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I have 2 questions about this: I have a brand new cable qualified for NPLF (non power limited fire systems; designed to withstand a fire when used to power high-voltage fire alarm systems). Text on the cable says (see attached photo): "BELDEN (brand name) 28110A E64057-M 3C12 600V TYPE TC-ER (UL) THHN or THWN CDRS 90C dry 75C wet OR 150V type NPLF 90C SUN RES DIR BUR --- FT4 IEEE 1202 ..."

https://www.belden.com/products/cable/control-cable/28110a

Q1: Did I correctly understand that it's qualified for use as either regular THHN or NPLF? By this logic, is it allowed for regular residential power wiring, where standard THHN cable is allowed? NEC code has an article that for NPLF systems you must use a NPLF compliant cable. But it doesn't explain if that cable is also qualified for regular, non-fire system usages.

My goal is to upgrade my current home's 8 ga THHN copper cables (40A max) power cables coming from building's electric meter to my electrical panel in my townhouse garage (through ~90 feet of burried conduit). I want to upgrade to 60A per hot.

This Belden cable has 3x12ga copper multistrand conductors, and each conductor is individually insulated, then all bound by external outer jacket you see in photo (to allow for DIRect BURial option; though I understand there is no restriction to use it in conduits).

Q2: Since each 12ga conductor allows for 20A max, twisting three 12ga together will give me 20*3=60A_max. Is this parallel summation allowed per code? I understand that the current splits equally and all 3 conductors are designed to flow max current simultaneously; so this physically makes sense. I plan to use three of these cables with twisted 3x12 conductors: 2 for hots and 1 for neutral. I bought a standard green 8ga THHN for GND.

I got this cable for free from the local power company working on upgrading our local power substations. So I trust its quality and its source. They told me they twist the 3 conductors in parallel to increase total max current; but couldn't comment on residential usage.

Still, if I were to instead buy a standard THHN 6 ga wire in 90feet*3, for a peace of mind, I'd pay ~$400, which I'm looking to avoid if above is allowed.

Thank you!

NPLF rated cable by Belden

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    You don't/can't add insulated wires together to get more amperage cable. Depending on the size(diameter) of the conduit, you might be able to 2-2-2-4 gauge aluminum wire and get it much cheaper than copper. That gauge allows up to 90 amps. If you sell the copper cable, it might pay for the aluminum.
    – crip659
    Commented Jun 2, 2023 at 17:16
  • Let me guess: EV charging? Two things: first, you almost certainly don't need more than 40A charging. Almost nobody does. It's a nice to have not a need to have in nearly every circumstance. Second: even using this cable in your home might raise an eyebrow for your AHJ, so I'd be wary of using it even though it's certainly high quality cable. This is in addition to the excellent answer Ecnerwal already gave you.
    – KMJ
    Commented Jun 2, 2023 at 17:18
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    What size and material is the conduit in place?
    – Ecnerwal
    Commented Jun 2, 2023 at 17:31
  • Can you confirm if it is from your meter to your panel(very low amps for a house) or from main panel to sub panel(makes more sense).
    – crip659
    Commented Jun 2, 2023 at 17:31
  • Thank you all! I'm increasing the ampacity as we will replace our home's gas central heat to heat pump and eventually gas water heater as well due to California laws which are banning gas heating. Plus EV charging in further future. This is for Service Entrance Conductor from the main panel on the building (where electrical meter is) to inside of our garage.
    – S.C.
    Commented Jun 2, 2023 at 20:53

3 Answers 3

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You can't parallel without listed equipment for paralleling, and you won't find that until the wire gauges you are permitted to parallel at all, which are large, not 12Ga. I think without looking it up that might start at 1/0. (I checked, and I recalled correctly.) So no. You are not permitted to use it like that.

Since it's rated THHN/THWN it will have to be run as THHN/THWN would be - i.e. in conduit. Conduit fill will be troublesome since it's a 3-wire cable, with a cross section larger than 3 individual wires. (That may not apply when using it in its fire alarm application, but if using it for power distribution the THHN/THWN rating is the relevant one, and that would then require it be treated like THHN/THWN are.)

Depending on the colors of the wires inside the jacket, you may be able to use it as 3 12 Ga wires (so, circuits up to 20A) in conduit, not paralleled. You'll need a white or gray neutral wire to do that, and a green or bare ground if it's not in metallic conduit, as it's Black-Red-Blue according to the catalog page.

But you can't do what you want to do with it.

If you want to upgrade your supply wires, look to 2 AWG aluminum. 2-2-2-4 "Mobile home feeder" (MHF) is 90 amp and sits at a very nice price point, as compared to 6 AWG copper, given your example. URD may be even less expensive, per a quick look. But 270 feet of 2 AWG XHHW might be cheapest, especially if the conduit is metallic and does not need a grounding conductor as a result. But 4 AWG aluminum run in conduit to/from 75°C terminals will do 70A if you like. It's not a lot cheaper than 2AWG...but it will fit in smaller conduits.

