Service wire and gas line trench?

Hey guys,

I’m getting some conflicting info from a few guys at work and they have me second guessing my plan.
My plan, trench 3’+ deep for the 1” gas line, back fill 12” and run the 2” pvc for electrical.

The trench is open, the gas line is in and I have the conduit ready to go. I’m running 200amps to the shop about 200’ from the new 400amp meter. My sparky tells me he prefers copper over aluminum. I’m not trying to be cheap but if I can save some money and still be within the safety limits I’m all about it.

1) Is copper better than aluminum in this situation and which do you guys prefer?

2) Is it ok to run a gas line and electric in the same trench? My sparky says it’s a non issue but “some” inspectors have issues with it and want the pipes 12”s apart. The guys at work are saying no way to gas and electric in the same trench. The more I deal with the guys at work, the more I question their opinions.


#3 THHN copper is $1.45/ft
#4 XHHW-2 aluminum is $.78/ft

Thanks for the help,
Andy

It's hard to put in 12" of fill to get the seperation vertically.

What we did was use a 18" wide bucket (kinda standard around here with all
the clay anyways) and put the one item (7500 volt line in this case) and the
other ont eh other side, (telephone in this case).
As you walk the trench to lay it in there, you simply plop some dirt
every couple of feet to hold the conductors in their respective places.

I've done a fair a mount of electrical over the years, including this shop, and likely the next. I'm no electrician. I always follow the code. Just makes sense. So why aren't you looking up the actual code?

Second, it's a $156 dollar difference. In the grand scheme of things, that is not even worth the time you've spent concerned about it. If you were to only be there for ONE YEAR, the difference is but $0.43 per day. Is that really worth niggling over right now?

Is your electrician doing this on the books? Is he lending his license to it? If so, it's his ass. Do what he wants.

As for the trench, I am guessing that you've done the trench yourself. If that's the case, then doing another 12" away is also of trivial concern. And if you ever have to dig up the gas, you are going to be dealing the with electric at that point if you do not. So why even bother worrying over that? Dig the extra trench.

Just my two pfennig, but I think you will have better things to worry about very shortly.

We are looking at building a new shop building in the near future, so I have to deal with these same issues soon, and neither of these would be worth my time in the grand scheme of things.

Hobby Shop said:

I’m getting some conflicting info from a few guys at work and they have me second guessing my plan.

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So will "some" inspectors.

The guys you want to ask are the minders and argument-sorters of those Inspectors, salaried County staff, and glad to help avoid problems before they BECOME problems and create a fuss on their patch.

To wit, whomever is head of Code enforcement, each speciality. They probably have offices right across the hall from each other, and this sort of query will not be anywhere close to their first, same subject.

You might find their names and phone numbers on a county website. I did, here, Loudoun County, VA, then went in for very brief, but very useful chat.

YEP...

The locals, the "Authority Having Jurisdiction" can actually require nearly anything, although most jurisdictions formally approve the national codes every few years. That means that you can do things to CURRENT code, and actually be WRONG, because they have not approved the new code yet.

Just ask them.

I do NOT like the idea of the double duty trench, it just means having to dig past the one to get at the other, as was said. Also, don't forget the tracer tape.... another reason to have two trenches.

Copper is a better conductor. Aluminum has to go at least a wire size larger, and maybe more for a long distance at use voltage, due to more voltage drop (resistance). That can cancel some of the cost difference.

#3 THHN copper is $1.45/ft
#4 XHHW-2 aluminum is $.78/ft

Thanks for the help,
Andy[/QUOTE]
Wrong size wires for 200 amp and distance. The chart I found online shows 3/0 copper and 250mcm Alum. on single phase 240 volt.

Andy,

Im not sure thoes guys at work or your sparky is helping you much on getting the job done correctly. Similar to grounding your 480V transformer.

As for two services in one trench, regulations can vary by location, but many utilities use 12" radial separation.

Whether its a common trench or separate, have a look HERE for an example.

Stacking utility lines in a vertical trench has its own problems. You need to be concerned about settlement and frost heaves, especially here in Michigan. If the area the trench crosses is low or collects groundwater, there is a greater risk for frost heave. In months like we just had, there tends to be a lot of line breaks. PVC is very brittle at low temperature and breaks like glass when moved. 42" is the frost line depth here, and I run all of my lines below that depth to ensure long term survive-ability.

