ECN Forum Forums Code Related Discussion NEC & other Code issues 250-32

And what if he'd been in the same building, but 1000' away? The extra GEC wouldn't be required or allowed by Code.

[This message has been edited by electure (edited 08-05-2001).]

Without getting into Code specifics, I would put the problem with the detached garage like this:
1. If you pull an EGC to the subpanel, then you treat it like a feeder, and DO NOT drive a ground rod, nor do you bond the neutral at the subpanel.
2. If you leave the EGC to the subpanel out, then, you treat the subpanel like a service. You would drive a ground rod, and bond the neutral at the subpanel.
In example #1 the fault current would travel along the EGC, back to the main panel, through the main bonding jumper, out to the utility transformer, back through the MCB, through the feeder breaker, through the feeder, and trip the branch circuit OCP.
Example #2 would basically be the same except the fault current would travel on the neutral from the subpanel back to the main panel.
electure,
I hope the above makes sense to you. I think if you do some research, you'll find it to be true. Good Luck.

SlamTex
I believe you are mistaken about not "driving a ground rod" when you bring an Equipment Grounding Conductor with the conductors supplying the building. If there is more than one branch circuit to or in the structure you must bond the panel or disconnect enclosure to a Grounding Electrode. That electrode could be any of the ones in 250-50. If you ran an Equipment Grounding Conductor with the supply circuit/s you do not bond the grounded conductor to the enclosure. If there are no metallic pathways of any kind between the buildings you could omit the Equipment Grounding Conductor from the supply circuits or feeder and bond the grounded conductor to the enclosure.

would a phone wire bettween buildings constitute a 'mettalic path"

I think the code says yes but that does not make sense to me. A coaxial cable might serve as a parallel path to the grounded circuit conductor but the telephone wiring is not itself deliberately grounded anywhere outside the telephone central office. The protectors at each building are grounded but if they fail they are designed to fail clear leaving a crude air gap lightning protector in place. The only time the telephone wiring would carry the circuit currents is after a power cross. Given there gauge they would last about a second.

Although SlamTex's interpretation of this section is incorrect, I believe it has more "common sense" merit than the actual Code. I see a big difference between an underground feeder with an Equip Grd and an aerial Triplex to an outbuilding.
A 30' length of #8 copper has a lower resistance than the homeowner's knee to concrete connection. In the case of a hot to box short, it will cause the OCPD to trip.
Lightning in this area (OC, CA) is a rarety.
For us to run a 700'+ feeder in a warehouse building is not at all uncommon.
Why then, is the Grounding Electrode required, even though the buildings might be only 1' apart, on the separate structure?
(As a side thought, would I be called if the ground rods were 2' apart from each other?? curious)

intent & theory do not coexist in 250. it would almost be better if 250 was formed into 2 lists, ground it, don't ground it...

case in point,
if i run a 100A 240V branch circuit to an outbuilding, no OCPD's, a branch circuit, let's pick a nice constant load, a hot h20 heater here....no GEC or G-rods required per 250-32.

there is no rationale to that

Just to set the record straight .....

Article 230 B. Overhead Service-Drop Conductors
230-21. Overhead Supply
Overhead service conductors to a building or other structure (such as a pole) on which a meter or disconnecting means is installed shall be considered as a service drop and installed accordingly.

[This message has been edited by Joe Tedesco (edited 08-09-2001).]

Joe,
that would just lead you to 250, and 250-32.
So if you where to generalize and require a G-rod(s) with this, we could have a situation where 30A overhead rates a GEC, 100 a UG does not....

again, confusion....

where is that 99' ad-hoc committee who's agenda was a user-freindly 250????