Is this #3 THHN

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DaSnake

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I’m trying to figure out what size my incoming service wire is. B/c the wires are wrapped in colored coded tape, I cannot read the writing on the jacket. I took a caliper to the neutral and got a reading of 8.84mm when reading an unwrapped section, and a reading of 9.71 when reading the wrapped portion (wrapped in white tape).

According to a chart I found on Outside diameter of THHN wire, its seems that I have #3 THHN wire. Is that correct?

https://lugsdirect.com/Wire_Insulation_Outside_Diameter_Thickness_600V.html

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infinity said:
According to your table it's a #2 AWG conductor.

Welcome to the Forum. :)
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I think it may be bigger than that. Table 8 states#1= 8.45 mm and #1/0 = 9.45. The table he has is measuring the jacket Table 8 uses the conductor itself-- What size breaker does it terminate into? Or is that a service cable?
 
Dennis Alwon said:
I think it may be bigger than that. Table 8 states#1= 8.45 mm and #1/0 = 9.45. The table he has is measuring the jacket Table 8 uses the conductor itself-- What size breaker does it terminate into? Or is that a service cable?
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I was responding based on his table which is for the insulation. #2 AWG has an outer insulation diameter of 9.63, his measurement with the tape is 9.71 making it a #2. Are you saying that his chart is incorrect?
 
I am guessing that the op is guessing on the insulation type. That chart is for 3 types of insulation. If you use the bare wire number he calibrated it appears to be a larger wire
 
Measuring over the taped insulation is a crapshoot since, with that much marking tape, you can't identify the insulation type with any degree of certainty. And measuring the bare conductors can be problematic because the wire profile has "hills and valleys" created by the twisting of the individual strands (look at those two bare copper wires in the background). Unless you're measuring compact aluminum wire, you will get different diameter results as you rotate your calipers around the circumference of the bare wire. Combine that with the fact that your calipers may be at an angle due to you trying to measure a wire that's already lugged into the cramped confines of a panel, so it's unlikely that you'll get an accurate measurement of the wire diameter.

Fortunately, there's a simple solution. Un-lug the wire, unwrap some of that marking tape, and read what's printed on the insulation. It's not that hard and much more definitive than measuring diameters. After you're done, you can wrap on some new marking tape and re-lug the wire. Easy-peasey.

Be sure to use the correct torque when lugging the wire.
 
Jon456 said:
Fortunately, there's a simple solution. Un-lug the wire, unwrap some of that marking tape, and read what's printed on the insulation. It's not that hard and much more definitive than measuring diameters. After you're done, you can wrap on some new marking tape and re-lug the wire. Easy-peasey.
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Make sure that you shut off the main before removing the neutral. :)
 
Hi guys, thanks for all the responses. And sorry for my late response.


Yes I am guessing at the insulation type.


I never measured the bare conductors. I just measured the :



  1. OD around white marking tape : 9.71mm
  2. OD around black nylon insulation: 8.84mm


The wire is 7 strands.


I looked up NEC Table 8 and found the following:


reference: https://www.buildmyowncabin.com/nec/nec2014_chap9_table8.html


Overall diameter for 7 stranded wire is
#4 - 5.89mm
#3 - 6.60mm
#2 - 7.42mm


There is no mention of the jacket thickness so I assume this table lists a bare wire thickness. Is that correct?


I found a table for 19 strand copper THHN wire which lists the insulation and nylon total thickness as 46 mils. 46 mils is 1.1684 mm.


reference: http://www.prioritywire.com/specs/Copper THHN-THWN-2.pdf


Adding 1.1684mm to the numbers above I get a total thickness of
#4 - 7.06mm
#3 - 7.77mm
#2 - 8.59mm


I realize I made a few assumptions here.



  1. I took thickness and simply added it to diameter. I’m not sure if the thickness # quoted is its contribution to diameter or just the thickness
  2. I’m using a 19 strand jacket insulation thickness number and adding it to a 7 strand wire to come up with a total diameter.


If my assumptions are correct, the thickness I found around the jacket 8.84mm is pretty close to 8.59mm. Making this a #2 wire.
 

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Your numbers do not correspond to what is in your table in post #1. There is says a #2 has an insulation diameter of 9.63 mm, now you're saying it's "OD around black nylon insulation: 8.84mm".
 
DaSnake said:
Hi guys, thanks for all the responses. And sorry for my late response.
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You haven't explained why you haven't taken one of the wires off the lugs and unwrapped the tape so you can positively identify the wire. Previously, I had assumed you were working in a de-energized panel. Now I suspect that the panel is still hot.

If indeed you're putting metal calipers into the panel to measure wire sizes... well, I just hope that your life insurance policy is paid up!
 
infinity; said:
Your numbers do not correspond to what is in your table in post #1. There is says a #2 has an insulation diameter of 9.63 mm, now you're saying it's "OD around black nylon insulation: 8.84mm".
Click to expand...

8.84mm is the measurement I'm getting on my calipers around the black insulation, but not around the white marking tape.

The table in post #1 is for 19 strand cable. I have 7 strand, so i think I was referencing the wrong table.
 
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Jon456; said:
You haven't explained why you haven't taken one of the wires off the lugs and unwrapped the tape so you can positively identify the wire. Previously, I had assumed you were working in a de-energized panel. Now I suspect that the panel is still hot.

If indeed you're putting metal calipers into the panel to measure wire sizes... well, I just hope that your life insurance policy is paid up!
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Yes the panel is hot. I was very careful to only touch the insulated wire. Yes kind of stupid.

The wires in question are coming from the meter and into the main breaker.
 
DaSnake said:
Yes the panel is hot. I was very careful to only touch the insulated wire. Yes kind of stupid.
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A dead short across live the service conductors, or panel the busbar, or from any phase to ground, will cause a deadly electrical explosion. Imagine that dream sequence in Terminator 2 where the nuclear blast strips all the flesh off Sarah Connor's bones. It will be something like that.
 
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DaSnake said:
8.84mm is the measurement I'm getting on my calipers around the black insulation, but not around the white marking tape.

The table in post #1 is for 19 strand cable. I have 7 strand, so i think I was referencing the wrong table.
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What is the reason you are worried about it?

Roger
 
DaSnake said:
8.84mm is the measurement I'm getting on my calipers around the black insulation, but not around the white marking tape.

The table in post #1 is for 19 strand cable. I have 7 strand, so i think I was referencing the wrong table.
Click to expand...

What it boils down to, IMO, is that you are not going to be able to definitively identify the gauge of the conductors by measuring the OD of the insulated wire if you don't know what type it is.
 
As already suggested just remove the white tape and read the lettering on the conductor.
 
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