120/240V circuit spacing in direct burial applications

Status
Not open for further replies.

Electron_Sam78

Senior Member
Location
Palm Bay, FL
I know you're supposed to derate for more than 3 CCs in a raceway, trench, etc. but what's the separation distance if I need to have several circuits in close proximity (direct burial application)? I know figure 310.60 is for circuits rated at 2001 V and up but I can't find similar information for a 120/240V direct burial service lateral/entrance and branch circuit installation.

I have one paralleled service circuit and 5 or 6 branch circuits. What I'm really concerned about is the service laterals and service entrance. What's the spacing of the trenches or the spacing of the circuits in the trench (if using the same trench for 2 circuits)?
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
You can search all you want, there is no NEC requirement for the separation of the circuits you describe.
 

Electron_Sam78

Senior Member
Location
Palm Bay, FL
So would that mean that no matter how much I separated the circuits with a layer of dirt (in the same trench) they would still be considered (by the NEC) in the same trench or would it mean that I could separate them with 6" or 12" and they'd be considered installed in separate trench? What's the SOP in a situation like this?
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
no.
I think what he meant was that there is no place in the code requiring to derate in a trench. The only code cite I am aware of is in the same conduit, race way.
 

Electron_Sam78

Senior Member
Location
Palm Bay, FL
hmm, is that what he meant because table 310.16 is ampacities for not more than 3 CCCs in raceway, cable, or earth (direct-buried)? Also 310.15(B)(2)(a) Exception No. 4 talks about underground conductors in a trench implying that 310.15(B)(2)(a) and T310.15(B)(2)(a) apply to trenches.
 
Last edited:

SEO

Senior Member
Location
Michigan
I think that the adjustment factors in table 310.15(B)(2)(a) would apply to conductors in trenches as well. As far as adding fill between the conductors IMO it would still be the same trench.
 

Electron_Sam78

Senior Member
Location
Palm Bay, FL
I think that the adjustment factors in table 310.15(B)(2)(a) would apply to conductors in trenches as well. As far as adding fill between the conductors IMO it would still be the same trench.

It would seem that way to me too but without clarification I could just dig a second trench 6" or 12" horizontally away from the first and it would be the same as adding 6" or 12" on top of the first circuit so this is why I'm cornfused. Elsewhere in the NEC, talking about permanent barriers being put into boxes it says that action creates two separate boxes (if one barrier is installed) as far as the code is concerned. This situation should be the same, there's just no language to address it - at least none that I've found yet.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Seems to me paragraph 310.15(B)(2)a clearly talks about single or multiconductors need to maintain spacing otherwise you will need to make an ampacity adjustment. That distance that's required is up to interpretation. Talk to your inspector.

We've had one inspector balk at one of our jobs when we ran fourteen 1.25 conduits side-side(touching), he claimed they needed some kind of spacing or they were going to overheat.:-?
 

SEO

Senior Member
Location
Michigan
Per the definition of trench (A long, narrow excacation in the ground) by adding fill to seperate the conductors you are still in the same trench. How many conductors are you installing in your trench? If you dug two seperate trenches the way the NEC is written you could comply even if the conductors were closer together in two seperate trenches than in one large trench. Might require a ruling from your AHJ.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Electron
Are you planning on placing those conductors in a conduit or a cable?
From what I understand direct burial conductors to be is individual conductors rated for burial. I have not seen that type of product used in years. Several conduits in the same trench that has spacing should not be a problem.
 

Electron_Sam78

Senior Member
Location
Palm Bay, FL
Per the definition of trench (A long, narrow excacation in the ground) by adding fill to seperate the conductors you are still in the same trench.
That would make sense but 314.28(D) says that permanent barriers installed inside boxes create sections that are considered separate boxes. I know that's not talking about the subject we're on, just using it as an example of barriers creating separate areas.

How many conductors are you installing in your trench?
The ones I'm concerned with are paralleled service lateral conductors consisting of 2 sets of 3 conductors each.

Electron
Are you planning on placing those conductors in a conduit or a cable?
Direct burial no conduit
 

SEO

Senior Member
Location
Michigan
I see your dilemma, what does your electrical inspector say? You may have to install larger conductors for the 80% adjustment.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
Why not put them in seperate pvc conduit runs. 1 ditch and save your behind if anything goes wrong. I will never run under ground without conduit just plain crazy to not .
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Why not put them in seperate pvc conduit runs. 1 ditch and save your behind if anything goes wrong. I will never run under ground without conduit just plain crazy to not .

Our POCO does not allow direct burial anymore.
Besides if that ever gets dug up and broke it is usually an easy fix.
 
Status
Not open for further replies.
Top