I have an old home with 1930s era wiring. There’s a long story about why I’m doing some electrical work in the place, but I’m on my phone now in Arizona, and can’t explain it in detail. In short, tenants keep replacing two prong outlets with three prong ungrounded outlets. Last month I went through and replaced every outlet in the place with a GFCI and put the little “No Ground” sticker on each one. The wiring is K-T.

They run window A/C units. I cannot down rate the K-T to 15a without removing some load. I want to run a couple new 20a circuits to the two bedrooms. Because of where the panel is located, it is on the opposite side of the house from the bedrooms. The panel is exterior, and the wiring runs to the attic through EMT. I also have a full roll of 12-3, but have a lot less 12-2.

In short, since I already have a bunch of 12-3, is there any real downside to running shared neutral circuits? The panel is a GE with space available. GE states that mod 3 AFCI breakers with a tie bar will work. The biggest advantage for me is:
1) I already have the wire
2) There is room in the conduit for the wire without having to add any, whereas 2x12-2 would require a new run of EMT.

What are your thoughts on circuits with two ungrounded conductors with one grounded conductor and one grounding conductor? Thanks.

This message has been edited. Last edited by: sigcrazy7,

There's nothing wrong with using three wire circuits. You will need to use a two pole breaker and if it covers bedroom outlets a two pole AFCI breaker. Also where the circuits split off you need to wire nut/pig tail the neutrals, do not use the outlet to make a splice. Other than that there's no down side.

The problem with your plan is running Romex in a wet location.

Thanks Jesse. The Romex is on the exterior of the house, but underneath a carport. It is not exposed to weather.

I plan on using an AFCI breaker even though Utah eliminated that requirement a few years ago.

Carport would be up to the local inspector. If he considers it a damp location you can't use Romex since it's rated for dry and would need to be UF wire. Romex can only be ran in dry locations and can only be used for short runs for physical protection, again that's up to AHJ (inspector).

Personally I'd run an additional conduit pull THHN (individual conductors) to a junction box in the attic, then switch over to Romex in the attic. This is because again the inspector will determine if the conduit has followed conduit fill requirements. There is no actual way to derate the conduit for stuffing Romex into it as the tables are based off THHN or other individual conductors. Some inspectors will say 40%, some will say 40% counting each ground in the assembly. Some will say only a single cable. Some will just wing it and say that looks ok to me.

Ok, thanks. I’ll talk to the AHJ beforehand.

The project is underway. I feel the first day went ok. It has been twenty years since I messed with EMT, so it took me some time to work it out. As a reminder, I'm doing this to fix problems and to remove all K-T wiring in the house so that I can insulate the attic up to code and remove all non-grounded circuits.

Here is one of the problems I corrected. The previous owner had run a circuit with exposed Romex. You can see the outer PVC and even the conductor thermoplastic insulation is failing.


Here is my new conduit run. You can see the old Romex hanging there. Mine is the new 3/4 conduit on the top.


Here is the exit into the attic, with the old Romex still in place.


End of the day, with the wiring pulled.



I pulled seven 12awg THWN-2 wires and two 14awg THWN-2. This will give me five circuits, four 20 amp and one 15 amp circuit.

My mistakes:
1) I didn't have a 4 11/16 box, and just used a 4 inch one. After calculating fill once I add the Romex, I *think* I would be about two inches over, so I had to add an extension ring.
2) I originally planned on terminating the EMT immediately inside the attic, but went a bit further and added an extra bend. I'm over 360 of bends without a box. I got the wire through ok, and I have four couplings along the way, so I can add a box in one of them if I have to.

All the Romex you see in the attic was done by the previous owner. I will be going through and re-doing most of it. It's just hacked in there and thrown around everywhere. There is K-T all buried under the small amount of insulation, so all that will be coming out as well.

