Trenched ground rod

[transferguy]

Posted By: Mr T

I have shallow bedrock and no choice but to dig a trench for my ground rod and lay it flat. Is there any requirement for the ground clamp location? Can I put the clamp in the middle of the rod? I saw no mention in the NEC about it.

[transferguy]

posted by: suemarkp

Anywhere on the electrode is fine -- one end, other end, middle...

Mark
Kent, WA

[transferguy]

posted by: chrisb

Can you use a ground plate in USA? Much less digging and becoming more common up here.

[transferguy]

posted by: suemarkp

Yes. They are treated like rods and pipe electrodes (e.g. general category of Made Electrode). Plate electrodes shall be installed not
less than 750 mm (30 in.) below the surface of the earth.

Mark
Kent, W

[transferguy]

posted by: Mr T

I thought about it but I dont have the room (width) for one before crossing over to my (bitchy) neighbors yard. Only have about 2.5 or so feet over there and my sewer line somewhere too.

I only have 2 feet of dirt till bedrock with less in other areas. The inspector gave me permission to bury the rod a inch or 2 above the bedrock.

On a related note.. My cable box is right next to my meter. What should I ground my cable drop to? Should I run a 2nd cable down to the rod or should I ground to the panel?

[transferguy]

posted by: suemarkp

Current code requires an "Intersystem Bonding Termination" (250.94), although you don't have to meet current code. This is a multi screw bar that is mounted outside near the meter or panel and is used for phone, CATV, satellite, etc -- whoever needs a ground connection. There may be kits now at the home centers for this. One of the screws or lugs on that should take a larger wire (a #6 is required), and that can go to the ground rod, the main panel neutral/ground bar, or a few other places. If you have an exposed Service Conduit (threaded rigid metal), you may also find an intersystem bonding kit that will bolt to it. Just using a bare copper wire from the disconnect to the rod would give you a point where you could tap on grounds to other systems. But it will oxidize and corrode over time, so the block is a better install, or use an insulated wire which a person can strip if they want to tap on in the future. The code says you can use this for existing buildings without an Intersystem Bonding Termination (must be installed at the Service Equipment and mounted outside):

(1) Exposed nonflexible metallic raceways
(2) An exposed grounding electrode conductor
(3) Approved means for the external connection of a copper or other corrosion-resistant bonding or grounding electrode conductor to the grounded raceway or equipment

Mark
Kent, WA

[transferguy]

posted by: Mr T

If I read this right this is something I can take care of after my ground rod is buried and done with. I don't need to run anything else to my ground rod...Correct?

[transferguy]

posted by: suemarkp

If you have a metal service conduit accessible on the outside of the house, or your main disconnect is mounted outside, then go ahead and bury the rod and GEC. Otherwise, you may just want to clamp on another #6 from the rod so you're covered.

Mark
Kent, WA

[transferguy]

posted by: Mr T

Thanks..

Now to threadjack my own thread...

The last thing I need to do before calling the inspector is my service riser. I am installing 200A service (meter/main) with a 100A feed to a sub panel that powers most of the house. My total demand load is about 115A with a 85A neutral load. I am trying to size my neutral for the riser and want to future-resistant it (not saying proof hehe). I am running 4/0Al up the riser (PVC-no mast) to the weatherhead for my hots. How much smaller should I make the neutral? 2/0 Al ok? There may be future (non continuous?) larger 120V loads down the road. (Air compressor, attic fan, etc) and I want to be safe for that.

[transferguy]

posted by: suemarkp

Since your calculated load is so low, it is difficult to answer. It only needs to be sized for the calculated load, and no smaller than table 250.66 (#2 AL). You can almost always reduce the neutral by 2 sizes without a problem. 4/0 AL is good for 180A, and 2/0 AL is good for 135A (assuming you can use it at 75C). If you can find an easy 45A of load that will never have a neutral, then 2/0 is easy to justify.

