Sub-panels - one more time

I’ve seen many discussions on this subject in general, but have one more (hopefully final) question… If there is a sub-panel in a remote building, where there is no other conducting path connecting the two, a 3-wire service was acceptable under earlier code editions. My question is - if all the conditions are present to qualify for that exception, should a ground rod be driven at the remote location and be connected to the neutral / ground bus in the sub-panel? TIA

Yes.

Jeff, I understand that to be required for detached buildings for lightning protection. Is that correct? :slight_smile:

Yes, that’s correct. I would add one thing, a ground rod is not required but a grounding electrode is. It could be something other than a rod. Here’s what the NEC has to say about why things are grounded:

Not approved In Canada .
The system ground must be carried with the two hot wires and the neutral.
The neutral is then complete isolated from the ground through out the rest of the system.
A secondary ground in out buildings frequently causes Eddie currents

( http://www.oeb.gov.on.ca/OEB/_Documents/EB-2007-0709/report_Kinectrics_20080530.pdf)

(http://www.mrec.org/pubs/ARSpub696/document.pdf )

Thanks Robert.

One more for you that I heard today from an electrician on the job.

The newest NEC code requires that there be two ground rods 6’ apart and a grounding conductor goes to the panel and a #6 ground wire has to go from the water service piping back to the meter and not the panel as it is now.
Is that the way it is now?:slight_smile:

The requirement for two 8’ ground rods has been around for a while, sort of. The old requirement was for a single rod to have a resistance or 25 ohms or less. So on a service you could buy expensive testing equipment and prove 25 ohms or less or you could simply install two rods a minimum of 6’ apart (we always just install two rods). The 2011 simply reverses the requirement, now you must install two rods or prove that a single rod has a resistance of 25 ohms or less. IMO this makes more sense.

I have not heard this for 2011. Under the 2008 and earlier code editions you need to connect all of the electrodes together to form a grounding electrode system (GES). You’re permitted to connect one electrode to another with a bonding jumper or a GEC back to the neutral bus at the service disconnect.

Here’s a nice GES graphic from Mike Holt:

http://www.mikeholt.com/onlinetraining/page_images/1113918256_2.jpg

Thanks Robert, that is a good illustration, I will print it out. :slight_smile:

I gave a simple answer, but you are certainly correct. The requirement is for an effective GE.