Along with my desire to re-insulate the property, here is what started all this now (see bottom of this post for bigger picture). I have owned this property since 1998, and have only had a couple of tenants during that time. Therefore, I have not done much to the place. In the process of doing a turnover in March, I noticed that the tenants keep changing out all of my two-prong outlets for ungrounded three prong. I decided it was time to swap them all out to GFCI outlets. All of the boxes were those tiny little metal boxes that would never fit a GFCI. Some of them are old BX boxes, and the fitting wouldn't allow a GFCI regardless.

Since the tenants were moving in the next day, I felt the quickest way was to use starter boxes. I didn't want to replace the outlet boxes and risk causing damage that would require any finish work.

What my tenants kept doing. Swapping out two prong outlet for three.


Mounting the adaptor plate and starter box.


Installing the GFCI outlet.



The finished outlet. I did all of the ungrounded circuits like this. I think they all look pretty good.


There's one curiosity, though. On some of the outlets, it looks like one or more of the conductors are 14 gauge. Look at the difference in the wire sizes. Using my wire strippers as a guide, the wire on the right (the grounded conductor) is 14 awg, while the ungrounded conductor is 12. This whole house is running on 20 amp breakers.


Has anybody seen this? Was it common back in the day when this house was built (1930s), to run a 12awg K-T "trunk" and then use 14awg drops to outlets? Or perhaps standards were so low and poorly enforced in those days that installers simply did whatever they wanted. Who knows. Either way, I'll be pulling this all out in the next few months. I'll hopefully be able to get the HVAC guys in to install central air in the next few weeks, and then we will retire all the window A/C units that are running on this old wiring.

Now that I know about this wiring it worries me, even though it's been in place for the last 90 years. It will be nice to have it redone.

*Bonus Content*
Why haven't I dealt with this earlier?
For the last decade and a half, the city/state has had a major infrastructure project afoot that would take this house under imminent domain. I had to wait and see if it would survive before I was going to invest any effort into it. Now that all the environmental studies and other red tape are complete, the master road plan goes elsewhere, and will leave this neighborhood intact. This is one of the reasons I'm putting money into it now.

Everything looks good except the number of conductors in the conduit.

First the ampacity for the conductors need to be derated due to more than three current carrying conductors. It should be derated by 75 or 80% depending on the number of conductors. Either way I think you're fine there because 12/14awg is 25/20a if doing derating due temperature or conduit fill. Even at 75% you are still good for the 14awg, if it's 80% than you're good on the 12awg too. If I'm reading it right you will have 5 hots, 3 neutrals and one ground. For conduit fill derating only the hots count, so 80% is OK for both 15 and 20a circuits.

Second you don't have space for that many circuits. You only have space for three circuits. So you can do two 20a on a skinny 2p breaker and one 15a on a single pole breaker. Can't tell for sure, but it looks like you have an unused 30a which you could swap for your last two 20's. The problem you will face is the AFCI protection which is needed at a minimum in bedrooms, but inspectors sometimes want all new circuits to be AFCI regardless of their location. Current code requires all standard outlets/switches to be AFCI, but few places adopted the newer code and still only require for bedroom outlets. You currently only have one slot that can accommodate an AFCI breaker. I've never seen a thin THQL breaker, but they may have started making them and I've just never seen them.

Overall besides the > 360° and box fill you mentioned, excellent looking installation. The wiremold boxes are a better idea than replacing old boxes because of the can of worms you open with plaster work and damaging fragile wiring. Nice job on wrapping the wires and using white on the neutrals.

Two two points I brought up, first one I'm just mentioning, but if I understand what you did correctly is moot. The second will depend on AFCI requirements for your jurisdiction and the end use of your new circuits and may or may not be an issue.

Had I understood your intention to add this many circuits I probably would have suggested a sub panel instead of individual circuits, especially with the potential for more rewiring.

As far as box fill, yeah, I would have gone with a bigger box. First it makes life easier and second a lot of inspectors don't like the use of extension rings, especially if you use a KO in the ring as it makes the other wiring less accessible, but that's inspector's personal preference as far as I know.

Overall, looks good, better than what I see from 75% of professional electricians.

As for your last question, I have no clue why you'd have a mix of wire sizes. With a house that old I can't even begin to speculate.