You can work this backwards by subtracting your 240V only loads and applying a demand factor. For example, if you have 20A from a 240V water heater, and 25A from a 240V HVAC unit, that is 45A that will never have a neutral load. The optional calculation puts a 40% factor on most loads (although HVAC is 100%), so multiply 45A * .40 and you get 18A. So you can easily reduce the neutral by 18A (or take the HVAC at 100% so you'd get to reduce by 33A if still taking the water heater at 40%). If you have an electric range or clothes dryer, you can subtract off 12% of its nameplate amps for a neutral reduction too. Anything else purely 240V you have connected?

You should have no problem running three 4/0 conductors up a 2" pipe if you don't want to reduce. You only need one size of wire that way and have a bit more leeway on cutting and waste when you only use one size.

Mark
Kent, WA

[transferguy]

posted by: Mr T

The only pure 240V load is my AC which draws a whopping 13 amps (there is a plus side to owning a hut).

With the exception of a garage workshop, I do not see any more loads (especially large 120V/ or 120V/240V loads) being added to this house. The service was sized up to 200A at a recomendation from the city and since the only suitable meter/mains I could find were 200A rated, so why not.... I may try my luck with a 2/0Al neutral.

Adding more fun to my situation, I have not found any local place (not near any big cities and very few supply houses around that sell to the public) that sells 4/0Al by the foot. I did run across a URD type wire of 4/0 4/0 2/0 Al that is USE-2 / XLPE and marked sunlight resistant. I looked it up and it's rated for underground use or 'in a duct'. I have found a few large arguments online about the use of USE above ground. Most of those involved cable that was not sunlight resistant and it seemed to be the factor that knocked the cable out. If USE-2 is not allowed above ground other then getting to the meter, why is it sunlight resistant? I've read about several situations where it was ok'd to be used when it was sunlight resistant. Is this a case by case thing? Should I keep looking?

[transferguy]

posted by: suemarkp

NEC 338.12 Uses Not Permitted.
(B) Underground Service-Entrance Cable. Underground service-entrance cable (USE) shall not be used under the following conditions or in the following locations:
(1) For interior wiring
(2) For above ground installations except where USE cable emerges from the ground and is terminated in an enclosure at an outdoor location and the cable is protected in accordance with 300.5(D)
(3) As aerial cable unless it is a multi conductor cable identified for use above ground and installed as messenger supported wiring in accordance with 225.10 and Part II of Article 396

The sunlight resistant rating would apply in few cases. One I can think of would be an intermediate pole where you are transitioning from overhead to under ground. That little bit above the conduit where you splice to the overheads would need to be sunlight resistant. Ducts are usually underground..

Doesn't your local home depot sell SEU cable in 4/0-2/0-4/0? Worst case, you could buy 2/0 CU THWN wire, as most of those are sunlight resistant. You could save a few dollars by dropping the neutral to 1/0 copper.

WEB LINK

Mark
Kent, WA

[transferguy]

posted by: Mr T

Can SEU be run in a conduit? (That cable is sold around here) I prefer the look of conduit over open cable. It just looks cleaner and it's visible from the road.

I was hoping to avoid copper but I may just go wtih it and be done.

FYI One of the first hope depot's in the country to close was the next city south of me. They opened too many too fast in saturated markets.

[transferguy]

posted by: Mr T

I ended up going with copper strands. I found a way to get it for 50 cents a foot cheaper so I went that way.

The inspector signed off on everything yesterday so I can have it hooked up. Now off to decide what to tear apart next.

FYI for anyone reading this thread. 250.94 / intersystem bonding was mentioned as new to "current code" earlier in this thread. It exists going back to the 2008 revision. The bonding bars are available in several styles at most major home improvement stores. The electrical dept employee at one place did not even know they carried them (or what they were).

[transferguy]

posted by: suemarkp

I thought I answered your previous post, but I guess I forgot. Yes, you can put SEU in conduit. But if it is a complete conduit system (weather head to box), it would have to follow conduit fill rules. If it is open on the top, it is just a sleeve, and you can certainly sleeve SEU for damage protection. The code requires that protection for heights up to 8' above grade.

Mark
Kent, WA