Service Entrance: Grounding & Bonding

[John Ramey]

Working in Afghanistan where a generator is my service provider (no x-fer switch).

I am grounded and bonded at the generator... about 25 ft. away is my MDP... does this also require a ground-rod and bonding of my grounded conductor at this point? The MDP feeds several other sub-panels that feed other units.

 

[zbang]

Is the MDP in a building/trailer/etc or just sitting on the earth? I'm assuming that the MDP and subpanels are in some sort of building or trailer.

Without actual reference to art. 250 and simplifying things a fair bit-
Bond neutral to ground at only one point, and as close to the supply as possible.
Once you're past the system bond, you must run N and G separately
Each 'structure' needs a grounding system (rods, water pipe, etc), which must be connected to the G conductor from the power source.

So, every building needs it's own rods or equivalent. There should be a grounding wire from gennerator to MDP. If there is a grounding wire run from the MDP to the building(s)/sub-panels*, then do not bond N & G at those panels. If there is not a ground wire between them, you'll have to bond again there in order to provide a fault current path inside that building (a floating ground wire doesn't do any good).

* that requirement changes between code cycles.

You can read the NEC online from www.nfpa.org and on several other public web sites.

 

[John Ramey]

Thanks for the answer zbang, though... the situation I'm in is a bit different. Here the Generator is the only supply to the building, and most of the buildings are wooden/poletent set-ups. Really, it's all temporary wiring, on a permanent basis... these sites are set-up much like a FEMA site would be in a natural disaster area in the states... like a permament/temp basis

So, we do our very best to follow code, but in most cases it's impossible or very difficult to find code that wholly encompasses our scenario. My experience with Generators is as a temporary service, or a back-up via transfer switch. It just seems redundant to me to drive a ground rod at both generator & MDP + run neutral & ground from generator to MDP... and bond the grounded conductor to the ground at both points. Maybe I'm just overthinking it... been going 12 hour days for 2 months now... kinda tired

thanks for the tips anyhoo...

 

[vikinggamer]

As z is saying you bond neutral and ground once within 10 ft of the source of power. there after you run ground and neutral seperate and put ground rods at buildings connected to the ground cable (not bonded again)! unless ofcourse as he said you did not run a ground back. Basically after you bond you'll need a neutral and ground from there on with ground rods when needed, but only connected to the ground cable.... not bonded again.