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| Subject - Grounding outbuildings | |
| sammyg |
When hooking up a building such as a barn, underground, from a meter and disconnect on a pole, should there be a ground wire run from the disconnect, or can a ground rod be driven at the barn. I usually see a seperate bare conductor run unerground. The same question for mobile homes. |
| Ryan_J | It depends on whether or not there are metallic paths between the two structures. See 250.32. |
| lctrc789 | Sammyg, I have always looked at article 250-32 in this manner,250-32 (b) I always use as my first choice 1. I always use 4 wires in all sub panels then the sub panel is always wired as a subpanel, meaning that the grounds and the neutrals are seperate, and the MAIN panel is the disconnect. In mobile homes BY the code the disconnect should be no more then 30 ft and in sight. It is state code here all mobile homes require a 4 wire system and that applies to all counties as well. Some counties do require you to drive a seperate ground rod to attach only the metal frame of the mobile home too. As a general rule of thumb and in accordance with local and state codes we teach all apprentices to use the 4 wire system here and always treat the disconnect as the main panel, the main neutral is where all your grounds always hook up to so henceforth you would have a ground wire suitable in length and size to use as a ground to your sub panel. |
| sammyg | That is a good point that I had not heard of, the disconnect should be no more than 30ft. The last one I did the power company set the pole with the service on it approx. 90ft. away from mobile home and 170ft. from where I had to run the wire into the home. I will mention this to them, since they are underbidding us for the services and need us to do final hookups. |
| lctrc789 | Sammyg if you have a code book in article 550-23 Mobile home service equipment it does state that the service equipment must be placed in sight and not more 30 feet from an exterior wall from the home it serves. As a basic rule of thumb all disconnects should be in sight of what they control. |
| sammyg | That service was in sight since it was in an open field, though much further than 30 ft. Is there anything wrong with running a bare ground underground or should it be insulated? |
| Ryan_J | Baregrounds are fine :) |
| lctrc789 | sammyg, your local jurisdiction may allow more then 30 ft for the disconnect means, all are different. As stated, by Ryan the bare grounds are fine to use. |
| kbsparky | With regard to bare ground wires for mobile homes .... It should be noted that the feeder cable or conductors for a mobile home shall have 4 continuous, insulated, color-coded feeder conductors, one of which shall be an equipment grounding conductor. (emphasis added) A bare equipment grounding wire is not acceptable as part of the feeder cable or conductor assembly. This includes using such wiring methods as type "SER" cable, a common violation I've encountered. See NEC 550.10(I) 550.16 550.16(B)(1) 550.33(A) All these sections refer to the insulated green-colored wire. I am referring to the feeders that connect from the required service disconnecting means located within 30 feet of the mobile home. Any grounding conductor(s) that feed to that disconnect, or the grounding electrode conductor(s) are not part of this assertion, and as such, may be insulated or bare.  |
| Ryan_J | Good catch. I overlooked the part of the question about mobile homes. |
| pimpskillet_sparky | Well I can say this for an outbuilding. I 'hooked' up the shed last year, after talking with the county's inspector, as I am not a residential electrician, and figured I would get the anal retentive guy, so I asked him for the easiest and cheapest way. Ran 10/2 Underground feeder out the bottom of the panel and moved it a feet to the side of where the panel was. Popped a hole in the siding, fit a surface mount GFCI weatherproof, blah blah blah.. lol a little carlon (pvc down to 24") and out to the shed, where I put in a lighted switch in for my disconnect. The GFCI was sufficent enough to trip the shed like it should have. Sure helps having nice halogens on the back acre.. midnight football anyone? golf even? :) |
| Wirenutz | isn't the theory behind 250-32 , and addendum articles such as livestock barns or pools, mobile homes etc that dictate isolation of and/or dedicated EGC a tad screwed up when the poco's only supply a 3-wire? aren't there plenty of meters on aluminum siding out there? what about a serving pad mount x-former within arms reach of said building ? further, if zero reference (sine wave) and lightning protection are the chief goals of GEC's , why is it that the single ciruit exception has no proximity or ampacity parameters? i could , hypothetically, run a single 240V multiwire to my pottery shed 1000' away up on a knoll without GEC's ~W~ |
| kbsparky | quote: And that would be perfectly acceptable as long as there was no other metal parallel path present, such as water lines, gas piping and such. |
| Wirenutz | understood kbsparky yet that said scenario is applicable after the meter, yet not before it also puts a tad of a damper on any iron clad theory here doesn't it? or are those those municipal h20 systems, cable , ph only potential conductors for us? ~W~ |
| Robertalphonso | A simple rule to remember is that the Earth can never be used to complete the ground path. Auxilary grounds are fine, but a hard wire connection must be maintained to the source of the Neutral/Grounded Conductor (service entrance or transformer) in order to assist Ground Fault Devices to clear faults and so the earth between the auxilary ground rod and the neutral bonded ground rod would not be energized in case of a fault. The single branch circuit to the shed would maintain this hard ground. Just to reiterate... the Service for a mobile home does not have to be within 30', but there must be a service disconnect within 30' (and be within "line of sight"). |