Dual grounding requirements

**Ken Amelin** · 05-04-2010, 05:34 AM

Many times I see homes that have a new service panel installed as replacement, but see no improvement to the ground connection. (dual ground connections vs. one).

Is it a requirement to update grounding (add a dual ground connection) when changing service panels?

Also, Does anyone know what edition (date) of NEC code was a dual ground requirement added?

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**Jerry Peck** · 05-04-2010, 06:20 PM

Not quite sure what you are referring to by "dual ground"?

Are you referring to the use of two ground rods?

**Ken Amelin** · 05-04-2010, 06:29 PM

Yes - Two ground rods.

**Ken Amelin** · 05-05-2010, 05:13 PM

Thanks Aaron.

Does anyone know if the second ground rod needs to be added when a service panel is replaced?

**Bill Kriegh** · 05-05-2010, 06:22 PM

The second ground rod only needs to be installed in certain conditions.

The policy of the local AHJ has much to do with whether the second ground rod gets installed when a panel gets replaced.

Philip · 05-05-2010, 08:59 PM

They have to drive another rod into the ground when the meter base is replaced due to storm and trees. The electrician told me, as he drove the rod into the ground at thirty degree, that when the requirement first hit they had to drive the rod straight at 90 degrees. He had to start hammering off of a ladder.

**Rollie Meyers** · 05-05-2010, 11:14 PM

See NEC art. 250.56 Here is a copy & paste from the 2008 edition.

250.56 Resistance of Rod, Pipe, and Plate Electrodes. A
single electrode consisting of a rod, pipe, or plate that does
not have a resistance to ground of 25 ohms or less shall be
augmented by one additional electrode of any of the types
specified by 250.52(A)(4) through (A)(8). Where multiple
rod, pipe, or plate electrodes are installed to meet the requirements
of this section, they shall not be less than 1.8 m
(6 ft) apart.
FPN: The paralleling efficiency of rods longer than 2.5 m
(8 ft) is improved by spacing greater than 1.8 m (6 ft).

The req. are unchanged from the 2005 NEC.

Rick Carpenter · 05-06-2010, 05:44 AM

I would agree about multiple ground rods only required if resistance measured does not meet Code 25 ohm standard.

Extra 2 cents..................

I would add however that if the service panel was replaced and also upgraded from say, 100 to 150 or 200 amps the size of the grounding conductor to the water meter piping would need to be increased in size appropriate for the upgrade. Again, only if the change included an upgrade in amperage.

**Jerry Peck** · 05-06-2010, 02:44 PM

Originally Posted by Rick Carpenter

I would agree about multiple ground rods only required if resistance measured does not meet Code 25 ohm standard.

To rephrase that ... if the resistance is not measured, or is measured and is greater than 25 ohms, then two ground rods are required.

To use only one means the resistance needs to have been measured and verified to be within the allowances.