Grounding multiple service disconnecting means

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mikehughes8

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I want to make sure I have this right.

A pad mounted transformer secondary feeds (3) 400A service disconnecting means. Each disconnecting means feeds a seperate load.

All of these disconnects a grouped in the same area. I want to drive (2) ground rods (at least 6' apart) and connect all of the service disconnecting means to a common grounding electrode system using the same GEC. Two of the disconnecting means would actually share the same GEC. The GEC will connect to each ground bus and connect via cad weld to the grounding electrodes along the way. The third would be connected via a cad weld to one of these grounding electrodes. Is this legal?
Could I get a code that permits this / doesn't permit this?

Any relevant codes will help.

Thanks in advance
 
If I understand what you want to do, the answer is yes. It's easier if you think about this as three parts:

1) The GES is all the grounding electrodes bonded to all the other electrodes.

2) The GEC is the wire that connects the disconnecting means to the GES (this needs to be continuous or Crimped/CadWelded).

3) If you have more than one disconnecting means, you can have GEC taps. These can be ordinary connections IAW 250.70.

You can also use more than one GEC and not directly bond the grounding electrodes (for example a residence with one wire to the ground rods and another to the water pipe).

The point here is that you don't need all that CadWelding (unless you really want to). What you are describing are GEC taps.

Mark
 
So if I have this right...

GES - (2) ground rods interconnected with with the appropriate sized piece of copper using listed pressure connecters

GEC - GEC from each disconnecting means connected to either of these ground rods with another listed pressure connector.

This will suffice?

The reason I chose cadwelds is because these connections will be buried making them more difficult to inspect.
 
Actually, you may be in a bit of a gray area by mixing the tap provision with the provision to connect to each grounding electrode separately. Look at 250.64 (D) and (F). I'd say you'd be on better ground to join the ground rods, then run a GEC in a continuous length to ONE of the enclosures and connect taps to the GEC using split bolts for each of the OTHER enclosures.

Seems easier and sure to be code compliant.

Mark
 
I would think post #5 or #7 either would be acceptable. as far as cadweld vs pressure, in either, it would seem the inspector will want to see the connection before being buried.
 
Where I am (Afghanistan) I am the AHJ. Even with my limited knowledge of the NEC I oversee the electrical contractor's work. I am the closest thing to a low voltage electrician the army has at this location. By trade, I operate MV power plants and design distribution systems.
You would think the contractor would know the answers to these questions already but they don't. They send guys with limited experience to no experience.
I have to correct the contractor on various things.
-Cable burial depth
-They have been running 5 wires from 3 phase 4 wire XFMR to main disconnects (had to correct them on that).
-Not applying 90 degree celcius cable at the 75 degree celcius rating.
-cutting off the top of grounding electrodes that they couldn't drive far enough into the ground

Just to name a few.

So I am trying to dictate to them, in situations with multiple services, how I want it done. Most installations are similiar. We use 150KVA, 300KVA, and 500KVA XFMRs only. They will have 1,2, or 3 400Amp disconnects respectively.

In an effort to get things right I often ask for help from the experts here. I am not willing to kid myself and pretend I know everything. It is to easy to miss a FPN, exception, or other applicable article in the NEC.
 
in this case 250.66A would size the GEC and taps would be taken to each service switch ground block OR grounded conductor if present. An additional rod should be driven and connected to the ungrounded conductor at the xfmr location
 
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Interesting location to be AHJ. Most of us, as inspectors, only worry about the "cussin' " and don't have to actually dodge bullets. Stay safe !
 
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