Marine Calcs

[bronco]

First time on marine installation. Feeding (36) 30 amp, 208v receptacles. Please help on calculating the feeder to the distribution panel. I have gotten several opinions.

In addition, one contractor wants to daisy chain feed three pedestals (with 2 30amp receptacles each) with one breaker. Others prefer one branch circuit per pedestal. Any opinions?

Thanks for any help.

 

[haskindm]

Are you sure they want 208 volt receptacles? That woud be very rare in a marine installation. More common would be 30-amp 120-volt. Next most common would be 50-amp 240-volt.

 

[dicklaxt]

Power receptacles(welding) or convenience receptacles and what system, single or 3 phase?

dick

 

[augie47]

Short answer: If each of your 30 amp receptacles supplies a separate slip, with 36 outlets you can apply a 60% demand factor.

It's been a while since I have inspected a marina but my memory tells me the requirement is more than likely 30 amp @ 120v. If the outlets are 208v please note the FPN in 555.19(A)(3).

Daisy chains are common on marina pedestals.

 

[bronco]

Not really sure on the 120 vs 208 part. The service drawing says 120/208v and the receptacles are just spec'd as 30 amp. This is a revision to an old existing marina. Any chance 208V was used long ago? This is shore power not GFCI receptacles.

The new addition to the marina is 120/240 with the receptacles being called out as 30amp or 50 amp. The info I've gotten from marina suppliers is 30 A receptacles are 120v, the 50's are 240v. Is there any such thing as a 30A, 240v receptacle for shore power?

Thanks for any help.

 

[Npstewart]

I would definitely loop feed them, with one branch circuit from a distribution panel, and take the diversity from the distribution panel. You will probably be able to get about 5 pedestals per branch circuit depending on the receptacle configuration you come up with.

When you calculate the total load on the pedestal you will be using 240 or 208V.

 

[bronco]

Not sure what you mean by loop feed in this case. I've seen loop fed welder distribution where the same bus is fed at each end by a different breaker but not familiar with this application.

The help here has been great.

 

[bronco]

If you use one branch circuit to feed several pedestals, can you apply the demand factor to the total number of receptacles that will be fed by the branch? I used the demand factor for sizing the feeder to the main distribution panel based on the total number of receptacles on the pier. Not sure if using it again for the branch sizing is allowed. Seems like double dipping.

 

[augie47]

Not sure what you mean by loop feed in this case. I've seen loop fed welder distribution where the same bus is fed at each end by a different breaker but not familiar with this application.

The help here has been great.

It will depend on what type pedestal you use. Many of the have the ability (lugs/buss) to be fed by a 100 or 200 amp feeder (in and out)
so you can use 1 feeder to many units.

If you use one branch circuit to feed several pedestals, can you apply the demand factor to the total number of receptacles that will be fed by the branch? I used the demand factor for sizing the feeder to the main distribution panel based on the total number of receptacles on the pier. Not sure if using it again for the branch sizing is allowed. Seems like double dipping.

\Since each ooulet will require its own OCP, if you are feeding more than one it will be a "feeder" supply several pedestals, not a brach circuit. This is one of many places in the Code where correct terminiology is important.
The demand factors can be applied to feeders and services but you at each separately. Look at the feeder, determine the number of outlets/slips being fed and apply the demand (there will be no adjustment until the 5th outlet) the look at the total number your service is feeding and apply the demand to that total number of outlets.

 

[Npstewart]

I would use the demand factor for the receptacles themselves.

I did a similar project, and I had a MDP feeding the smaller panels, which fed the pedestals. I only used the diversity to size the MDP panel. I think your asking for trouble if you try to take diversity after the MDP.

 

[bronco]

The design I'm reviewing for one pier only works if the demand factor is taken for the pedestals as well. If no demand factor is used, the breaker is under sized if it is an 80% rated breaker. If a 100% rated breaker, it will work.

Another pier has a dedicated feed to each pedestal. Two, 50amp, 240v receptacles per pedestal. However the breaker feeding it is a 100amp, 2 pole. I'm thinking if this is an 80% rated breaker, this is no good.

Is there a norm for the breaker type used for marinas as far as 80% vs 100%?

Thanks for any help.

 

[augie47]

Your load would not be considered a continuous load so a 100 amp feeder breaker to (2) 50 amp breakers and outlets would be compliant.