Power to a pier

C

Captains Cat

New member
I need to run underground power to my pier from up near the garage/apt. The run will be about 750' (Seven Hundered and Fifty Feet) and will come from a separate power meter that has a 100 Amp main breaker on it. I want to have 110/220 at the pier to run lights(110), shore power(110) and the boat lift electric motors (probably 220 but they're not installed yet). I probably need two 20 amp 110 circuits and a 30 amp 220 circuit in the box at the head of the pier.

I'll probably run three phase power down there, 110 either side of neutral plus a ground wire. What size/type of wire should I run, as I said, it'll be underground...

Thanks

Charlie
 
joeC":jddwize2 said:
About double Ought, Which is welding cable that run is near impossible.
JoeC
Click to expand...

I wouldn't think it "impossible".... Many houses have a run like that from the transformer on the pole to the house, and that's 3 phase 220 I'm pretty sure....I've got 200 amps in the big house here in No VA and the run is about that long. I guess I could look in the breaker box at the main and see what size the wire is from the street. It's underground.

I was looking to see if someone had a calculation that would definitively size the wire... doesn't necessarily have to be copper either. How about aluminum?

Charlie
 
Charlie.... I have done a similar thing,but with not so long a run. I looked in the "CABO", local building codes book which dictates the wire size for various distances. I am pretty sure some electrical internet site could do similar for you. They have special gray, waterresistant underground wire bundles for that. I think that same wire covering, however, is subject to ultra violet damage from sun exposure, so the codes require a conduit from 18-24 inches under ground (based upon our freeze depth here) up to the outlet box. Just have the run checked for obstacles such as gas, elelctric, water lines, cable, etc, then rent a ditcher and go for it. But copper costs will kill you right now!

John
 
Charlie-

Here's a LINK to a calculator to figure out your wire sizing. (Look near the bottom of the page.)

The local codes will have to also be addressed, but separately.

I'm surprised you can get 3-phase power to your house. We can't do that in suburbia, but in farm and rural country........... (Would be great for welding, big motors, etc.)

Joe.
 
On rethinking it, I don't get three phase power, I should know that. It's 220 three wire, 110 either side of neutral and then a ground... :oops:

Thanks for the calculator, I'll try it.

Well, it says that with 2AWG copper, i'll have a 6% voltage drop at the end of a 750ft run with a 60AMP load. It won't get that high, I'm sure and i can live with that even if it does. Looks like that's the way to go. Now to go rob a copper mine somewhere.

Thanks a lot Joe, right on as usual... :thup :thup

Charlie
 
Definately go Aluminum. There are some relitatively cheap--that is relitatively!== three conductors plus neutral at Home Depot,Lowes for long runs that are in the #2 to #2/0. If you want 3% voltage drop you will go with 2/0. For 7 1/2 % voltage drop #2. This is assuming only a 30 amp load. What I do is run 230 volts/two legs down--30 amps each and then split the two to give a total of 60 amps 110. I suspect that you have single phase, being residential--but if it is an industerial area you might have 3 phase.

I have always found that putting in a conduit gave much better longivity--especially near salt water--and bring the conduit up well above any potential storm surge. Also see my post about boat wiring--I put a second ground rod in at the box on the dock. Drive it in the bottom, and run copper wire to it for the neutral.

I don' know what you are hoisting--but we run 110 motors with no problems for the Tom Cat 255--lift rated at 11,000 lbs. I run the two motors at the same time on a 30 amp 110 volt circuit--I could determine the load and voltage drop--but this house is only about 250 feet (Previous was a little over 500 feet) from the box.
 
Intro:
Master Electrician/ Electrical Adminstrator, 30 years in trade.

Some random info for you, only having your description, and limited info, these are only estimates (guesstimates) on my, and should not be used for the actual installation.

1) You have a 240 v single phase service (2 hots, 1 neut, 1 ground)

2) Do not install 120v 15 amp or 20 amp devices at the end of a 30 amp circut as previously suggested. These devices are only rated for the current (amps) they are marked with. You may have a device start to fail due to overcurrent, but the circut is not protected below 30 amps.

3) Probably the best way to install this if you are going to do it is to set a breaker panel at the far end near your pier. Run 2 hots, 1 neut and 1 ground from this point (ground may or may not need to be run the total distance depending on the interpretation of what you are doing and local codes. Split power into individual circuts at that point based on need.

