Conductor ampacity

[Therealcrt]

That’s why everyone shames the NEC because thered certain rules to follow sometimes not always and those rules only apply to some things not all things.

 

[Jpflex]

That's not how it is worded in the Code at all.

The Code says... Ampacities for conductors rated 0 volts to 2000 volts shall be as specified in the Ampacity Table 310.16 through Table 310.21, as modified by 310.15(A) through (F) and 310.12.

There's no wording in the Code about the other ampacity tables being used to start with a higher ampacity but reduced to table 310.16.

You did not read nec 110.14c1

 

[Therealcrt]

Table 310.16 is for conductors not more than three current carrying and a raceway cable or earth. We should never use this table because nine times out of 10 as an electrician. We’re discussing this table and amities based on what wire size we need to run through a conduit And many times we’ve run more than three current carry conductors in conduit anyways so we shouldn’t even use this table in the real world because of a piece of equipment. The nameplate rating is max overcurrent protection 20 A then we use a number 12 gauge wire nine times out of 10 I would almost say 10 times out of 10 if a nameplate rating is maxed over current protection 30 amps same situation nine times out of 10 we’re gonna use number 10 gauge wire even though table 310.16 says in the 90° C number 12 gauge wire is rated for 30 A we’re never gonna use that because that’s for not more than three current carrying conductors Who in this thread is an actual electrician not just a guy trying to figure out a problem on a quiz.

 

[Jaybone812]

It

It is and i even submited the necs explanation as to why. See pictute of nec text

It’s not and you’re the only one on the thread that seems to that it is . You’re description in no way lines up with the actual words in the code and you’ve been given proof to that multiple times over the course of this thread ,


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[david luchini]

You did not read nec 110.14c1

I did in fact read NEC 110.14(C)(1). It doesn't say anything about the other ampacity tables being used to start with a higher ampacity but reduced to table 310.16.

 

[Jaybone812]

See NEC 240.4(D) and what follows. There is a difference between a wire's nominal ampacity and what OCP may be used to protect it under various circumstances.

Very good point . If it’s one of the specific applications listed in 240.4(g) it’s not subject to the restrictions of 240.4(d)(1-8)

 

[Jaybone812]

You did not read nec 110.14c1

I def did but obviously you didn’t or just don’t know what it means . Nothing in 110.14(c)(1) says the wiring method dictates the table used for conductor ampacity . Idk where you think it says that . It says unless the equipment is listed and marked otherwise all ampacities used to determine equipment termination provisions shall be based on 310.16 as appropriately modified by 310.12
Meaning only time l amapcity values from another table can be used for any reason is if the equipment is specifically listed and Marked for that use . Which means its dictated by the equipment not the wiring method


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[Jaybone812]

You did not read nec 110.14c1

And when they say modified by 310.12 they are referring to a feeden that is a dwelling units main source of power as in it’s serving the entire load of the dwelling


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[wwhitney]

Meaning only time l amapcity values from another table can be used for any reason is if the equipment is specifically listed and Marked for that use . Which means its dictated by the equipment not the wiring method

No, not "for any reason," only for "termination provisions".

For an example, say I have a branch circuit that needs to supply some equipment within a wood-drying kiln where part of the run is exposed to 90C ambient. Obviously I can't use 90C conductors, but I could use Type Z conductors rated at 150C per Table 310.4(A) footnote 3. Type Z conductors in conduit can use Table 310.18 for their ampacity. But at the panel supplying the branch circuit, per 110.14(C) I would need to use Table 310.16 for the termination ampacity.

Cheers, Wayne

 

[Jaybone812]

No, not "for any reason," only for "termination provisions".

For an example, say I have a branch circuit that needs to supply some equipment within a wood-drying kiln where part of the run is exposed to 90C ambient. Obviously I can't use 90C conductors, but I could use Type Z conductors rated at 150C per Table 310.4(A) footnote 3. Type Z conductors in conduit can use Table 310.18 for their ampacity. But at the panel supplying the branch circuit, per 110.14(C) I would need to use Table 310.16 for the termination ampacity.

Cheers, Wayne

Thank you for the clarity I worded my entire comment incorrectly as you pointed out . I think What I was trying to say is in line with your comment and please correct me if I’m wrong , is that a conductor’s termination ampacity at the branch circuit ocpd needs to come from from 310.16 regardless of what conductors ampacity value is found elsewhere in another table . Does that make sense ??

 

[Jaybone812]

No, not "for any reason," only for "termination provisions".

For an example, say I have a branch circuit that needs to supply some equipment within a wood-drying kiln where part of the run is exposed to 90C ambient. Obviously I can't use 90C conductors, but I could use Type Z conductors rated at 150C per Table 310.4(A) footnote 3. Type Z conductors in conduit can use Table 310.18 for their ampacity. But at the panel supplying the branch circuit, per 110.14(C) I would need to use Table 310.16 for the termination ampacity.

