Overhead electrical service to a storage shed

[Timothy J. Trace]

Greetings,

I'd like to run electrical and telephone service to my storage shed, which is located 40' from my home. I'd appreciate any advice that the experts in this group can provide.

I am planning on a 20' 4x4" pole at the shed, buried 5', with a pair of Par-38's near the top of the pole for general yard lighting. There will be a single 15A outlet inside the shed, which will supply handheld power tools and low-voltage lighting around the shed.

The entire electrical circuit will be three-way switched, similar to a stairwell, with one switch inside the house and the other inside the storage shed. See

. I'll use a single-gang digital timer inside the house, if such a beast exists for three-way circuits @ a full 15a (doubtful).

The voice cable will terminate inside the shed.

I cannot bury the cabling because the roots of a very large, very healthy oak tree lay in the most obvious path of a trench. I do not want to risk killing the tree, so trenching is out of the question.

However, the lower limbs of the tree are at least 15' above ground, in the direct path between my service entrance, and the storage shed. If the overhead cable was carefully strung, it could easily maintain 2-3' of clearance under the lowest branches. Judging from some of the other electrical work around my neighborhood, it appears that you are allowed to have wire suspended underneath a limb.

Questions thus far:

1> What type of electrical cable, and voice cable, are required for overhead suspension, given the application (note the 3-way switch requirement)? Is the cable self-suspending, or is some type of separate weight-bearing carrier required?

2> Can the electrical and voice cables be run in close proximity?

3> Is a service disconnect required on the house end of the run, or can I simply use a new breaker in my 200a panel?

4> Should I use a 15a GFCI inside the shed, or a circuit-breaker type GFCI in the 200a panel?

5> What gauge electrical wire is appropriate? I estimate the entire run, from the breaker to the farthest point, at 115'.

6> How high for the suspension points? How high for the lowest point on the overhead run?

7> For safety and durability, I want to conduit the runs at both ends, from the suspension point to the entrance point. What kind of junction is appropriate between the pipe and the overhead cable? Between the pipe and the interior cable? Can Romex be run through conduit, or must THHN be used?

Best regards,

Tim == (substitute 'tcsys.com' for 'nospam.co.uk') _________________

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[Tom Horne]

self-suspending,

Quadplex cable is three insulated aluminum conductors wrapped around an aluminum clad steel reinforced conductor that will serve as the Equipment Grounding Conductor (EGC) as well as being the messenger that supports the other three conductors.

NO! It is dangerous to do so and it will induce noise into the voice circuit.

simply use a new

You will need to provide a service disconnect at the garage end of the circuit but if you have a pair of three way switches that will open all of the ungrounded conductors that is all that is required on residential property. No separate disconnect is required at the house end.

I would use the GFCI as the first receptacle in the shed in order to avoid nuisance tripping due to leakage current in the overhead span during wet whether.

the breaker

If the entire run were going to be the aluminum triplex then you would need six gauge to avoid excessive voltage drop. I would imagine that eight gauge would be fine since it is less than half of the total run length. I assumed a twenty ampere total load for that calculation.

overhead run?

225.18 Clearance from Ground. Overhead spans of open conductors and open multiconductor cables of not over 600 volts, nominal, shall conform to the following: (1) 3.0 m (10 ft) ? above finished grade, sidewalks, or from any platform or projection from which they might be reached where the voltage does not exceed 150 volts to ground and accessible to pedestrians only (2) 3.7 m (12 ft) ? over residential property and driveways, and those commercial areas not subject to truck traffic where the voltage does not exceed 300 volts to ground (3) 4.5 m (15 ft) ? for those areas listed in the 3.7-m (12-ft) classification where the voltage exceeds 300 volts to ground (4) 5.5 m (18 ft) ? over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other land traversed by vehicles, such as cultivated, grazing, forest, and orchard

the suspension

Install service heads on the tops of both raceways. Splice the quadplex to the conduit wiring using pre insulated patent splices that are available from any decent electrical supply house. Each conduit will terminate in an LB that connects to a Jbox located inside the building. Make your transition from the raceway wiring to cable in the junction box. It is currently a matter of debate whether it is permissible to run NM cable in conduit. I think it is a poor practice at best and would recommend avoiding it.

Other questions please ask.

-- Tom H

[Jeff Cochran]

Okay, but it's the advice of the experts at your local building official's office that really matter to you...

stairwell, with one

Directed boring might be a better option, or a route around the tree. Burial is always preferable, and locally it's required.

Quadplex cable is self-suspending, and though I don't like the stuff it would likely be suited to your installation. It's aluminum so you need appropriate terminations. Locally it's common for mobile homes and small sheds such as yours, though as of last year locally we're required to bury cable and not run overhead. For the voice, you'll want a suspending wire run with it to strap the cable to, though I'd recommend burial, either direct or in conduit. Direct burial would miss tree roots for the most part.

No. Generally a three foot separation, though you can run low voltage voice lower than the height requirement for electrical feeds. But you can also bury the voice cable quite easily and that may be the best option.

simply use a new

Check your local jurisdiction on this. You should be able to use a disconnect on the shed end, with none on the house, but local interpretations sometimes interfere.

I like the breaker, but I'm tempted to say a GFCI in the shed end as the first device on the line. Aerial runs can induce some false tripping in GFCI.

the breaker

At 20 amp, that works out to a 8 guage, but I'd upsize to 6 on the aerial run, especially in aluminum.

overhead run?

No closer than 10' from ground, though some jurisdictions may have other rules. Check with yours to be sure. 12' if you're over a driveway, even a dirt vehicle path. A pool would alter this even more.

suspension

THHN in conduit, spliced to the quad cable at a service head atop the conduit/mast on both ends. Romex can't be in conduit, so in your situation I'd run conduit to the first receptacle with THHN, then use Romex if appropriate for the rest. Make sure to use the correct splices to go from aluminum to copper, and rent or borrow the appropriate crimpers.

Although actually, I'd run a subpanel in the shed and at least 30 amp (likely 40 to 60) from the main. You'll surely want to add lights, outlets, etc. at a later date anyway. :)

Jeff