jtomara37

110.14(C)(1)(a) & (b) confuses the hell out of me.

My understanding is if you are going to use thhn wire you would use the ambient temp correction factor in the 90 degree (thhn) wire column and use the ampere rating

does 110.14(C)(1)(a) & (b) have to do with sizing your wire and the ampacity of the wire at all..... or is it just for terminations that you will use????

Do you have to use the ampacity rating of the wire based on the weakest length.. ex: if the equipment is rated 90 degree, wire is rated 75 degree and terminations (wirenutts, breaker etc) are rated 60 degree do you have to use the 60 degree column for the ampacity of your 75 degree rated wire? and which Ambient Temp column do you use.

thx in advance

qckrun

In your example you would use the 60 degree column. But to do the derate of the wire you would use the 75 degree column. You just have to make sure that your derate factor is not higher than the 60degree column amperage otherwise you have to upsize your wire.

Note... no equipment will ever be rated 90 degree's. The 90 degree's column is strictly for derating purposes.

TheRick

Short answer - YES

According to 110.14(C)(1)(a) & (b) you have to use conductors with a temperature rating equal to or greater than the terminations.....however if conductors with a greater temperature rating are used, the lower rating of the terminations must be used in determining the ampacity of the conductors.

EX: 60 degree rated terminations + 90 degree rated conductors = 60 degree ampacity.

Hope that helps!

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jtomara37

If I am using a #1 thhn wire (rated for 150 amps in 90 degree column) but the terminations were 60 degree rated, I would only be allowed to 110 amps on that #1 thhn wire?

If the ambient temp was 120 degrees.. would i use the .58 in 60 degree column or .82 from the 90 degree column as my derating factor?

Chris Kennedy

?..........

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NolaTigaBait

Derate from the 90 column.

TheRick

YES

Derate from the 90 degree column, unless it is more than the 60 degree ampacity......use the lower of the two.

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hardworkingstiff

And now it really gets goofy if you using a cord and get your ampacities from table 400.5(B). For the termination, the cord must be sized to the appropiate ampacity from table 310.16, not from table 400.5(B).

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jtomara37

ok so......


If I am using a #1 thhn wire (rated for 150 amps in 90 degree column) but the terminations were 60 degree rated, would I only be allowed to 110 amps on that #1 thhn wire or could i use the 75 degree column ampacity because of 110.14(C)(1)(a) & (b) ?

If the termination degrees for some reason were not known would I be able to use the ampacity from the 75 degree column per 110.14(C)(1)(a) & (b) ?

If the ambient temp was 120 degrees (of the #1 thhn wire).. would i use the .58 in 60 degree column or .82 from the 90 degree column as my derating factor?

After derating would I use the ampacity value from the of the terminations, or if the terms were unknown 110.14(C)(1)(a) & (b), or from the column i of insulation where i got my derating factor?

Lastly in short.... please explain if the following statements are acurate.

1. If no derating you base the ampacity of the wire on 110.14(C)(1)(a) & (b) Either 60 degree or 75 degree column based on the wiresize?

2. If you derate for more than 3 current carrying conductors in a raceway or for ambient temp... you use the ampacity value from the column the insulation temp is rated for?

Thx for all the replys..

Magnettica

Answer to #1: Based on wire size and insulation type.

Answer to #2: Correct.

Example: #12 THWN/ THHN is rated for 30 amps in the 90º column. Six #12 current carrying conductors in the same conduit. Those 6 conductors get derated by 80%. The ampacity for that #12 THHN is now 24 amps (30A x .80 = 24).

Also, be sure the equipment you are using is rated for either 60º or 75º or dual-rated for 60º/ 75º.

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480sparky

What does the right-hand column of T310.15(B)(2)(a) say?

Nowhere does it refer to, mention, or otherwise reference 110.14. It states, quite simply, to use the values in Tables 310.16 through 310.19. THHN is a 90°C conductor, based on Table 310.13(A). If you are derating THHN, then you derate using the 90°C column.

Table 310.15(B)(2)(c) only references T 310.15(B)(2)(a), so you still haven't gotten to 110.14 yet.

So what is the rating of THHN in the 90°C column? Then you derate using that figure.

It's that simple.

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qckrun

You still have to use 110.14 if you are unsure of the ratings of the terminals. So if the ampacity of the wire is less than 100amps and you do not know the terminal ratings you would base your wire size off of the 60* column. If it is over 100amps and you do not know the terminal ratings, then it's based off the 75*column.

For derating purposes, 110.14 isnt used until you select a wire size.

480sparky

Show me where in the Code it says ampacity derating is based on anything in 110.14.

Other than a FPN, I see nothing in 310.15 at all.

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qckrun

I never said 110.14 was used for derating. The only things you use for derating purposes are Ambient Temp, and conductor fill.

You use 110.14 if and only if you are unsure of the terminal ratings if you are selecting a wire size only.

So if you had 78a load and you were sizing the wire size only, and you were unsure of the terminal ratings, then you would have to select a size wire according to the 60* column. If the load were 112a then you would have to select the wire size out of the 75* column.

110.14 isn't used in the derating process, its only used in the wire selection process when terminals are unknown.

jtomara37

If the terminations are unknown you must use the 60* or 75* columns, depending on 110.14?

I am told by my instructor that if you have to derate for any purpose, whether it be more than 3 current carrying conductors in a raceway, or ambient temperature, you then are allowed to use the ampacity values in the column that insulation is rated for..... for example thhn if the terminations are unknown you use (according to 110.14) either the 60 or 75 degree columns to get your ampacity, but if you derate for ambient temperature then you can use the deration factor in the column of what the insulation is rated for then finally choose the wire size in the 90 degree column based on those ampacity values.

Thx

NolaTigaBait

You can almost never use the 90 column for the size of the wire. I've never seen one, but you would need a moulded case breaker etc etc. If you don't know what the terminals are rated for, then yeah i'd be on teh safe side and use the 60 column for ampacity.

jtomara37

would i use the ampacity values in the 90* column to get my wire size after I use the 90* column derating factor?

jtomara37

when you derate using the 90*C column do you then use the ampacity and wire size values of that 90*C or only use the derating factor of the 90*C column then use the 75 or 60 degree column to size your wire/ampacity needed....based on the terminations?

What if you are not derating, what column do you use for your ampacity/wire size?

What if the terminations are unknown?

How does 110.14 play into this?

Sorry if for me its a little confusing still, thx for the help

480sparky

Derating applies only to the conductor. Section 310 is only about conductors and nothing else. 110.14 isn't part of the equation until you install the conductor to a termination. Of course, it seems silly to do calculations on a conductor unless you plan on terminating them at both ends, but nontheless, derating only applies to wires.

Take #12 THHN. Ampacity is 30 amps all day long per 310.16.

Take 8 of 'em and stuff 'em into a raceway, and 310.15(B)(2)(a) says they can now only carry 21 amps (30 * 0.7).

Now, according to 110.14(C), you must use the 60°C column, which is 25 amps. You have a conductor with a calculated ampacity of 21 amps, so it does not exceed the value of the 60°C column. Install a 20a breaker, and life is good.

However, take that same 30-amp condurcor and wrestle 15 into a raceway. Ampacity is now 15 amps (30 * 0.5). I must now install a 15-amp overcurrent device or else run another raceway and split the circuits apart.

If I go so far as to cram more than 40 into a pipe, then I gotta ask the boss where I can find a 10amp breaker as the ampacity is now 10.5 amps (30 * 0.35)

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