I read that K&T traditionally used 12 gauge wire but sometimes 14 gauge was used too, I’ll bet the Ye Olde Electrician of that era used what he had on hand that day.

Remember, 1930’s = Great Depression

quote:

Originally posted by Skins2881:
Overall, looks good, better than what I see from 75% of professional electricians.

Thank you for reviewing my work. It means a lot to me to have someone with your experience looking it over.

Being a DIYer, I pretty much am going on what I can Google along with what I get from some electrician’s channels on YouTube. The chart says I can go with sixteen 12awg wires in 3/4 EMT, but somehow I got the idea that I wouldn’t need to derate until nine conductors. Maybe that is just some people’s shorthand rule of thumb where it derates below the 15/20 amp amount to matter? Anyway, thanks for looking it over. If I understand your comments, I should be ok with four 12awg and two 14 awg conductors. (The 14 gauge circuit is not a multi wire circuit, so the neutral counts, right?)

As for the space in the panel, I didn’t take the picture at the best time. Those GE mini breakers are kind of tricky, so I had already inserted a couple of them in an effort to figure them out. You spotted the 30a 240v breaker, but on the right side, there is already a 20a 240v breaker installed. I still hadn’t inserted the other 20a 240 or the 15a single when I took the picture. That should leave me the space to land all five circuits. This Thurs the HVAC guys are scheduled to install central air, so that is why I already installed that 30a.

As for the AFCI requirement, the state of Utah removed all AFCI requirements statewide a couple years ago, so the AHJ cannot require me to install them. If I ever decide or need to, I could put a sub below this box, or perhaps just go with some outlet style ones. I know AFCIs would be ideal, but I don’t want to make perfection the enemy of improvement.

Thanks again for your comments.

As for PAsig’s observations, yea, you’re probably correct. Considering how Utah is less code strict today, I suspect it was really relaxed in 1930. The “old west” was only thirty years old in 1930. You’d be code enforcing against guys who may have personally hung out in Dodge City or Tombstone, or at least embodied the sentiment. Telling a man how to build his house required a delicate touch in those days, I’d guess.

quote:

I don’t want to make perfection the enemy of improvement

Something I need to remember in general.

Finished day three. I added a bit more conduit.

I know I could have used Romex, but:
1) I had extra EMT.
2) I purchased the THHN on 500ft rolls.
3) Extra junction box helps with box fill.
4) Conduit looks cool, and I was having fun doing it.

Firstly, I corrected some of my problems from day one. I added a pull box, and switched the junction box to a larger size. This fixes the >360 degree angle problem with day one's work.


I ran some extra conduit to the other side of the attic and added a junction box there. This will make the romex runs to those areas of the house much shorter. If I were to do this again, two 45 degree angles would have been better than the two 90s.


I ran some 1/2" conduit off the first junction box and added a light, with a switch back to the attic opening.




I ran conduit from the first light to add another light over top the furnace. Then extended off that box to add a service outlet beside the furnace. I also deprecated the old furnace power supply and connected the furnace to this new circuit. I used a MC cable whip. The old furnace cable is just capped off. I'll remove it at a future date.



For the MC whip, I used MC specific connectors with those little red eye inserts. I didn't have any MC clamps or anymore tapcons, so I didn't connect it to the brick. I'm a little unclear if it must be connected, being a whip less than six feet. If anybody knows, please tell me. Thanks.

Overall, I think it looks ok. I struggled a little bit with many bends in a single piece of conduit. Once, I just cut it in half and used a splice connector to get it right. I will be doing the rest of the wiring job with NM.

quote:

Originally posted by sigcrazy7:
Finished day three. I added a bit more conduit.

I know I could have used Romex, but:
1) I had extra EMT.
2) I purchased the THHN on 500ft rolls.
3) Extra junction box helps with box fill.
4) Conduit looks cool, and I was having fun doing it.

I ran some 1/2" conduit off the first junction box and added a light, with a switch back to the attic opening.

That does look cool...Nice work!