ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
New tool
by gfretwell - 10/22/20 12:08 PM
Where is Everyone?
by Bill Addiss - 10/17/20 07:04 PM
Beyond Belief
by gfretwell - 09/27/20 12:03 AM
New in the Gallery:
Facebook follies, bad wiring
FPE in Germany pt.2
Who's Online Now
0 registered members (), 18 guests, and 18 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
PVC vs Rigid pipe underground #48502 02/14/05 01:50 AM
Joined: Aug 2001
Posts: 545
A
aldav53 Offline OP
Member
I have come across more metal ridgid pipe underground (even wrapped with 20ml tape) that was rusted out. I've come to the conclusion that PVC is the way to go. Schedule 80 is so thick, it is probably almost as strong as metal ridgid. It should be legal to use at a 6" depth like metal ridgid, think PVC is 18" now.
The schedule 80 PVC also says ridgid on it, is it legal at 6"?
Any thoughts?


The Golden Rule - "The man with the gold makes the rule"
Work Gear for Electricians and the Trades
Re: PVC vs Rigid pipe underground #48503 02/14/05 04:16 AM
Joined: May 2003
Posts: 2,876
E
e57 Offline
Member
PVC isn't nearly as strong as RMC when it comes to shovels, pick axes, and drilling. Which is why it requires deeper burial. Always dig deeper that the landscaper would, someone once told me. Imagine a home owner or landscaper putting a pick axe through the side of service conductors.

Even a ditch-witch! From experiance I can tell you larger RMC makes a distinctive pinging sound when the teeth first hit it. Fair warning to stop. PVC you just see it come up, and hope its only a water line, as opposed to anything else, like gas or electric, or worse both! Even if you call before you dig, there is alway a chance of hitting something.

They unfortunately haven't found anything that will stand up to back-hoe abuse. Or the pavement saw.


Mark Heller
"Well - I oughta....." -Jackie Gleason
Re: PVC vs Rigid pipe underground #48504 02/14/05 07:17 AM
Joined: Jan 2003
Posts: 4,391
I
iwire Offline
Moderator
I agree with Mark (e57) RNC (Rigid Non Metallic Conduit) even schedule 80, does not come close the the strength of RMC (Rigid Metallic Conduit)

That said we use plastic almost exclusively underground for the same reason you brought up. Metal conduits rust out and even when they do not rust through they rust enough to make the conductors stick to the conduit so replacement can be tough.

I do not believe you will see the burial depths for RNC reduced. Take a look at Table 300.5

The burial depths for RNC range from 0' under a building to 24" under a parking lot.

You said;

Quote
It should be legal to use at a 6" depth like metal rigid,

That depends on the location, the burial depths for RMC range again from 0" under a building to 24" under a parking lot or road.

As a matter of fact there are only two places in the table where the burial depth differs between RNC and RMC.

1)In trench below 50-mm (2-in.) thick concrete or equivalent

RMC 6"

RNC 12"

2)The row titled "All locations not specified below"

RMC 6"

RNC 18"

Keep in mind very few locations are "not specified below" in the table.

You really need to study the table, if you are in an area with tough digging you can choose to run the RNC at 12" with 2" of concrete on top of it.

We do mostly commercial jobs and many times the specifications call for RNC at 24" depth with concrete encasement. [Linked Image]

Of course a machine is doing the digging. [Linked Image]

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

Featured:

2020 National Electrical Code
2020 National Electrical
Code (NEC)

* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
watersparkfalls
watersparkfalls
Washington...Not DC
Posts: 236
Joined: March 2005
Show All Member Profiles 
Top Posters(30 Days)
BigB 3
Popular Topics(Views)
270,742 Are you busy
204,967 Re: Forum
193,087 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3