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Shore Power and Electricity Concepts (LONG POST - was "Power Cords")

Jim Healy

Tue, Jul 29, 2008 5:01 PM

This is a long post related to shore power electrics. Quit now if the
subject isn't your thing.

Several errors in understanding of electrical principles and systems were
posted on the "Power Cord" thread in the past 24 hours.

It doesn't really matter much if people refer to a 230V residential circuit
as "two phase" or not. It's a terminology shortcut like so many we use in
everyday conversation. What's important is that the underlying concepts are
clear. In the case of today's post, that understanding seemed confused. In
fact, a 230V residential circuit is not a two-phased circuit; not.
there are two-phase circuits; rare, and used primarily in heavy industrial
applications. In North America, 60-cycle, three phase generating machines
and a three-phase power distribution grids are the standard. Three Phase
power is commonly used in commercial and all industrial applications; it's
unusual, but possible, in residences. Single phase circuits power the
overwhelming majority of residential applications. Here's the concept: a
230V circuit is comprised of two hot "lines" that are the terminal ends of
the secondary winding of the omni-present single phase transformers found on
poles in every locale across the country. In North America, this secondary
winding has a center tap. The primary winding of the transformer is
attached to a single phase primary or one leg of a 3-phase primary
distribution line, usually located on a pole (or underground) at the street.
If you see one transformer, you get single phase power; if you see three
transformers mounted together as a set, in all likelihood there is a
three-phase service for some nearby commercial customer. You do not get
two phase output from single phased input. Between the center tap and L1,
there is 115V. Between the center tap and L2, there is 115V. In North
America, it is conventional (for good technical reasons) to consider the
center tap as the neutral, but not necessary. In the laboratory - NEVER ON
THE STREET, PLEASE - you could just as easily "ground" L1, and get 115V from
L1 to the center tap, 115V between the center tap and L2, and 230 V between
L1 and L2.

Another poster has already corrected the post error about 50A breakers. A
2-pole 50A breaker is, in fact, two mechanically interconnected 50A
breakers. These breakers are manufactured that way for several reasons but
always used where a fault in one leg will also trip the other leg. In
actual practice, most 230V appliances we use today are not truly 230V
electricity consumers, but in fact, hybrids that require both 115V and 230V
to run. A Dryer needs 230V for the heating element, but 115V for the
control timer and the drum motor. Larger A/C units require 230V for their
compressors, but may require 115V for their fans, pumps and controllers.
Since in this configuration, there could be a fault in either one of, but
not both, legs, both legs must be simultaneously protected. The mechanical
linkage on the breaker does that. Secondly, true 230V devices require both
hot legs, but no neutral; think of electric space heaters and deep well
pumps. If one leg were to fault, the other would still be delivering 230V
to heaven-only-knows-where downstream. So, a double pole breaker is used to
simultaneously disconnect both legs. The first case, above, results in a
very complex interplay of circulating currents flowing, respectively, in L1,
L2, and the Neutral. An interesting theoretical observation is that with
only 115V loads distributed equally (balanced) across both sides of the
center tap, you may actually have no current flowing in the neutral at all.
The Neutral provides the circuit's reference voltage, but all of the current
flows only in L1 and L2. The more unbalanced the loads, the more current
flows in the neutral. Again, not two phase; the current flowing in the
neutral is single phase. This is all predicted and described by Kirchhoff's
Laws.

Another poster mentioned 208V 3-phase power. In marinas, many "mega yachts"
require 3-phase shore power, often for large pumps and A/C compressors. So
it is possible to encounter a marina wired for 3-phase power. HOWEVER,
3-phase shore power connectors are quite different from single phase
connectors, 3-phase circuit breakers are obviously different from single
phase breakers, and connectors are generally 100A or more, so physically
very different. It's inconceivable that you could encounter one to which
could actually plug a 30A or 50A single phase connector. And if you did,
you would almost certainly have a shower of sparks in you hand as you tried
(a good reason to make sure the breakers are "off" when you attach them).
When 3-phase circuits are used to source downstream single phase circuits,
3-phase circuits should always be interconnected via single phase
transformers that correct the characteristic voltage differences between the
two. In my experience, I have never seen 3-phase "accidentally" delivered
into a residential service. I HAVE SEEN LOW SHORE POWER VOLTAGE AT THE
PEDESTAL, THAT WAS SUPPOSED TO BE 230/115. IF YOU ENCOUNTER THAT CONDITION,
DO NOT STAY CONNECTED TO IT. THAT IS EQUIVALENT TO A SERIOUS BROWN OUT, AND
WILL DAMAGE EQUIPMENT BY OVERHEATING (again, predicted by Ohm's Law).

