Definition of 'Solid Rock' 300.5 Ex. 5

tortuga

Senior Member
Greetings all
We had a backhoe operator digging a trench say " I hit solid rock can't trench any deeper", a seasoned Electrician went out there and sad ‘yep’ and installed PVC pipe, and the contractor planned to encase it in 2" of concrete. Inspector said its not 'solid rock' its ‘layered rock’.

It got me wondering what is the legal definition of 'Solid Rock' as used in 300.5 Ex. 5?

Thanks in advance
 

Hv&Lv

Senior Member
I know in most construction contracts “solid rock” requires drilling, blasting, or rock hammers to remove.
Im not an inspector but I would say the man on the backhoe is a better judge of what his equipment will remove and what he considers solid rock.
Any definition leaves some ambiguity, as not all definitions are the same.
 

hbiss

EC, Westchester, New York NEC: 2014
I agree with @Hv&Lv. What does the inspector care as long as it's installed in a Code compliant manner? It's not like you are asking for an exception.

-Hal
 

tortuga

Senior Member
I agree with @Hv&Lv. What does the inspector care as long as it's installed in a Code compliant manner? It's not like you are asking for an exception.

-Hal
In some places there would be barely 3" of cover, its pretty remote rocky terrain, the inspector says the exception can only be used where 'solid rock' is encountered, so therefore a code violation...
It had just rained pretty heavy before the inspector was there and the trench was muddy and the rock was not clearly visible. I demonstrated with a large metal digging bar that it was solid rock.

Yeah @Hv&Lv that makes sense and will be helpful in making an argument.
 

hbiss

EC, Westchester, New York NEC: 2014
It had just rained pretty heavy before the inspector was there and the trench was muddy and the rock was not clearly visible.
So how does he know that it was "layered rock" if he couldn't see it? I don't know how you could settle this other than having him there while your backhoe operator tries to break it up.

I remember being on a job where they actually had a blasting contractor (who was on the site anyway) blast maybe ten feet of rock for a service. I seem to recall there would be about 3" of cover above the rock also.

-Hal
 
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infinity

Moderator
Staff member
Just my opinion but if you cannot dig it with a backhoe then it's solid rock. If the guy digging was using a hand shovel then maybe the inspector would have an argument.
 

kwired

Electron manager
Wouldn't "layered rock" be a geological definition of how it formed? Why should NEC care? I think the point NEC intended is if it will be difficult to trench through it they have given you other possible options.
 

hbiss

EC, Westchester, New York NEC: 2014
I guess "layered rock" would be shale, at least around here. A big excavator can usually rip it out. If the distance isn't that great you might be able to jack hammer a channel through it. If you have something like granite (which is very common also) only way is to blast, or a rock splitter.

Problem is who gets to decide how much money you have to throw at this?

-Hal
 

LarryFine

Master Electrician Electric Contractor Richmond VA
To me, "solid rock" means not crumbled rock. If there is one rock bigger than the hole, or wider than the trench, it's solid rock.

How does the inspector know the rock is layered? What would make it solid to him?

Rigid metal conduit allows only 6" cover without an exception.
 

infinity

Moderator
Staff member
To me, "solid rock" means not crumbled rock. If there is one rock bigger than the hole, or wider than the trench, it's solid rock.

How does the inspector know the rock is layered? What would make it solid to him?

Rigid metal conduit allows only 6" cover without an exception.
I agree, do we really need to call in a geologist if the backhoe won't go through the rock?
 

jap

Senior Member
I encountered solid rock one time driving a ground rod.

As I was driving it, it made a complete U when it hit the rock, came up behind me and poked me in the rear.

JAP>
 
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