Grounding Electrode

Specific Inspection Topics Electrical Inspections
1

With this in mind. . .

**250.24(A)(1) General. **
The connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.

Scenario. . .

400 amp service with a single switch (disconnect) located at the exterior of the home.

Approx. 30 feet of continuous, 3 inch, RMC to the first distribution panel (three wire feed plus RMC). This distribution panel fed four additional panels down stream, plus a portion of the homes branch circuits.

The grounding electrode (ground rod) was attached to the grounding bus of the first distribution panel via (approx) 15 feet of cable and LFMC, with no connection (other than the RMC) back to the service equipment.

This was a “no-brainer” because the grounding bus was not bonded to the distribution panel, therefore, not bonded to the service eq.

Question. . .

If the bonding had been there, would this have been acceptable under the GE requirements of 250.24?

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2

I read this:

"any accessible point from the load end of the service drop or service lateral "

[FONT=Verdana]As not “any point” on the service equipment but location (House wise) in relation to the “Main” service panel near the service entry point.

What your describing / showing is any point along the service equipment installation. I see this as problem. The difference in potential at the service panel with respect to any point down stream of the service panel could be enough to kill someone. I equate this to two GEC’s not bonded 30 feet away… What is the difference in potential there? Three wire feeds…:roll:

Also looks as if you have 3 phase power from that one picture…

Sure RMC but are we sure it’s a continuous electrical path with least resistance (impedance)?

What is the deal with the grounding rod…I have the impression it is not copper skin but a plated deal corrosion special…

Where are the sparkies?? tick tock tick tock…:wink:

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3

It was a 3-wire system (via 6 conductors) plus the RMC, which is okay if done properly.

I questioned the distance (and method) from the service to the electrode and was hammered by the EC.

As far as I could tell, the rod was just painted.

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4

It was a 3-wire system (via 6 conductors) plus the RMC, which is okay if done properly.

I questioned the distance (and method) from the service to the electrode and was hammered by the EC.

As far as I could tell, the rod was just painted.

5

Jeff,

Can’t tell you if this is or isn’t acceptable. Don’t know:(
Local AHJ thing??
I can tell you from what I see here that the GEC (RMC and wire)for example in my house alone is over 25 feet in length BUT this is Chicago where A GEC system is a cold (old) Galvanized steel pipe into soil.

I have seen even longer runs … There is an issue with resistivity and diameter of a wire / conductor and rod itself so perhaps Paul , Greg, Joe, can elaborate on that .

R=rho x length/A rho for copper is 10.37 based on CM (circular Mils) /Foot @ Temp of 20deg Centi (77 deg F) A.K.A room temp

For example:
If you have a 3/0 for the GEC.

A 3/0 is 167,810 Circular mils… “A”

So lets take a 3/0 and say 15 feet length and you have:
rho (0.0618 ohms per 1000 feet) that gives you .0000618 per foot. So
15 times .0000618 =.000927 ohms… Not much Resistance / Impedance.

It depends on the AWG used I would think and the run…

My NERD side…:D:D:D

6

The “switch” was the service disconnect. That is the last place the GEC could be connected and that is where the main bonding jumper should be.

7

Thanks Greg (you too Pat ;)). That’s pretty much what I thought.