# Marina Load Calc



## Southeast Power (Jan 18, 2009)

There is a calculation for de-rating receptacles.
It's in the NEC under "Marinas" it's an easy read.
I have 4 50 amps on one dock and it required 200 amps.
They each have a 50 amp twist lock and a separate 20 amp GFI receptacle.
I was required to only count the 50 for the calculations.

How are your receptacles configured, do you have some 50 amp docks and some 30s or does each dock have a choice?


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## Shawn23 (Jan 5, 2011)

No 50s. These outlets are basically for dry dock repairs. All the outlets will be mounted on a wall and clients will roll out cords while working on boats and roll back up when repairs are done.


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## 220wire (Aug 18, 2008)

Shawn23 said:


> I find myself in new territory again. While the physical work is no problem, I need to provide a load calc for this new service.
> 
> Power source is 120/208 to a 200 amp meter which will feed a 200 amp MB outdoor panel. Here is where im unsure of how to calculate. The panel will be feeding receptacles for the boats. 6-30 amp 3 wire and 8-standard 20 amp gfci outlets.
> I know a dryer is 5000 watts and a fridge is 1200 watts and so on.
> ...


 
Try 555.12


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## Southeast Power (Jan 18, 2009)

Shawn23 said:


> No 50s. These outlets are basically for dry dock repairs. All the outlets will be mounted on a wall and clients will roll out cords while working on boats and roll back up when repairs are done.


Ok so, don't let me lead you to slaughter here but this in the way we just figured our dry dock receptacles.

There is no limit on dry dock.
This is the reasoning.
Is you have small boats, they are being used for lighting. Same thing for big boats.
Air conditioning units are usually water cooled and if these need service, it is rare and won't be on very much at all.
You might be running some battery tenders on bigger boats.

The only reason that you would need 30s or 50s is that boat cords, aka shore power, is what someone would expect to find out in the wild and most all boats have these configurations and carry adapters for where they don't.

Your load couldn't be 30 amps in dry dock. If a boat is really big, they will have a couple of 50s plugged into a magic box to make it 100 amps and everybody will know about it.

Right now I have about six 50' plus boats plugged in and all together they pull about 30 to 50 amps depending on what tools the guys are using. 

So, lots of little boats, little power consumed per sf of yard. Big boats take up more space, might have a fridge running, lights and battery tender. All about the same until the portable welder comes out of the tool shed.


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## hardworkingstiff (Jan 22, 2007)

Since this is dry dock repairs, does 555 even apply?

If people are working on their boats with this power, does it need to be GFCI protected?


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## Southeast Power (Jan 18, 2009)

hardworkingstiff said:


> Since this is dry dock repairs, does 555 even apply?
> 
> If people are working on their boats with this power, does it need to be GFCI protected?


Here, the 20amp 120 volt have a GFI but not for the power outlets.


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## hardworkingstiff (Jan 22, 2007)

jrannis said:


> Here, the 20amp 120 volt have a GFI but not for the power outlets.


I understand, but these outlets are for people working on boats, no? If someone is plugging an adapter into a 30-amp receptacle and running a drill or sander or ??? then they won't have the GFI protection. 

I've never seen receptacles in dry dock locations. The dry dock locations I've seen don't really allow for people to work on their boats, they had a boatyard type area for that. I'm a little confused about the OP's application.


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## Shawn23 (Jan 5, 2011)

Not being a boat guy I didn't use the right terms. The area is in the boat yard.
I read the entire 555 art. I learned a lot, thanks.

Lets say im treating it like a marina.

6- 30 amp 120 volt circuits = 21,600 va 
6- 20 amp 120 volt circuits = 0 va (they don't count if im reading right.)
Apply 90% demand factor = 19440
which of the below is correct
19440 va divided by voltage 208 volts = 93 amps
or 
19440 va divided by voltage 120 volts = 162 amps


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## hardworkingstiff (Jan 22, 2007)

Shawn23 said:


> Not being a boat guy I didn't use the right terms. The area is in the boat yard.
> I read the entire 555 art. I learned a lot, thanks.
> 
> Lets say im treating it like a marina.
> ...


I would do it like this.

19440/(208*1.732)=54A

19440/120/3(phases)=54A

This of course assumes that you can perfectly balance the loads.

Edit: I went back and looked at the OP again, the voltage was stated as 120/208 instead of 208Y/120. So based on that, I would do it this way.

19440/120/2(120V legs) = 81A. The neutral will carry about the same load as the ungrounded conductors since it's derived from a Y distribution.


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## 220wire (Aug 18, 2008)

hardworkingstiff said:


> Since this is dry dock repairs, does 555 even apply?


