Rewiring the 110 - looking for advice

If we ever get done our current trip with its list of projects, we're going to haul Gray Hawk and I intend to replace the 110 volt wiring.* She's got a typical 1980 era electrical panel which wouldn't meet code today and which is frankly inadequate for her equipment complement.* In particular she is wired so that we can only use 3600 watts of our 6500 watt genset capacity but that's not the only issue I want to deal with.

My initial goal was to rewire her to 2 x 30 amp services.* I've seen that configuration on other boats and I ass/u/me the two 30 amp services are wired to opposite sides of the electrical panel.* Further reflection has lead me to question why I wouldn't just wire her to one 50 amp (240 volt) service.* Is there something I'm missing here?* What is the point of 2 x 30 amp service on boats?* I'm pretty familiar with RV wiring configurations and that one is something you never see in RVs.*

The question that kicked this off for me is, if I do go with 2 x 30 amp services, how do I wire a transfer switch to handle that?* Currently there is no auto transfer switch on Gray Hawk - there are 2 breakers in the panel with a flapper to prevent them both being "ON" simultaneously.* One of the outcomes of the electrical refit will be an auto transfer switch to handle the generator/shore priority and to remove the manual breakers from the system but I can't think how to easily do that with 2 x 30 amp service.* For that matter I can't think of any way to securely handle the transfer manually with a 2 x 30 service either.

My boat has a manual transfer switch for 2 panels...not sure about auto transfer switches.

I'm gonna go from 2 30 amp circuits to one 50 amp as the two legs will be 50 amp which is over a 50 percent increase in total wattage.* In other words a 100 amp service compared to a 60 amp service.

The main reason people don't like 50 amp shore power is*the cord*is BIG, HEAVY, and*EXPENSIVE (around $500)

Most of the boats I've seen with two 30 amp inlets have two panels, one for each inlet. Usually one is dedicated to the HVAC and the other powers everything else. If you go with the two 30's, you should get a Y-adapter, 50A240V X 2 30A120V.

If your power demands are increasing , I would go for the 50/240 service.

No difference in the individual 120v circuits , you just get more of them.

True, 2-30A power hoses are lighter/easier to handle , esp. for an O'nite quick stop.

But if the individual circuits are selected with some thought , a single 30A line will do most of the time.

You might even contemplate having load shedding included in the single line , so you can live comfortably on a 15A plug.

Bob, I would suggest a lot more research on your part before you begin to tackle this since errors can be serious. I have never seen a boat with two 30 amp services that has a transfer switch. The single panel wired properly or two separate panels don't get switched back and forth. A 50 amp shore power inlet is a good idea, the main reason for two 30 amps is that most marinas have two 30 amp services available, not all have 50 amp. Wiring a 50 amp is a little tricky compared to two separate 30 amp inlets. A good start for you is Nigal Calder's book on electrical and mechanical for boats, or get some assistance from a qualified marine service tech. Here are two posts on our blog that might help. We have two 30 amp services but one is almost exclusively for the air conditioning, otherwise we would not need it. I also don't understand your comment about you genset. It either works or it does not and I am not sure how you only get partial wattage. Chuck

http://trawler-beach-house.blogspot.com/2011/01/replacing-boats-main-electrical-panel.html

*

http://trawler-beach-house.blogspot.com/2010/06/marine-electrical-panel-installation.html

Capt. Chuck -

What I have seen done and don't undestand why it doesn't work as long as the old panels can handle 50 amp and the wiring is sized right....Iif you just take one leg of the 50 amp service to each panel (one red one black)*just as each panel gets the hot from each 30. as long as the neutrals are tied together and the grounds through an isolator...what's the diff?


-- Edited by psneeld on Monday 17th of October 2011 08:17:26 AM

psneeld wrote:
Capt. Chuck -

What I have seen done and don't undestand why it doesn't work as long as the old panels can handle 50 amp and the wiring is sized right....Iif you just take one leg of the 50 amp service to each panel (one red one black)*just as each panel gets the hot from each 30. as long as the neutrals are tied together and the grounds through an isolator...what's the diff?



-- Edited by psneeld on Monday 17th of October 2011 08:17:26 AM

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*Really not much difference except you need to be sure you have the seperate legs wired correctly. The only difference is as I said, not every marina will have a 50 amp service at every slip and some will not have it at all. Other than that, no big deal. Chuck

My Monk 36 is wired as Hopcar described, one 30 amp inlet for a separate panel which supplies to Aicon and heat. The other to the main 110 Panel. If we don't need the climate control we only use one cord to the main panel.
Steve W.

The consensus seems to be that 50 amp service is the way to go which is pretty much what I had decided anyway.

@CapnChuck: the genset is wired to a 30 amp panel through a 30 amp breaker. 30 amps @ 120 is 3600 watts.

The more interesting part of the wiring is HOW you transfer the neutral and ground when using either noisemaker or inverter power.

These must be joined at the source , so the power hose is combined somewhere on the dock.

The noisemaker and inverter ARE sources , so will be combined there.

I am lazy , so my solution is to have a plug (Da Boat) that plugs into the socket that is the source you wish to use.

Dock, noisemaker or inverter. DONE

bobofthenorth wrote:
30 amps @ 120 is 3600 watts.

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*It is more like 2880 watts unless all you are supplying is heaters with no fans.

FF wrote:
The more interesting part of the wiring is HOW you transfer the neutral and ground when using either noisemaker or inverter power.

These must be joined at the source , so the power hose is combined somewhere on the dock.

The noisemaker and inverter ARE sources , so will be combined there.

I am lazy , so my solution is to have a plug (Da Boat) that plugs into the socket that is the source you wish to use.

Dock, noisemaker or inverter. DONE

Click to expand...

*Prior to starting this thread my inclination was to use an auto transfer switch but I'm well acquainted with the benefits of the KISS system.* After*drooling over*CapnChuck's links project creep has already set in before I remove the first cable.* Those Paneltronics custom panels are WAY COOL.* So cool that I think we need one with the 3 source mains.* I need to wait until we're back on the boat to order it though so I can get all the labels right.*

@Rick - as usual you miss the point in order to show us how smart you are.

Gee, I was beat by Rickb. So I will say anyway, Do not use 3600 watts, it is ideal and does not take into account line, starting*and switch losses. Even if all is properly sized, assume 85% effective transfer or about 3000 watts.

sunchaser wrote:
Even if all is properly sized, assume 85% effective transfer or about 3000 watts.

Click to expand...

My calculation had nothing to do with line losses.

AC power is not calculated like DC power, it is not amps X volts, it is amps X volts X power factor. If most of your loads are motors or transformers you can have a power factor down in the .7 or .75 range.