Opinions, please, on this wiring plan

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  #1  
Old 11-16-02, 06:56 AM
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Opinions, please, on this wiring plan

I'd like to know what you think of this wiring plan for what will basically be a 672-Sq.Ft. vacation/hunting/fishing cabin.

This would not be inspected, because the area where it's located doesn't have a building department, let alone any electrical inspectors. I'm interested in a safe and sensible installation, not necessarily one that is absolutely squeaky clean with the 2002 NEC, of which I have a copy. (For example, I'm not going to spend any money on AFCIs for the two 8' x 16' bedrooms.)

Beyond lighting, larger loads would be up to a full-size electric range, a 30-gallon, 3500-watt water heater, 1100-watt microwave and the usual blender, crockpot, etc., and other kitchen gadgets. One bath/utility room.

UTILITY POLE: Disconnect panel below meter, with 200-amp breaker. Available terminals for two feeds and a neutral, to which I plan to connect. The other available terminals here are used by underground feeds to a three-bedroom, two-bath trailer about 15 feet from the pole. There are also two sets of service feeds coming from the meter can, one going to a barn, the other to a pump house. Both are free-air feeds. I haven't seen inside this meter can, but the disconnect also shuts off these feeds. Apparently one set travels back up the riser and back out the weatherhead, then is split into two for the barn and pump house. I haven't determined the size of these feeds, but I'm guessing they're No. 8 or no larger than No. 6. The pump house load is basically a 240v submersible well pump and the barn is nothing more than lighting.

PROPOSED PANEL: Square-D QO Series 125-amp main-lug only, with 12 spaces and 24 circuits. (Might end up getting a main breaker for this panel before hookup.) Grounding and neutral busbars seem to be connected and I don't see any way to separate them. However, this shouldn't be necessary, since this will be a main panel. Neutral bonding screw would be installed.

SERVICE FEEDS: Three 1/0 AWG copper THWN from utility pole disconnect terminals previously mentioned, running approximately 200 feet in 1-1/2" PVC conduit buried at least two feet deep. I sized this based on 100 amps maximum load and I'm particularly interested in your opinions on this part of the plan.

GROUND AT PROPOSED PANEL: I'm not sure about the best way to go about this, since this is very rocky earth and driving an 8-foot ground rod completely in and below grade would be difficult if not impossible. I'm considering laying two eight-foot ground rods horizontally longways in the bottom of the two-foot-deep ditch containing the service feed conduit and connecting them six feet apart end-to-end with No. 6 bare ground wire. The first one would be connected to the neutral busbar of the panel with No. 6 bare ground wire. Would that provide an adequately safe ground? Any other solutions? There's a large, deep pond in a year-round creek about six feet away, so this soil should stay at least somewhat damp.

SEPARATE CIRCUITS: Utility/bath. Water heater. Each of two bedrooms. Livingroom. Kitchen (open to and off to one side of the livingroom) appliance outlets. Range. Exterior W/T receptacles would be on all sides of the building, wired to whatever circuits are nearest.

That's the plan and I think I've included all the relevant stuff. What do you think?
 
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Old 11-16-02, 08:13 AM
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Lots of stuff to consider. I'll comment on one for now. It sounds like there is a 200A circuit breaker fed by the meter that will act as your main disconnecting means. If this is the case, then from the main breaker down stream is your responsibility. Then you must provide 200A worth of wire from the 200A breaker to your panel. Then, if the panel is rated at less than 200A (you said 125A) you must have a main breaker to further protect the panel at its rating.
 
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Old 11-16-02, 08:22 AM
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Okay. That makes sense. Service wire protected by 200-amp disconnect must have ampacity of at least 200 amps. (Duh!! Can't believe I misfigured that one.)

And as for the panel I should go ahead and add a 125-amp main.

Without my running back to the tables right now, would you say 2/0 copper for the service cables would have the needed 200-amp ampacity for this?

