Spacing between new underground conduits in trench

Status
Not open for further replies.

clint2000

Member
I am wondering if there is a minimum space required between rigid steel conduits installed in a new trench. I was reviewing annex B of the NEC but am not sure if those specified distances are an installation requirement for physical conduit clearances or for the calculation of conductor ampacities. We are clear on the ampacities but not sure on the physical clearances required. We work off of engineered drawings for the most part that details the trench and conduit but this time the engineer stated something like; install conduits in trench per code and reiterated that verbally when asked. The application is (1) 4? RSC and (1) 3? RSC to be installed in a common trench. They both are 3 phase 4 wire with 5th conductor as grounding conductor. They will be installed side by side on the same plane of the trench buried at 24?. There will be no other cables, conductors nor conduits in this trench. The voltage of both of these are 120/208 volt.

Thank you
 

sparkyboys

Senior Member
Location
Columbus, ga
the use of chairs would be as minimum as you can get, which is about 1 1/2". but i do not think there is a minimum gap between conduits nderground, unless next to water or gas piping
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Many of the figures associated with ampacity tables show a spacing of 7-1/2 inches. Some people have interpreted that as being a code minimum spacing. It is not. There is no minimum spacing. The code would allow you to wrap the conduits around each other like the strands in a wire, if you could manage to build it that way. ;)
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Despite what Charlie mentioned, our inspector still likes to call us on conduit spacing in a trench. I need to see if I can find the inspection report to see which code he cited...:confused:
 

Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
Thanks for killing some nasty urban legend! People need to go back and read "Charlie for reading the NEC" -

It doesn't say what you think it says, nor remember it to have said, and certqinly not what you want it to say.If by chance you are an instructor, it doesn't say what you've been teaching that it says.....

Pipe in a ditch is just that - pipe in a ditch for the NEC;HOWEVER be aware of what the scope of the contract says (others have already bought the urban myth,) and you should charge accordingly if they won't budge on the issue.
 

Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
Despite what Charlie mentioned, our inspector still likes to call us on conduit spacing in a trench. I need to see if I can find the inspection report to see which code he cited

Take your inspector by the hand and show him 300.50

If you go to Annex B the first few lines are -

This annex is not part of the requirements of this NFPA document but is included for informational purposes only

Remind the inspsctor that his job is to enforce code and the legal amendments per state and local, not how he feels.
 
Status
Not open for further replies.
Top