Multi-unit grounding

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iloveskydiving

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I have a 4-plex, each 100 amp feed #2 alum, 40yr old bld. each has a disconnect on the outside of the bld.Im upgrading each panel to a new one and getting rid of the federal pacific panels I dont care for.My question is can I install one ground rod and run one common grounding conductor for all 4-units and tap off of it,Im having trouble finding my answers in the code book.
Of coarse all the panels are in the center of the bld. You have to try jumping out of a plane if you haven't already. Thx Dave..........:cool:
 
Yes, taps are permitted to the GEC for multiple service disconnects. You'll probably need two ground rods. Are there any other grounding electrodes present? Here's a graphic form the NECH:

250.66%20Taps.JPG
 
Theres a #6 or #4 bare GEC ran from the meter cans to inside the building to the water pipe where it enters the building. No GEC are ran to any of the panels. On the outside below the 4 meter cans are 4ea. 100 amp disconnect breakers for each unit,no GEC in those either just the 2/2/2 alum srevice entrance cable. the GEC that goes the meter cans is taped off of and goes to one ground rod. Can I tap off the # 4 at the water pipe and feed the 4 panels, and add one ground rod outside and be within code,and where is that info Im having trouble finding...........:cool: Thx
 
OK., first thing we have to get straight is how many #2 conductors are between the

Main Disconnect and the 100a panel ? 3 or 4. Is it SE Cable or is it SER Cable ? With answers

to these questions, We can get you the proper response.
 
Thanks for your response, I have one #2 bare copper wire running from the main hoffman box on the outside of the building where the main power comes in.( from that hoffman box my 4 meters are feed and then the 4 disconnects)It runs from the hoffman box(which is locked) to the water pipe where it enters the 4-plex and ends there.There are no other GEC going anywhere.
Can I tap off the #2 close to where it hooks up to the water pipe and feed my 4 panels. The #2 outside by the hoffman box is taped with a #4 and is going to a ground rod........Thx :roll:
 
Disconnect to panel, how many wires , 3 or 4 ??? What I think you are trying to do is

run a wire from the cold water pipe to each panel and use it for the equipment grounding

conductor. I say this because the grounding electrode conductor is already run from the

water pipe to the neutral in the 'hoffman box' along with the ground rod, as it should be.

So, I'm going to say "No, you can not feed the panels from the water pipe". 250.24(B)
 
multi-unit grounding

multi-unit grounding

Sorry, 3 wires from disconnects to main panels.Maybe I'll just run #6 from each panel to their own seperate groung rod,but since I have a #2 solid copper going from the hoffman box outside the building (where the power feeds the disconnects)to the water pipe inside the building,I was interested in if I could tap off the #2 outside to a ground rod, 2 of them, and also tap off the #2 inside and run to my panels.....???? Instead of running 4ea # 6 from each panel.Thanks for your comments, I haven't been explaining it clearly enough.:confused:
 
You can't do that either, a wire to a ground rod will do nothing. You need four conductors

from the Main Disconnect to each 'sub-panel'.
 
I think we need a little more information. Is there a main disconnect at the meter, or is it just a meter that feeds four disconnects? Maybe that information is in one of the posts and I just missed it.
 
multi-unit grounding

multi-unit grounding

I have 4 meter cans, with 4 federal pacific 100 amp breaker in a seperate enclosure below the meter cans. 3 wire 2/2/2 feeding my panels from there.I have a #2 bare copper from outside to inside,Im wanting to tap off that #2 and feed each panel inside and 2 ground rods outside from the #2. Then 4ea #6 from water pipe to panels.????
 
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