Backfilling PVC conduit

T

Therealcrt

Member
Location
Kansas City
Occupation
Electrician
Is there anywhere in the NEC that says when it’s necessary to backfill underground conduits with gravel or AB3 or just straight dirt? I understand that when you’re under a road you should backfil your trench with gravel but what about under sidewalks or other cases? Is there an actual code that says weather or not gravel has to be used
 
This might help to explain.
 

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Therealcrt said:
Is there anywhere in the NEC that says when it’s necessary to backfill underground conduits with gravel or AB3 or just straight dirt? I understand that when you’re under a road you should backfil your trench with gravel but what about under sidewalks or other cases? Is there an actual code that says weather or not gravel has to be used
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No
Depends if you want to tamp or can handle settling
NO
 
No that doesn’t answer my question that’s burial depth which there’s a whole table pertaining to that. I was just asking when it’s permitted to backfill with all dirt not gravel or shouldn’t gravel always be used on top of conduits in a trench then fill with dirt that’s my question
 
Therealcrt said:
No that doesn’t answer my question that’s burial depth which there’s a whole table pertaining to that. I was just asking when it’s permitted to backfill with all dirt not gravel or shouldn’t gravel always be used on top of conduits in a trench then fill with dirt that’s my question
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Do not back-fill a trench with rocks, debris, or
similar coarse material, Section 300-5(f).
 
mtnelect said:
Do not back-fill a trench with rocks, debris, or
similar coarse material, Section 300-5(f).
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That is a rather old reference. The 2017 states:

(F) Backfill. Backfill that contains large rocks, paving materi als, cinders, large or sharply angular substances, or corrosive material shall not be placed in an excavation where materials may damage raceways, cables, conductors, or other substructures or prevent adequate compaction of fill or contribute to corrosion of raceways, cables, or other substructures. Where necessary to prevent physical damage to the raceway, cable, or conductor, protection shall be provided in the form of granular or selected material, suitable running boards, suitable sleeves, or other approved means.

IMO that section should just be deleted, it doesnt really say anything meaningful, of value or that is enforceable.
 
electrofelon said:
That is a rather old reference. The 2017 states:

(F) Backfill. Backfill that contains large rocks, paving materi als, cinders, large or sharply angular substances, or corrosive material shall not be placed in an excavation where materials may damage raceways, cables, conductors, or other substructures or prevent adequate compaction of fill or contribute to corrosion of raceways, cables, or other substructures. Where necessary to prevent physical damage to the raceway, cable, or conductor, protection shall be provided in the form of granular or selected material, suitable running boards, suitable sleeves, or other approved means.

IMO that section should just be deleted, it doesnt really say anything meaningful, of value or that is enforceable.
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I agree ... It's common sense to not backfill with debris. When I am trenching, I will always order filtered soil for backfilling before and after placement of conduit.
 
It’s not an NEC requirement.

You can’t backfill with anything that is going to damage the conduit or cable, and if you’re backfilling over a road or parking area, the spec’s may call out a compaction test

Other than that, there are not really any requirements for materials for backfill. I regularly backfill with native soil that was excavated for the trench.
 
electrofelon said:
Yes very rocky here too. As long as the rocks are not large and not dropped on the conduit, they will not damage the conduit.
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It sounds like you are located in a mountainous area, where I am located is at the base of Angeles National Forest. This area is called an Alluvial Fan where all the debris is washed down from the mountains above. This area is so rocky, that boulders the size of a bus can be seen in front yards.
 
electrofelon said:
Yes very rocky here too. As long as the rocks are not large and not dropped on the conduit, they will not damage the conduit.
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Yes, I agree ... Normally, when backfilling you can separate the large rocks from the trenched dirt without using special filtered dirt.
 
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