I find myself in a bit of an argument with our electrical contractor.
We are burying <600V 4/0 aluminum service entrance cableEdit- my mistake, wire used is URD], and in some locations are having trouble achieving the 24" of ground cover necessary for direct burial.
We are looking at using RMT or IMT at a minimal burial depth, which according to table 300.5 looks to be just 6". Our electrician seems to think that a concrete cover must be added as well, though the table seems to show that wouldn’t gain us anything, when using RMT or IMT (for direct burial, it reduces ground cover needed from 24" to 18" with 2" of concrete.)
Looking for confirmation or any additional info I may be missing.
Ask your local building official/inspector. They are the only ones that can approve your installation.
You have not supplied enough information. What surface are you running under? What type of wiring?
SE cable is not listed for direct burial.
Are you encountering rock? If so note #5 may apply.
Thank you for the replies. I will check with my local inspector.
The issue is solid rock; I can’t make much of a dent in it with the excavator, demo hammer, or demolition grout. I have achieved 6" in all locations, however, so I don’t believe that note 5 will apply, unless I am mistake on another point.
The wire is URD triplex 4/0 & 2/0. I’ve run about 2000’ of it here in the last year.
This is in a campground. Most are in areas not subject to vehicular traffic. Where exposed to traffic, we are burying under 24" of cover, with PVC conduit.
Thankfully, the areas where I am running into ledge are in areas not subject to vehicular traffic, so it appears I only need 6" of cover, with RMC or IMC. As I said, I will be checking with the local authority for final word.
Thanks again for the help.
FYI- In those areas where you have “achieved 6 inches” be aware that the cover requirement is 6 inches and not the depth is to be 6 inches. Very common mistake when someone digs a trench. They dig a 18" trench and place a tradesize 4 non-metallic raceway into it and now they only have approximately 14 " of cover…
Based on what you have stated (limited info) it appears you can only get 6 inches of depth…the cover is required to be minimum of 6 inches…so depending on your RMC or IMC you intend to use…anything 1/2 or larger would mean you will have less than 6 inches of cover…this may by why the electrician is talking about the concrete in order to reduce your minimum cover to 4 inches with 4 inches of concrete…if you can’t even meet that then note 5 intends that you can’t meet any of the depth of cover requirements in the table so it is giving you an option.
Just food for thought…
Thank you. I am aware of coverage requirements, though I see now that my previous posts were written poorly in that regard. I have at least 12" of total depth in all areas, leaving me with more than 8" of cover with a bed of sand (unnecessary underneath the RMC) and a 2.5" conduit.
Incidentally, I had the inspector come in and he OK’d the plan with no concrete, and a minimum of 6" cover over the RMC.
Also, my supply house doesn’t stock IMC, so RMC is the 'script.
Thanks again all for the replies.