Schedule 80 vs 40

[macmikeman]

Not only is it unreasonable to think a schedule 40 under a residential concrete driveway is subject to physical damage, it is also unreasonable to have to bury it so deep under the driveway for the same reason. Its more unproven myth creeping into the codebook from the zealots. Right under 4" of concrete slab is protected imho. The slab would be cracked and moved about by overweight vehicles (and how often does a residential driveway slab suffer from this malady?) long before the schedule 40 conduit gets damaged by the fill gravel pressing onto it. Under a road may be a different thing altogether.

 

[jxofaltrds]

??

Too many 5's.

I thought OP said this was not a POCO service install.



Okay, you lost me. ( I do understand the analogy, but not how it applies here). Any install can fail, the question seems to be " What is required by the NEC for reasonable safety under the conditions described?".

Not only is it unreasonable to think a schedule 40 under a residential concrete driveway is subject to physical damage, it is also unreasonable to have to bury it so deep under the driveway for the same reason. Its more unproven myth creeping into the codebook from the zealots. Right under 4" of concrete slab is protected imho. The slab would be cracked and moved about by overweight vehicles (and how often does a residential driveway slab suffer from this malady?) long before the schedule 40 conduit gets damaged by the fill gravel pressing onto it. Under a road may be a different thing altogether.

I guess I do not understand Table 300.5.

 

[cpal]

I guess the answer to my question is there is no nec requirement to use 80, and i don't see any requirement in the ma. amendments. I just believe the inspector was misinformed about the requirements, if I just threw direct burial in the ditch and ran no pipe then he probably wouldn't have mentioned it. It wasn't a big deal to change it this time.

Well it's awful nice of you to have changed out to sch 80, but there is no reason to use it in the case you described. Not in the NEC or the MEC. If as Augie mentioned it is not a POCO issue.

A code reference would have helped!

 

[jxofaltrds]

Well it's awful nice of you to have changed out to sch 80, but there is no reason to use it in the case you described. Not in the NEC or the MEC. If as Augie mentioned it is not a POCO issue.

A code reference would have helped!

This is probably the ONLY time that I think that it is 'required' in a residential application.

 

[hurk27]

Too many 5's.





I guess I do not understand Table 300.5.

Don't feel like the Lone Ranger, this table has always made no sense to me, well at least some of it, and PVC requirements in it are one of them, we can put it at 4" if under a 4" slab of concrete, but add vehicle traffic and it jumps to 24" for non dwelling and 18" for dwelling concrete or not?

 

[jxofaltrds]

Don't feel like the Lone Ranger, this table has always made no sense to me, well at least some of it, and PVC requirements in it are one of them, we can put it at 4" if under a 4" slab of concrete, but add vehicle traffic and it jumps to 24" for non dwelling and 18" for dwelling concrete or not?

I think that we both know what it means.

 

[hurk27]

I think that we both know what it means.

Yea they didn't want to take the time to add another section for concrete slab with vehicle traffic I would not have a problem with PVC under a slab with vehicle traffic at maybe 12" for non dwelling and 6" for dwelling or at the most 14" non and 8" for dwelling, I have seen PVC under concrete drives after over 20 years and never saw a problem.

The only problem I have seen is at the edge of the slab where a truck drove off the slab and got stuck hitting the PVC, and even then it didnt damage the PVC it just put black marks on it, but it could have, but that is a "what if"

 

[kwired]

Yea they didn't want to take the time to add another section for concrete slab with vehicle traffic I would not have a problem with PVC under a slab with vehicle traffic at maybe 12" for non dwelling and 6" for dwelling or at the most 14" non and 8" for dwelling, I have seen PVC under concrete drives after over 20 years and never saw a problem.

The only problem I have seen is at the edge of the slab where a truck drove off the slab and got stuck hitting the PVC, and even then it didnt damage the PVC it just put black marks on it, but it could have, but that is a "what if"

but the portion not under the slab falls under a different category in the table and whether is is the actual table or the one some of us would like to see the racway or conductors should never be hit by a truck driving off the slab.

 

[Eyeseeitall]

Regular plumbing PVC (white stuuf from big box store) is often not listed for electrical applications. Schedule 80 is required as previously posted due to 300.5/d/4. It needs protection due to being contact with the gravel.

The amount of frost heave/movement in the soil can cause a significant amount of damage; I work in a village where drainage culverts in driveways when not installed correctly (with at least 4" of base over them) will heave through the apshalt creating a speed bump at the entrance to the driveway; this happens frequently. I could only imagine what it would do to unprotected sheathed wire in a year or two.

 

[roger]

Regular plumbing PVC (white stuuf from big box store) is often not listed for electrical applications.

It never is

Schedule 80 is required as previously posted due to 300.5/d/4. It needs protection due to being contact with the gravel.

Where can we find this?

The amount of frost heave/movement in the soil can cause a significant amount of damage; I work in a village where drainage culverts in driveways when not installed correctly (with at least 4" of base over them) will heave through the apshalt creating a speed bump at the entrance to the driveway; this happens frequently. I could only imagine what it would do to unprotected sheathed wire in a year or two.

