Sub-panels - one more time

[Frank P. Newman]

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

[Jeffrey R. Pope]

Yes.

[Marcel R. Cyr]

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

[Robert Meier]

Originally Posted by mcyr

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

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:

250.4 General Requirements for Grounding and Bonding.
The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.
(A) Grounded Systems.
(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.
FPN: An important consideration for limiting the imposed voltage is the routing of bonding and grounding conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided.
(2) Grounding of Electrical Equipment. Normally non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.
(3) Bonding of Electrical Equipment. Normally non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.
(4) Bonding of Electrically Conductive Materials and Other Equipment. Normally non–current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.
(5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.

[Roy D. Cooke, Sr]

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/_Docume...s_20080530.pdf)



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

[Marcel R. Cyr]

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?

[Robert Meier]

Originally Posted by mcyr

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

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.

Originally Posted by mcyr

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?

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:

[Marcel R. Cyr]

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

[Jeffrey R. Pope]

Originally Posted by Robert Meier

I would add one thing, a ground rod is not required but a grounding electrode is. It could be something other than a rod.

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