T&T: 30 amp service vs. 50 amp service

[Larry N. Brown]

This thread, as the filter thread did before, threatens to spin out of 
control. There are multiple ways to skin a cat and here's the skin of my 
electrical cat.

When I retrofitted my boat, I designed the electrical system to basically 
run on 240 VAC because I had some heavy loads best served by the high 
voltage/low current service. I stripped out the old wires ad replaced 
everything from the shore panel to each jbox and outlet. Spent just over 3 
boat units at Best Boat Wire and countless hours of labor. At full rated 
load, I consume 12,000 watts of power, 240 VAC, shore power or genset.

It's dead dirt simple. Plug the python into 240 VAC/50a shore power and it 
runs through a 50a, 3 leg breaker, 1' inside the boat and  and from there, 
22' of AWG 6, 4 conductor,  to the 240 v main distribution panel I had built 
for me by Paneltronics of FLL. My "sure enough" 240v loads are my SCUBA 
compressor, watermaker, washer/dryer and Home Depot 30 gal hot water heater. 
They CANNOT work without 240v,  either shore power or genset, but with power 
management, they can work off 240/30.

My 4 Flagship Marine air-conditioners and two raw water pumps are 120v and 
are balanced across L1 and L2. Most incidental 120 loads- reefer, freezer, 
microwave, etc., are powered through my Victron 2500 inverter charger on L1. 
At low power levels, I see a slight load imbalance, but as I approach the 
full design load of 12 KW, there's never over a couple volts difference 
between L1 and L2. A clamp-on ammeter shows only trace current on the 
neutral.

In my misspent youth, I spent a couple summers wiring houses and an old 
electrician once told me, that if a house had a well designed electrical 
system, THEORETICALLY, the neutral would carry little, if any load. You 
could, once again in theory, snip the neutral and all the 120 loads would 
find themselves in series across the 240. The 1500 watt waffle iron on L1 
would be in series with the 1500 watt coffee maker on L2. The 240 v electric 
hot water heater would be a wash.

I can run my boat with anything from 240/50 shore power to a 15a outlet 
shared with a Coke machine on a dock in Belize. Question of power management 
and pigtails. Without 240 I have to nurse my hot water, SCUBA bottles, fresh 
water and laundry or run the genset. If there's 240/30 available, I have a 
homebrew splitter pigtail that will feed it to the python. Everything works 
but with power management. If I over reach, the 30 shore breaker(s) will 
trip. Elegantly simple. I watch the incoming shore power voltage to see it 
doesn't sag and adjust loads accordingly.

If the dock has only one leg of 120 but 2 30a outlets, I lose the 4 high 
load items but everything elso works. If it has 1 30a plug, I have a cover 
for one leg of my dumb splitter so's I don't accidentally electrifry myself. 
If I have to share the 15a outlet with the coke machine in Belize, I can 
plug the python into a 15a reducing pigtail and sleep with the aft stateroom 
AC unit, reefer and freezer running.

Regards.

Larry
Cigano, 47' Prairie Sundeck
Lying Covington, LA


----- Original Message ----- 
From: "ron barr" <rwhb@msn.com>
To: <trawlers-and-trawlering@lists.samurai.com>
Cc: <bob_england@hotmail.com>
Sent: Sunday, July 09, 2006 10:19 PM
Subject: T&T: 30 amp service vs. 50 amp service


> SNIP:"I you have a 30/50 splitter that plugs into a 50 amp
> receptacle then you are utilizing a 50 amp service, with a pair of 50 amp
> breakers tied together. after having used a 50A cable for awhile, I much
> prefer a splitter and two thirties tied into a 50 amp service.That 50 amp
> cord is like an python, and expensive !" Bob England
>
> I don't quite get what you are saying here Bob. If I take two 30A's the 
> first
> question is whether they are on the same phase or not- that affects what I 
> can
> pull.
> Secondly where do the two 50A breakers you mention come from? The shore 
> has two
> 30A.
> Finally these Y's cost close to $400 new - although some are a lot cheaper 
> at
> consignment stores - curious whey are so many around second hand- people 
> tried
> them and had problems maybe with phase matching? Given that price a 50A 
> python
> may be cheaper!
>
> Ron Barr
> Lady Brookhaven Hatteras LRC 42
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