marina panel breakdown

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Recently iquired about load calc method for a marina service. had 48 receptacles @30 amp for 172800 va and 21 receptacles @ 20 A for 50400 va total of 223200 va x40% = 89200 /240 = 372 A. So far so good as to service size. But I am still confused as to how the best way may be to break these loads down on standard 200 amp panels. Can anyone help clear the fog?
 
Re: marina panel breakdown

The code does not take any of this into consideration. They use te diversity tables to allow for variations in laods etc. Im just real cofused as to how each panel and its feeders are treated to be able to know whats correct as far as calc on each panel
 
Re: marina panel breakdown

You could get the job done with 2 panels.I believe i would make each one a dedicated circuit.Without knowing a bit more would be hard to lay this out.I assume you have taken voltage drops into consideration.All marinas are different as to the real load.Have seen slips for small 20 footers so almost no load.The only marina i wired was for yauhts,so demand was far higher.

[ January 14, 2004, 09:41 PM: Message edited by: jimwalker ]
 
Re: marina panel breakdown

What I am trying to determine is to do the proper load calc using the tables provided in 555.12. I agree that 2 200 amp panels seem sufficient however each feeder must be calculated separatly and I am having a bit of a problem when using the tables to come up with a correct load calc per panel and per feeder. Just a bit confusing.
 
Re: marina panel breakdown

And yes I agree each marina is different when it comes to actual load conditions but this is really not a consideration when doing the theoretical load calc. Voltage drop has to do only with wire sizing and not load. Obviously drop comes into plat somewhat but not as it applies to demand on the panels feeders or service.
 
Re: marina panel breakdown

Let me start by saying that, if you are talking about 69 separate slips, then a pair of 200 amp panels will not get the job done. Let me explain.

First, what version of the code applies? As of the 2002 version, the shore power receptacles have to be a minimum of 30 amps. The 1999 version allowed 20 amp shore power receptacles.

Secondly, do you mean to say that the 48 (30 amp) receptacles serve different slips than the 21 (20 amp) receptacles? What I am asking is whether a single boat moored at this marina has a choice of whether to plug into the 30 or the 20? If you have both receptacles at a single slip, then you need only count the larger of the two. Specific example: Suppose your marina had exactly 48 slips. Suppose that you want to install a 30 amp at every slip, and install a 20 amp at 21 of the 48 slips. In this specific example, for the purposes of load calculations, you can ignore the existence of the 20 amp receptacles. The total load would be 48 times 30 times 50%, or 86,400 VA (360 amps).

Finally, let?s suppose that you have a total of 69 slips, with 48 served at 30 amps and 21 served at 20 amps, and that the 1999 code applies. Suppose further that you want to use two panels of the smallest size that satisfies code. Then you have to use the demand factor (1999 Table 555-6, 2002 Table 555.12) for the number of receptacles connected to each panel. Specific example: Suppose you split the load in half. You put 24 (30 amp) and 11 (20 amp) on one panel, and you put 24 (30 amp) and 10 (20 amp) on the other panel. The load on the first panel is calculated as follows:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">24 times 30 times 120 = 172,800
    11 times 20 times 120 = 26,400
    Subtotal = 112,800
    Demand factor for 35 receptacles = 60%
    112,800 times 60% = 67,680
    67,680 divided by 240 = 282 amps.
    Similarly, the load on the other panel is 276 amps.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">
 
Re: marina panel breakdown

Charlie The WAC wash code makes an exception to the NEC and still allows 20 amp receptacles. This is an upgrade project and 21 receptacles will remain at 20 amp and the other 48 will be upgraded to 30. Some stalls are for smaller boats and are 20 amp and the rest are going to be 30. each receptacle serves one stall. I wanted to use 200 amp panels as they would be les expensive than using a 300 amp I think.I came up with 4 panels. putting all the 20 amp receptacles on one ,16 on 2 others and the balance(15) on the last. Does this compute or am I way off base here?
 
Re: marina panel breakdown

I didn?t realize you were here in Washington State. I agree, WAC 296-46B-555(8) does permit 20 amp receptacles. I also agree that your scheme would work. I computed the load on the four panels at 147, 168, 168, and 158 amps.
 
Re: marina panel breakdown

Thanks for the confirmation. I let myself get confused when I calculated the laods on each phase of each panel and of course found that when you do that you end up with a lesser demand factor and when you make the calculation that way you end up not having as much room on each panel. So to boil it down the feeder load is calculated by adding up all the receptacles and multiplying by 120 v to get va and then applying the demand factor based on the number of receptacles and further dividing by 240 to get the demand amps on the feeders. Anyhow thats now my understanding of the proper way to calculate feeder deamand in this case. Thanks again Joe
 
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