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#4661 10/07/01 11:51 PM
Joined: Jun 2001
Posts: 141
amp-man Offline OP
Would appreciate your opinion on this--

A client has approached me to wire a 60' x 40' barn. It now has a 240V, 30A dedicated branch circuit supplying a well pump. Fed with 10/2 WG romex via 3/4" GRC underground from main panel at house (about 90').

Theere are now no other electricals in barn. Client would like to add a few fluorescent fixtures and a few general-use outlets. No plans for shop in the building, however, there is a partial second floor storage area that may be converted later to a mother-in-law apartment.

To meet immediate need, I propose to: pull out romex, pull in three AWG 8 THWN conductors (protected at main panel at 40A) to a new subpanel, using GRC as the EGC. Drive a ground rod. Bond panel to the well casing via galv supply pipe. Feed 240V to the pump from the subpanel. Wire in two 20A branch circuits--one for lights, one for plugs. Wiring in the barn will be exposed, so I will use MC cable. GFI receptacles.

Now, what if the client wants to instead run a bigger feeder (say 60-70A) to barn now to provide power to the future apartment? I'd run new GRC (or sched 80 w/4-wire feeder) to a barn subpanel. Should I leave well pump on the existing branch ckt from the main panel, or abandon the branch circuit and feed the pump from the new subpanel?

I don't see the requirement that a building have only one service as applicable here. This is not a service. I also do not see any obvious hazard from having a feeder and a branch circuit from the same panel come into the barn. Keep in mind that I would run both a neutral and an equipment grounding conductor to the subpanel (because the branch circuit conductors are parallel metallic paths between the two buildings. I didn't notice if the water pipe was galv. iron or PVC. If it's galv iron, another reason to run a 4-conductor feed).

Any thoughts about my general approach or the specific question?

Thanks in advance...

#4662 10/08/01 02:36 PM
Joined: Oct 2000
Posts: 5,392
215-2(B) comes to mind where it states 'feeder conductors', my Q would be just what would the plural of conductors refer to as applied to the 30A ?

How would the demand load calc reflect the futiure 'living area' apply , per 220 ?

i like the in-law idea!

are there any animals???

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#4663 10/08/01 06:25 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
You're going to have to get rid of the circuit to the well if you go with the larger feeder. Article 225 deals with outside branch circuits & feeders & is frequently overlooked. You're right, you aren't running a service, but you're only allowed one feeder or one branch circuit (generally speaking). See 225-30(b)

You'll also need 2 ground rods unless you are able to test the rod resistance & it ends up less than 25 ohms.


Few things are harder to put up with than the annoyance of a good example.
#4664 10/08/01 07:25 PM
Joined: Jun 2001
Posts: 141
amp-man Offline OP
Tom & Sparky,

Thanks very much. Tom, I see that 225-30 is the pertinent requirement. My situation does not fit any of the exceptions. And your point about ground rods is well taken.

Sparky, no animals in the barn. It's more a storage area for boat, tractor, etc. I also thought about animals & ground currents.

Your thought on Sec 220 & load calcs is right on; I wouldn't install a new raceway & feeder until I got an idea of how the mother-in-law unit would be set up (HVAC load, kitchenette?). Although the MIL unit is "just a thought" right now, I want the client to be aware that the upgrade we're talking about will not give them the power for the apartment, IF they ever do it.

Work safe,


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