Greetings, Wrenches~ I'm advising some clients on an existing off grid power system. They have inverters and multiple AC sub-panels which feed several different structures. The various structures have their own breaker panels. The power runs 50 feet here, 20 feet there, 60 feet this-a-way and 220 feet that-a-way. In this African location there are no code inspectors; just a wish to do things right.
The gentleman who does their wiring installation has written as follows: "I am not sure whether it is right or not, but I have bonded netural to the ground rod at each box. The electrical container is grounded with 4 rods and all the grounds (at all sub-panels and main panels are all tided together. I tried to ground everything, everywhere--rods are cheep insurance." Mick says: I need to explain as simply as I can how to clean this up. Normally I would say that the neutral is bonded to earth at only one place on the entire property...the first AC box after the inverter stack. However, with one of the sub-panels 220 feet away, does that "single point" advice still apply? I became confused on this point when an inspector told me that it was OK to bond the neutral again if the sub-panel was over a certain distance away...but I can't recall what that distance is and I don't know if that's in the code or if it's just the opinion of that inspector. Mick continues: I've heard the term "separately derived" in this context, but what determines that? If a premise wiring system has a direct electrical connection to another system, can it even meet the definition of "separately derived"? Mick continues: If the client modifies things and reverts to a neutral that is grounded only at the first disconnect, the next issue is the question of how the grounds are "tied together". If that bonding occurs by virtue of the metal lugs on the metal housings of the various metal boxes, we want no other conductor connecting ground rod A to ground rod B, etc. Is that correct? Thanks for helping with my education so I can help with that of my clients. Mick Abraham, Proprietor www.abrahamsolar.com Voice: 970-731-4675
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