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Old 07-16-2008, 12:25 PM   #1
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Is 30A sub-panel enough?


I have a boat dock that I want to add an electric hoist to. I figured I might as well go ahead and add a couple of conv outlets. Maybe a service light. The dock is about 200' away from my 200A main. I read several threads on all the code requirements (GFs, etc.) and Stubbie's excellent pictorial in one of the threads on boat house installs was a tremendous help. The boat hoist pulls about 8.3A/220V or 15A/120V version. With the price of copper it's a hard hit to the pocket to run #4 for a 60A service, so I'm contemplating whether I'll be happy with a 30A service. I don't anticipate adding any additional loads beyond the above with the exception of a possible second hoist, but those would never run concurrently. Would a 30A sub be sufficient for this application?
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Old 07-16-2008, 01:35 PM   #2
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Is 30A sub-panel enough?


I would say yes, but I would also suggest you jump to #8 wire due to the distance.
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Old 07-16-2008, 01:45 PM   #3
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Is 30A sub-panel enough?


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I would say yes, but I would also suggest you jump to #8 wire due to the distance.
Yeah, I was figuring on a 8/3 UF....I haven't found a good online price comparision, but I have to imagine it's quite a bit in savings over #4's.
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Old 07-16-2008, 02:12 PM   #4
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Is 30A sub-panel enough?


Okay, another question....In the thread where Stubbie posted his excellent diagram Long underground run there was discussion about whether the sub panel could be mounted on the dock itself. In talking to the local contractors, they indicate that in this municipality, they can be (usually in the storage shed) and are not required to be installed on shore. However, the requirement for a local ground rod off the shore line is required.

Soooo....How best to approach this? Should I run the 8/3 + gnd all the way to the sub panel and then a separate gnd back to the ground rod in the same pipe? Seems a bit redundant. Or is there a way that I take the gnd by itself to the rod first and then continue to the sub panel?
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Old 07-16-2008, 02:32 PM   #5
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Is 30A sub-panel enough?


The remote panel will need it's own ground rod. Run the 8/3 to the panel and a separate #6CU to a rod near the panel on shore. Keep the #6cu out of harm's way.
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Old 07-16-2008, 02:37 PM   #6
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Is 30A sub-panel enough?


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The remote panel will need it's own ground rod. Run the 8/3 to the panel and a separate #6CU to a rod near the panel on shore. Keep the #6cu out of harm's way.
Right, but with the 2008 code change and detached buildings, I have to run an 8/3 + gnd to the panel. So, I guess my question boils down to can the TWO gnds share the same pipe above ground? I'll have the equipment ground from the main going to the panel along the walkway, and then I'll have to return from the panel back along the same walkway to the ground rod, correct?
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Old 07-16-2008, 03:02 PM   #7
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Is 30A sub-panel enough?


I'm not sure I understand.
You do not have to go all the way back to the main service ground rod. You sink another at the dock panel.
I think that is easier/cheaper than running the GEC (grounding electrode conductor) all the way back.
The bare in the UF is your egc (equipment grounding conductor).
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Old 07-16-2008, 03:57 PM   #8
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Is 30A sub-panel enough?


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I'm not sure I understand.
You do not have to go all the way back to the main service ground rod. You sink another at the dock panel.
I think that is easier/cheaper than running the GEC (grounding electrode conductor) all the way back.
The bare in the UF is your egc (equipment grounding conductor).
I can see the confusion...I'll try to clear it up.

The sub-panel will be installed in the utility shed on the boat dock which is 30' out in the water. There is a 30' pier that services the dock from the shore. The new sub-panel ground rod is of course on the shore line.

So, I'll have my 8/3+gnd coming from my 200A main, to the sub-panel via the 30' walkway. I then have to turn around and go back with another ground to the new ground rod on the shore line via the same walkway. If I have to do it this way, I'm assuming I can share the pipe that runs along the walkway to house both bare grounds?

Before 2008, I could have just used an 8/3 (no ground) with a single bare back to the ground rod. Now that I have two bares that have to travel quite a distance, I'm curious if they can A) share the same pipe, or B) can I interrupt the bare service equp ground on the way out, tie it to the gnd rod, then continue to the sub-panel.

Last edited by robertmee; 07-16-2008 at 04:01 PM.
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Old 07-16-2008, 04:48 PM   #9
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Is 30A sub-panel enough?


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Before 2008, I could have just used an 8/3 (no ground) with a single bare back to the ground rod. Now that I have two bares that have to travel quite a distance, I'm curious if they can A) share the same pipe, or B) can I interrupt the bare service equp ground on the way out, tie it to the gnd rod, then continue to the sub-panel.
Get a diver to drive a ground rod for you...