And does the THWN running in conduit sound okay?

Also, would you recommend 2" conduit?
 

Last edited by HBB; 11-16-02 at 09:38 AM.
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Old 11-16-02, 11:11 AM
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Ground and nuetral are connected as they are the same rose with differant names.

Can't you sink a ground rod near the water? Earth should be soft there, I would think. Or is there a ground on the pole, like a guy wire?
 
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Old 11-16-02, 11:21 AM
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There's a guy wire on the transformer pole and none on the meter pole. Either one would be too far away anyway.

This is a dug pond in the creek, mostly clay bottom and sides but containing a LOT of rock. I might be able to drive an 8' rod all the way down about a foot into the pond from the bank, which would be very wet and probably make a pretty good ground.
 
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Old 11-16-02, 11:24 AM
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Wouldn't that be closer to code than your horizontal idea? I agree that you don't have to stricly adhere to code in your situation, but I'd still try to be as close as possible. The safer the better.
 
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Old 11-16-02, 11:31 AM
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Yeah, seems to me it would -- especially if I drove two rods connected as described before.

But the possibility remains that it may not be possible -- just haven't tried it yet. That ground is a beast. Putting in T-posts is a major nightmare.

What do you think about that THWN 2/0 copper for the service wires? Table says it's good for 195 amps at 90-deg. C.
 
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Old 11-16-02, 01:33 PM
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Yeah, 2/0 should be ok. You'll probalbly never approach 1/2 that.
 
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Old 11-16-02, 05:13 PM
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First I will start with the grounding. Your first panel is considered the 200 amp disconnect switch. Anything after this must be a 4-wire with grounded and grounding wires seperated. That is a very inportant safety issue. There are exceptions to this, but if you want my oppinion on it they are not safe. As for the ground rods, I will have to check on laying them in the trench. You use to be able to do this if the trench was over 2 feet deep, but I do not know if that has changed. You will need a main in the panel. I would use at least a 2 inch PVC conduit. As for circuits, you need a sepreat circuit for your bathroom as well as a minnium of 2 circuits for the kitchen. If it was mine I would put 3 or 4 in the kitchen. Crock pots and microwaves are killers.
Let us know how it turns out
Hope this helps
Brian
 
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Old 11-16-02, 05:37 PM
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Appreciate your comments on this, Brian.

Yes, I'm a believer in lots of outlets -- and minimum wiring of 12 AWG with combination 15/20-amp receptacles.

As to the grounding/neutral situation, this is farm wiring in rural Oklahoma. Meter poles all have disconnects after the meters -- I assume as a means of shutting off the power to everything without having to call the power company.

Since the mobile home mentioned above has only two hots and a neutral service leads to this disconnect and no grounding wire, I assume it is considered the same as connecting the house leads directly to the meter, with the grounding/neutral busbars combined in the house main panel and connected to the neutral and grouding wires at the pole.

Hope I didn't lose you there.

My plan was to follow this configuration -- with the addition now, however, of a 125-amp main breaker in my panel.

The bottom line here is that my panel, just as the panel in the mobile home, would be a main panel rather than a sub and would not need a separate grounding wire. That was to be made from my panel.

Any of this make sense to you?
 
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Old 11-16-02, 06:24 PM
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If there is a disconnect on the pole this is considered your first panel. Anything after this disconnect would be a sub-panel. How you wire the sub panel is your choice, but you asked for oppinions. I believe that the mobile home is wired incorrectly. Mobile homes fall under a different code section and require 4-wire instalations. Anyhow, that is a different story.
 
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Old 11-16-02, 06:34 PM
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My opinion is that Brian is correct.
 
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Old 11-16-02, 08:13 PM
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Hmmmm.... I could look that up if I had my 2002 NEC here, but I forgot it and left it up there in an RV where I'm planning to build the cabin.

The trailer could be wired incorrectly -- they do some strange things out here.

But I can see the service entrance may need a little further investigation.
 
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