[gulley]

Inspecting the attic of my 1950 California ranch house I discovered – under the blow-in insulation – that during a previous remodel someone connected runs of THHN without electrical boxes simply by stripping the two ends, twisting them together and wrapping the heck out of the splice with electrical tape. Not good I suspect. Should I undo the splices and remake them with wire nuts inside boxes?

Also, what is the longest run I can make with 14 Romex on a 15 amp circuit? Would 12 gauge be better for a long run?

Many thanks.

 

[hornetd]

Inspecting the attic of my 1950 California ranch house I discovered – under the blow-in insulation – that during a previous remodel someone connected runs of THHN without electrical boxes simply by stripping the two ends, twisting them together and wrapping the heck out of the splice with electrical tape. Not good I suspect. Should I undo the splices and remake them with wire nuts inside boxes?

Also, what is the longest run I can make with 14 Romex on a 15 amp circuit? Would 12 gauge be better for a long run?

Many thanks.

When you type THHN are you writing about individual wires with no overall covering or are you writing about a cable with THHN Wires in it. If it's individual wires then they must be replaced with cable or you will have to run them inside some kind of conduit. That last would be hard to do because the only type of conduit which would be fairly easy to run and wouldn't be too expensive is Flexible Non Metallic Conduit (FNMC); commonly called smurf tube. FNMC is not permitted to be run exposed. It can only be installed were it would end up enclosed by at least 1/2 thick plaster board. That means that you cannot just put it under the insulation and call it good.

Providing that we are talking about cable there are 2 ways to redo those splices to that they will stay connected and safe. One you already wrote about is to make up the cables in electrical boxes so that they are properly clamped to the box and connected to each other inside the box. You make up your splices with wire nuts fold them gently back into the box and install a cover. The cable has to be secured every 4-1/2 feet and within 1 foot of each box to which it is clamped. If you find plastic boxes that do not have clamps then the cable has to be held in place within 9 inches of the box. If there is enough slack in the cable to allow you to do that then somebody upstairs loves you. The other way to join Non Metallic Sheathed Cable together both electrically and mechanically are Tyco Electronics Non Metallic Splice kits.

These were developed for the manufactured building industry to splice cables inside of very shallow walls without having to install electrical boxes. They are now listed for use in regular buildings as well as in manufactured ones. They would be much easier to use to re-splice your cable.

Tom Horne

 

[seharper]

If you mean literal THHN wires that are single wires with writing on the insulation, that is not legal to use except inside conduits. Either install conduits or replace with Romex or MC cable depending on what your jurisdiction requires (e.g. Chicagoland requires MC or conduit).

If you mean NM "Romex" cable with THHN individual conductors, those aren't real THHN lol.

I recommend metal boxes. Use proper cable clamps, either built into the box or fit into knockouts. Ground all wires to the metal box.

Also, what is the longest run I can make with 14 Romex on a 15 amp circuit? Would 12 gauge be better for a long run?

If you were in Canada you would need to think about that for runs longer than 75 feet. Americans have freedom to flex a bit on on that to suit their needs. However what causes voltage drop is the actual usage not the number on the breaker handle. So if the circuit is 12 AWG you might as well use a 20A breaker lol.

Honestly if you're going to have a bunch of long runs like that, perhaps a sub panel at the far end of the run is appropriate, that way you're running one 2-2-2-4 SER cable (maybe $2/foot) instead of a bunch of parallel Romex.

 

[hornetd]

Ground all wires to the metal box.

He means connect, bond, all of the bare or green Equipment Grounding Conductors (EGC)s to the box!

Tom Horne

 

[SW Dweller]

Lets define what the cable is used for. If the voltage is less than 50v like your door bell.
Then do not worry about it.
If there is 120v or higher on the wires then there has been plenty of good advise posted.

I have run thhn for a 12 v lighting system for a dance studio. Laid in above the ceiling tiles and when the inspector showed up I was ready to show him the power supply output voltages. All was good.

Chances are it is line voltage, unfortunately a practice that is still used by people who think they are electricians.
The important part know the use and voltage before you decide to rewire your attic.

 

[gulley]

Thank you all for your excellent advice, but oh brother, here's the back story... The original part of the house was wired with knob and tube and that old school rubberized(?) wire. At some point, long before we bought the house, the old wire was replaced by individual strands of THHN – not sheathed cable. To make matters weirder and worse, they ran the THHN through the old knobs and tubes with the hot, neutral and ground parallel about eight inches apart so replacing with Romex is trickier than it might have been. Here are the questions that replacement raises for me:

Is replacing part of a circuit with cable better or worse than replacing none of it?

Is it permissible to run cable on top of the ceiling joists if I attach a 1 x 2 alongside?

Everything about this house is funky, but little by little, weekend by weekend, I am setting things right, or at least righter. Bet you've all been there, done that. Thanks again, and yes, I will ground to the boxes.

 

[gulley]

PS My big box doesn't sell the Tyco splice kits. Would the plastic butt splices (sounds kinda obscene) work? Or maybe they're not permitted in California.

 

[gulley]

PPS What do you all think of using Wagoboxes?

 

[SW Dweller]

Should have led with the information you just posted. Yes you will have to replace all of the conductors that are not what is commonly called romex.
There is at least 10 different ways to do this. Some would fish the romex to the boxes below and then mount junction boxes so that the splices can be properly done. Makes for a lot of junction boxes. Generally easier than trying to get 2 cables down into the wall.

 

[hornetd]

If you need to connect knob and tube wiring to Non Metallic Sheathed Cable there is a code compliant way to do that but you must do it carefully and completely by the rules.

In order to give you good advice we would need to know the answers to a few questions.