555 covers Marinas and boatyards, to me a boatyard, laydown area, haulout, etc. are all the same.

An angle grinder is around 7amps running and air compressor 15amps? 

I'm not sure if an electrician or an engineer can call out the horse**** "load diversity" part of the code, but it might be something worth talking to the AHJ about

Whatever you do, I'd advise not to go hack and use aluminum wiring in a marina


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## Shawn23 (Jan 5, 2011)

hardworkingstiff said:


> I would do it like this.
> 
> 19440/(208*1.732)=54A
> 
> ...


 
It is 120 volt on each leg. It is a 4 wire system.


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## hardworkingstiff (Jan 22, 2007)

Shawn23 said:


> It is 120 volt on each leg. It is a 4 wire system.


OK, so it's a 208Y/120 system (indicates a 4-wire system) instead of a 120/208 system (which indicates a 3-wire system).

Then I stick with the 54-amp calculation.


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## Shawn23 (Jan 5, 2011)

hardworkingstiff said:


> OK, so it's a 208Y/120 system (indicates a 4-wire system) instead of a 120/208 system (which indicates a 3-wire system).
> 
> Then I stick with the 54-amp calculation.


Customer just requested that I change the quote to 12- 30 amp 120 volt recepts and zero 120 volt
So now my calc would look like this?
30x120=3600 VA per recep
3600x12=43200 VA total
80% per table = 34560 VA
34560 VA / 120 x 3 legs =96


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## hardworkingstiff (Jan 22, 2007)

Shawn23 said:


> Customer just requested that I change the quote to 12- 30 amp 120 volt recepts and zero 120 volt
> So now my calc would look like this?
> 30x120=3600 VA per recep
> 3600x12=43200 VA total
> ...


The answer looks right, but, the order of operations for what you wrote would not equal what you got. It should be written 34560/(120*3) or 34560/120/3

Another way you could do it is 30A * (12/3 phases) * .8 = 96A


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## Shawn23 (Jan 5, 2011)

*Back to square one*

Now we are building a new service so she can have the 50 amp 250 volt recepts. Customer is now talking about installing pedestals. One side with a 50 amp 240v, 30 amp 120v and the other side with a 30 amp 120v and 20 amp gfci.
Total of 4 pedestals
Am I correct that each pedestal will require 15,600VA/240V = 65 Amps each.
65 amps*4= 260 total amps.
I did not use a demand factor due to only having 4 or less of each?


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## 220wire (Aug 18, 2008)

Shawn23 said:


> Now we are building a new service so she can have the 50 amp 250 volt recepts. Customer is now talking about installing pedestals. One side with a 50 amp 240v, 30 amp 120v and the other side with a 30 amp 120v and 20 amp gfci.
> Total of 4 pedestals
> Am I correct that each pedestal will require 15,600VA/240V = 65 Amps each.
> 65 amps*4= 260 total amps.


You would only calculate the highest amperage recep per slip/stall or whatever each space is called


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## Shawn23 (Jan 5, 2011)

220wire said:


> You would only calculate the highest amperage recep per slip/stall or whatever each space is called


If the pedestal is designed to be used by 2 boats at a time I would calculate the highest amperage per side? Or the highest at the pedestal?


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## 220wire (Aug 18, 2008)

Shawn23 said:


> If the pedestal is designed to be used by 2 boats at a time I would calculate the highest amperage per side? Or the highest at the pedestal?


Per side

Give yourself some room for the unknown loads, or you might be tripping OCP


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## hardworkingstiff (Jan 22, 2007)

Shawn23 said:


> Now we are building a new service so she can have the 50 amp 250 volt recepts. Customer is now talking about installing pedestals. One side with a 50 amp 240v, 30 amp 120v and the other side with a 30 amp 120v and 20 amp gfci.
> Total of 4 pedestals
> Am I correct that each pedestal will require 15,600VA/240V = 65 Amps each.
> 65 amps*4= 260 total amps.


It sounds like you have a 50/30 side A and 50/30 side B. You would take the highest rated receptacle per side, so 50+50 = 100. 100*240 = 24kVA per pedestal (which serves 2 slips). 

A couple of things. The 50-amp is normally a 120/240 receptacle and not a 240 receptacle (actually it's rated 125/250). Make sure to include the neutral in your cable.

Although it's done a lot, feeding a 120/240 receptacle with 120/208 is a code violation. See 555.19(A)(3).


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## 220wire (Aug 18, 2008)

hardworkingstiff said:


> Although it's done a lot, feeding a 120/240 receptacle with 120/208 is a code violation. See 555.19(A)(3).


