electric questions?

[muldoon]

I am working to bring in electric pretty soon into the project.  I have a few questions and would love some input from others who have undertaken the same thing.  I do plan to have an electrician come out to do the final hookups in both panels and review the work.  However I am not really up for paying someone else to do the manual labor part of the job.  That would be my part.

I currently have a 200amp panel mounted on a pole about 150 feet away from the cabin.  I am about halfway done with wiring the outlets, lighting and switches.  My plan is to install a 70amp sub panel in the cabin and run 4 circuits inside.  I know I need to bury conduit between the pole and the cabin and run 4 THWN conductors in the conduit.  Distance and amps define the size of those cables. 

Question?  -- On the pole, I would tie a dipole 30amp breaker to these wires providing 60amps@110 to the cabin? 

The conduit run itself must enter into the cabin.  I can either come up directly under the panel (with a hole saw going through the subfloor and bottom plate) than caulk the entrance around the conduit.  Or I can bring it up just outside the panel and stab in from the outside, again with a hole saw only coming in through the sheathing. 

Question -- Which approach would be better and why?

Question -- I am still trying to interpret the standards, but more importantly the logic behind it.  I have read contradicting statements about grounding.  I have 2 copper rods out at the pole but it is unclear to me if I need to add additional rods at the cabin and ground there.  Should I use the ground from the main panel or do I need a rod for the sub panel?  Along the same lines, does the ground blocking kit for the panel need to be installed at the cabin? 

[glenn kangiser]

I'll start on this, muldoon but I don't do a lot of it.

I assume your 200 amp service has 220 so if you put in a double breaker you will have either 110 from each side to neutral or 220 across both hot legs available at the cabin.  You would need 4 conductors going to the cabin I believe 2 hot legs, a neutral and a ground.

I'm not sure on the grounding and bonding on the sub panel.

[muldoon]

Thanks glen.   I'm going to go ahead with the grounding rod locally and acorn clamp into equipment bus on the subpanel.  As for the other, I do plan on using 4 conductors.  3 #4 THWNs hot,hot,neutral and one #6 ground back to the main panel.  This should be adequate to cover the 70amp panel at 130 feet, and give me some flexibility for future growth over what circuits I plan to wire up on day one.  (always got to have room to add a shed roof wing later right?)

Any thoughts on where and how the conduit enters the cabin?  From under the edge and into the bottom plate between studs or from the middle of the exterior wall and through the sheathing?  I'm leaning towards bottom plate but am cautious if there is something I am not considering that should stop me from doing so. 

[glenn kangiser]

I don't see why that would be a problem as it's more of a mechanical thing and personal preference.  The only consideration I would have is that there is plenty of access for pulling and not an excessive amount of bends.  I think you are allowed a total of 360 degrees but I like less if possible.  Keeps it from getting hard to pull.

I think that should give you plenty of power and you have checked the ampacities of the wire.  Looks plenty large to me without looking it up.  On shorter runs, #10 will carry 30 amps each leg.