Basic Wire Size Question

15 years ago

Please help. I am trying to decode what I see in my wall and to understand it in terms of the postings I've read in this forum. My house is 85 years old, and I was told by the PO that they had "completely rewired the house" in the early 1980s. But in our attempt to relocate a wall switch, we can see that they didn't.

I appear to have 12-2 Romax used for my outlets. Why 12-2 instead of 12-3? Does this mean the Romax contains no ground wire? Are my outlets ungrounded?

A much heavier-looking cable reads "Cable Type NM" and then the printing goes bad. Possibly says "600 Volts 14 / 3" (but only the bottom half is readable, so for all I know it says "800 Volts 14 / 5"). This 14 gauge cable looks much more substantial than the 12-2; it's thick and round, rather than flat like the 12-2. But I thought 14 gauge wire was less robust than 12 gauge?

Inside a junction box, the 14 gauge wire is spliced into post and knob wiring coming down from the overhead light fixture (although I see other instances of 14 gauge wire split and stretched open, spliced onto the older wiring just below the knobs using electricians' tape). Below the junction box, the 14 gauge wire AND a length of the old p&k wire BOTH enter the switch box, which has 2 switches: a dimmer and a toggle. Why the extra piece of wire? Shouldn't the old p&k end at the junction box? The extra wire does end in the switch box--only the 14 connects to the circuit box.

On the whole, the old p&k looks ok. It's fabric is torn a little bit in places, but on the whole it looks sound. Except that I'm uneasy about the way it's been spliced into the NM. Do I have anything to be concerned about? The overhead fixture is less than 2 feet from the wall, so I don't understand why new Romax through wasn't fished through from the light--clearly the wall was opened for the rewire. That could have done away with the p&k entirely for this switch--except for that extra wire from the junction box to the switch?

I'm sorry if these questions are elementary--I just get so confused looking at it. I used to be smarter, back when I was younger... Thank you for your help.

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Comments (4)

terribletom
15 years ago
I appear to have 12-2 Romax used for my outlets. Why 12-2 instead of 12-3? Does this mean the Romax contains no ground wire? Are my outlets ungrounded?

"12-2" means the cable has two current-carrying conductors--one black and one white. That designation, alone, is silent as to whether the cable also has a ground. There was a time when 12-2 without ground was common (say, 1960ish), but not generally by 1980. By then, newly manufactured 12-2 typically included a ground. (In the intervening years, the term "with ground" was often stamped on cables, but that largely phased out as ground wires became "normal".)

Assuming that the 1980 date is accurate, your "12-2" almost certainly includes a ground and it's an entirely normal cable for use with receptacles.

Moreover, it's easy enough to check: Just peek into a receptacle and/or switch box. Does the cable supply a bare ground wire?

"12-3" (or "14-3", for that matter) implies three current-carrying conductors (black, red and white) and would be used for such things as switch legs involving 3-way switches, split switched receptacles, 120/240v circuits and other specific uses needing three current-carrying wires in addition to an equipment ground.

House wiring in general consists of a mixture of 12-2, 12-3, 14-2 and 14-3 and does not suggest that any of these wires have grounds or not.

A much heavier-looking cable reads "Cable Type NM" and then the printing goes bad. Possibly says "600 Volts 14 / 3" (but only the bottom half is readable, so for all I know it says "800 Volts 14 / 5").

It says "600 volts". Trust me. Essentially all reasonably modern NM (non-metallic) cable in a house is technically rated for 600 volts and that's of little significance with respect to your post. ("NM" is more or less the generic designation for what you refer to as Romex, which is actually a brand name.)

This 14 gauge cable looks much more substantial than the 12-2; it's thick and round, rather than flat like the 12-2. But I thought 14 gauge wire was less robust than 12 gauge?

Not sure what "robust" means in this context, but the three-wire cables in general (e.g., 12-3 and 14-3) tend to be round (and, for obvious reasons, larger) whereas the two-wire cables tend to be flat. That's just a packaging issue. Not to worry.

As for your other questions regarding the splicing of "Romex" and knob and tube (K&T) wiring, it's pretty hard to tell without seeing the splices in context. How new wiring is integrated with old involves quite a bit of judgement on the part of the electrician. Perhaps other commenters will be more helpful than I in providing answers. (I have only a smattering of experience with K&T.)
brooksideiris
Original Author
15 years ago
Thank you. That makes a lot of sense--and also provides a possible explanation for why the K&T negative would have gone all the way thru the junction box, in addition to the 14/3. At least till I opened that junction box to look at it.
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brooksideiris
Original Author
15 years ago
OK, not only did I not mean to post the above (was just testing to see if my photo posted properly before posting a second), but my other post has disappeared entirely.

I know that the photo is blurry, so I hope you can see what's going on in this box. On the bottom of the photo, the K&T negative is connected to another short strand of K&T wire which enters the top of the switch box, about 6 inches below the junction box.

On the top of the photo, the K&T positive (I assume) comes in from the left and is connected to the 14-3's black wire. The 14-3's red wire is cut flush with the floor of the junction box. The 14-3's white wire is capped off, attached to nothing.

Is there any reason to have capped off the white wire, rather than connecting it to the K&T negative? Why cap the white wire but just cut the red wire flush? Does this make sense? Here is a second photo of the junction box, if that helps.

Thank you for your help.
brickeyee
15 years ago
You need a little better background to be working on this.
AC wiring does not have a "positive" or "negative" wire.

"Wiring Simplified" would be a good place to start.
While it will not cover K&T it will give you enough information to understand how the circuits operate and the vocabulary to describe what you are looking at.

Basic Wire Size Question

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