I'm in need of a structural engineer

Chad Culbertson · **Posted:** Fri Oct 21, 2016 11:42 am

Totally worth renting a ditch witch if you have to do very much. Just double check you don't have water lines or existing utilities buried where you plan to trench, the ditch witch will make quick work of them also.

RobLupella · **Posted:** Fri Oct 21, 2016 1:10 pm

It depends on how deep you want to dig and how fast. The ditch with thing that looks like a chain saw would be slow if you are digging deep and going a longer distance.

The guy who dug my trenches used a small backhoe with a 2' bucket and it made pretty quick work of digging. Takes a little skill.

Rob

Cash Davidson · **Posted:** Sat Oct 22, 2016 3:37 pm

Code says 24" if it is direct buried, 6" if installed in raceway (except if it is under a driveway - then its back to 24").

I agree with VK - run a couple conduits. Direct buried cable will fail if it is not bedded and covered with sand. The smallest rock will eventually work thru the insulation.

Cash

RodneyWright · **Posted:** Sun Oct 23, 2016 8:22 pm

JamesMilko wrote:

The most important thing is to put a bunch of string in the conduit so you can pull other things through later. Non-organic would be preferable.

^^^ this...

RodneyWright · **Posted:** Sun Oct 23, 2016 8:25 pm

Cash Davidson wrote:

Code says 24" if it is direct buried, 6" if installed in raceway (except if it is under a driveway - then its back to 24").

I agree with VK - run a couple conduits. Direct buried cable will fail if it is not bedded and covered with sand. The smallest rock will eventually work thru the insulation.

Cash

That's excellent to hear Cash! Are you aware of any restrictions running over the septic drain lines with conduit? That's the part I'd like to nail down. I know the drain lines are at least 18" down. 6" down and conduit would make this insulation a breeze so to speak...

Cash Davidson · **Posted:** Mon Oct 24, 2016 12:31 pm

RodneyWright wrote:

Cash Davidson wrote:

Code says 24" if it is direct buried, 6" if installed in raceway (except if it is under a driveway - then its back to 24").

I agree with VK - run a couple conduits. Direct buried cable will fail if it is not bedded and covered with sand. The smallest rock will eventually work thru the insulation.

Cash

That's excellent to hear Cash! Are you aware of any restrictions running over the septic drain lines with conduit? That's the part I'd like to nail down. I know the drain lines are at least 18" down. 6" down and conduit would make this insulation a breeze so to speak...

One reason I hate to give engineering advice over the internet is there are so many exceptions that are specific to your installation. For example, let me clarify my prior statement:

Direct buried cable requires 24" cover
- Exception: if it is a 120v, 20A circuit protected by a GFCI on a residential property it requires 12" cover
Wiring within RMC or IMC requires 6" cover (this is threaded rigid conduit)
Wiring within PVC requires 18" cover
Under residential driveway requires 18" cover (regardless of raceway)
and there are other exceptions covering concrete encasement, etc.

So if you are running just a 120V, 20A circuit to your shed, I would use UF cable direct buried with 12" cover. If you want 220V or more than 20A, I'd run it in PVC with 18" cover. You probably are not going to use RMC unless you have a pipe threading machine and hydraulic bender.

As for utility crossings, generally, if they are privately owned (ie, you own them) you can cross at will. If they are publicly owned (city, county, utility company), you'll need to have them located and may need an encroachment agreement to cross. Also there is a difference between a sanitary drain line (solid pipe for transporting sanitary sewer from house to tank) and septic field lines (perforated lines for dispersing effluent). You can cross your DRAIN line at will. The county can be picky about digging around your septic field lines - I'd check with them.

Good luck!
Cash

Vincent Keene · **Posted:** Mon Oct 24, 2016 1:20 pm

Cash Davidson wrote:

The county can be picky about digging around your septic field lines - I'd check with them.

In Wilson Co., the Health Dept has to come and check that your slab isn't encroaching into the drain field OR the repair area. Cash didn't mention the repair area, but you can't build in that area either. You can relocate the repair area, after being approved by a soil scientist. Therefore my septic drain field and repair area dictated where my building was placed on my lot.

