PVC alternative?

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  #1  
Old 04-01-04, 07:24 AM
8NTX
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PVC alternative?

I'm finally getting around to installing the 600' run to my boathouse. Seems most electriciand don't want to do the job, or are more than I can afford ($6,000). So, I have decided to do the grunt work myself after consulting with an electrician on the design. He will also make final connections and check it out.

I will be running 2-#2, 1-#6, and 1#8 wires through underground sched. 40. The problem is, this run is full of sharp turns and a winding trail. I understand this stuff is pretty rigid and you must get a special heating apparatus to bend it. Uh-oh. I have gophers that would chew up direct burial wire. Any tips you can give here will be appreciated on possible alternatives and the best way to pull those lines through. Thanks.

Steve
 
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Old 04-01-04, 10:14 AM
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When running conduit, you are not permitted to have more that a total of 360 degrees of bend between 'pull points'. This means that you can't bend left then right then left then right a bunch of times to get to your destination; you have to put a suitably sized junction box or 'conduit body' in every so often so that you can pull the wires part way, then through the next portion of the run, and so on until your destination. Additionally, while code is 360 degrees, the fewer bends the easier it is to pull the wire. Larger conduit and larger radius bends can also make pulling easier.

So whatever solution you go with, remember that you probably won't be able to do the entire run in a single 'pull'.

Also, I have a strong hunch that your electrician did not properly size your ground wire. I presume that the #2 wires are increased in size for reasons of voltage drop; if so then the ground wire also needs to be increased in size. What size panel (breaker amps) are you installing at your boathouse?

-Jon
 
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Old 04-01-04, 11:39 AM
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Thanks for the reply. It's a 60 amp panel, I believe. But I don't have the final word from him yet; that's just what he mentioned along with the tentative wire sizes. My needs are: 13.5 amp 1HP boat hoist, 1 flourescent work light, 1-60w bulb fixure and 1 double bulb floodlight (at boathouse); plus 5 double bulb floodlights along the trail; ability to turn on lights at either end of the run. The electrician is supposed to calll me in the next couple of days with a list of supplies to buy. I was gonna get 2" pvc to make the pull a little easier. I also plan to break the pull down into 100 to 180 ft. runs because of the curves and turns(and since I am only getting a 200' tape). Can the 4 wires be pulled at once if I wire them together?
 
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Old 04-01-04, 12:48 PM
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Why a #6 for the neutral? Depending on how big the load is and how well it is balanced, this may cause more voltage drop than you want.
 
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Old 04-01-04, 01:03 PM
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Originally posted by John Nelson
Why a #6 for the neutral? Depending on how big the load is and how well it is balanced, this may cause more voltage drop than you want.
I have no idea. What do you think it should be?
 
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Old 04-01-04, 01:31 PM
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You might want to take a look at this material. I do not know if it is actually suitable for your application; you will need to call the manufacturer to find out. But I came across it and happened to think about your application.
http://www.alflex.com/catalog/detail...te_type_nm.pdf

-Jon
 
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Old 04-01-04, 03:20 PM
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In casually reading this thread, I read the statement "ability to turn on lights at either end of the run. " Won't this require at least 2 more conductors (travelers) in addition to the feeder conductors? Just my $0.02.
 
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Old 04-02-04, 04:23 AM
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Voltage drop and wire size:

Note: I am presuming _copper_ wire. For aluminium wire you need larger wires than the below.

To figure voltage drop, take the resistance of the wire that you are using, and multiply it by the current flowing through the wire.

Usually you look up the resistance in ohms per 1000 feet of wire, and have to take that number and multiply by the number of feet involved. Remember that a circuit goes 'out and back'

http://www.paigewire.com/copperAWG.htm

So if we presume a 60A 240V load on your 1200' of #2 wire we get a voltage drop of 11V. The usual rule of thumb is that you want the total voltage drop (panel feeder plus final circuit) to be less than 5%; this just squeaks in if the load is near the subpanel. But the load is never really exactly the subpanel rating, and is usually much lower...but with motors it can be higher for brief periods of time.

However the above calculation is bogus because you don't have anything near a 60A load. Your 13.6A motor is a 120V load, and probably could be converted to a 7A 240V load (motor reconnection), and the other loads are tiny. All of the loads described could be served with a single 20A 120/240V three wire circuit, probably using 4 #6 wires (two hot, one full size neutral for a large 120V load, one full size ground because the ground for a 20A circuit is the same size as the hot). But this doesn't leave room for future expansion, and since most of the work and cost is in burying that conduit and actually pulling the wire, the electrician is suggesting a reasonably sized subpanel.

IMHO the #6 neutral is fine if your 120V unbalanced load never exceeds 20A. This just means taking any large 120V loads and balancing them on opposite hot supplies. You should get your motor reconnected for 240V and run it from a double pole breaker and double pole switch. The startup current on your motor will exceed 20A, and would require larger than a #6 for the neutral, but with the motor reconnected, this becomes a non-issue.

The normal ground size for a 60A circuit is #10, so you should increase it to a #6 to match the increased size of the hots.

Since you are putting in lights, I would recommend that you also add receptacles. IMHO you should do this with a single 20A circuit, using a #8 as the supply for the receptacles and 2 #12 as travellers for controlling the lights, sharing the neutral. Power this from the subpanel in the boat house so that you don't have neutral current when the boat house subpanel is off.

-Jon
 
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