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Old 08-20-2009, 04:37 AM   #16
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Yeah that's pretty darn close. Just a few clarifications. Thwn and thhn are going to be one and the same... if you buy new wire. The wire will be essentially dual rated. It must carry the thwn in order to be put in conduit underground which is rated wet location (Wet = w). so the wire is going to say on the outside jacket both thhn and thwn...probably will have thwn-2 which puts the isulation the same a thhn. None the less must have the w in the insulation code. Don't be surprised to see additional ratings as well.

I like your idea of a disconnect box where your feeder leaves the house this will eliminate bulky splices and JB and considering your wiring method. Be sure it is rated for your feeder. Might check out the Qo200tr by square d. It is a 60 amp disconnect primarily used for air conditioners but is also service rated if upstream OCPD (like yours is present) not exceeding 60 amps 10000 amp rms and ground bar is installed. It is non-fusible and is essentially a Qo double pole breaker case (switch only) without overcurrent protection. Very cost friendly. Common at the big box store

Please note that this disconnect box does not have provisions for connection of the neutral conductor when using a 4-wire feeder such as you have in this scenario. You will have to "wire-nut" the neutral wires, and it will be very crowded inside the enclosure. Some inspector-critters may not like the wire-fill when using #6 conductors.
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Old 08-20-2009, 08:10 AM   #17
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Roy

I want to be sure you understand the grounding electrode system and the equipment ground system. They are not the same thing.

The ground rod is connected to the panel for protection of property (your electrical equipment) from high voltage events like lightning and utility power surges. It has nothing to do with the equipment grounds in the branch circuits or the feeder ground.

The equipment grounds are for human safety and bond all metal that is likely to become energized in a ground fault to an ungrounded conductor. This creates a low impedance/resistance path we call the effective ground fault path back to the transformer.. not to earth or any ground rod. The resistance to earth is too high to allow enough current to flow thru a breaker to trip on fault. Fault current must be able to get back to the transformer in order for the resistance to be low enough to get lots of amps (current) to flow thru the breaker to trip it.

As you know we bond the neutral and equipment grounds at the neutral bar in the main panel where the main disconnect for the dwelling is located. We have to do this because there is only one low impedance/resistance path back to the transformer at that point. That is the service neutral. I've made a diagram to show this relationship with the grounding electrodes and the equipments grounds as I've shown below..... hope it helps if you need clarification.
***********************************************
Thanks. Just to be sure I have it:
Since the ground in my sub-panel is connected to the ground feed from my main panel, and the main panel common and ground are bonded together in the main panel, then the ground from my sub-panel is electrically the same as the common throughout. There should be no difference of potential between any ground and the common. The path of least resistance from my sub-panel ground to earth is the driven rod at my workshop, therefore it will carry any fault currents to earth. None of this really matters to me as long as I don't see smoke. Just kidding. I know it is important to have it correctly wired.
Thanks again.
By the way I think it is OK to be scared 1/2 to death twice, as long as its the same half.
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Old 08-20-2009, 09:53 AM   #18
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Please note that this disconnect box does not have provisions for connection of the neutral conductor when using a 4-wire feeder such as you have in this scenario. You will have to "wire-nut" the neutral wires, and it will be very crowded inside the enclosure. Some inspector-critters may not like the wire-fill when using #6 conductors.
Kbsparky does bring up a point I left out, forgot...or was asleep. You will have a splice on the neutral but I never wirenut #6....I use an insulated connector called a splicer (similar to a polaris) for this disconnect... it is tight. It is possible you could be pretty borderline on box fill. There are certainly 'better' disconnects that have provisions for neutral connection. Siemens actually has some knife style (side handle) disconnects you may like better with the neutral provision. I believe the big box may carry these but not sure. I was trying to give a nice disconnect that didn't hurt budget and was good for the job but as kbsparky says it is not wire friendly with #6's and the addition of the neutral splice.

If I am using a junction box to transition #6 wires from cable to thhn/thwn....I never wirenut these big size wires though it is perfectly acceptable. I use power distribution blocks (splice boxes) and install them in the JB. And I install the accessory protective cover over the splice box. I usually use a 6x6x4 metal JB by weigmann.

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Old 08-20-2009, 10:30 AM   #19
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The path of least resistance from my sub-panel ground to earth is the driven rod at my workshop, therefore it will carry any fault currents to earth.
Nope....it will not carry any fault current to earth. It will carry current from lightning strikes or power surges to earth...big high voltage events...

Fault current from a single phase fault on a branch circuit returns to the transformer via the equipment grounds and over the service neutral... not to earth...it is not a low resistance path back to the transformer because the current has to go thru dirt to get there...
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Old 08-20-2009, 10:55 AM   #20
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Debate (continues) about method of splicing Neutral in (outdoor) box!


Stubbie 10:53AM, #18. I'm certain KB Sparky #16 didn't mean "Wirenutting" literally. I haven't seen someone "Wirenutting" Two #6 wires, yet. My method would be securing the splice with a Burndy "BUG" of the appropriate size, in addition to Rubber tape and plastic insulating tape! (Now more than ever) Don't Drink and Drive!!!
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Old 08-20-2009, 11:15 AM   #21
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Actually Kbsparky makes a very good point about this disconnect. It ain't got a lot of room.... and it is all at the bottom where the ground bar is. I've discovered a way to use a special connector to make the neutral splice when using #6 and "fit" it all in this disconnect. Problem was I flat forgot to bring that point up. I like the disconnect for those who have a low budget which I do not think was the case with Roy in this thread. It might be better for him to move to a different disconnect with more room and a neutral provision.
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Old 08-20-2009, 06:55 PM   #22
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Stubbie 10:53AM, #18. I'm certain KB Sparky #16 didn't mean "Wirenutting" literally. I haven't seen someone "Wirenutting" Two #6 wires...
Actually I did. Ideal makes a wirenut suitable for (2)-#6 wires. Some folks call them big blues.

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