2

I have an old stone 18th C. Pennsylvania farm house. In several rooms, wall sconces were installed when the house was first electrified - with knob & tube wiring. The knob and tube wired to old outlets are being rewired with romex to handle modern heavier loads. But for the sconces, I wanted to explore the possibility of connecting the knob & tube wiring from a low voltage 12v source.

Questions:

  1. I imagine 12 volt is safer than 120 volt. I have read here elsewhere that NFPA70 (National Electic Code) does not exclude use of knob & tube, but that some insurance companies will not insure a house with active knob & tube. I wonder how an insurance underwriter would react to the use of old knob & tube for 12v lighting only?
  2. Would a 12v system work with K&T wiring? And old sconces?
  • One insurance company in my area (Oregon, USA) won't insure a home even if it has inactive K&T wiring! – bitsmack Mar 19 at 15:35
  • That old wiring would need to be changed as 12v will need a larger current (ie more heating ) than running at 110V... – Solar Mike Mar 19 at 15:39
1

The NEC, except for a few exceptions, doesn't really concern itself with anything under 50V. There used to be some commercial showroom lighting that actually did what you are talking about back in the 90's, but I never saw any of it applied to residential.

I would make sure of a few things before I did it. 1. Make sure the transition from 120V to 12V was code compliant. 2. Make sure that whatever you are installing is an approved system for your use. 3. I would still talk to your AHJ and get their input before doing anything.

Hope this helps and good luck.

0

I can't answer about wiring code compliance, but using an isolating low-voltage transformer is an established way of making old light fittings safe. You can get transformers intended for display lights suspended on bare wires.

In terms of current, the old wiring probably handled 30 or 40 watt filament bulbs. If you replace them with 3-4 watt LED bulbs you will be using about 1/3 or 1/4 amp at 12 volt. Presumably this is for decorative effect rather than main lighting.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.