Personally if I was doing this job, I would run pvc conduit from the house to the dock, pull aluminum wires to the dock panel, the just run a #6AWG copper to the ground rod, your talking 35' for the ground rod... I dont see the same problem as you do.

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Old 07-16-2008, 05:15 PM   #10
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Is 30A sub-panel enough?


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Get a diver to drive a ground rod for you...

Personally if I was doing this job, I would run pvc conduit from the house to the dock, pull aluminum wires to the dock panel, the just run a #6AWG copper to the ground rod, your talking 35' for the ground rod... I dont see the same problem as you do.
Because, AFAIK with 2008 code changes, you can't run just an aluminum service from the main to the sub (the old 2 hot/neutral). It has to now include a ground. So that's ground from Main to Sub and ground from Sub to rod. Since these are both bare, they of course will be in contact with each other in a common PVC pipe along the walkway. My question is: Is this okay?

EDIT: I've also heard and perhaps untrue, that in this type of application, aluminum even in PVC might not be the best because of the possible water intrusion and corrosion issues. I'd rather pull aluminum as it is cheaper.

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Old 07-16-2008, 05:23 PM   #11
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Is 30A sub-panel enough?


I only have a 30A service out to my pier. It runs a two motor boat lift, post lantern, and outlet. You might want to consider upgrading if you want to have a shore power connection for a larger boat.
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Old 07-16-2008, 05:26 PM   #12
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Is 30A sub-panel enough?


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Because, AFAIK with 2008 code changes, you can't run just an aluminum service from the main to the sub (the old 2 hot/neutral). It has to now include a ground. So that's ground from Main to Sub and ground from Sub to rod. Since these are both bare, they of course will be in contact with each other in a common PVC pipe along the walkway. My question is: Is this okay?

EDIT: I've also heard and perhaps untrue, that in this type of application, aluminum even in PVC might not be the best because of the possible water intrusion and corrosion issues. I'd rather pull aluminum as it is cheaper.

Lets clear up the misconceptions,

1st. The 2008 only requires 4 wires to a seperate structure, not 3, I always run 4 to begin with...
2nd. your dock power is NOT a service, its a sub-panel.
3rd. I wouldn't use uninsulated wires, your thinking of triplex or something else... Your a little misinformed and your basic knowledge of material available to you is going to hinder your job install...
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Old 07-16-2008, 05:50 PM   #13
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Is 30A sub-panel enough?


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Lets clear up the misconceptions,

1st. The 2008 only requires 4 wires to a seperate structure, not 3, I always run 4 to begin with...
2nd. your dock power is NOT a service, its a sub-panel.
3rd. I wouldn't use uninsulated wires, your thinking of triplex or something else... Your a little misinformed and your basic knowledge of material available to you is going to hinder your job install...
Huh? I think maybe we are both guilty of mis-reading....

1st....Correct - 2 hots, neutral and ground...That's what I've been saying all along. I never said a 3 wire. I assumed that's what you were referring to.

2nd....Of course. My slip of terminology. I installed the 200A service in my home so I know the difference.

3rd....The only uninsulated I mentioned was the ground. I've always run uninsulated copper from a panel to a ground rod. Are you now telling me that's wrong and I'm misinformed?

I think I understand, however, through all the muddling I'll run a 8/3cu + gnd (insulated) from the main to the sub and an uninsulated cu from sub to rod. That's what I was planning but maybe didn't convey it correctly. I may have confused the issue with the thought of an uninsulated ground from panel to sub.
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Old 07-16-2008, 06:18 PM   #14
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Is 30A sub-panel enough?


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I only have a 30A service out to my pier. It runs a two motor boat lift, post lantern, and outlet. You might want to consider upgrading if you want to have a shore power connection for a larger boat.
Thanks!
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Old 07-16-2008, 07:06 PM   #15
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Is 30A sub-panel enough?


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Huh? I think maybe we are both guilty of mis-reading....

1st....Correct - 2 hots, neutral and ground...That's what I've been saying all along. I never said a 3 wire. I assumed that's what you were referring to.

2nd....Of course. My slip of terminology. I installed the 200A service in my home so I know the difference.

3rd....The only uninsulated I mentioned was the ground. I've always run uninsulated copper from a panel to a ground rod. Are you now telling me that's wrong and I'm misinformed?

I think I understand, however, through all the muddling I'll run a 8/3cu + gnd (insulated) from the main to the sub and an uninsulated cu from sub to rod. That's what I was planning but maybe didn't convey it correctly. I may have confused the issue with the thought of an uninsulated ground from panel to sub.

Probably, but sounds like you have it under control...
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