Power to a pier

[Jimbo]

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

[Captains Cat]

Jimbo, what does that Teck stuff cost and is it available in the US?

Charlie

[Captains Cat]

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

[thataway]

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.

[oldgrowth]

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

[Jimbo]

Captains Choice
Sorry it took abit to get back to you. I was in at my suppliers today and asked if they sell into the States. He said they sell to the mills in Washington State and also to a company in Maine so I assume it can be gotten.
I asked for a quote for 3 conductor #1 teck and was given $32.16 PER METER.
Your 750' equals 229 meters so 229X32.16=7364.64 CDN. Not cheap but it sure beats having to put in conduit and then doing the pull.
Hope this helps.
Tnx, Jimbo

[Captains Cat]

Thanks Jimbo. As I posted earlier, I found some for about $2700 (US) that's three conductors of 4AWG for the power and one of 6AWG for the ground, suitable for burial in Richmond. If I do this, that's probably the way to go. I've still got an extra, nearly new 7500 Watt Generator that I could use but I'd hate to have that noise. I've gotta dig a trench for the water line anyway, we'll see after I measure it accurately...

Thanks all for the help.

Charlie

[Minnow]

As another 30 year electrical contractor, I thought I'd throw in my 2 cents.
I'd use #2 aluminum type URD. This is a direct burial tri-plexed cable, meaning that it is three, or four conductors, twisted together, but without an overall jacket. It should be installed in a carefully prepared trench with sand backfill. Use anti-oxidation compound on the terminations, and tighten with a torque wrench. Given the price of copper, and the fact that the panel terminations are aluminum, why not? My today cost is $1.16 per foot for the three conductor. (2 X #2, 1 X #4). I think this is about the cheapest way to get some power that far.
The reason a reduced-size neutral is allowed because with a 240 volt load, there is no current flowing on the nuetral. With 120 volt loads, the neutral will only flow the difference in loads between the two phases. E.G.- One leg drawing 15 Amps, the other drawing 5 Amps, the neutral will be carrying 10 Amps.
The technicallities about grounding are much mis-understood. You see, the conductors leave the house as a "branch circuit", but miraculously arrive at another building as "feeders". What this means to you, is that if you are installing a sub-panel in another building, you don't take a ground wire with the feeders, just 2 hots and a neutral. At that panel, you install the bonding screw, (to bond the neutral bar to the ground bar) and install a grounding electrode system. The best grounding electrode is the re-bar in a concrete slab or footing, but not having that, ground rod or two will make a mediocr second best. The point of this is to create a local ground reference, so that you can't get a shock from a grounded surface to a natural ground, especially with a loose or broken neutral. If for some insane reason you decide to install a copper water pipe, then you must install an isolating coupling at the house so that it breaks the current path.

Thataway mentioned installing an extra ground rod at the dock, but you cannot, and must not, bond it to the neutral if you also have a ground wire run with the feeders. You don't want to have the neutral return current flowing on parrallel wires. If you run a ground wire with the feeders, then you don't bond the neutral to ground, and you don't need an additional ground rod, although it's a good idea because of the voltage drop on wires that long.
Speaking of voltage drop, it's worth clarifying that it's a function of how close you are to the ampacity of the wire. The voltage drop calculations that others have listed are based on those maximum loads. If you're not drawing that much power, you're actual voltage will be higher. Motors are generally tolerant of a 10% + or - voltage range, and many motors are rated 208/230, when you're probably starting with 240. In my area, it's common to see 125/250, so every little bit helps.

[Captains Cat]

Thanks Minnow, I'll look at that solution too. You are right about voltage drop being dependent on the current flow. Joe's (Sea Wolf) calculator posted early in this thread clearly shows that the drop decreases when the current does. I see you are in NJ, got any recommended sources for that cable? I'd like to use 4 conductor and run a ground all the way from the source.

Charlie

[akbpilot]

I was going to try to post again yesterday, but every time I sat down something else would come up.

I am not familiar with the Teck cable mentioned, but it sounds a lot like a jacketed MC cable we use. Ours has a jacket rated for direct burial, and is sunlight resistant. We use miles of it in the plants and utilidors, easy to install. Does the cable you were quoted have a rubber jacket? If so, I've probably used that too, pretty durable, but hard to deal with in the cold. That's probably not going to be an issue where you are at.

If you are going to direct bury, it's worth seeing what kind of soil it's going to be. Good advice from Minnow, if your soil is rocky, cleaning the bottom of the trench, and bedding the cable in sand should work. If it's clean soil, sand, no rocks direct burial will work. The sand also helps drain water away from the installation. We generally can't get away with that here because of the freezing depth, the ground freezes at different rates and jacks around. We've even had steel conduit pull apart. The specs on our facility for underground require PVC coated rigid steel conduit with a 12" sand bed on both sides.

Minnow is also right about the neutral only carrying the imbalance of current from the "hot" phases. We can't reduce neutral size due to engineering standards and harmonics, but with your usage the neutral should not be carrying much load. He's also spot on about the grounding and neutral bonding which is what I was alluding to in my previous post. If your not sure how to do it, find out how to do it correctly.

