for a chasis load, chasis load/amp ratings per wire gauge are much higher than they are for power transmission purposes. 22/2, 20/2, 18/2 will easily get you by even with the 8 lamp fixtures assuming the fixtures will not be continuously exposed to extreme high temperatures above 100 degrees F. Personally I would go with 18/2 cable inside the fixtures because it is small enough to maneuver inside a tight fixture. I’m only talking about the wiring inside the fixtures and not the wire that supplies power to the lights themselves!