334.80

[fireryan]

In reading 334.80 I have a question. Does this section prohibit running more than 2, 12-2 nm's in a bored hole if there is insulation in the wall? And if there is no insulation in the wall you can run as many as you want?

 

[Dennis Alwon]

In reading 334.80 I have a question. Does this section prohibit running more than 2, 12-2 nm's in a bored hole if there is insulation in the wall? And if there is no insulation in the wall you can run as many as you want?

Not exactly, if you bore a hole thru the top or bottom plates they usually get fire caulk. With the fire caulking in place there seems to be a buildup of heat so you must start to derate when you have more then 2 nm cables in the hole. Since NM cable has 90C conductors you may derate from the 90C column. This will basically allow 4 nm cables in a hole with fire caulk without affecting the ampacity of the nm.

Example.

4- 12/2 nm cables in a hole with firecaulk. Look at T. 310.15(B)(2) for 8 conductors. We see that 7-9 conductors we can derate at 70%. #12 @ 90C is good for 30 amps. 30 * .7 = 21 amps so we are good.
We can in fact have 3- 12/2 and one 12/3 without an issue for the same reason.

 

[fireryan]

Thanks. What about when it refers to thermal insulation? Is this refering to insulation in the wall cavaties?

 

[Dennis Alwon]

Thanks. What about when it refers to thermal insulation? Is this refering to insulation in the wall cavaties?

That is correct.

 

[augie47]

Dennis,
I have only applied this rule when the hole itself is "caulked" (sealed), not when there is only wall thermal.
(a mute point here as the building inspectors require that hole to be caulked)
Do you see it differently ?

 

[infinity]

We can in fact have 3- 12/2 and one 12/3 without an issue for the same reason.

In many cases you could run 4-12/3 cables through that same hole and still only have 8 CCC's.

 

[Dennis Alwon]

Dennis,
I have only applied this rule when the hole itself is "caulked" (sealed), not when there is only wall thermal.
(a mute point here as the building inspectors require that hole to be caulked)
Do you see it differently ?

Yes, and No
I am not sure what the difference is but the last paragraph in 334.80 states

Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).

so what is the difference between this paragraph and bundling without insulation. The net result is the same as T. 310.15(B)(2)(a) when bundled.

Also the paragraph above the one quoted states a hole that is to be fire- or- draft stopped using thermal insulation, caulk or sealing foam then you must derate. So yes, if the hole is filled with thermal insulation then you have the same issue as if it were filled with caulk.

 

[Dennis Alwon]

In many cases you could run 4-12/3 cables through that same hole and still only have 8 CCC's.

This is true also. I didn't feel the need to cover every scenario as there are other possibilities also.

 

[kwired]

You must also consider what is the load on the conductors, just like you would if you were running the conductors in a raceway.

If you have known fixed load less than 15 amps on several 12 AWG cables you could run more than 4 12-2 cables. You could in fact run 10 cables through the same hole. This could be the case with say several baseboard heater circuits.

I think I should do this if I ever get the chance and educate the inspector if he jumps all over it without finding out what exactly is going on

Many inspectors will just see a lot of cables in a hole and get all bent out of shape without finding out more about the situation.

 

[infinity]

This is true also. I didn't feel the need to cover every scenario as there are other possibilities also.

True. I was just pointing out that the "can't run more than three cables in that hole" code enforcement is completely incorrect.

 

[Dennis Alwon]

You must also consider what is the load on the conductors, just like you would if you were running the conductors in a raceway.

If you have known fixed load less than 15 amps on several 12 AWG cables you could run more than 4 12-2 cables. You could in fact run 10 cables through the same hole. This could be the case with say several baseboard heater circuits.

Can you quote an article that supports what you say. I hear you but that is not what the code states.

 

[infinity]

If you have known fixed load less than 15 amps on several 12 AWG cables you could run more than 4 12-2 cables. You could in fact run 10 cables through the same hole. This could be the case with say several baseboard heater circuits.

Can you quote an article that supports what you say. I hear you but that is not what the code states.

I think that he meant this:

#12 conductors = 30amp @ 90?
10-2 wire cables = 20 CCC's
10-20 CCC's = 50% derating
30 amps * 50% = 15 amps
OK for 15 amp OCPD.

 

[Dennis Alwon]

I think that he meant this:

I believe you are right. Thanks.

 

[fireryan]

Good info guys. Thanks. Fow whatever reason this new section gives me fits

 

[jxofaltrds]

What is (are) the minimum spacing requirement(s) in 334.80?

Can sealant be used as the spacing?

When was the last time that you saw more than 9 CCC in a hole?

I see this, 334.80, as hard to enforce.

I think that you would 'burn' the insulation off the wire trying to pull that many NM wires through a too small of hole.

 

[kwired]

I think that he meant this:

#12 conductors = 30amp @ 90?
10-2 wire cables = 20 CCC's
10-20 CCC's = 50% derating
30 amps * 50% = 15 amps
OK for 15 amp OCPD.

Should be ok for 20 amp OCPD if supplying a fixed load that is less than 15 amps. The fixed load will not change no matter what the OCPD is. Which is what I was getting at in my post. 310.15 is about conductor ampacity not overcurrent protection. Many inspectors would see ten cables in the hole(s) and immediately say you can't do that. But there are conditions where you could. They need to question what is going on before jumping to conclusion that it can't be done.

 

[infinity]

Originally Posted by infinity
I think that he meant this:

#12 conductors = 30amp @ 90?
10-2 wire cables = 20 CCC's
10-20 CCC's = 50% derating
30 amps * 50% = 15 amps
OK for 15 amp OCPD.

Should be ok for 20 amp OCPD if supplying a fixed load that is less than 15 amps. The fixed load will not change no matter what the OCPD is. Which is what I was getting at in my post. 310.15 is about conductor ampacity not overcurrent protection. Many inspectors would see ten cables in the hole(s) and immediately say you can't do that. But there are conditions where you could. They need to question what is going on before jumping to conclusion that it can't be done.

How is that possible with an adjusted conductor ampacity of 15 amps?

 

[Dennis Alwon]

Should be ok for 20 amp OCPD if supplying a fixed load that is less than 15 amps. The fixed load will not change no matter what the OCPD is. Which is what I was getting at in my post. 310.15 is about conductor ampacity not overcurrent protection. Many inspectors would see ten cables in the hole(s) and immediately say you can't do that. But there are conditions where you could. They need to question what is going on before jumping to conclusion that it can't be done.

This is what I thought you were saying but I thought I read it wrong. You cannot have 10 CCC in a hole with a 20 amp device and say 12/2 NM. If you are saying that you can then I would definitely disagree. It doesn't matter if the load on every wire is one amp or 20 amps. Enlighten us.

 

[kwired]

This is what I thought you were saying but I thought I read it wrong. You cannot have 10 CCC in a hole with a 20 amp device and say 12/2 NM. If you are saying that you can then I would definitely disagree. It doesn't matter if the load on every wire is one amp or 20 amps. Enlighten us.

Sorry, you are right - with most circuits.

I've been sizing a lot of motor circuits lately and have some of that on my mind. That is one place where the overcurrent device could be 20 amps or more on a 12 AWG and still have a circuit ampacity of less than 15.

Conductor ampacity and overcurrent protection are not as related with motors as they are for other loads.

I still don't doubt that there are inspectorsout there that see ten 12-2 cables in the same hole immediately assume that you can't do that. In my example it would have still been acceptable if protected by 15 amp OCPD's.