Farm wiring? Overhead service drop.

[Dean Hoffman]

I want to upgrade some of the wiring at the farm. The original wiring was done with little, if any, grounding. The utility's transformer pole is on the edge of a pasture. There is an overhead triplex cable running to another pole that has the utility's meter and circuit breaker box. It's maybe 100 feet between the poles.

240 vac single phase. There are two single overhead uninsulated wires running from the meter pole to a machine shed supplying 120 vac to that shed. I want to replace those wires to provide grounding and maybe 240 to that building. Should I use quad or triplex from the meter pole to the shed?

[dpb]

1. You under a City or County Code requirement?
2. What's your personal style?

We're outside city and county doesn't know about only wiring changes so past the REA meter is up to me. I'm content with 3-wire so that's all I've ever pulled.

There's three in service to all the major buildings but still a couple of old small outbuildings with the OH 2-wire that hasn't ever been updated. My intent is to bury both of those sometime this year, but it'll also be 3-wire.

When put in the new well, had half the trench towards the old machine shed that had never had power at all so had them dig the trench to it off the well feed where they split and took the opportunity to add power out there. Again, just 3.

[Anonymous]

IDK, just curious. Should there be a grounding rod at the meter pole, AND at the shed in this case ?

[Dean Hoffman]

I intend to put one at the shed. The code says something about installing the first one then testing it to see if it has less than 25 ohms resistance to earth. A second one is required if the first one doesn't measure under that 25 ohms. I guess it takes some sort of special tester and no one carries them with. It's simpler to install the 2nd ground rod. I don't know if code actually requires the 2nd one otherwise.

[dpb]

If the building has an outlet or more than one branch circuit it must be grounded; if it is to house animals must be regardless.

You can either put the ground rod at the building or if run a ground conductor back to the feed location. Depending on size of the farmstead that can get pricey.

[gfretwell]

The separate equipment grounding conductor on feeders on the load side of the service disconnect has been required since the 90s so that is a slam dunk (3 wires for 120, 4 wires for 120/240). The article on agriculture buildings (547) also requires an equipotential grid if there is a concrete floor (bonding the wire in the concrete) but that ship has probably already sailed. It is mostly to address livestock that may be hooked up to machines like a dairy cow. Drive at least 2 rods, 6 feet apart at each building, separate the ground from the neutral in the panel and run the appropriate wire. You will be OK.

[dpb]

On 3/8/2020 12:37 PM, [e-mail] wrote: ...

...

It's always baffled me when there are only two from the the 3-phase service to the transformer pole and then a single ground there as to what is the point for a new conductor afterwards.

Granted, if one wants/needs be compliant it's what it says, but I fail to see what is gained.

[gfretwell]

There is always voltage drop in the neutral and that shows up as a voltage rise on the ground. You are also using the earth as a current path. The service point is seen as the demarcation point where that voltage gradient stops on the ground. From that point on the equipment grounding conductor is not supposed to carry circuit current so you avoid creating your own stray current on grounding conductors (250.6) On the line side of the service point there is stray current everywhere.

[Clare Snyder]

What does your electrician reccomend, and what does code require? How much more is quad than triplex? Does using quad improve the ground?

[Clare Snyder]

Running the ground conductor helps reduce ground leakage currents that can cause cattle to get shocks drinking from water toughs etc. GENERALLY SPEAKING a single point ground is always preferred. No "ground loops" and "floating grounds"

[dpb]

In the 70 years since the hookup to REA haven't had any cattle, horses, hogs, chickens, ... zapped yet.

I suppose it can and may on rare occasion happen, but seems way overdone to me. I'd have to take shoes off, too, to count the number of heaters in all the locations so not like it's just one for the bird bath/cats/dog in the yard.

[gfretwell]

This has little to do with ground loops since all grounding electrodes on a service are required to be bonded together but it is about a single place where the neutral gets grounded. It is required to be in the service equipment.

You are really just trying to avoid circuit current in grounding conductors.

[SNAG]

When I installed a 100 amp 3 wire service to my shop an electrician friend told me to put a ground rod out there plus ground it to the steel frame of the shop and bond it to the neutral - the only other place the neutral is bonded is in the meter enclosure at the main panel. I would think any "downstream" panels or devices should be wired with 4 wires if

220 , 3 for a 110 service .

[gfretwell]

The separate grounding conductor and the isolated neutral has been code since 1996.