how many ground rods at a sub fed panel?

[Matt the electrician]

Hello,
My question is when installing a 60 amp sub fed panel to a detached building do you install 1 or 2 ground rods. In the Hampton roads area of Virginia we are required to install 2 ground rods for a main distribution panel even when you bring up NEC 250.53 (2) and its exception.

 

[augie47]

Local jurisdiction issue. The NEC only requires you establish a grounding electrode.

 

[wwhitney]

In the Hampton roads area of Virginia we are required to install 2 ground rods for a main distribution panel even when you bring up NEC 250.53 (2) and its exception.

Absent local amendment, if you really do the proper earth resistance test to show 25 ohms or less, then yes, NEC 250.53(A)(2) Exception says one rod is enough. But there is an inspection/enforcement issue--are you going to have your test set up when the inspector comes, so they can verify the 25 ohms or less? And is doing all that actually easier than installing a 2nd rod, which should be easy for an inspector to verify?

Cheers, Wayne

 

[Joe.B]

This is something that was changed/clarified in the 2020 NEC right? A subtle change for sure, but I thought previously you could have just a single rod at separate buildings?

2017 NEC
250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
(A) Grounding Electrode.
Building(s) or structure(s) supplied by a feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.
Exception: A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non—current-carrying metal parts of equipment.

2020 NEC
250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s)
(A) Grounding Electrode
A building(s) or structure(s) supplied by a feeder(s) or branch circuit(s) shall have a grounding electrode system and grounding electrode conductor installed in accordance with Part III of Article 250. Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.
Exception: A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non—current-carrying metal parts of equipment.

 

[infinity]

This is something that was changed/clarified in the 2020 NEC right? A subtle change for sure, but I thought previously you could have just a single rod at separate buildings?

Not really. You needed to create a GES so if you were using ground rods to make the GES you needed either one rod proven to be 25 ohms or less or just pound in two rods. That requirement has been around a for a few decades.

 

[Seven-Delta-FortyOne]

Always 2 here.