I would suggest calling the manufacturer of your lift and finding out what the full load current of the motor is going to be. My generic motor guide shows a 5hp 240v single phase motor full load current of 28 amps, recommended min. breaker size of 40 amps. General rule of thumb for min. motor circut size is 125% of full load current (28 amps x 125% =35 amps). Standard trade size breakers don't come in 35 amp, so 40 would be the min. size, which is probably where the 40 amp size in my generic guide comes from. Some motor installations have an initial start-up "surge" which can be multiple times the full load current. Generally the surge only lasts for a second or fraction of a second. Some single phase motors use a centrifugal switch which switches between starting and running "mode". If the motor can't build up speed due to excessive voltage drop or excessive initial load, the switch stays in start "mode" which generates excessive heat, leading to component or winding failure. In essence the motor "stalls".

Also at this point it would be useful to determine what your actual voltage is at your source, that will be useful in making your calculations. You indicated you are running from a separate service, so you should not have issues with excessive drop to start with. Your final power is going to be a function of what the grid voltage from your utility is, and how much actual load is on your portion of the grid, so it may vary some from time to time.

Now, before you purchase anything or begin digging, is a good time to find out how much "local oversight" i.e. inspection/permitting will be required. It's a real bummer to have everything nearly completed then have a local inspector show up and tell you to dig everything back up so he can check the cable or conduit installation or that your locale requires engineering to comply with local codes before work can commence. Find out also if you can do the work, or if a licensed contractor has to do it. Here, we can do our own work on a private residence, but we still have to pull a permit and comply with all codes, local, state, and national.

[Jimbo]

akpilot
My supplier mentioned that the states also uses MC cable which is similar to teck but not quite as flexible.
Captains Choice
I didn't bother quoting you on the aluminum cable as you seemed dead against it but in this day and age with the price of copper going through the roof I would give it a second thought. As long as you install it properly using the right compound at your lugs, it will work as well as copper and for a lot less in cost.
Tnx, Jimbo

[Minnow]

Charlie- that URD cable (Underground Residential Distribution) is in stock at most of the electrical supply houses in my area. The #2 is used for 100 Amp underground services, and a 4/0 is for 200 Amp. One utility company I deal with allows its use as-is, and the other will not allow direct burial of aluminum conductors, so I install it in conduit. I wouldn't even consider a 750' conduit run, just isn't worth it. Cable faults can be located and repaired easily.
The 4 conductor would be special order, there just isn't enough demand.
I'm not sure why you want to run a separate ground wire. Keep in mind, just because you don't run a ground wire with the feeders, doesn't mean that you don't have an equipment ground at the loads. It's the neutral (groundED conductor, not groundING conductor). This is why you bond the ground and neutral at a remote panel. A ground rod by itself cannot possibly flow enough current through the dirt to trip a breaker. That's not what it's for. This is same way dryers and ranges have been grounded from WWII through a code change in, I think, the 1996 code.

Another good point was brought up about the AHJ (Authority Having Jurisdiction). If you are going to be getting permits and inspections, draw up the details and submit to the AHJ before you buy anything.
And make sure you find an electrician that understands the details.

[Butch]

Charlie... akbpilot did a magnificent job spelling out what you should have. There is one thing that I have noticed in Maryland and that is 4 conductor line inputs; two 110V. lines, a neutral, and an isolated ground. The reason I say this is because when I built my garage/shop I had the power company to up my feed lines to 400 amps. The meter base is approximately 2 ft. wide and 3 ft. long. On the load side of the meter base connector I installed a buss bars with 4 taps for each leg, the ground, and neutral. One leg goes to the house, one to the garage/shop, the third to an out building barn shed, and the fourth is a spare just incase I get another hair brained idea to build something. Cecil County inspectors required the isolated ground and the installation of 3/4" x 10' copper clad grounding rods. Two rods at the meter base, and one for each down stream breaker panel.

One interesting note though... Delmarva Power was going to charge me, the home owner, $10,000.00 to change out my feed lines. The reason for the charge, which is bogus, was my non-commercial garage/shop was defined by them as a commercial building because it was detached from the house. It costs me about $2500.00 to put a breeze way roof between the house and new garage. Now it was considered semi-attached and the power company was obligated to up my input lines to the meter.

They did not like it because they had to replace the current step down transformer with a 50 KVA and horizontal bore under 2 driveways to get the proper gauge supply lines to the meter.

[Captains Cat]

Thanks Butch. I had 400 amps run to the new Garage/Apt when I built it, with the idea of feeding the house (when I build it, through that box using 200 amps of the capacity. The extra 100 amp service I have (with its own meter) is from when I had the trailer in the middle of the lot. It's on a pole right near the transformer box which is fed underground from the street. It's right near the well head too and I intend to feed water from that down the same trench as the power. I'll either use the Kubota/Backhoe and dig a 1 ft wide trench 2 ft deep or borrow a trencher and put em both in a 2ft deep trench. The water will be in rigid PVC or some sort of plastic suitable for burial and deep enough to ward off a freeze. I intend to bring both power and water up somewhere along the line to put a campground type connection to hook up a camper to power/water for when we want to do that.

Lots of good info on this site, need to get down there again and make an accurate measurement and then decide aluminum vs copper, and wire size.

Charlie

[Minnow]

Sorry Butch, but it's been a long time since you've been able to run an equipment grounding conductor to a remote "building or structure".
Check out NEC 70:250.32