horrorsix said:
What is the correct way to ground a sub-panel box. I know the ground and neutral must be separated. But does the ground of the sub-panel have to go to the grounding rod or can it ground to the main panel box.
Is a 4 wire feed required from the main to the sub. 2 hot, 1 neutral, 1 ground?
"But does the ground of the sub-panel have to go to the grounding rod ....."
When I hear a question like this I realize that the asker doesn't understand the conductor categories.
#1
Ungrounded Conductor, commonly called "phase conductor" or "
hot wire"
#2 Ground
ed Conductor, most often the
neutral wire [but also a grounded phase conductor on a corner grounded delta transformer]
#3 Ground
ing Conductor, commonly called "
ground wire"
#3a
Equipment Ground
ing Conductor
#3b Ground
ing Electrode Conductor
#3c
Equipotential Bonding Conductor
#3d various types of bonding conductors, most commonly covered by 250.104
The subpanel is connected to the grounding system thru an
Equipment Ground
ing Conductor back to the main disconnect.
The
Equipment Ground
ing Conductor is required to be run with the other circuit/feeder conductors and can't go "solo" [250.134(B) + 300.3(B)] except in very limited situations such as 250.130(C). . The
Equipment Ground
ing Conductor can
not be connected to a ground rod. . Focus on Article 250 part 6 + 7 [250.110 - 250.148] when dealing with the
Equipment Ground
ing Conductor.
The Ground
ing Electrode Conductor is run "solo" all the time. . It is the one that would be connected to a ground rod. . Focus on Article 250 part 3 [250.50 - 250.70] when dealing with the Ground
ing Electrode Conductor.
There are very
limited situations when you can connect a Ground
ing Electrode Conductor to a
subpanel. . Separate buildings must have to have their own electrode [250.32 + 250.50]. . The panel in the separate building is a subpanel even if you bond the neutral under the conditions allowed before '08 under 250.32(B)(2). . You connect your Ground
ing Electrode Conductor to the separate building subpanel.
A strip store single service with feeders to individual tenants could be another uncommon example of a Ground
ing Electrode Conductor to a subpanel. . If there's
separate individual metal watermains for each tentant, the tenant subpanel would need to bond its individual watermain [250.52(A)(1) + 250.104(A)(2)]. . But if its a
single watermain for the whole strip but distributes from unit to unit in non-metallic, the conductor to your panel is classified as a
Bonding Conductor, sized by 250.122, and is not classified as a Ground
ing Electrode Conductor.
First disconnect/panel on the load side of a
transformer, let's not even "go there" right now. . Just get your basics straight first.
Equipotential Bonding Conductor is separate subject. . You'll find it in 547.10 [Ag Buildings], 680.26 [Pools], 680.74 [Whirlpools], 682.33 [Bodies of Water].
"Is a 4 wire feed required from the main to the sub. 2 hot, 1 neutral, 1 ground?"
In almost all situations, the answer is
YES.
You have a very limited situation for separate buildings covered by 250.32(B)(2) that allows a 3 wire from the main to the sub. 2 hot, 1 neutral,
0 ground [Equipment Grounding Conductor]. . This allowance/exception to the general rule is almost totally cut out in '08. . For '08 only existing runs can remain, no new 3 wires from building to building [unless the 3 wire is
1 hot, 1 neutral, 1 equipment ground].
David
