Marinas and voltage drops

[hardworkingstiff]

I've been getting involved in marinas lately. Maintaining a 3% or less voltage drop is impossible without installing transformers on the docks. That gets pretty expensive and there is too much competition willing to do it without transformers.

I?ve spoken with three different boat manufacturers and they all agree that the boats will operate down to 200-volts before they have problems. This makes sense since most single-phase motors today are able to operate on two legs of a 3-phase wye service.

I am of the opinion that the wire should be sized to deliver 200+ volts at 100% of the connected load if the power company has a 5% voltage drop, and the wire should be sized to deliver 220+ volts at 80% of the connected load if the power company maintains 240-volts. In our area, the power company is delivering about 246 during non-peak hours.

I would like to hear comments on what you feel an acceptable voltage drop would be for a 240-volt 1-phase feeder to the marine power pedestal.

 

[charlie tuna]

Re: Marinas and voltage drops

forget the nec standards for a minute and remember that the equipment on the average boat is usually single phase 120/240 volts. the utility specification(usually) allows ten per cent variation in system voltage. so a 240 volt circuit could get down to 216 volts legally. now you are considering allowing a near 17 per cent voltage drop! this equipment's amperage at this voltage will be almost double --- this will not work and over time will cause major problems! the proper way is to oversize the feeders to prevent voltage drop. i have wired a few marinas, and i know the runs are long, but in the long run, buck-boost transformers will drive the owner crazy. and they must be oversized and installed in a weatherproof enclosure! we oversized the raceways from what the plans called for to cut down on pulling wire labor costs. we also special ordered 5000' spools of wire to reduce the waste and set up time. my $.02!

 

[charlie b]

Re: Marinas and voltage drops

I did a study once for an upgrade to a large marina in the Seattle area. The study?s purpose was to determine the relative costs of two options. Option 1 was to install 480V ? 120/208V transformers at the head of each pier, and run large conductors out to the power pedestals. Option 2 was to bring 480V onto the pier, install three 480V ? 120/240V transformers spaced evenly on the pier, and run smaller (and much shorter) conductors to the power pedestals. For that study, Option 2 worked out to be much cheaper.

The results may not be the same for every marina. The key variables include the number and lengths of the piers, the number and ratings of the slips (i.e., 30 amp 120V versus 50 amp 120/240V), and the construction environment (i.e., new construction, with the freedom to include conduits as the pier is being built, versus working within an existing structure).

I do suggest that you take a look at the two options. Option 2 does eliminate the voltage drop problem. And in at least my case, it was the cheaper way to go.

 

[charlie tuna]

Re: Marinas and voltage drops

most large marinas require metering and this would enter into the cost scope. most management companies don't want to get into the selling of power and billing with deposits etc.. the cost of private metering is expensive, although, in florida you are allowed to charge for administration costs i believe 3 per cent?

 

[charlie b]

Re: Marinas and voltage drops

But if you do install individual meters, then there is an additional 90% demand factor that you can apply. I included this factor into the study that I performed. The meters were built into the power pedestals, and were included in the materials cost. The owner had to decide whether the cost (and administrative work) of individual billing was worth that additional savings in the initial installation (i.e., material and labor savings).

 

[hardworkingstiff]

Re: Marinas and voltage drops

Thank you all for your replies.

 

[oliver100]

Re: Marinas and voltage drops

Here is my 2 cents on the subject of Voltage Variations at the marina.

1. Most of the modern boats have under voltage protection and upon activation a generator kicks out automatically or the load is switched to the batteries. So they are relatively immune to any voltage variation.

2. The small boats have few lights, cocking range, TV etc. So they are not so much affected from voltage variation.

3. Charlie b: In your study Option 1 calls for 208/120, and Option 2 calls for 240/120. I assume that 22 volts difference in your study is considered tolerable.

To summarize: The end user Voltage Variation has two components: One is caused by the utility (up to 10% as posted here) and Second caused by the voltage drop in the cables that we are trying to minimize or eliminate. Fighting for that is a big war with a very small gain.

In my opinion 5% voltage is very reasonable base for calculations (as suggested in NEC - I assume that their figures are based on statistical/probability analysis of the utility power). I omit 3%, since the service to the piers cannot be considered branch circuits. In reality everything is a branch circuit.

Based on the above criteria I would suggest that simple cost analysis be performed to determine what is the best economical solution.

A small note: It is very difficult to determine the expected power demand at the marina - number of vessels and their power requirements. So it is up to the management to direct the vessels based on the occupancy level and the of the of the boats and to provide them with a reasonable electrical power sand docking space.

 

[charlie b]

Re: Marinas and voltage drops

Originally posted by oliver100: 3. Charlie b: In your study Option 1 calls for 208/120, and Option 2 calls for 240/120. I assume that 22 volts difference in your study is considered tolerable.

It?s a fair question. I never liked the idea of going with 208 volts. I think it violates the intent, if not the actual wording, of 555.19(A)(3). The FPN that follows that article supports my view. But one of the owner?s representatives wanted to go that way.

Part of my study was to contact boat manufacturers throughout the country, and some overseas. I limited my research to those manufacturers who made boats large enough to use the 50 amp, 250 volt receptacle. I asked them if their 240 volt equipment could tolerate a supply voltage of 208 volts. Not one manufacturer told me that 208 volts would be acceptable. Several were very clear in their statements that 208 volts would not be acceptable.

I don?t think I prejudiced my study with foreknowledge of what I hoped the study would conclude. But I was glad that the technical solution that I preferred (i.e., 480V - 120/240 volt transformers on the piers) proved to be the lesser expensive solution.

[ February 23, 2005, 12:56 PM: Message edited by: charlie b ]