Physical Damage

[iwire]

I can't help but to be reminded of Scott's experience with SE cable services vs. ones in conduit in the aftermath of a big o'le ice storm . the cable installations fared far better than did the conduit installations, . The physical damage was ,IMO , severe,. yet the exposed cable was superior.

Great point but we don't let facts cloud our fear of NM cables here. :grin:

 

[mivey]

Great point but we don't let facts cloud our fear of NM cables here. :grin:

Yeah, they survived the ice storm only to have their house burnt down by the NM cable. We need AFCI devices for service drops. :grin:

 

[Master of ONE]

Ok, so ive read all of your replies on "physical damage" and have come to the conclusion that exposed conduit of any sort are exposed to "physical damage" If this is so, then would a schedule 40 pvc conduit in an area designated for pool equipment where only a maintenance person would enter be required to be changed to schedule 80 due to "physical damage" conditions?? What would the "physical damage" risk be here in an area where there is no regular traffic?

 

[Hendrix]

Ok, so ive read all of your replies on "physical damage" and have come to the conclusion that exposed conduit of any sort are exposed to "physical damage" If this is so, then would a schedule 40 pvc conduit in an area designated for pool equipment where only a maintenance person would enter be required to be changed to schedule 80 due to "physical damage" conditions?? What would the "physical damage" risk be here in an area where there is no regular traffic?

Corosive conditions.

 

[kwired]

Corosive conditions.

Sch 40 and Sch 80 PVC conduit are the same when it comes to corrosion resistance

Corrosion is not physical damage anyhow it is chemical damage.

 

[Master of ONE]

So where would schedule 40 pvc be legal if exposed to the elements? NEC is so brief about explaining "areas exposed to physical damage". I understand using schedule 80 where there is vehicular traffic or public traffic but how about a residential backyard? or an interior mechanical room? Is there a definite answer as to where these areas of "physical damage" are?:-?

 

[hurk27]

I view "subject to physical damage" as follows:
Exterior wiring or conduits within 18" of finish grade unless located in a parking lot, then 36" above grade.
Interior wiring that does not follow a framing member and properly secured. If a wire runs perpendicular through a stud space in an unfinished area, it needs protected. Exception: floor joist spaces that are a minimum 6'8" above finish floor.
All roof top installation.
Each inspector will be different until it is spelled out in the code.

The stud spaces where a wire runs perpendicular has been ruled on by the state here in Indiana, as long as there is a surface (I.E. drywall) on one side it is not subject to physical damage such as in garages and basments like around the stairs, this was done at a state meeting in Merriville by Raleigh Kouns.

 

[hurk27]

I have been doing risers that are not supporting the service drop in PVC for a while in our area, allowed by our state code and our POCO, the idea of this is because your not going to keep a falling tree or large branch from taking down a service drop, I don't care if you bolt the attachment insulator to a 4x4 across all the stud in the gable, it will take the gable out of the house, and I have seen it do it, so I found that designing it to fail in a more safer manner is much better, by installing PVC, and using the PVC two hole straps, will allow the riser to pull off the wall without damaging the house, or in most cases the wire or meter, it will break the pvc right at of above the meter, and all I have to do to repair it is to disconnect the drop, unhook the conductors from the meter remove the old male adapter glue a new one on and re-strap it to the house, re install the attachment insulator re-hook up the drop and they are back in power in less then 30-45 minutes, the wire don't even short out on the meter as the male adaptor protects it, and many times they even still have power when I get there, now with RMC, most times meter is damaged, riser is bent, service conductors has shorted in the riser or on the broken hub, and a few times it started a fire.

I had one inspector try to say that PVC couldn't be used and it had to be RMC because it was subject to be damaged, so a quick call down state got him straight right away, he then tried to make me use sch. 80, state again over ruled him, so I asked him why he thought it was subject to be damaged, kidding I said what, maybe an airplane might hit it? he wasn't amused but passed it and left.

 

[e57]

Great point but we don't let facts cloud our fear of NM cables here. :grin:

Fear is a reaction to danger... Since we know the danger - we wouldn't chew on it - would we? But a squirrel would..... Cause it doesn't know the danger. If you can't see them - you don't know its there... Making the idiot blindly chopping/cutting into walls no smarter than a squirrel. But none of this changes the fact that NM is nothing more than glorified extension cord.... (Which can take more abuse?)

 

[iwire]

Apparently SE cable is better than pipe as Scott was able to easily repair the SE services but had to start from scratch with piped services.

 

[hurk27]

Keep in mind when we start saying N/M is subject to be damage, then think about all the lamp cords you have around your house just laying there, many times can be stepped on, dropped on, children can grab them, dogs can chew them (once), think of that before you start making requirements for N/M