RodneyWright · **Posted:** Mon Oct 24, 2016 1:34 pm

Vincent Keene wrote:

In Wilson Co., the Health Dept has to come and check that your slab isn't encroaching into the drain field OR the repair area. Cash didn't mention the repair area, but you can't build in that area either. You can relocate the repair area, after being approved by a soil scientist. Therefore my septic drain field and repair area dictated where my building was placed on my lot.

Both my building location and the cable run will miss the repair area, so I should be good to go...

Scott Johnson · **Posted:** Wed Oct 26, 2016 7:22 am

Cash Davidson wrote:

Direct buried cable requires 24" cover
- Exception: if it is a 120v, 20A circuit protected by a GFCI on a residential property it requires 12" cover
Wiring within RMC or IMC requires 6" cover (this is threaded rigid conduit)

Good luck!
Cash

Can I run two 120V 20A lines in the same trench 12" down.
1) Ensure that each one is on a separate feed in the main breaker.
2) Bridge them back together in a sub panel for 40A of 220V service.

Does it work that way?

Home ownership is a breeding ground for bad ideas

Cash Davidson · **Posted:** Wed Oct 26, 2016 4:19 pm

Scott Johnson wrote:

Cash Davidson wrote:

Direct buried cable requires 24" cover
- Exception: if it is a 120v, 20A circuit protected by a GFCI on a residential property it requires 12" cover
Wiring within RMC or IMC requires 6" cover (this is threaded rigid conduit)

Good luck!
Cash

Can I run two 120V 20A lines in the same trench 12" down.
1) Ensure that each one is on a separate feed in the main breaker.
2) Bridge them back together in a sub panel for 40A of 220V service.

Does it work that way?

Home ownership is a breeding ground for bad ideas

NO! That is dangerous - It doesn't work that way.

JamesMilko · **Posted:** Wed Oct 26, 2016 9:49 pm

Even with seperate breakers on the feed side? I know 2 20A rated lines is a super no-no on a 40A branch, but thinking through the failure modes of that isn't it safe?

Cash Davidson · **Posted:** Thu Oct 27, 2016 8:01 am

The separate breakers on the line side is just one of the things that make it unsafe.

1) If you use two separate 120V, 20A circuits to serve a 240V load, there is a real risk that during a fault only one breaker will trip. The other breaker could feed the fault or the load and overheat and cause a fire. That's one reason the code requires the two breaker handles to be tied together (2-pole breaker) - if one trips the other will trip.
2) The code also requires that a 240V feeder to a sub-panel or a 240V circuit to a load have a SINGLE disconnecting means so if a person needs to work on the equipment all power can be disconnected in a single operation and locked off.

BTW, two 20A, 120V circuits is equivalent to one 20A, 240V circuit, NOT one 40A, 240V circuit.

2*20*120=4800W
1*20*240=4800W
1*40*240=9600W

Cash

PS: I teach a 4hr electrical safety class. The next one is scheduled for 11/11/16 at 8am if you'd like to come.

Scott Johnson · **Posted:** Thu Oct 27, 2016 9:57 am

OK, so aside from my math (20+20 != 40), you are totally saying it will work

I can hot glue a stick between the breakers so they will trip together (unless the heat softens the hot glue and the stick falls off).

Jordan Normark · **Posted:** Thu Oct 27, 2016 1:32 pm

Scott Johnson wrote:

OK, so aside from my math (20+20 != 40), you are totally saying it will work

I can hot glue a stick between the breakers so they will trip together (unless the heat softens the hot glue and the stick falls off).

Amateurs geez. Gorilla glue for electrical, hot glue is for plumbing repairs.

Scott Johnson · **Posted:** Thu Oct 27, 2016 2:07 pm

Rodney should just get his inspection with no electrical, then wire up a few outlets in the shop, with at least one outdoor receptacle.

After that's done, he can lop one end off an extension cord and replace it with a male plug, and just run the extension cord from the house to the shed's outdoor receptacle.

That's way cheaper than anything else that has been discussed. If the power ever goes out, he can just plug that same extension cord into the generator and power the house.

THSCC Forums

I'm in need of a structural engineer

Who is online