First time burying cable - need tips

[grow nerd]

As thread title suggests, I've never buried wire underground. Right now with what I've got planned, I'm planning on carrying three (3) runs of #6/3's about 30 feet to a detached guest house which currently only has very limited power (I won't be using that for much except shopvac, etc.) Why 3 x #6? 'Cuz it was cheaper / more convenient to buy a 125' roll of #6/3 than deal with getting larger wire by the foot, especially when my requirements can handle this setup easily with three separate subpanels.

Tried going for the UF cable, but the wide shape bothered me and thought a well sealed conduit will be fine, right? Is Romex NM technically THHN-only, or THWN/THHN?

Anyways, right now as it stands I'm thinking 3 sets of 3/4" electrical conduit PVC, one for each #6/3. Rather than something like a 1 1/4" or 1 1/2", since it just seems much easier to deal with and also in my head it feels easier to feed one wire per tube than three (thick, stiff ones) together. I figure I'll need less 45/90 fittings as I can bend it a bit as needed.

Plan: Dig 4" deep: is that enough? probably not for code but should weather most conditions for rentals, right? Anchor down using something like spikes for flexible lawn sprinkler pipes, etc. Cover back up with dirt, mulch, etc...

I've looked at the "liquid tight" or whatever flexible PVC conduit, but it looks really expensive and doesn't seem to really offer me any real advantages except maybe slight increase in flexibility. Also looks like a pain in the ass to couple, whereas with the rigid PVC it's just belled connectors & glue.

 

[PharmaCan]

It sounds like you have some kind of bundled/Romex-like wire. Sadly, that's not for use inside conduit. It's a heat thing. You need to get the single wire. Once you have the right kind of wire, you'll have ten wires. I don't know the code off the top of my head, and I'm not going to look it up, but ten #6's should pull okay through one 3" conduit, maybe smaller - Idk, I don't recall ever pulling that many #6's at one time. Probably someone will read this that know the code. Anyhoo - one conduit, pull into a small box and go from there to your individual subpanels. You want to pull your wires all at the same time.

Once the the pipe is in the trench, you have to make sure no rocks go through it so you need to get in the trench and "shade" over the conduit for about 12" with soil with no rocks in it - small pebles, gravel and assorted small rocks are okay, just keep the baseball size and bigger out. While you are shading the trench, you can step on the conduit and hold it down where you want it while you throw some dirt on top. You're going to have tons of dirt on top of that pipe, Bro, wuffo you want to waste money and time on clamps to hold it down?

PC

 

[pushlimits]

4 inches down only works with low voltage installations. If you plan on getting it inspected, code is 36 inches. (Between you and me, I wouldn't) From a professional point of view, it is rare to see someone pull in a harness (a bundle of wires tied together) with cables and not wire. Not to mention Non-Metallic cable. (there is some cable meant for direct burial. probably not for your application thought.)

If you are pulling in #6 cable I image you are going to draw some serious power. What you are doing will work, but there are cheaper and better ways of doing it if you are willing to go to a electrical supply warehouse. I can help you if you like just let me know, you would need to answer a few questions first. (I cannot seem to see what you are running)

P.S. DON'T BURY SEAL/LIQUITIGHT! it will decay and it's way expensive

 

[grow nerd]

PharmaCan, why can't the bundled Romex NM be run in conduits? :-( How about the Romex UF cables? Certainly that can be?

I really can't see around why running bundled Romex NM #6 inside 3/4" buried 4-6" deep for a 1-3 year (hopefully longer but being realistic) project. In short I'm not really interested in doing things "to code" as long as it's reasonably safe and so on. I'm smarter than your average bear, for the most part.

pushlimits, yeah I thought it might be something like 24-36 inches. But I "don't plan on getting inspected"... I guess that's really the short and best way to put it. I'm pulling a total of 150A from a 200A main panel. There is the main house, then there's the detached guest house which has only two #12's running to it. It's a rental, and growing in the guest house is really and truly ideal in this situation (except for having to secretly bury cable).

Note taken on burying LiquidTight stuff. I'm working with the gray electrical PVC conduit, by the way.

Any additional input / info would be appreciated. Thanks!