Cheers, Wayne

And on that note the a conductors termination ampacity is dictated by the terminal temp rating of the equipment, ie: equipment provisions . Correct ?

 

[tortuga]

Why would it depend on the conductor size connected to it? If the termination can carry 200A without exceeding it's 75deg rating,, then the rating is 200A.

Whats interesting is how 110.14(C)(1) states in part;

Unless the equipment is listed and marked otherwise,
conductor ampacities used in determining equipment termination
provisions shall be based on Table 310.16 as appropriately
modified by 310.12

So let me ask you all from the perspective of a equipment designer;
Say I need to size a lug or terminal strip AKA "equipment termination
provisions" for some equipment that can be used either in an enclosure or not and I have a 150A calculated load.

110.14(C)(1) is going to send me to 310.16 or 310.12 to find the largest wire my lug needs
to accommodate; a 1/0 CU at 150A.
So I get a lug rated for #4-250 rated 200A 75C.
Now if my equipment with that same lug can be used in free air (per the definition) could that lug
still handle 150A from a #2 CU (Based on 310.17) without me needing to mark the equipment otherwise?

 

[wwhitney]

Now if my equipment with that same lug can be used in free air (per the definition) could that lug
still handle 150A from a #2 CU (Based on 310.17) without me needing to mark the equipment otherwise?

Obviously no, as the sentence you quoted says to use Table 310.16 "unless the equipment is listed and marked otherwise." So unmarked = use Table 310.16. But as the equipment manufacturer, you could choose to have it so listed and marked, so that the installer has the option to use #2 Cu when the equipment is installed with unenclosed terminations.

Which of course raises the question of whether the listing standard for the equipment has provisions for such listing and marking. If it does not, the manufacturer and installer are out of luck, and 1/0 Cu minimum will be required at the termination in all cases.

To explore this question further would require choosing an equipment type that is plausibly installed with unenclosed terminations and free air conductors leading to them, and then to check the listing standard for that type of equipment.

Cheers, Wayne

 

[tortuga]

Obviously no, as the sentence you quoted says to use Table 310.16 "unless the equipment is listed and marked otherwise." So unmarked = use Table 310.16.

Nothing is obvious to me you should know that by now.
110.14(C)(1) is saying to use 310.16 or 310.12 in determining equipment termination
provisions , so do you think 'equipment termination provisions ' includes the branch circuit conductor?

 

[wwhitney]

Nothing is obvious to me you should know that by now.
110.14(C)(1) is saying to use 310.16 or 310.12 in determining equipment termination
provisions , so do you think 'equipment termination provisions ' includes the branch circuit conductor?

It includes the conductor size terminated on the equipment, and the ampacity we associate to that combination. It does not cover anything about determining the ampacity of a circuit conductor at a location outside the equipment.

Cheers, Wayne

 

[Jaybone812]

I did in fact read NEC 110.14(C)(1). It doesn't say anything about the other ampacity tables being used to start with a higher ampacity but reduced to table 310.16.

It if sounds to me like he thinks 110.14(c)(1) is saying we can use ampacity values from other tables as a starting point when applying any required ampacity correction adjustment factors (derate) Which to me makes no sense since the ampacity of a conductor at its termination point can only come from table 310.16 unless the equipment is specifically listed and marked saying otherwise

 

[tortuga]

It includes the conductor size terminated on the equipment, and the ampacity we associate to that combination.

Are you sure thats how UL 486A-B does it?
So is a connector lug rated for a single wire in the range of #4AWG - 250MCM tested per UL 486A-B for each wire size only up to that wire size's value in Table 7 "test Current for connectors intended for a single conductor"?
Or do they just test the smallest conductor that 310.16 allows that lug to have?

 

[ggunn]

You can go round and round with the code, but what it boils down to is that you do not want a conductor that is connected to a 75 degree terminal to get any hotter than 75 degrees.

 

[Therealcrt]

Can somebody stop reciting every code article and just make a very simple response? You size your wire based on the over current protection device. There’s no need to get into the wires ampacity capability in 100 different situations. I have never looked at a piece of equipment and seen the amp rating but the looked at the lug rating to determine the wire amp rating to use. Quit over killing it if it’s 20a use #12 if it’s 30a use #10 if it’s 40a use #8 ect..

 

[ActionDave]

Can somebody stop reciting every code article and just make a very simple response? You size your wire based on the over current protection device.

No you don't.

There’s no need to get into the wires ampacity capability in 100 different situations.

There are ambient temperature correction factors, number of conductors in a conduit, termination temperature ratings, free air allowances, manufacture specs, and some more I can't think of.

I have never looked at a piece of equipment and seen the amp rating but the looked at the lug rating to determine the wire amp rating to use. Quit over killing it if it’s 20a use #12 if it’s 30a use #10 if it’s 40a use #8 ect..

Most of the time that works, but not all the time.