• How many panels do you have in the house?
• Were does the knob and tube (K&T) wiring begin,
  • Does it start at a panel or at an electrical outlet or junction box,
    • An outlet box is one were a load is connected such as a Luminaire or a Receptacle. A junction box is one that is used to protect splices or taps to other conductors
• Is the insulation of the K&T wire still in intact?
  • If any of the insulation has crumbled to dust or been removed by someone or something then it is simply no longer usable and must be removed were accessible and abandoned were inaccessible. Best practice is that before abandonment the conductors to be abandoned are bonded to any of the places that the US NEC allows for connection of Equipment Grounding Conductors (EGC)s to circuits which do not have a EGC run with the circuit conductors. That is done so that should any of the abandoned conductors, which are now bonded to the neutral of the service entry conductors from the utility supply, were to become energized the Over Current Protective Device, read fuse or circuit breaker in residential applications, protecting the energizing circuit would open and deenergize the dangerously energized conductors.
• Is any of the K&T wiring now covered or enclosed in thermal insulation other than those THHN conductors you have already told us about?
  • Any K&T wiring that is now enclosed in thermal insulation must be replaced by cabled wiring with due regard for the possible need for derating due to ambient temperature around the conductors. The US NEC requires that type NM cable be used at not more than its 60 degrees centigrade ampacity but it does allow you to use its 90 degree centigrade ampacity to calculate the ampacity after derating. Should the derated ampacity of the cable conductors fall below that needed by the circuits loading then the rated opening current of the Fuse or circuit breaker must be reduced to the derated ampacity or the wire used. Alternatively the cable must be increased in gauge to compensate for the reduced ampacity allowed at the maximum ambient temperature to which it can be expected to be exposed.

Once we know the answers to those questions we can offer ways to properly bridge or extend the existing K&T wiring were it is safe to do so. If you do bridge out or extend K&T conductors you will be using techniques that were normal practice ~100 years ago. The only thing that nobody, who has any sense at all, would suggest that you do is to solder the new conductors to the existing K&T wiring even though that was the original way the wires were joined in K&T wiring.

Tom Horne

 

[seharper]

To make matters weirder and worse, they ran the THHN through the old knobs and tubes with the hot, neutral and ground parallel about eight inches apart

No, that's alright actually. I must eat my words, in-kind replacement in K&T is a fit use for THHN outside conduit.

There's really nothing WRONG with K&T if it's maintained properly and behind GFCI protection since there is no ground. The problem is "maintaining properly" includes "not continuing 80 year old wire in service" and there you are stringing THHN through knobs and tubes, and if you have the access to do that, then you should really be using MC or Romex if your jurisdiction allows Romex.

I wouldn't sit there and say Romex is better than K&T. What's the complaint about K&T, wires with just 2 layers of insulation between them and building materials? Well that's Romex... Except K&T has ceramic tubes through studs and Romex does not. What Romex brings is grounding. Which is less important now that we have GFCIs but still useful.

Anyway decisions are made on actual safety data collected from fire investigations, and they don't see a high incidence of Romex starting fires due to not having a ceramic tube through studs.

Rather than sweat bullets of replacing K&T "for the safetiez", I would put a GFCI/AFCI breaker on it and not worry about it.


Y'know, on the Romex, you need to use #12 sometimes and #12 is allowed on 15A circuits. So what is the rationale, exactly, for ever using #14 ever? Easy: "It's cheaper". Is it really, though? it's cheaper by the foot, but that only holds if you're a pro installing a mile a month. The DIYer who has to put 3-4 spools in their shopping cart of 14/2, 14/3, 12/2 and maybe 12/3... is going to pay more at the register than the DIYer who only buys 12/2 and 12/3. (especially because of the weird way the shorter spools are much more costly per foot). Price it yourself and see.

 

[seharper]

PS My big box doesn't sell the Tyco splice kits.

You're in a "big box rut". People shop at big box so much they forget other suppliers exist. The problem is big-box store selection is crap - they only sell popular stuff based on what their computers tell them. There'll be some complex system e.g. for surface conduit, and they'll sell the left-handed elbow but won't sell the right-handed elbow because their computer said it fell just under the analytics threshold. Stupid stuff like that.

They also disgustingly overcharge for less popular items. If it isn't regularly price-checked, the algorithm marks it up.

You need to know about and frequent local family-owned lumberyards, local family-owned hardware stores including ACE and HWI affiliates, and local electrical supply houses (which may be chains such as City Electric, Graybar etc.) A good relationship with a local electrical supply is worth its weight in gold.

Would the plastic butt splices (sounds kinda obscene) work?

The hokey things used in automotive? I've never seen that and I fully expect any inspector who sees those in a box will red-flag them.

In-wall splices are a tough problem. The only thing that was ever legal was the Tyco type, and when they were approved they were immediately over-used - basically anytime an electrician reached the end of a spool they slapped on a Tyco splice and kept going lol. Because of this they were re-outlawed for all uses except wire repairs.

This is not a wire repair so I don't think even a Tyco splice would b e allowed.

Or maybe they're not permitted in California.

That's NEVER stopped them. Check the outlet aisle for NEMA 10-30 dryer outlets, those were banned in 1996.

 

[gulley]

Thanks again for the info and opinions. I certainly am going to remake the connections inside boxes and run cable where I can. This question didn’t get addressed though: Is replacing part of a circuit with cable better or worse than replacing none of it?

Also, among other facts I thoughtlessly omitted, the panel is only five years old and it is mounted to an exterior wall (climate is mild here). THHN runs from the panel to the attic through a big conduit.

I found the answer to my question about guard ships alongside cable.

And no, I’m not in a ‘big box’ rut. I do patronize local and small businesses when I can, and that’s often.

 

[gulley]

...guard STRIPS...