UF Cable Ampacity

Status
Not open for further replies.
infinity said:
That is only when being uses as a subtitute for NM cable. For UF applications it's 60° C for everything, including derating.
Click to expand...
Seems to me 340.12 applies to dry locations.

340.112 Insulation. .. Where installed as a substitute wiring method for NM cable, the conductor insulation shall be rated 90°C (194°F)
 
ramsy said:
Seems to me 340.12 applies to dry locations.

340.112 Insulation. .. Where installed as a substitute wiring method for NM cable, the conductor insulation shall be rated 90°C (194°F)
Click to expand...
That's correct the -B is 90° insulation but for UF applications you cannot use the 90° C conductor rating for anything.
 
ramsy said:
Most UF feeder cable is UF-B. May not be able to get plain UF cable if you tried.
Click to expand...
With the price of wire, I've been seeing a lot of UF and NM (no -B) surfacing on Facebook Marketplace the last couple of years. Some of it still sealed in the original packaging. Hopefully people are paying attention to what they are buying..... Naw.
 
tortuga said:
For UF in the ground you can adjust the ampacity with table 310.15(B)(1)
Click to expand...
So the portion of the UF cable circuit that is buried in the permafrost can use an ampacity multiplier of sqrt(2) = 1.414. : - )

At least until that permafrost starts melting as is becoming increasingly common.

Cheers, Wayne
 
wwhitney said:
So the portion of the UF cable circuit that is buried in the permafrost can use an ampacity multiplier of sqrt(2) = 1.414. : - )

At least until that permafrost starts melting as is becoming increasingly common.

Cheers, Wayne
Click to expand...
What do you think your average ambient soil temp is 18" - 24" deep on the hottest week of the year? I'd say the 16C - 20C would be safe that would be a 15% bump so UF would effectively be back at the 75C column
 
@wwhitney I found this at southwire and I know this is 10 years old but I doubt that has changed. This appears to say we can use UF at 90C indoors but does nothing for us on UF used outdoors.

Southwire® copper UF-B cable is generally used as feeder to outside post lamps, pumps, and other loads or apparatus fed from a distribution point in an existing building as specified in the 2011 National Electrical Code. UF-B cable may be used underground, including direct burial. Multiple conductor UF-B cable may be used for interior branch circuit wiring in residential or agricultural buildings at conductor temperatures not to exceed 90°C (with ampacity limited to that for 60°C conductors) as specified by the National Electrical Code. UF-B can be used in applications permitted for NMC in Section 334.10(B) of the National Electrical Code. Voltage rating for UF-B cable is 600 volts.
Click to expand...
 
Dennis Alwon said:
I found this at southwire and I know this is 10 years old but I doubt that has changed.
Click to expand...
Ah, if the UF-B is dual listed as NM-C as the text suggests [a possibility I mentioned in post #17], then yes you can use it indoors with the 334.80 allowances. So is all UF-B automatically listed as NM-C? Does it say NM-C on the jacket?

Cheers, Wayne
 
wwhitney said:
Ah, if the UF-B is dual listed as NM-C as the text suggests [a possibility I mentioned in post #17], then yes you can use it indoors with the 334.80 allowances. So is all UF-B automatically listed as NM-C? Does it say NM-C on the jacket?

Cheers, Wayne
Click to expand...

I must read poorly but I don't see nmc as entering into the 90C rating. The Uf-b being used for nmc is just a different sentence and has nothing to do with what is written above, IMO.
 
tortuga said:
UF used outdoors

Dennis why does the UF need to be derated? is it bundled? Is it outdoors underground or ?
Click to expand...

Suppose you need to get a few circuits into an attic that is being upgraded. Normally I would add a panel but that is not always desirable. If you run a conduit up the side of the house you could have a few uf cables going up there (maybe 4-5 circuits)
 
infinity said:
That's correct the -B is 90° insulation but for UF applications you cannot use the 90° C conductor rating for anything.
Click to expand...
and the UF application would be the portion that is underground.

Come into a building and bundle it with other cables and you can start with 90C ampacity for adjustments in that bundle.

Multiple cables in close proximity underground - chances are the ambient temp is low enough you can adjust ampacity upward instead of downward, but you do have to use the 60C ampacity column.
 
@wwhitney

Article 340.10 appears to allow uf to be used at 90C when used as nm cable

Part II. Installation
340.10 Uses Permitted. Type UF cable shall be permitted as
follows:
(1) For use underground, including direct burial in the
earth. For underground requirements, see 300.5.
(2) As single-conductor cables. Where installed as singleconductor
cables, all conductors of the feeder grounded
conductor or branch circuit, including the grounded
conductor and equipment grounding conductor, if any,
shall be installed in accordance with 300.3.
(3) For wiring in wet, dry, or corrosive locations under the
recognized wiring methods of this Code.
(4) Installed as nonmetallic-sheathed cable. Where so installed,
the installation and conductor requirements shall
comply with Parts II and III of Article 334 and shall be of
the multiconductor type.
(5) For solar photovoltaic systems in accordance with 690.31.
(6) As single-conductor cables as the nonheating leads for
heating cables as provided in 424.43.
Click to expand...
 
Dennis Alwon said:
Article 340.10 appears to allow uf to be used at 90C when used as nm cable
Click to expand...
Looking at the language you quoted, you end up with the provisions that the UF shall comply with 334.80, but you still have the requirement that it shall comply with 340.80. Nothing provides a relief or an exception to 340.80. So the stricter requirement controls, and you are stuck with the 60C ampacity.