I don't understand, are you saying UF or other types of direct burial conductors can not be used unless it is in a raceway?

Roger

 

[Eyeseeitall]

Assuming you are talking about using UF cable directly burried...

Schedule 80 is required where 'subject to physical damage' :NEC 300.5 d,4
It would be considered subject to physical damage due to: NEC 300.5 f

UF cable still needs to meet the requirements of 300.5... as per 340.10, 1

If UF was burried 18 below grade/under the driveway and the ground around it was soil, not gravel, it would be okay... but I didn't see that as the question. If he was using PVC, pressumably because the soil wasn't acceptable for direct burial, it needs to be schedule 80, or another method of protection as described in 300.5 d,4.

 

[hurk27]

Lack of knowledge of the physics is the reason why some make requirements like this, first soil, gravel, or just about any loose material distributes the weight out from the point of pressure, it does not place pressure vertically straight down, sand is about the best with a 3/2 weight distribution, so placing a 1,000Lb of force per inch 18" above a pipe will only result in very little pressure on the pipe, I would think less then 100lb's maybe a engineer could chime in on this, this is the scientific facts that the NEC uses for the reason of allowing wiring methods under drives and roadways, road ways that might get heavier loads require a little deeper thats all, the table in the NEC has taken accounting for the spread of the weight already per the requirement of the depth.

I challenge any inspector who make a requirement like this to place a fragile egg at 18" in sand then drive over it with their truck, then dig it back up, bet it wont be broken! I've seen this done.

 

[roger]

Schedule 80 is required where 'subject to physical damage' :NEC 300.5 d,4

300.5(D)(4) would only be applicable if the raceway is subject to physical damage and if the raceway is installed per Table 300.5 subject to physical damage is not a concern.

It would be considered subject to physical damage due to: NEC 300.5 f

This is where I am asking for some substantiation. Where can we see that gravel can be considered a reason for concern? If gravel can not be in contact with schedule 40 PVC there are multitudes of slab on grade installations that are in violation.

If UF was burried 18 below grade/under the driveway and the ground around it was soil, not gravel, it would be okay... but I didn't see that as the question. If he was using PVC, pressumably because the soil wasn't acceptable for direct burial, it needs to be schedule 80, or another method of protection as described in 300.5 d,4.

Please offer a little more back up to your stance.

Roger

 

[Eyeseeitall]

If its in contact with gravel it needs to be protected per the NEC and that fact is defined in the NEC. Both code references are above. Not much else to say.

Show me a reference saying schedule 40 PVC is okay in this application?

 

[Twoskinsoneman]

If its in contact with gravel it needs to be protected per the NEC and that fact is defined in the NEC. Both code references are above. Not much else to say.

Show me a reference saying schedule 40 PVC is okay in this application?

The NEC doesn't quite say that. 300.5(F) says you shall not backfill with large rocks etc. where they could damage raceways. It then says where necessary to prevent damage...protect the raceway with sand etc.

Your leap to "contact with gravel" = subject to damage is a stretch...

 

[roger]

Your leap to "contact with gravel" = subject to damage is a stretch...

Yes it is and once agin I'll point out that when roughing slabs I have never used sched 80 PVC.

Roger

 

[Eyeseeitall]

I disagree. Where the conductors are located such that they will be subject to physical damage, they shall be installed in RMC, IMC, Sch 80, or equivalent. In your opinion you are saying it is not subject to physical damage, in my opinion, it is.

Driveway pressure and frost heave are all the movement I need in my mind to be concerned.

 

[kwired]

I disagree. Where the conductors are located such that they will be subject to physical damage, they shall be installed in RMC, IMC, Sch 80, or equivalent. In your opinion you are saying it is not subject to physical damage, in my opinion, it is.

Driveway pressure and frost heave are all the movement I need in my mind to be concerned.

I have never seen frost heave be a problem for buried raceway. Raceway emerging from ground yes. Sch80 is not answer for that either, although it may still be needed for other physical protection, expansion fittings are what is needed for this protection.

 

[iwire]

I have never seen frost heave be a problem for buried raceway. Raceway emerging from ground yes. Sch80 is not answer for that either, although it may still be needed for other physical protection, expansion fittings are what is needed for this protection.

Exactly.

 

[Eyeseeitall]

Everyone here has way more field experience than I do; I guess what I am trying to get at is do you think I am interpreting the NEC incorrectly? And if yes, why?

I understand years of experience may tell you one thing, but the NEC may say another. I am trying to get at the root of the issue.

Is laying Sch 40 as a raceway for UF cable in a trench with gravel (rarely see trenches w/o gravel), under a driveway (presumably 18" under the driveway), something that requires 'protection' per the NEC or not?

I have referenced why I believe Sch80 is required, but I haven't seen a referenced counter-point short of 'my experience'; I can't reference your opinion/experience the next time this comes up.... I need a code reference. Show me the wording/code reference that would free me from making the decision I referenced above.

I have an open mind- unchain me from this restriction