4 wire feeders for outbuildings

[Don Hester]

Hey all,

I have a general question on residential sub- subpanels (distribution panel). When was 4 wires feeds required for out buildings?

If anyone has some dates on when this was implemented I would sure love to know.

Thanks in advance.

[Bruce King]

Its not even required nowadays as long as no other metallic path is present between the detached building and the house. Determining this is beyond the scope and should be done by an electrician. A ground rod or equivalent is also needed unless <25 ohms can be proven on the main rod.

[Don Hester]

Its not even required nowadays as long as no other metallic path is present between the detached building and the house. Determining this is beyond the scope and should be done by an electrician. A ground rod or equivalent is also needed unless <25 ohms can be proven on the main rod.

Bruce, I understand and should of made it a bit clearer/defined. I still want to know when it became effective.

And just because it is beyond scope does not mean I can not know ; ) I am curious.

And as you know sometimes the electrician do not even know ;)

[Bruce King]

Bruce, I understand and should of made it a bit clearer/defined. I still want to know when it became effective.

And just because it is beyond scope does not mean I can not know ; ) I am curious.

And as you know sometimes the electrician do not even know ;)


It also depends on whether or not the feeder has a metal conduit for the ground. I think 1996 had some clarifications and changes but basically a three wire feed without a metal conduit has been wrong for decades even though it was allowed by most AHJ's due to the cost or availability of 4-wire cable several years back.

Maybe one of the code experts can chime in here.

[Jim Port]

Its not even required nowadays as long as no other metallic path is present between the detached building and the house. .

The option of installing a 3 wire feeder was removed in the 2008 NEC regardless of other metallic paths between buildings. An existing 3 wire feeder can remain.

[Jerry Peck]

Just repeating what Jim posted to make sure it is understood: the 3-wire option is *no longer allowed*, regardless of what does or does not connect the two structures.

Also, as Jim stated, that change was in the 2008 NEC.

[Don Hester]

Bruce, Jim and Jerry, Perfect this is exactly what I was looking for.

Thanks

[Jim Port]

Thanks Jerry.

[Rollie Meyers]

Its not even required nowadays as long as no other metallic path is present between the detached building and the house. Determining this is beyond the scope and should be done by an electrician. A ground rod or equivalent is also needed unless <25 ohms can be proven on the main rod.


If a rod is used for a grounding electrode, a 2d rod must be driven unless 25 Ohms of resistance or less can be proven. There is nothing about the "main rod" resistance exempting a GEC at a detached structure.

Here is the text from the 2008 NEC.

250.56 Resistance of Rod, Pipe, and Plate Electrodes. A
single electrode consisting of a rod, pipe, or plate that does
not have a resistance to ground of 25 ohms or less shall be
augmented by one additional electrode of any of the types
specified by 250.52(A)(4) through (A)(8). Where multiple
rod, pipe, or plate electrodes are installed to meet the requirements
of this section, they shall not be less than 1.8 m
(6 ft) apart.
FPN: The paralleling efficiency of rods longer than 2.5 m
(8 ft) is improved by spacing greater than 1.8 m (6 ft).