Rubber Cord Ampacity

[oldsparky52]

... but I'm thinking the equipment being listed and identified for use with such conductors is going to be a key no matter what.

I think that is exactly what needs to be looked at. But, what would the listing have to say, that the terminations are rated for use at the 75c ampacities given in Table 400.5?

 

[Dennis Alwon]

Does 110.14(C)(1)(b)(2) cover this?



Not quite clear because we are still talking about a cord rated 75C, but I'm thinking the equipment being listed and identified for use with such conductors is going to be a key no matter what.

I still don't get it. If the rubber cord is rated 240 amps at 75C what is the issue since the equipment is rated 75C. I would think that Chapter 4 is either in conflict with 110.14 or it can override it.

 

[don_resqcapt19]

90C can be used for de-rating and it often comes into play

But you can't use it at a 90°C ampacity at the terminations ... it is a heat issue....the same heat issue occurs when you use the rubber cord ampacities from Article 400 at a termination.

 

[Dennis Alwon]

But you can't use it at a 90°C ampacity at the terminations ... it is a heat issue....the same heat issue occurs when you use the rubber cord ampacities from Article 400 at a termination.

Yes but I thought you were saying I could not use a 250 amp or even a 225 amp overcurrent protective device even at 75C

 

[kwired]

I still don't get it. If the rubber cord is rated 240 amps at 75C what is the issue since the equipment is rated 75C. I would think that Chapter 4 is either in conflict with 110.14 or it can override it.

The insulation on the cord is what is rated 240 amps 75C.

Kind of doesn't make sense yet it does - land 3/0 THHN/THWN in a lug and most agree the conductor and lug are 75C rated @ 200 amps.

Now land a conductor same size but with insulation rated for 240 amps - does the lug operate hotter then if there were only 200 amps of current?

I think it does, how does this work with the 75C rating of the lug I really don't have an answer other then the lug/device may need to be listed for use with said cord conductors - which will typically be fine stranded conductors and will not be compliant in just any ordinary lug either.

 

[Dennis Alwon]

Now land a conductor same size but with insulation rated for 240 amps - does the lug operate hotter then if there were only 200 amps of current?

How is that any different than landing a 200 amp wire on a panel rated 400 amp or using a 400 amp panel. If the equipment is listed for a 250 amp breaker then it seems the cord should be good. I wonder if the insulation on the cord is rated 240 amps but the wire in the cable may well be thhw. That would make sense

3/0 is 3/0 so either this is special insulation or I don't get it

 

[kwired]

How is that any different than landing a 200 amp wire on a panel rated 400 amp or using a 400 amp panel. If the equipment is listed for a 250 amp breaker then it seems the cord should be good. I wonder if the insulation on the cord is rated 240 amps but the wire in the cable may well be thhw. That would make sense

3/0 is 3/0 so either this is special insulation or I don't get it

Landing 200 amp wire on a panel rated 400 amp is ok as long as you don't load it to more then 200.

Here we are sort of the other way around with things - higher rated conductor ampacity then the termination - which with 310 selected conductors can happen - but at the lower rating dictated by termination temperature.

Then again often termination temp is dependent on using conductor as a heat sink, maybe the fact the conductor in the cord is 240 amps rated @ 75C allows you to sink more heat into the conductor and still be within 75C rating?? Seems to me same conductor size and type is going to create same heat at termination though at same current levels.

 

[Dennis Alwon]

Landing 200 amp wire on a panel rated 400 amp is ok as long as you don't load it to more then 200.

Here we are sort of the other way around with things - higher rated conductor ampacity then the termination - which with 310 selected conductors can happen - but at the lower rating dictated by termination temperature.

Then again often termination temp is dependent on using conductor as a heat sink, maybe the fact the conductor in the cord is 240 amps rated @ 75C allows you to sink more heat into the conductor and still be within 75C rating?? Seems to me same conductor size and type is going to create same heat at termination though at same current levels.

I don't understand the other way around. We are using 3/0 conductor rated 240 map- next size 250 amps- if the panel is rated for a 250 amp breaker than why can I not use the 3/0 cord which is rated 240@ 75C..:?

I must be missing something here

 

[oldsparky52]

I think some of it is that the listing company testing is done with Table 310.15(B)(16) ampacities and no one has tested the equipment with Table 400.5(A)(2) ampacities.

I have to wonder if the higher ratings for the cord are because it is not installed in conduit but in open air or on the ground (look at the ampacities of conductors in free air, even higher than cord ampacities).

That brings me to another couple of questions, may you install a cord in conduit, and if you do, must you switch to Table 310.15(B)(16) ampacities because of the cord being in a conduit?


