Underground Conduit Tid-Bits


Senior Member
There has been a few questions about UG conduit installations lately.I am not going to attempt to answer any of those question,I'll just list a few "Do's" I'm famiiar with.

This will be talking about conduit serving 600 volt users and less,2001 voltand greater is covered in the code but some of this still applies.

When conduit is encased in concrete ductbanks,,,,

1. Maintain a minimum 2" separation between conduits walls (not centerline).

2. Maintain a minimum of 3" concrete cover(topside) and 2" on sides and bottom.

3. Allow 20%, 2" spare conduits with pull wire/rope.

4. Position conduits thus
a, High current users to the outside
b, control conduits in center
c, spare user conduits towards center
d, spare conduit interspersed at random.

5. Stub up field conduits with a concrete kick pad that is sloped so water doesn't set/stand around conduit.Stub up with exposed cplg and plug for later extension.

6. Conduit stub ups inside of buildings should be flush with finished floor with recessed plug and cplg.

7. Stub ups below SWGR,MCC and any open bottom floor cabinets that are feeding to classified areas may or may not require conduit seals,,the use of a Sealing Hub(See Cooper Crouse-Hinds Catalog) is a good application here.

8. Conduit runs and duct banks should never infringe on the cone of deflection imparted by poured grade beams,piers,spread footings etc.Let me try to explain the "cone of deflection" in you look at an elevation or cross section of a poured concrete structure and draw a 45 degree line off and from the outer most bottom edge downward on both sides you will have constructed a cone or wedge shape(point up).This the area you must not place any UG electrical in. The above ground structure will create downward forces that can and will break or damage the concrete duct bank.
If you must pass under a poured grade beam(one not suspended between to columns) you will need to co-ordinate that activity with the Civil/Structural Group for the project. I have even had to design access openings for conduit runs thru grade beams at times.

9.We used to use red dyed concrete but the concrete drivers had a hard time with the red oxide discoloring everything and it was a must to get it all out of the hopper bin as the next guy may be pouring a patio in his back yard.So the practice now is to just sprinkle dry red oxide powder over the top of the wet concrete.

10.Crossings under roads and drives need special considerations such as depth and additional rebar. I once had a client/owner who spec'ed that all conduits below roads be 4",needless to say we didn't need any rebar. Yep 4" by x reducers as required. The normal duct banks should have a 1/2 rebar run longitudinally with the conduit placed in each corner of the duct bank.

These are some of the things I have worked to in heavy industry applications over the years and have basicly become an industry std between engineering firms,,,,,,,but some owners have their own way of doing things. These practices are also good in residential and commercial applications IMO

Take the above with a grain of salt if you will but it may help some of the younger folks.

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Senior Member
Olathe, Kansas
dicklaxt Thank You for your pointers on conduit installations. It is tid bits like these that I will

remember. "O yea, dicklaxt said do it like this......No not that way you nincompoop"