A note on length - if you have not measured the "as the conduit runs" length, it's too soon to buy any wire, as you risk 90 feet being several feet short of the actual conduit path between two locations that are 90 feet apart.

And given this is a Townhouse, or "Multiple Dwelling Unit"

...you're going to need a licensed electrician anyway, so no getting away with "the power company guys said they do" (they work to a different code book anyway, though I doubt it approves of that trick) and just violating code while doing it yourself. MDUs are under stricter rules because more people are affected by the fire resulting from sub-standard work than in a single-family home. Not permitting DIY electrical is one of those stricter rules.

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  • Thank you for the info! Is this what you are referring to regarding 1/0awg+ is ok to legally run in parallel: NEC 310.10(h) ? I see Exception 1 allows smaller wires to run in parallel for control and instrument equipment, which may be why the utility company electricians were it. This may have started my confusion. My father is a licensed electrician. He is very good at certain things, but didn't have an answer for this non-standard wire. Asked me to research it for a chance to save some money. Aluminum 2awg may be to thick for the conduit. I'll check but may just pay for copper.
    – S.C.
    Commented Jun 2, 2023 at 21:13
  • The length is 80 feet actually - my father (he is a licensed electrician) pulled the original wires out, with the rope electricians use, measured it and pulled it back in as it was. So we got the length correctly. But we want some margin so it's easier and can trim it after pulling the wires.
    – S.C.
    Commented Jun 2, 2023 at 21:25
  • Can you suggest why running wires in parallel is not allowed? Is it because of sharing heat from the same current? Or because one conductor could break off, overloading the others? Or because they are hard to inspect and calculate that way? This would be useful to build more knowledge.
    – S.C.
    Commented Jun 2, 2023 at 21:42
  • Without using the listed equipment made and tested for the purpose, paralleling 3 12Ga wires would mean you could have 3 wires carrying 20A, 2 wires carrying 30A, or one wire carrying 60A due to common, ordinary junction failures that normally mean the one wire goes from carrying 20A to 0 A so someone notices and fixes it.
    – Ecnerwal
    Commented Jun 3, 2023 at 20:48
  • this makes sense! Thanks!!
    – S.C.
    Commented Jun 3, 2023 at 22:00
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You've skipped the most important label on that cable

Where your logic goes awry is that what you're looking at is a type of cable in its own right, namely TC-ER (Tray Cable, Exposed Run), and thus has its own cable article in the NEC. That article, however, prohibits the use of ordinary TC-ER by itself (i.e. outside of conduit) in residential applications; instead, it also requires a JP (Joist Pull) rating in order to be used by itself in a residential stud wall.

And the paralleling thing is a no-go to begin with

While the previous point isn't an issue when you're running cables in conduit (where TC is allowed, full stop), paralleling is prohibited for wires smaller than 1/0 due to issues with disconnected wires, fault currents, and so on. So, your plan is dead on arrival anyway.

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  • Thanks! I’ll add that label to my mental vocabulary. Appreciate your hints on some possible reasons why the rule exists.
    – S.C.
    Commented Jun 3, 2023 at 21:59
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Ecnerwal explained it all quite well. But as far as cost:

THHN 6 ga wire in 90feet*3, for a peace of mind, I'd pay ~$400

That is a bit high, but actually matches Home Depot's by-the-foot price. Since on a spool it costs a lot less even at Home Depot, you could probably go to an electrical supply house and get it for a lot less. Plenty of electricians will stock spools of 14 AWG, 12 AWG and 10 AWG cable (or wires in conduit-land) in their trucks but not larger because in residential you just don't need the big stuff all that much. So a supply house should be able to cut to order at a reasonable price.

That being said, aluminum will save you a lot. At Home Depot 2 AWG AL will cost you $0.95/foot (vs. $1.52 for 6 AWG CU) so that drops more than $100. And again, a supply house will likely do better.

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  • Thank you for the tips! Are HD wires - Southwire brand, made in USA - better quaity then the cheaper electrical supply ones?
    – S.C.
    Commented Jun 2, 2023 at 21:22
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    They're often the very same ones. Southwire is a major manufacturer. But in the end, it comes down to the specs. If a wire (unless counterfeit, but due to shipping costs I don't think that is such a big problem) has the proper ratings - THWN, proper size, etc. then it really doesn't matter who makes it. Home Depot (and many other stores) sells some things at very low markup (or even a loss leader) but the less common items at a higher markup - this is normal business. But for an electrical supply house, bulk wire is one of their common items - they generally just do electrical, not Commented Jun 2, 2023 at 21:30
  • electrical + plumbing+ garden + tools + lighting + lawn furniture + appliances + paint, etc. like Home Depot or Lowes. Just a different business structure. Commented Jun 2, 2023 at 21:31

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