How many outlets and lights should go on a 15 amp circuit with knob and tube wiring?
I was replacing a light fixture and dimmer switch on one circuit yesterday and I noticed that there are at least four ceiling lights and four or five outlets on this one particular circuit. The wiring looks like 14 gauge but it is knob and tube I believe. I say it is knob and tube because the insulation appears to be of a woven string/paper type material.
Also of note was the method that the three light switches were wired. The live wire went from one switch then directly connected to another and then to the third. That’s not right is it?
Replies
Your description of the swithces is a bit confusing.....
But as to how many devices you might find on a 15 amp circuit, it depends on when the house was built. I once owned a house that was built in 1917. It was wired with K&T. Big two story,total 9 rooms (plus baths).
It had a total of 15 amps in the entire house, until I bought and rewired it it 1982. (If the refridgerator kicked on while I was brewing coffee, the main fuse blew.) And there were some weird things with the wiring too. A number of circuits had the switches on the ground wire instead of the hot. Some circuits had grounds that crossed over to other circuits. Scary.
In my case, it would have taken so long to trace the circuits that it wasn't worth it. I just ran all new. Led to some interesting lessons in fishing through old walls.
Knob and tube uses separate single wires, which are sometimes covered with a much thicker braided insulator near switches and fixtures in walls. It sounds like you have the earliest form of non-metallic which is a cloth braid over oiled/wax paper over 2 conducters in thick rubber/plastic. My experience with this stuff is to not touch it unless you want to replace it then and there as the insulation becomes very brittle and a slight movement will cause it to crumble. It is especially bad news in overhead light fixtures subject to heating.
That being said, my inclination would be to leave the ceiling lights on that circuit and if possible put in another circuit for the outlets since it is likely they aren't grounded. Trying to rewire ceiling lights can be very time consuming and expensive if they are located on a ceiling with a finished floor above it. If you really want sleep well at night, consider putting those ceiling lights on an arc-fault breaker, which costs about $30. Then you can use the original breaker for those new grounded outlets.
I think my house had four 15 amp circuits in the beginning. This was for 10 rooms, 2 baths and 1900 finished sq ft. Now there is more than that in just the kitchen
Could it be that it's not knob and tube after all?
The plaster walls have been replaced with drywall in the past and I couldn't figure out why they didn't replace the wiring at that time.
From what I can see each wire has a woven sheath made of what looks like thread. On top of that is a thicker covering. I don't think it is rubber. The walls would have been done in the '80.
>>I say it is knob and tube because the insulation appears to be of a woven string/paper type material.
That's not determinitive - the was also "rag wire" configured much as NM is configured today which can look like K&T.
Ohm's law: Power (watts) = I (amps) x E (volts)
Power = 15 x 110
Available wattage for a 15 amp circuit: 1650 watts, or 16 100watt light bulbs.
Remember though, that K&T (if it is) was designed for and rated on being in open air - often K&T has been encased under thermal insulation and should be derated or replaced.
_______________________
Tool Donations Sought
I'm matching tool donors to a church mission to Haiti - we're shipping a bus converted to a medical facility in (now it looks like) April and can fill it with clothes, tools and all sorts of stuff needed in that poorest of all countries. A few hand tools or power tools can provide a livelihood for an otherwise destitute family. Please email me if you have tools to donate.
Thanks to Jeff and David and Jim and Rich and Steven and Mark and Jason and Shep and Jen and Mike and Joe and Bill and Ken for their offers!
Several donations have arrived! Thanks and God bless!
1650 watts then dereg to 80% so thats like 1200( I do not have my calculator) 1650 x .08. You can have as many plug as you want but cannot go over 1200 watts. It depends on what you plug in. Most of mine I have nine plugs.The TV circuit I have two. The computer circuit I have two. You must add all the watts for each appliance. It written on the back. Stereo run about 400, computer about 400 big screens 250
The 1650 is where it will pop the ciruit breaker, 80 % is the safety factor, so 1200 would be safe limit. The 80 is from NEC
Edited 2/4/2004 8:05:34 AM ET by BROWNBAGG
Good point, I forgot the 80% derating applied if the load will run more than 3 hours.
_______________________
Tool Donations Sought
I'm matching tool donors to a church mission to Haiti - we're shipping a bus converted to a medical facility in (now it looks like) April and can fill it with clothes, tools and all sorts of stuff needed in that poorest of all countries. A few hand tools or power tools can provide a livelihood for an otherwise destitute family. Please email me if you have tools to donate.
Thanks to Jeff and David and Jim and Rich and Steven and Mark and Jason and Shep and Jen and Mike and Joe and Bill and Ken for their offers!
Several donations have arrived! Thanks and God bless!
K&T is theoretically good for slightly more ampacity than Romex, since the conductors are separated, and 'open air' like Bob said.
In reality, it is safer to go conservative on this, since you cannot see what is going on. Like another poster said, rewiring the outlets is a practical halfway solution. When these circuits went in, the were intended primarily for lighting. The had not invented hair dryers, space heaters, or power tools yet. In my own home, the original Edison fuse box (not in service) is 30amps. Plenty for the miracle of electric lighting...