Running a underground feeder line

I am switching from a lp gas fired stock tank heater to an electric heater. Today I pushed the 10 - 2 w/g underground feeder wire through a 3" plastic tile line I had put in a couple weeks ago (goes to the edge of the barn from the new 100 amp box). This new 100 amp box was installed this summer at the central distribution pole. Only one breaker is presently installed feeding the grain bins. I am hooking into this 100 amp central box. Coming down the pole are 4 wires - 2 hot wires (no identifying tape), one wire taped with white electrical tape (neutral), and one wire taped with green electrical tape (ground). The two hot wires go to the bus bars the fuses snap into. The white taped wire goes to the neutral bar. The green taped wire is in a connector which is screwed tight to the electrical box along with the green taped wire that goes to the grain bin. The white taped wire from the grain bin is attached to the neutral bar with the other white. Of course the black wires from the grain bin attach to the 2 pole fuse. So, it seems that the ground wires (green taped) and the neutral wires (white taped) are not ever connected in this box to a common bar. Also the screw typically provided to bond the neutral bar to the box isn't in place. The neutrals and the grounds are not connected as in many boxes I have worked with. There is no earth ground rod either. Maybe this box would be considered a sub-panel where the neutrals and grounds do not connect.

A lifelong excellent electrician installed the new box the summer. Anyway, how do I connect this new 10 - 2 w/g????? I know the black goes on the new fuse. The white goes on the neutral bar. But, should I just attach the ground to the box and stay away from the neutral bar???????? Maybe the new feeder wire ground should be slid in the connector where the two other big grounds are connected. Thanks.

Sounds like your in good shape. Connect your new grounding conductor to the same point as the incoming grounding conductor is connected. Not to the neutral. The neutral and grounding conductor should only be connected together at 1 location, at the main service.
Be safe!

You dont mention if your heater is 120v. or 240v. If in reality it is 120v. connect it just as you thought, black to the breaker, white to the neutral and the bare ground to the isolated ground bar.
Your electrician was correct in his method. It all has to do with ground potential. I would be lieing if i said i understand it well enough to explain it.

And if the heater is 240v. you need a two pole breaker. Then both the black and the white go to the breaker and the ground still goes to the isolated bar

The heater you will be running, is it 220v or 120v?

If 220v, you will need to add a 2 pole 30 amp breaker. Connect a black to one leg, a white to the other, the bare to the green ground strip.

If 120v, add a single pole 30 amp breaker. Connect the black to the breaker, the white to the neutral strip, the bare to the ground strip.

Yes, heater is 110 volts. Single pole breaker.

There really is no ground strip. The two big ground wires (one coming down the pole and the one going underground) are in a purchased connector (might have two set screws clamping the wires in) and then the connector is screwed to the back of the metal panel. I think everyone is saying to add the new ground to this connector with the other two big wires. I guess I could just fasten this new ground to the back of the panel individually, but would be concerned with conductivity years down the road. Probably attached to the other big grounds would be better.

The local big box home store's electrical department will likely have small ground bars you can buy. These will have several set screw wire connectors and 2 open holes to bolt the ground bar to the back of your panel. A more cost efficient option would be to tap a small screw in to the back of your panel, and wrap your solid grounding conductor around the screw and tighten it down. They actually sell green #8-32 ground screws just for this. You may even have tapped holes in the back of your panel for adding a ground bus.

Either way will work.

If there is room, loosen the ground and slide it in along side the other wire.

Or attach it to the panel case with a ground lug, or under a screw and washer. If you think there will eventually be other circuits added, you can add a ground strip with several terminals.

Even though it's only 30 amps you are setting up a sub-panel. You should isolate the neutral and the ground wires at the main box and install a earth ground at the barn to tie in the ground. Since you are only using 10-2 wire you must be only running 120v.

Be sure to use a GFI Recptacle at the water tank to plug into for the protection of you and your livestock.

Andy, as typical electrical (and legal) questions draw a lot of responses. Not being there I cant know if the box you're talking about is a main or a sub (I suspect) panel so I will describe the proper NEC and trade practice and let you figure it all out.

1) ONLY the Main distribution panel should have a Neutral Ground Bond, that's Single Point Grounding. Neutral is bonded to Ground there and the box's metal frame is bonded to the Ground, which is of course bonded to the Neutral Buss. Also at or near the main service entrance panel (Up at weatherhead riser,,,,,,,,Or in the Meter Base,,,,,,,,,,,Or in the Panel) the Neutral is bonded to all readily available "Grounding Electrodes" (via the Grounding Electrode Conductor like #4 bare copper wire) such as metal conductive utility buried pipes or structural steel or ground grids or "made electrodes" such as one or more copper driven into earth Ground Rods.......

2) At a SUB PANEL fed from the main panel NEUTRAL AND GROUND ARE ELECTRICALY INSULATED AND ISOLATED FROM EACH OTHER. There is a separate Neutral Buss and a separate Ground Buss. The metal frame is of course bonded to the Ground Buss (but NOT the Neutral Buss)

3) If you're running 12/2 w Ground wire using a single pole breaker out to your heater, that's good for 120 VAC likely 30 amps subject to enclosure and insulation etc. It has a White "Grounded Conductor" (Neutral), a Bare/Green Equipment Ground, and a Black UNgrounded Conductor (Hot). If you used a 240 ONLY volt heater you could run 12/2 w Ground but the Black and White would be 240 VAC and the Bare/Green the Equipment Grounding Conductor, and of course a two pole breaker.

4) Even if your wire has an ampacity of 30 amps, there is a voltage drop subject to wire size and length and current which may affect your project IE if voltage drop is too much you may need bigger wire.

5) As I recall NO WARRANTY things may have changed, per the NEC any buildings electrical service requires grounding which means if you wire a sub panel at the barn it needs proper grounding.

SOOOOOOOOOO if that box is a sub it needs separate and isolated and Ground and Neutral Busses and if you run yet another sub off it the same.

Hope this helps

John T Longggggggggg retired Electrical Power Distribution Design Engineer and the NEC may have changed and I'm rusty so NO WARRANTY

You have it correct. The only thing I would add is the neutral connection point in the 100 amp panel should be isolated from the back box. No continuity at the box between neutral and ground. { meter won't read that.]