ECN Forum Forums Code Related Discussion NEC & other Code issues Manholes

I don't want you to take this the wrong way but it might be informative for you to look this stuff up yourself.
Learning how to use the table of contents and the index is a handy skill.

I am not being cranky here, just trying to help you improve your skills.

akmaster:
You said..."the specs call for a 0.3% slope TOWARDS the manhole.."

Based on that sentence, it sounds like this project was designed by a Lic Design Professional, and hopefully reviewed and approved by an AHJ.

That said, is the .3% slope spec'd for the duct bank, or the grade surrounding the manhole?

I have not seen any spec that stated any slope for duct banks. There is a grading spec which slopes the grade away from the hole to reduce (not prevent) runoff.

BTW, manhole covers are usually not bonded, a few jobs called for the ring to be bonded. If you think about this, the ring is cast in the concrete, which is buried in the earth!

@ greg..no offense taken..I do not have my code books onsite yet..and can look things up via internet but mostly just seeking support for what i find..i apprecite your help.

@ hotline..the specs call for the ductbank to be at .03% slope oriented to the electrical manholes..

the entrance to these manholes is a large metal ring with a cover that says "Electrical" but contain medium voltage feeders...the ring and plate are part of a concrete lid that sits on top of the 8x8x8 manhole with a separate base...the manhole cover is isolated from the earth..

will post a pic..

thanks

gw

btw..i found nothing in the code about sloping to the manhole for grade or ductbank...it is a design by a PE....he said it was in the code..

regards,

greg

I would think you would always want the slope, at grade, away from the manhole

Greg:
Based on .3% slpoe, does this sound right??

500' run, sloped at .3% equates to 1.5' end to end.
Now if the spec says 'oriented to the 'holes, you would have 9" of pitch from the center of the run to each 'hole.

I had a 13.2 KV job last fall at a college campus; 5" PVC, 4 over 4 over 4, concrete (red) and some rebar, and I don't remember any pitch in the specs. Five 'holes & a new substation added, 4 over 4 same encasement to a new building and ties into the loop. I'll have to dig out the plans/spec if they are still in the office, or call the EC.

Greg,

IMHO, the old National Electrical Safety Code states in it that Safety signs have to meet ANSI standards. ( The book lists several standards.) So my guess is if there is High Voltage in that manhole then a sign stating that would be required.

Harold:
I would like to see if that applies to man holes, as they are not accessable without proper tools.

Rooms, switchyards, etc., that have a fence that can be climbed, or a door that may be unlocked/forced require signage.

Hi,
Thanks for the helpful responses. I am also looking for the article on spacing of conduits containing medium volatge cables and how close other conduits can be to those conduits.

Fiber and or data would be included in these distances as well would they not?

I am researching duct bank spacing requirements for medium voltage runs..

Thank you for your help,

Greg

310.60 is where the NEC talks about ducts but the general rule is 7.5" between raceways and using that spacing you use the tables 310.77 - 310.80 for the ampacity of MV conductors.