# of boat lifts on a feeder

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hardworkingstiff

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Wilmington, NC
I'm pricing a job that will have 28 boatlifts. There will be a power center with breakers (2 per power center) for the boatlift between 2 slips (for a total of 14 power centers).

What I want to do is run a feeder looping from power center to power center, then the branch breaker in the power center will provide the overcurrent protection for the boatlift motors. Each lift should have (2) 1-HP or less motors.

I want to put 7 power centers on each feeder (for a total of 14 boatlifts per feeder). I want to use #4 type W cable which gives me an ampacity on the feeder of 115 amps (table 400.5(B)). If you add all the motor ampacity together you get 224-amps (28 motors * 8-amps) not adding in 25% of 2 motors for the starting current.

The chances of multiple boatlifts being operated simultaneously are small. The chances of 4 lifts being operated at the same time are very very small. When these lifts operate, at most, they will run for 5-7 minutes (probably more like 3-4 minutes).

Now to the question. Does the code allow/prevent me from loading these feeders this much?
 
Look at 430.24. This requires that the feeder be calculated at "not less than" 125% of the largest motor plus the full load current of all of the other motors. Exception 3 allows you to derate if there are interlocks that eliminate the possibility of multiple motors running at one time. I don't believe any of the exceptions apply to your installation. I don't see anything that would allow you to reduce the size of the feeder because you "don't think" that multiple lifts will be running at one time. But, also look at 430.22 for duty cycle. What is the duty cycle of the motor? Perhaps this will help you. It looks to me like you will need to run a full-sized feeder. You will also need to evaluate the effects of voltage drop. If you run a full-sized feeder and in fact only one or two lifts are used at once, then the additional capacity of the feeder will help reduce voltage drop on what are typically long circuits.
 
I would also think that you would need to consider voltage drop in there as well..I would assume somewhere in the area of 350 ft or maybe little more in distance...But do not know the layout just assumed in a straight line..
 
Lou,
Can you consider the power centers as power pedestals? Then I would considering using the demand factors on 555.12. That would certainly justify using the smaller feeder cables.
The most boat lifts I have designed for was 4 and it wasn't any where near the length of runs that you like doing! As you know at a marina voltage drop calcs are King!!!

hope this helps!
 
I called the AHJ to explain the job. He agreed that a 100% demand was not necessary. I asked them to review 430.26 and comment on what they would think a reasonable demant factor would be.

He said he would 'try' to get back to me tomorrow. :smile:
I'll let you know what he says.
 
I want to put 7 power centers on each feeder (for a total of 14 boatlifts per feeder). I want to use #4 type W cable which gives me an ampacity on the feeder of 115 amps (table 400.5(B)). If you add all the motor ampacity together you get 224-amps (28 motors * 8-amps) not adding in 25% of 2 motors for the starting current.
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Keep in mind that IF these motors are 120 Volt, AND you are installing a 240 Volt feeder, then you only have a total of 14 connected PER LEG of your feeder. Then, your total load calculation would be 14 motors times 8 Amps each, with a total of 112 Amps. Adding another 2 Amps (25% of the largest motor) = 114 Amps.

Considering this, a feeder with a 115 Amp capacity sounds just about right.
 
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