4) The portion from your service(100amp breaker) to the pier panel is a feeder as per NEC, may be called something different in your locale depending on local codes and interpretations. Voltage drop in this portion of the circut is limited to 3%, 5% total at end of branch circuts. Size the circut down at the main breaker to say 50 amps by using fuses or circut breaker. The run from the 50 amp fuse to pier panel now becomes a 50 amp feeder. You can adjust feeder size down to 30 amps (min allowed by NEC) or up to 100 amps depending on your final load. Your min size may be vary depending on local codes.

5) Using a 3% drop limitation, my calculator shows 750ft, @ 240 volts @ 50 amps, @ 3% = 3/0 copper XHHW, don't have aluminum figures, we don't use it on our jobs, may be able to find it. Be careful using aluminum around salt water, as the corrosion factor is brutal.

6) 750ft 3/0 xhhw x 3 (2 hots, 1 neut) = 2250 ft x $9693.86/ 1000 ft (9/06 distributor prices from American Cable Mansfield, Mass, not sure what retail would be at your local) = $21,811.19, wire price. (Note, we would pay a good bit more that conductor where we live). Price may be more if you have to run ground conductor full length. Also may be less if neutral can be de-rated, but a lot of locales don't allow us to do that anymore. This wire type needs to be run in conduit, a direct burial type will be more per foot. Add in the cost of a run of conduit, min size 2", probably larger due to run length ( I'd hate to think of pulling a 750 ft run w/2 bends thru 2")

7) Add in cost of nema 3 or 4 panel at pier end, any associated breakers and fuses or breaker needed to size feeder down.

8) If you don't know proper grounding and bonding practices, add in cost of hiring someone who does. IT IS CRITICAL ( note emphasis) to have this installation correctly grounded and bonded.

9) My suggestion would be to hire a contractor or engineer to design this for you or at least give you a ballpark on the feasibilty. You can cheap out, and do things however you want, but if someone gets injured or killed due to your installation, even if they are on your property unknown to you, whatever amount of liability insurance you have will not be enough. I live in a state where someone has probably the least chance of of ever being sued due to negligence, and I never take chances. I have been consulted on on injury/ death cases for the plaintiffs, and I can assure you being the defendant in one of those cases is a place you don't want to be.
 
EDIT TO ABOVE POST

Price seemed high when I looked it up on the internet, not sure about the website I used, not my standard price sheet, but I was looking for something in your area. I called my supplier. He quoted me $3270.00/ 1000ft, so 2250 ft @ 3.27 = $7357.50 for conductor. We're a non-profit utility, so not sure of the pricing scheme, but you probably could find a competitive price in your area. Probably $10,000 or less, give or take for materials total.
 
Wow... :shock: I called a local place (Richmond) for a quote, they haven't gotten back to me yet. Found some cable on a General Cable website. Great analysis akbpilot, thanks a lot!

Joe, the generator idea is looking better and better. I've got two 7500 watt generators on wheels, with 12500 surge capacity, looks like I may be using one of them! Had no idea the cable run would cost that much...

Still need the trench, have to run fresh water down there. Unfortunately, I don't have a water generator!

I'll let everyone know what I decide and get pix too when the time comes.

thanks again...

Charlie
 
Several other thoughts--down size the power requirements.
Have the utility company put another power pole down by the dock.
I suspect that all of the options above would require permitting.

One of my friends got some "cheap" aluminum cables, and did not put them in sealed conduit--the insullation was poor, the voltage drop was huge and the cables shorted out in a year--poor purchase!

I would normally recommend copper--but with the price it is almost out of sight when you get the large sizes--but I didn't realize it was as much as akbpilot noted!
 
Several other thoughts--
1. down size the power requirements.
2. Have the utility company put another power pole down by the dock.
I suspect that all of the options above would require permitting.
3. Use solar power for the boat's charging system.
4. alternative (belt drive off a small engine, hydraulic pump etc to run the hoist.

One of my friends got some "cheap" aluminum cables used, and did not put them in sealed conduit--the insullation was poor, the voltage drop was huge and the cables shorted out in a year--poor purchase!