Edit: What if you use a cord rated for direct bury, must you switch to Table 310.15(B)(16) ampacities?

 

[kwired]

I don't understand the other way around. We are using 3/0 conductor rated 240 map- next size 250 amps- if the panel is rated for a 250 amp breaker than why can I not use the 3/0 cord which is rated 240@ 75C..:?

I must be missing something here

The question is why is same lug only good for 200 amps even though a THHN insulation is good for 225 if we didn't have to use it at 75C value because of the termination.

Now with the cord we can put more current through same circular mils, which is just as understandable as 90C insulation having higher ampacity then 75C insulation yet you don't see termination temp rising if we run more current through same circular mils of conductor and same termination type regardless of what kind or if there even is any insulation on the conductor?

 

[Dennis Alwon]

I don't see this as a lug question since both are rated 75C. Why do we keep talking about the lug being rated 200 amps. Let's say the lug is rated 300 amps at 75C---Can I install a 250 OCDP ( urely those lugs are rated for 250 amps) on the 3/0 wire from the cord? Also assume all terminations are rated 300 amps. That is my question, I am sorry I still don't get where you are going with this-- It is obviously my issue with understanding---

 

[oldsparky52]

No one has paid for the listing company testing. If someone paid for the testing of the cord conductor at the ampacity of the Tables in 400, and it passed, we would be able to do it. That is my understanding, no one has done the testing, therefore, it is not allowed.

Someone (I can't remember if it was someone at UL or a wire manufacturer or breaker manufacturer) told me (about 10 years ago) that terminations were tested with a 4' conductor at the ampacities from Table 310.15(B)(16). So that was the reasoning behind 110.14(C). Someone else had mentioned you had to make sure the enclosure was rated for the heat, which I didn't understand but because of 110.14(C) I didn't pursue it because I had more important things to do and it seemed I was getting the run around.

Edit: My gut tells me that it will work just fine, because around here, up until 2008, marinas were wired using the ampacities in the Tables in chapter 400 and as far as I know, there have been no problems.

 

[Dennis Alwon]

If it wasn't tested at the Table ratings then how did they get those numbers? It must have been tested but the question is why is it higher in rubber cord than in conduit? Maybe it breathes better, IDK

 

[Dennis Alwon]

I just sent an email to Dave Mercier from Southwire who is an alternative on the CMP for article 400. I suspect he is going to agree with you all.

 

[oldsparky52]

If it wasn't tested at the Table ratings then how did they get those numbers? It must have been tested but the question is why is it higher in rubber cord than in conduit? Maybe it breathes better, IDK

IDK either, but my guess would be the terminations and conductor ampacities are two different tests. Tests cost a lot of money, and so few people use cords the way we are talking about, it's not worth the expense. Just guessing.

 

[oldsparky52]

I just sent an email to Dave Mercier from Southwire who is an alternative on the CMP for article 400. I suspect he is going to agree with you all.

I know you will share what Dave has to say, I'm going to put cheese in my mouth and wait with baited breath for the info.

 

[Dennis Alwon]

I know you will share what Dave has to say, I'm going to put cheese in my mouth and wait with baited breath for the info.

I know it is illegal to kill a crow but I may have to eat some--- we'll see. Honestly it does seem odd to allow 241 amps for the cord but hey- why is the table there?

 

[wwhitney]

If you compare the following two columns of ampacity values:

(1) (2011) Table 400.5(A)(2), "Ampacity of Cable Types SC, . . . W", the 75C column F (3 current carrying conductors)
(2) (2011) Table 310.15(B)(20) "Ampacities of Not More Than Three Single Insulated Conductors Supported on a Messenger", the 75 C column

Then you will find that the numbers are very close.

My conclusion is that the ampacities for cord in Article 400 are based on free air conditions, because cords are typically not enclosed. While different types of 75C insulation might have different ampacity values, because the insulation's thickness or R-value differs, I think that is a small effect. It could, however, explain the small differences in the above comparison.

It stands to reason, then, that when you are terminating a cord on a piece of equipment in an enclosure, since the cord is not longer in free air, the lower ampacity values of Table 310.15(B)(16) apply, as specified by 110.14(C)(1).

Cheers, Wayne

 

[GoldDigger]

And then the 10% or ten feet rule might apply and save you.

 

[wwhitney]

And then the 10% or ten feet rule might apply and save you.

Huh? I thought (2011) 310.15(A)(2) Exception doesn't apply at terminations. If it did, 110.14(C) would be meaningless.

Cheers, Wayne