Dennis Alwon said:
I must read poorly but I don't see nmc as entering into the 90C rating. The Uf-b being used for nmc is just a different sentence and has nothing to do with what is written above, IMO.
Click to expand...
I read the bolded sentence of your quote as being true because of the following sentence. Which all works if the UF cable is dual listed as NMC cable (the stuff that can be used in damp locations).

Cheers, Wayne
 
wwhitney said:
Looking at the language you quoted, you end up with the provisions that the UF shall comply with 334.80, but you still have the requirement that it shall comply with 340.80. Nothing provides a relief or an exception to 340.80. So the stricter requirement controls, and you are stuck with the 60C ampacity.


I read the bolded sentence of your quote as being true because of the following sentence. Which all works if the UF cable is dual listed as NMC cable (the stuff that can be used in damp locations).

Cheers, Wayne
Click to expand...


I think we will have to disagree on this one.
 
Dennis Alwon said:
I think we will have to disagree on this one.
Click to expand...
That's fine. It would take some language saying that 340.80 is overridden, or some reason to ignore Article 340 entirely (e.g. listing as NMC cable) to convince me that 340.80 doesn't apply.

I'll probably submit a 2026 PI to clarify this. Probably amending 340.80 is the way to go.

Cheers, Wayne
 
wwhitney said:
That's fine. It would take some language saying that 340.80 is overridden, or some reason to ignore Article 340 entirely (e.g. listing as NMC cable) to convince me that 340.80 doesn't apply.

I'll probably submit a 2026 PI to clarify this. Probably amending 340.80 is the way to go.

Cheers, Wayne
Click to expand...
Maybe some mentioning that UF cable meets or exceeds design of NMC in an informational note is fine, otherwise I see no need for any change.

It is saying that when used as NM cable UF is allowed to follow parts II and III of art 334, which contains the requirement that it be treated as 60C ampacity, but that the 90C rating can be used as starting point for ampacity adjustments.
 
kwired said:
It is saying that when used as NM cable UF is allowed to follow parts II and III of art 334, which contains the requirement that it be treated as 60C ampacity, but that the 90C rating can be used as starting point for ampacity adjustments.
Click to expand...
It doesn't actually says "is allowed to" it says "shall comply". And it doesn't say "plus 340.80 doesn't apply." So you end up with both 334.80 and 340.80 applying, which means that 340.80 controls.

Cheers, Wayne
 
wwhitney said:
It doesn't actually says "is allowed to" it says "shall comply". And it doesn't say "plus 340.80 doesn't apply." So you end up with both 334.80 and 340.80 applying, which means that 340.80 controls.

Cheers, Wayne
Click to expand...
I guess I see
(4) Installed as nonmetallic-sheathed cable.
meaning it is considered to be non metallic sheathed cable in the application, especially when they tell you to follow certain requirements in the non metallic sheath cable section immediately afterward.

I think the intent is there to consider this being equivalent to NM cable in such situations possibly could use little different wording if not being understood.
 
While doing my own research (going through 2020 and 2023 codes) on the interchangeability of NM-B and UF-B cable indoor and the ampacity of 60C vs 90C, I stumbled upon yet another issue, flame retardant. The UF-B wire (atleast the Southwire) doesn't have flame retardant certifications. Then I went to check the UL standards in both the NM-B and UF-B cables listed at Sourthwire.com (same wires listed at Homedepot with pdf spec sheets) and the only difference between the two was UL 719 and UL 493, which i'm not sure covers flame retardant. UL 83 listed on both cables might have some flame/smoke properties per UL 83 point 5.12.

I would prefer to use the flame retardant wire indoors so I did some more research. The plot thickened because I found two separate spec sheets for the 12/2 NM-B cable at southwire.com and other at cabletechsupport.southwire.com. The NM-B cable listed at cabletechsupport.southwire.com had additional fire certifications but missing (or not printed on the same cable at southwire.com). The stock# of both cable is same #288282. Fire specs only apply to larger cables which generally are not found in homes/indoors. So the question remains is NM-B cable 12/2 or 10/2 has flame retardant and UF-B doesn't?

Reference links are below.

UL 83 5.12 https://www.intertek.com/standards-updates/ul-83-thermoplastic-insulated-wires-and-cables/

NM-B cable with fire certifications Spec 10029
http://cabletechsupport.southwire.com/en/tile/30/cable/25634/?country=US
  1. ASTM B3 Standard Specification for Soft or Annealed Copper Wire
  2. ASTM B8 Concentric-Lay-Stranded Copper Conductors
  3. ASTM B787 19 Wire Combination Unilay-Stranded Copper Conductors
  4. UL 719 Nonmetallic-Sheathed Cables
  5. UL 1685 Vertical-Tray Fire Propagation and Smoke Release Test (1/0 and Larger)
  6. UL 2556 Standard for Safety Wire and Cable Test Methods
  7. ICEA S-95-658 (NEMA WC70) Power Cables Rated 2000 Volts or Less for the Distribution of Electrical Energy
  8. IEEE 1202/FT4 Flame Test (70,000 BTU/hr) 350kcmil and Larger

NM-B cable without fire certifications
https://www.southwire.com/wire-cable/building-wire/romex-brand-simpull-type-nm-b-cable/p/BW7
Southwire Romex® Brand SIMpull® NM-B cable complies with the following:
  1. Listed per UL Standard 719
  2. UL 83 (Conductor Construction)
  3. ASTM B-3 and B-8
  4. Federal Specification A-A-59544
  5. National Electrical Code, NFPA 70
  6. REACH/RoHS Compliant
 
Status
Not open for further replies.
Top