Back filling is another issue, if that backfill is not tamped between the runs, you will get settlement, and the PVC will not be uniformly supported and place additional stress on it, especially near the termination ends. 200' of trench is a lot of hand tamping, and it should be done in layers to be effective.

If your going to do an inspection, the trench needs to be inspected before the pipe goes in, and again after the piping is installed, before back filling begins. With 2 runs that means several inspection if done vertically.

Then comes the issue of the wiring. If the outbuilding circuit is connected directly to the meter terminals, at the supply end, you will need 3 wires. If there is a breaker or fuses at the meter end, then that makes it a feeder which requires 4 wires instead of 3. The latter makes the outbuilding panel a subpanel.

For the wire you want to ensure that you get insulation that is rated for wet location. All underground wiring is considered a wet location. Insulation types XHHW, USE, THHW, RHW are types that are approved for wet locations.

For the conductor material both aluminum and copper are suitable. With copper #3/0 is the smallest size you can use for a 200A service. For Aluminum you must bump up the size to #4/0 minimum, as it has higher resistance. With Aluminum it is subject to deterioration, if you get any scratches or holes in the jacket, during installation, that lets in any water inside the jacket. The metal will turn into an oxide powder. Copper on the other hand will just turn black, but continue to perform acceptably. Aluminum is normally the conductor of choice for distribution circuits due to the cost. Copper is better but comes at a pretty high premium in the sizes your looking at.

At 200' of run voltage drop starts becoming an issue, especially if the circuit is near fully loaded. For the hobby shop that's probably not as much of an issue, but the code recommends no more than 5% drop at the loads.
Aluminum will have more voltage drop than copper. At around 100' that is when you should start considering increasing the size conductors to compensate for it. If you did that then you would need a bigger conduit than 2". If you have several turns in the run, you might also consider using a larger conduit for making the pulling go easier.

For an idea on the wire pricing have a look here.
4/0 Alu $1.07/ft Southwire 5 ft. 4/ Black Stranded 3E AL XHHW Wire-11277115 - The Home Depot

3/0 Cu $3.08/ft this insulation type is not the proper type, but gives an idea on copper cost.
Cerrowire 25 ft. 3/ Black Stranded THHN Wire-112-541T - The Home Depot

When purchasing it's better to go to a wholesale house than a box store. They can cut what you need from 1000' spools so that your not stuck with short pieces left over from 500' spools. Make sure you install a fish line and measure the actual installed length, BEFORE you order wire cut to length, and add about 5' extra for each end to make up for the pulling attachment damage and minor errors.

SAF Ω

I ran Aluminum ground cable because it was cheaper then my electrician quoted using copper in a PVC Pipe. I have kicked myself ever since for not listening to him. I rented a trencher and laid in the 3 lead cable Then filled in the trench with dirt. It was fine for about 2 years and the 220 V single phase stopped working. Had to buy a tester that I could push in the ground the measure broken voltage. It looked like a pen, but it gave me a pretty good idea where the break was. Also called 611 or what ever the number is.. The cable was thick. about the 1/2" dia per strand. My shop is around 200 feet from the house and I wanted 200 Amps. sighhh

Turned off the juice and had to carefully dig...We discovered a Ground squirrel loved the wire coating and shorted out the aluminum wire. The bare aluminum wire corroded and I had to hire my electrician to come and splice it. That worked for about another year and it happened again. Now I have 110 V only in the shop. Disconnected the open wire. Now I kick myself everytime I wish I need 220. The price of copper has gone up now...will trench in a new line next year ... I have heard I should bite the bullet and use a thick walled flexible tube to run copper inside.

I had the gas company company come in and burry the flexible PVC and rubber hose inside it, because they told me the Gophers in my area love to chew rubber hoses too. They put a meter on my shop too. I followed code the first time too, as I had to get a permit and have it inspected too afterwards.

Richard King said:

I have heard I should bite the bullet and use a thick walled flexible tube to run copper inside.

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I don't want to bury even low-voltage yard light wiring without some sort of tubing these days. Too old and creaky to play in the dirt twice, too cheap to hire it done if a re-do can be avoided.

Medium-density Poly as used for water-wells is inexpensive if Code allows it vs bespoke electrical conduit. I've used it for Copper waterline protection. I don't know what NEC has to say about it.