That's a matter of opinion and left more to the AHJ or the equipment manufacturer. Not to high jack your thread but, try to find a receptacle that's only rated at 208! You won't unless it's a 3phase plug! We've been down this path before and I do value your opinion, but like yourself I make mistakes as well


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## hardworkingstiff (Jan 22, 2007)

220wire said:


> That's a matter of opinion and left more to the AHJ or the equipment manufacturer. Not to high jack your thread but, try to find a receptacle that's only rated at 208! You won't unless it's a 3phase plug! We've been down this path before and I do value your opinion, but like yourself I make mistakes as well


I don't see how you can read 555.19(A)(3) and say that it's an opinion. It seems pretty clear to me that the NEC does not want you to feed a shore power receptacle rated 120/240 with 120/208. They even give an FPN to explain why. Now, enforcement is another issue.

Years ago I was paid $17,000 to remove a 208Y/120 600A service and install a 120/240 1,000A service because of the complaints from the boat owners about low power (they were using the 50A receptacle with 120/208).

If you were to find a 120/208 receptacle, you could not use it because the boats using the 50A receptacle want the 120/240 receptacle, that's what is on their cord.


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## Shawn23 (Jan 5, 2011)

hardworkingstiff said:


> It sounds like you have a 50/30 side A and 50/30 side B. You would take the highest rated receptacle per side, so 50+50 = 100. 100*240 = 24kVA per pedestal (which serves 2 slips).
> *I either mistyped or you misread, probably me:thumbsup:. *
> *1 pedestal, side A has 50 and 30, side B has a 30 and a 20 amp gfci. This is why I calculated the 50 on side A and the 30 on side B.
> *
> ...


*This is why I said that the customer now has me building a new 120/240 service so she will be in compliance and most of all not burn up a customers boat*:thumbup:


Thanks Hardworking for going back and forth with me on this. And to the others as well for your help.


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## hardworkingstiff (Jan 22, 2007)

Shawn23 said:


> 1 pedestal, side A has 50 and 30, side B has a 30 and a 20 amp gfci. This is why I calculated the 50 on side A and the 30 on side B.


OK, I see where you got the 65A. The only thing though, if both receptacles are using the full rated amperage at the same time the load on 1 phase will be 80A and the other phase will be 50A since the 30 is 120V. When you size your feeder, you need to size it for the 80A load.


> Thanks Hardworking for going back and forth with me on this. And to the others as well for your help.


Your welcome. We love to help.


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## Shawn23 (Jan 5, 2011)

I am thinking of feeding each pedestal with #4cu. on a 100 amp breaker and the pedestals have built in breaker protection for each recept


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## 220wire (Aug 18, 2008)

hardworkingstiff said:


> I don't see how you can read 555.19(A)(3) and say that it's an opinion. It seems pretty clear to me that the NEC does not want you to feed a shore power receptacle rated 120/240 with 120/208. They even give an FPN to explain why. Now, enforcement is another issue.
> .


 
A FPN is not an electrical code. An FPN is advice (kind of like this forum) and is not code.


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## hardworkingstiff (Jan 22, 2007)

Shawn23 said:


> I am thinking of feeding each pedestal with #4cu. on a 100 amp breaker and the pedestals have built in breaker protection for each recept


Sounds good.


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## Shawn23 (Jan 5, 2011)

hardworkingstiff said:


> Sounds good.




Would you still agree with #4 if my distance is 170' to the 50 amp/30 amp pedestals?


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## hardworkingstiff (Jan 22, 2007)

Shawn23 said:


> Would you still agree with #4 if my distance is 170' to the 50 amp/30 amp pedestals?


Yes, I would do it. It exceeds the NEC recommendation for voltage drop, but that load is not going to be 100% of the receptacles.


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## Shawn23 (Jan 5, 2011)

If customer decides to go with a 400 amp service would I be better off with 400mcm or parallel 3/0?
Ive never ran anything parallel so would I have to use the same conduit for the feeders from the power company to my meter or would I be better off with 2- 2" conduits?
I will be running back to back long radius 90s from power companies hand hole to my meter. Then coming off each side to feed 2- 200 amp mb panels.


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## Hashmi (Jun 28, 2021)

If i have total of 32amps 220volt single phase socket 16. 63amps 220volt single phase socket 32 .
How should I calculate for marina.
And what size of transformer i should fix if i have 220/400volt 3phase when total connected load is shown as 1500kva


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## just the cowboy (Sep 4, 2013)

Hashmi said:


> If i have total of 32amps 220volt single phase socket 16. 63amps 220volt single phase socket 32 .
> How should I calculate for marina.
> And what size of transformer i should fix if i have 220/400volt 3phase when total connected load is shown as 1500kva


You will need to open a new post if you want answers, this one is 7 years old.


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