MNSPD Wiring for 120V AC Panel

[vtmaps]

There's a separate ground rod for the cabin and one for the detached garage. If there is no ground wire running between the cabin and the detached garage (I'll need to check if there is), would I need to do a separate nuetral-to-ground bond in the cabin also?

I have much the same question.  If two buildings are very far apart, isn't it permissible to NOT run a cable between the ground rods at each building? 

I'm off grid, but from what I understand of the power company, they run hot and neutral between houses, but do not run a ground wire from one house's ground rod to another house's ground rod.

--vtMaps

[Halfcrazy]

On systems that have 2 panels some distance apart it is permissible to use a 3 wire (Neutral, L1 and L2) between the structures with a ground rod at both structures and a neutral to ground bond at both structures as well. So the Neutral wire is actually bonding the 2 grounds together in this case and NEC makes a provision for that

[tecnodave]

Under NEC 2008 the feeder to the second dwelling must have the ground wire and it must be bonded to the ground rod at each building. I had to redo one installation where I had run the 4 wire 240 volt service in conduit and used a separate 6 ga ground wire to each ground rod but I had a real picky inspector who insisted that the ground wire had no splices. He considered that two separate ground wires to be spliced. So I added another ground wire that ran from the meter main through the first ground then direct buried in the conduit trench to the second ground rod and through it to the sub panel ground buss.

As I read the NEC 2008 there is no instance that you would be permitted to run L1 , L2 , and Neutral with no ground wire to the separate building. It " must be a 4 wire service" (240 volt service). This was a new requirement first implemented in NEC 2008 . This may not be required everywhere but is mandatory here. (Santa Cruz County, California also in the Cities of Santa Cruz and Watsonville). The panel in the second dwelling is a " sub panel" therefore not bonded neutral to ground. The theory here is to NEVER have current flowing in the ground wire which you would have if the neutral and ground would be bonded at two places. The voltage drop due to current loading occurs on both parts of the circuit and there would be voltage offset of neutral to ground in the second dwelling. Only a couple of volts but current in the ground is to occur only in fault conditions.

As I said before the code is how your local inspector interprets it. Here in California we have tough inspectors and two electrical codes the NEC National Electrical Code and the CEC California Electrical Code. If you saw some of the stuff that was done here in the 30's through 50's it would make you cringe. Basically I will only do a complete rewire to current codes no matter wether  you get a permit or not. I do not patch old junk, just too much liability. A few companies namely Stab-Lok and Zinsco have burned down so many homes here that the only thing that I will do with these panels is rip them out and replace them.

[vtmaps]

As I read the NEC 2008 there is no instance that you would be permitted to run L1 , L2 , and Neutral with no ground wire to the separate building.

As I mentioned earlier, the power company does it all the time... I've never seen a ground wire connecting the ground rods of two nearby homes.   Why is it OK for them, but not permissible for my two buildings on one lot?

--vtMaps

[tecnodave]

The power companies run under the NESC (National Electrical Safety Code) but all local jurisdictions run under the NEC ( National Electrical Code) or some variant  of it such as the CEC (California Electric Code)

The provision of which I am speaking covers one power drop to multiple dwellings no matter wether it has one or two or more power meters. In California the PUC (Public Utilities Commission) has ruled that utility companies may require all metering on a single property to be at one location (where practical) with the exception of different voltages such as a farm which has a 240 volt single phase drop for the buildings and a 480 volt 3 phase drop for the water  pumps and refrigeration.

Where there is two separate power drops to separate buildings the connecting of the building ground rods is not required no matter wether they are on the same property or on adjoining properties.

The code is very hard to understand and there is a book "Understanding the National Electrical Code" that is a must have even for people in the business. It is very difficult to use only the "National Electric Code" alone and get a full understanding of what is required.

Hope this explanation helps to clear up this issue, I had worked in industrial electrical and electronic fields for many years before I went into construction but I still had to learn much more to do this field.

td

[wb7qni]

I know this is an old topic but have very similar question. Running single-phase 120VAC on Outback inverter off-grid system (20 years old) and just tried to put a Midnite SPD on the AC side. Neutral and ground are bonded within this panel and I ran GREEN wire to ground, then both BLACK and RED wires to AC L1. No LEDs lighting up. Any suggestions most welcome.

Here's what I read from Ryan on this topic:

Here is how I would do it. Presumably one of these panels has the AC neutral and ground bonded. In that panel I would put the red and black on the AC hot lead and the green to ground. In the panel without the bond as the neutral floats sort of I would wire it Red to AC hot, Black (with included white heat shrink) on the AC Neutral and green to ground

We tend to over look Neutrals and in cases where the bond is a ways away this can be problematic. Electrically it is at ground potential but during a strike or very strong surge the resistance in the wire can make it look isolated from ground.

Ryan