Floating Subdivision Service Calculations

[cdauph99]

I am trying to design and size up the electrical service for a fairly unique application.

My client has a subdivision of permanently anchored, floating homes (approx 300 or so). They vary in size from about 600sq ft to almost 3000. with electric ranges & ovens, washer dryer split ac heat with ac being the larger load, electric water heater etc.

The plan is to feed each of the homes from a tenant metering bank located out on the docks, these will be fed from a 480v 3 phase to 208v/120 Y 3 phase transformer, also located on the dock. The transformers will be fed from a 4160 to 480 transformer located on shore and distributed through an MDP.

My questions are really as follows

 

[augie47]

It may not be, but my first thought was that this is an Art 555 situation.
If it meets the scope off 555.1, please see 555.4
This has been a major obstacle in similar installs I've seen.

 

[skeshesh]

I'm impressed. Augie is so pro he's answering the question before it's even asked

 

[jwjrw]

I'm impressed. Augie is so pro he's answering the question before it's even asked

I had no idea what the op meant by floating till Gus said art 555

 

[augie47]

augie may be well off base, but I've seen a lot of "floating plans" which included high voltage because 555.4 is not widely known.

 

[muckusmc]

I am trying to design and size up the electrical service for a fairly unique application.

My client has a subdivision of permanently anchored, floating homes (approx 300 or so). They vary in size from about 600sq ft to almost 3000. with electric ranges & ovens, washer dryer split ac heat with ac being the larger load, electric water heater etc.

The plan is to feed each of the homes from a tenant metering bank located out on the docks, these will be fed from a 480v 3 phase to 208v/120 Y 3 phase transformer, also located on the dock. The transformers will be fed from a 4160 to 480 transformer located on shore and distributed through an MDP.

My questions are really as follows

What is the configuration of the docks?

 

[cdauph99]

I have reviewed art 555 and here is the challenge. Technically these are not house boats, they have no propulsion systems, they are permanently fastened to the dock structure. So they are almost more of a floating building. The services range in size from 100a to 150a. The docks are on two different sides of the lake with an approx equal number of slips on each one.

The question I am asking all in all is what would be the best method to calculate the required load for the service to each dock section. If I utilize the Marina calculations, which assumes a transient clientele, I am concerned that on the 4th of July weekend when it is 105 degrees and everyone shows up and fires up their A/C we will overrun the capacity of the main if we use those derration factors. All in all I believe this is best calculated more like a utility would calculate the loads for a subdivision. So the question is, how do they do that.

 

[George Stolz]

The plan is to feed each of the homes from a tenant metering bank located out on the docks...

The question I am asking all in all is what would be the best method to calculate the required load for the service to each dock section.

It sounds like each house is supplied by it's own feeder. It which case the wire size should be according to 310.15(B)(6).

If, by "dock section" you mean the service conductors supplying the meter banks, then you could see some diversity there that the NESC would probably provide more relief on. Where does the utility come into the picture in all of this?

 

[cdauph99]

The utility structure is like this, the entire facility, including the shore installations are fed from a single high voltage substation, the entire facility will be metered as a single unit. We are planning to bring 4160 down to a point 10' above the highest possible flood point. At that point it will be stepped down to 480v 3 phase and brought out to the individual dock sections via mining cable, at that point it will be stepped down again to 208/120 for distribution through a main to individual tenant meters for each floating home.

We have worked out the physical details as to the how, my question remains, how to calculate the load from each dock section so that it will provide sufficient service without supplying 10000amps if its not necessary. The closest parrell I can draw is the way a utility would calculate the distribution plans for a subdivision. This is what I need help with.

 

[George Stolz]

You could treat each dock section as a house, and use the demand factors given in Article 220 of the NEC for some relief - but you're going to get a smaller load calculation from the NESC, not the NEC. I can't be of much help about the NESC, never have seen it. You might get friendly with the local utility engineers, they would probably be a good source to talk to.