I would normally recommend copper--but with the price it is almost out of sight when you get the large sizes--but I didn't realize it was as much as akbpilot noted! No wonder the crooks are stealing the condensors out of the airconditioning roof units!
 
thataway":3ri480wh said:
Several other thoughts--
1. down size the power requirements.
2. Have the utility company put another power pole down by the dock.
I suspect that all of the options above would require permitting.
3. Use solar power for the boat's charging system.
4. alternative (belt drive off a small engine, hydraulic pump etc to run the hoist.

One of my friends got some "cheap" aluminum cables used, and did not put them in sealed conduit--the insullation was poor, the voltage drop was huge and the cables shorted out in a year--poor purchase!

I would normally recommend copper--but with the price it is almost out of sight when you get the large sizes--but I didn't realize it was as much as akbpilot noted! No wonder the crooks are stealing the condensors out of the airconditioning roof units!
Click to expand...

Yeah,the price of copper is out of sight. We lost 1000' of 500mcm cable to some wire thieves, along with some other smaller runs. If I remember correctly it weighs about 2#/ft. 2000# @ $1.85/# for scrap, someone made off with a bundle. Cost us about 12K to replace it.
My experiences with AL wire and salt enviroment have been less then satisfactory. Had a guy lose a leg of his service to his boatyard shop. When we pulled out the old cable, one leg was corroded in half, looked like white powder inside the cable jacket for about 6 inches. jacket looked fine, but there must have been a nick in the cable which allowed water inside. Being inside PVC conduit, there was no clear path to ground, at least not enough to trip the main breaker. He said he had noticed some of the lights dimming and his bathroom fan was running kind of slow. Not sure how long he had been having a problem, but it must have been going on for a while.
 
Captains Choice
In Canada we have a product called Teck cable that is used for direct burial. It has a rubber sheath on top of the conductors, a steel armour on top of that and then pvc jacket on top of that. We use it all the time up here. I have wired a couple of marinas and we use it going down the walk ways even allowing it to drop into the water to allow for slack on the tide changes. It also goes under the deck of the docks and comes up where required. It is available in copper or aluminum 3 conductor and ground. It has special watertight connectors as well. In your calculations it seems you have figured on the entire load listed will all be running at the same time which probably won't happen. We wired a custom home on a lakefront property and had a 700' run to his boat house. We put in 3 conductor #1 cu teck fused it at 70 amps at the house and put a subpanel in the boat house. Once completed we checked the voltage drop with his boat lift running (It was a 5hp 220volt unit) We had 114 volts phase the neutral and 212 volts phase to phase. You can also use a product called PVC conduit and even just roughin the pipe when you put your water line in. Then later you could pull in 3 lines of #1 copper. I agree the a 750' pull is not going to be easy and would not go with less than 2" pipe.
Thoughts from the great white north
Jimbo
 
I'm still pondering. Got a quote from a Richmond VA company for some underground utility cable, 4 conductor. three #4AWG copper and one #6AWG copper (the ground) for $3.25 a foot. That would cost me $2512.50 for a 750ft run. I'm going to measure it exactly next time I'm down there and make a decision.

Thanks for the help all...

Charlie
 
I don't know what your loads are going to be--but I learned the hard way. I started out with too small cable--and had to replace it. If you have small loads you can get away with the #4--but if you start drawing 30 amps you may have excessive voltage drop.

We did fine until air conditioning time.
 
Using copper wire
4AWG 750 ft 30-amp load 240 input voltage
Voltage drop is 11.5 volts / output voltage is 228.5 volts

Using aluminum wire
4AWG 750 ft 30-amp load 240 input voltage
Voltage drop is 22.4 volts / output voltage is 217.6 volts

Using copper wire
6AWG 750 ft 30-amp load 240 input voltage
Voltage drop is 18.3 volts / output voltage is 221.7 volts

Using aluminum wire
4AWG 750 ft 30-amp load 240 input voltage
Voltage drop is 35.6 volts / output voltage is 204.4 volts

4AWG will handle 60 amps but you will drop 23 volts in the above example with copper. Aluminum will drop almost 45 volts so is not capable of handling 60 amps with a 750 foot run.
6AWG will handle 37 amps
_________
Dave dlt.gif
 
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