[hardworkingstiff]

Looking at a marina that might have about at 1100' run from the PoCo transformer to a location on the floating dock where a distribution panel would be installed (it would not be the service disconnect because it's on the dock).

The PoCo around here typically will not deliver a 480-volt single-phase service. Because of something I saw years ago, I'm very leery of using 2 legs of a 3-phase service to power single-phase loads on docks (really don't want to get distracted with this).

I was thinking about stepping up a 120/240-volt service to 600-volts, then install a step down transformer on the dock to step it down to 120/240-volts.

If I fed a 100kVA single-phase step up transformer to feed a step down transformer, and protected it with a 400-amp breaker feeding the step up transformer, do you think I would have problems with inrush current tripping the breaker when the transformer is initially energized?

With GFP requirements for marinas, would there be capacitive coupling that might look like a current leakage to the GFP (max setting 100-ma) device?

 

[macmikeman]

Transformers and docks, Hmmmmmmmmmmm......... Something in me says slow down and think it out very carefully .

 

[hardworkingstiff]

Transformers and docks, Hmmmmmmmmmmm......... Something in me says slow down and think it out very carefully .

I understand, and I am soliciting your concerns.

Transformers and docks are done all the time, but I have not done any myself.

 

[Ninjazx916r]

Looking at a marina that might have about at 1100' run from the PoCo transformer to a location on the floating dock where a distribution panel would be installed (it would not be the service disconnect because it's on the dock).

The PoCo around here typically will not deliver a 480-volt single-phase service. Because of something I saw years ago, I'm very leery of using 2 legs of a 3-phase service to power single-phase loads on docks (really don't want to get distracted with this).

I was thinking about stepping up a 120/240-volt service to 600-volts, then install a step down transformer on the dock to step it down to 120/240-volts.

If I fed a 100kVA single-phase step up transformer to feed a step down transformer, and protected it with a 400-amp breaker feeding the step up transformer, do you think I would have problems with inrush current tripping the breaker when the transformer is initially energized?

With GFP requirements for marinas, would there be capacitive coupling that might look like a current leakage to the GFP (max setting 100-ma) device?

I have only been in the trade for a few years but during my time in class I was taught they over come inrush current by using Time Delay Overcurrent Protection Device or fuse. That concept was taught in my motor class. I am not sure if it can be apply to transformer. Just a thought.

 

[macmikeman]

Well Lou, I put in and helped design a Zog worthy sized utility xfmr out on a dock at a certain military base at a certain harbor at a certain large state on the west coast of the country once that I am not allowed to talk about the job, and it all went really well, except that when I watched the video's of the Fukushima tsunami it was suddenly all I could think about for a while.... Maybe not such a great idea after all....

 

[macmikeman]

I can say this though- Flipper was one of my favorite tv shows when I was a kid.

 

[Cow]

I have a very similar project coming up. A customer is putting up a building about 2800' from the closest pole. The plan right now is to have the power company bring the poles 1600' closer, cutting it down to a 1200' run.

My plan at this point is to install a 480v 3 phase service at the pole with either a fused disco or MB panelboard. Then haul 2 or 3 phases(I haven't decided yet if I want the extra expense of 3 phase) 1200' to the building stepping it down to 100 amps of 240v single phase.

I initially thought of step up and step down transformers but why not have the POCO give you a higher voltage service to begin with? It's one less idle transformer that would be using current $$$ and one less failure point in the system.

 

[hardworkingstiff]

I initially thought of step up and step down transformers but why not have the POCO give you a higher voltage service to begin with? It's one less idle transformer that would be using current $$$ and one less failure point in the system.

Good points. I have a concern in that I was called in to look at a marina I did not wire. There was a report of someone getting a shock when they reached into the water. It was quite a few years ago, so I don't remember all the details. 480 3-phase service, only 2 legs installed out to a subpanel on the dock and then branch breakers from there to transformers on the dock. No neutral used, just 2 of 3 phases of a wye distribution. An engineering firm was brought in and did some additional grounding but never could get the voltage to go away. Owner finally cut off funding.

I'll check with PoCo again, but I don't think they will provide a single-phase 480-volt service.

With the 100-ma threshold for GFP at marinas, I'm concerned about some capacative mumbo jumbo above my education level causing a bunch of nuisance tripping. I may be completely wrong, but until I see EE drawings, my budget numbers will be just that, budget. I still like to work through different scenarios.