 

[Medium Pimpin']

if u wanna pull the romex thru pipe, strip the outer insulation off 1st.
you cannot bury Rx.
code states 4" is deep enough if covered by 2" concrete.
UF must be 24" deep, pvc 18"
dont go over 360 degrees in bends in your run.
you will be pulling against yourself at that point.
i guess your going to put each 6/3 on a 50a breaker?
or are you pulling them as parallel conductors?
you wont be ale to find a 150a breaker that will fit in your panel, thats not a main.
100a is the highest u can go for a post main bus snap in.

 

[grow nerd]

Medium Pimpin', oh... UF cables are meant for direct burial (no conduit)? I see! I plan on burying in PVC.

Why strip the outer jacket? :curious:

No more than 360 degrees TOTAL? Interesting, just curious, how much of a difference does that make in the real world? Or is that for electrical or physical purposes? I'm guessing physical for pull.

Yes each 6/3 on DP 50A. Cheapo $15 SquareD HomeLine 100A subpanel at the other end of each 6/3. One for lights, one for A/C + lights, one for aux. + lights. Best way I could figure to partition it w/o using larger cable.

Love the name & avatar, by the way.

 

[humble1]

get a trencher and bury it deeper.
4" can (and probably will) rise and/or sink creating either a hummock or a depression that will be painfully obvious.
If you don't want to dig it to code you should probably go at least a foot down. Also get the right glue. I forget if it's ABS or PVC that needs glue AND primer, but for buried work you DO NOT want any moisture in there. Does the back yard have sprinklers or anything like that?
I ran 2x 10 gauge extension cords (had'em on hand and no $ for Romex) through 2" PVC about 2' underground to a shed w/ 4x 600s in it for about a year. Worked fine. When I got sick of using the shed I just pulled the cords back through and now I'm using them on a different project.

 

[Medium Pimpin']

like pharma said, its due to heat.
by outer jacket, i mean the very outer insulation on the Rx, not the insulation around the wires themselves.
just to clarify for you and any1 else.

once you hit 360 degrees, you wont be able to pull the wire thru the pipe.
all your force pulling will be directed right back at u. thus pulling against yourself.
so no more 3 90's (270) and 1 45 (315)
at least thats my practice.
if you need over 360 worth of bends, i would recommend a pull box somewhere in the run.

 

[grow nerd]

Due to heat being built up inside the conduit? I figured that might be the case, but why is it that #6 copper in NM format is insufficient for conduit, while "loose" #6 copper is OK (for heat)? Is it because the NM format (like the Romex I have) is too tightly bound / spiraled? Would removing the outer sheathing (not the wire insulation obviously, LOL) alleviate this?

Is the heat thing a concern even if the ground stays fairly cold most of the time, and running @ 80% or less of wire amperage capacity?

How about venting the pull / junction boxes from the inside (i.e., leaving cover open or drilling holes) to allow some of the heat to escape out of the conduit? Will that help much or at all?

I'm a bit confused still, hopefully the next few replies will clarify.

 

[grow nerd]

humble1, first time using electrical conduit PVC but found only cement / glue @ Home Depot, no primer in sight. Just out of stock / bad location, or not used for gray conduit?

I've done plenty of work with liquid PVC (white) and know that ideally you want to use primer for proper installation. (Although I've done plenty w/o primer w/ Christy's Red Hot Blue Glue.)

 

[Danks2005]

Pulling Romex through pipe is an absolute pain in the ass, and against code. Just get large roll of thhn and phase them w/ tape.

That pipe is full of air, if it rains and it is only 4" deep, it won't be very secret anymore, rent a ditch witch if you can't do it with a shovel, can't be much to rent for a day. I guess you could stake it down, but I personally wouldn't feel comfortable with 150A only 4" deep, that can be a dangerous amount of power if somthing were to go wrong.

I personally don't go over 180 degrees of bend without a pull point, especially over 100'. You said this is about 125', that can be a very tough pull w/ too many bends.

When done, use a shop vac to suck in some jet line tied to a plastic bag corner with some air in it (mouse) then use the string to pull your wire.

 

[PharmaCan]

LOL - When I first read this I thought the OP said 4 feet deep. Four inches is moronic.

PC

 

[dtfsux]

My BIL is a journeyman and I can assure you, you can not run romex through conduit. Maybe for short runs through a wall, or through a foundation to a kitchen island etc.

It has to do with heat and induction I believe. Just dont do it.