Either way, don't make it too close-fitting or you may have to de-rate the Ampacity. Run it so as to support pulling, add a modest pulling anchor, each end, as if it were a water-line, and you'll not have to dig ever-again unless .. you overheat it sooo bad it's jacket welds itself to the wall of the conduit.

Day Job had that happened at one of their buildings, so they had to dig up a paved carpark anyway.

Cute, curious, but destructive little rodents have been forever established right where the run to my gen set wants to be.

I'll probably run oversized steel conduit in concrete for teeth-proofing and so it can be re-pulled if need be, rather than dug-up. Short run for my one, thankfully. Mebbe 20 feet.

Thanks guys, two trenches and copper it is, that was my electricians plan from the beginning also. It was me who wanted to change his plan.
If I used the same trench, I could’ve installed the new 400amp service now, instead of waiting until the spring.

The 2nd trench will run along the perimeter of the septic field and between some trees. There’s no way I can dig it now without destroying the field because the ground is still frozen. I used a 12” bucket for this trench and some chunks were coming up 6’x6’.

Only the new 400amp service will be inspected but always do everything to code with no short cuts. Tracer wire will go in both trenches. I pressure tested the gas line, risers and new piping so I’m finally ready to warm this place up.

Andy

You might have this backwards. When I did mine, different state obviously, the electrical trench was 3' min and the gas trench was 18" min.

Hobby Shop said:

There’s no way I can dig it now without destroying the field because the ground is still frozen. I used a 12” bucket for this trench and some chunks were coming up 6’x6’.

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Not sure it makes sense for your soils, run-length or budget, but might a Ditch Witch with rock-cutter chain rather than backhoe be an option?

Tough to get a 12"-18" trench with a Ditch Witch. But schedule 80 pvc conduit below the frost line would be the way to go. Separate one for gas line, and separation per local authorities. Should be last time you need to get in the trench.

Chip

Chip Chester said:

Tough to get a 12"-18" trench with a Ditch Witch.

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No sweat for the larger ones. Nor adequate width. Two foot or a fraction-of is eminently practical. Reason they live and thrive, after all.

Mind.. BIG rocks can be a bitch, yes, roots and gravels not so much.

Monarchist said:

Not sure it makes sense for your soils, run-length or budget, but might a Ditch Witch with rock-cutter chain rather than backhoe be an option?

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Its a good idea but I never considered renting a trencher because the backhoe is always right there. I wouldn’t use a Ditch Witch for this new trench because I want to see how far the roots are creeping into the tile field. If the roots are in there, out they come while I’m putting in the conduit. $400 extra for the copper over the aluminum isn’t going to break the bank but I’d rather not spend anymore $$$ than I have to. It will only take a couple hours to get that trench dug when things thaw out.

Andy

Larry Dickman said:

You might have this backwards. When I did mine, different state obviously, the electrical trench was 3' min and the gas trench was 18" min.

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Nothing backwards here. The only requirement is, the gas line and the electrical conduit must be a Minimum of 18” deep.

Out here in Kalifornia, electric and gas service in the same trench is what is referred to as a "JOINT TRENCH". Joint trenches are standard and preferred when installing both commodities from the utility mains (both gas and electric). Our separation requirements are 6" between gas line and secondary/service electrical ducts both sitting in the bottom of the trench side by side on a 2" sand bedding.

Aluminum wire is our standard installation for both primary and secondary voltage. We do install copper conductors on occasion in certain circumstances, ie; converting local primary lines to main primary lines utilizing existing ducts so as to not have to excavate to install new larger duct.

Of course your utility, state and local requirements will vary.

Murf

Hobby Shop said:

Nothing backwards here. The only requirement is, the gas line and the electrical conduit must be a Minimum of 18” deep.

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You're lucky. My electric was 330' long, minimum of 3 feet deep, through granite. that was a rough weekend.

Larry Dickman said:

You're lucky. My electric was 330' long, minimum of 3 feet deep, through granite. that was a rough weekend.

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Granite? Sheesh! And I'd bet a Blaster's permit - even with mats - simply wasn't even a dream in current-epoch California, either!

How did you manage that in a "weekend"? Or was it a "Saturn weekend"?

Monarchist said:

Granite? Sheesh! And I'd bet a Blaster's permit - even with mats - simply wasn't even a dream in current-epoch California, either!

How did you manage that in a "weekend"? Or was it a "Saturn weekend"?

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A Vermeer trencher, a couple jack hammers, and a lot of Bud Light.