4" is way too shallow, go at least a foot. hell a 4" trench with a 3" pipe leaves 1" of dirt

I would try to go with direct burial cable and save all the hassle. No pipe, no pulling, narrower trench, etc. Propably a little easier to do w/o anyone noticing as well.

 

[<~Hades~>]

My BIL is a journeyman and I can assure you, you can not run romex through conduit. Maybe for short runs through a wall, or through a foundation to a kitchen island etc.

It has to do with heat and induction I believe. Just dont do it.

4" is way too shallow, go at least a foot. hell a 4" trench with a 3" pipe leaves 1" of dirt

I would try to go with direct burial cable and save all the hassle. No pipe, no pulling, narrower trench, etc. Propably a little easier to do w/o anyone noticing as well.

Props did not know they made direct burial cable

 

[Danks2005]

I would not feel comfortable with a 150A circuit, if it is not in pipe, maybe that is just me. That is a lot of power guys.

 

[jonnypotseed]

back when i did trenching and irrigation we would bury direct burial wire in high $$ yards using a sharpshooter shovel and at the end of the day u could barely tell we had been there. work the tip of the shove into the dirt about 4-6 inches at a slight angle then carefully push down to pry the soil up. once the soil raises a few inches push back on the shovel pushing the dirt up and making a small opening in the soil. do this in an overlapping pattern like this:
(
(
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once you got a few feet of dirt lifted u can go back and put the shovel back in the hole to push it open then roll ur wire behind the tip of the shovel then repeat. after ur wire is all buried u walk down the wire line to push the grass back down.no dirt was removed no "trench" was made.

if u decide on a trench and shovel is ur tool use a sharpshooter shovel. put the grass clumps on one side of the trench and the loose dirt on the other. when its time to cover up rake(i use a garden rake not feather) the loose dirt in first then place the clumps of grass in with grass upright. walk the trenchline to pack when done

 

[grow nerd]

The direct burial cable is the UF cable, I assume? Largest I could find was 6/3 (which is what I have in Romex NM anyways).

I will take the advice and either unsheath the Romex, or buy a roll of THHN. If unsheathing the Romex, can the paper wrapper around the ground wire stay? And can it stay in its original tightly bundled format? I have a feeling unsheathed will actually be harder to pull than sheathed, as far as 6/3 through 3/4". (I was gonna pull only 10' at a time.)

I'm starting to reconsider and thinking of going with a roll of THHN, and if so I will consider a larger gauge wire for a larger breaker and re-arrange the subpanel partitioning and setup.

As far as 4" being moronic, why? I can imagine only if you were a moron and started to dig in your own back yard where you buried your own wire, or other mess... but again, I'm a little bit smarter than your average bear.

 

[grow nerd]

johnnypotseed, thanks for the excellent tip on the Sharpshooter Shovel!

Danks2005, I kinda feel the same way... but what do I know? Kinda letting the pros weigh in on this one more than I normally would, especially on the sheathing issue, etc.

 

[grow nerd]

Sorry for the stupid question, but is the "50A" rating for the 6/3 NM-B (like the Romex I have) already the de-rated value? Looking at the wire amperage chart at Home Depot (same as this one) seems to indicate that the same #6 wire in stranded THHN can carry up to 65A or 75A, while the NM-B rating for the same copper #6 says 55A. Is the 65A/75A for "open-air" ratings and not really for conduits application? Or can the stranded THHN simply carry more due to the skin effect?

If that's the case then I'd rather run two sets (6 x #6 THHN + 2 x #10 for ground?) of THHN instead of the NM-B Romex I have.

Something tells me it's still not safe to be running more than 50A on that #6 regardless, but I'll let you guys chime in again.

Thanks!

 

[grow nerd]

Just read up on the limitations on the temperature rating of equipment, 60C, 75C, and 90C and how that affects things. I think that answered the questions but any input would still be appreciated.

If anyone's curious, here's what I'm talking about:

http://www.askmehelpdesk.com/electrical-lighting/wire-temperature-rating-348895.html

Looks like I'm dealing with 50A limit for #8, 65A limit for #6, or 85A limit for #4. Cost per 500' spool is $156, $240 and $391, respectively. Thinking of buying a spool or two of #8 and pulling three runs of that for cost + same setup + wire flexibility reasons.

What do you think? Am I still as confused as when I started?