Another post said:

SNIP

"Both ABYC and the Canadian Standards Association require that separate
shore power inlets must be isolated - the neutrals must not be connected
together on board. This is, I think, primarily a safety precaution to
protect against incorrectly wired dock outlets, where hot and neutral may be
reversed."

ENDSNIP

I think this is actually related to a concept other than reversed polarity.
If the neutrals were connected together on the boat, you'd be "paralleling"
the two neutral wires into one, single conductor. If one of the shore power
lines/connections had a high resistance anywhere along it's run, the current
from the high resistance line would transfer (predicted by Ohm's Law) to the
line with lesser resistance. The theoretical worst case would be that both
30A services were maxed on a hot summer day with A/C and refer/battery
charger/hot water heater/washer/dryer all running, and the single
functioning neutral would now have to handle 60A. If it's #10 AWG, it's
ampacity is seriously exceeded and poof, fire or worse. The concept here
is, never NEVER parallel two or more individual wires to achieve ampacity;
always, always, always install a larger diameter, single piece of wire rated
in excess of the design point ampacity requirement!!!

Finally, (well, I said this was a humongous, long post) one poster said that
reverse polarity circuits would result in the absence of overload
protection. That is not correct. The circuit would still be fully
protected in the "overload" sense of the word, but yet, very dangerous to
human life. The danger is because the hot line of the service would be
feeding the neutral line(s) on the boat, and the neutral line of the service
would be connected to the hot side of the boat circuits; i.e., reversed.
That would possible raise the exposed metal parts of all attached appliances
(pumps, electronic enclosures, washer, dryers, stoves, etc, etc) to 115V.
So, touching the metal part of the stove and the sink at the same time could
be a shocking - potentiall lethally shocking - experience. Double-insulated
tools are designed specifically to accommodate this condition, but home
appliances as frequently found on boats are generally not.

I have been following this list for some months now, and am constantly
impressed with the knowledge and experience I find here. My thanks to all
who contribute so much. I didn't create this post (a couple of hours, now)
to embarrass anyone or impress anyone. Here's my basic point: There are
lots and lots of ways to "make things work;" There are only a couple of
ways to "do it right." So, in all matters like this, AFTER YOU GET THE
INPUT FROM THE LIST that enables you to talk intelligently to professionals,
I urge everyone to never, never "just trust the input," mine included. I
urge one and all to always, always, always, always "check-it-out" with
professionals when dealing with electricity, low temp/pressure flammable
fuels, (gasoline, propane, CNG), etc. This stuff, done wrong, however
innocently, can kill you, your family, and your marina neighbors. I
apologize if I'm preaching. I've seen a boat fire that cost several lives,
and I don't want that to happen to anyone, ever again.

Jim Healy aboard Sanctuary,
currently at Rock Creek, Pasadena, MD

This is a long post related to shore power electrics. Quit now if the subject isn't your thing. Several errors in understanding of electrical principles and systems were posted on the "Power Cord" thread in the past 24 hours. It doesn't really matter much if people refer to a 230V residential circuit as "two phase" or not. It's a terminology shortcut like so many we use in everyday conversation. What's important is that the underlying concepts are clear. In the case of today's post, that understanding seemed confused. In fact, a 230V residential circuit is *not* a two-phased circuit; *not*. there are two-phase circuits; rare, and used primarily in heavy industrial applications. In North America, 60-cycle, three phase generating machines and a three-phase power distribution grids are the standard. Three Phase power is commonly used in commercial and all industrial applications; it's unusual, but possible, in residences. Single phase circuits power the overwhelming majority of residential applications. Here's the concept: a 230V circuit is comprised of two hot "lines" that are the terminal ends of the secondary winding of the omni-present single phase transformers found on poles in every locale across the country. In North America, this secondary winding has a center tap. The primary winding of the transformer is attached to a single phase primary or one leg of a 3-phase primary distribution line, usually located on a pole (or underground) at the street. If you see one transformer, you get single phase power; if you see three transformers mounted together as a set, in all likelihood there is a three-phase service for some nearby commercial customer. You do *not* get two phase output from single phased input. Between the center tap and L1, there is 115V. Between the center tap and L2, there is 115V. In North America, it is conventional (for good technical reasons) to consider the center tap as the neutral, but not necessary. In the laboratory - NEVER ON THE STREET, PLEASE - you could just as easily "ground" L1, and get 115V from L1 to the center tap, 115V between the center tap and L2, and 230 V between L1 and L2. Another poster has already corrected the post error about 50A breakers. A 2-pole 50A breaker is, in fact, two mechanically interconnected 50A breakers. These breakers are manufactured that way for several reasons but always used where a fault in one leg will *also* trip the other leg. In actual practice, most 230V appliances we use today are not truly 230V electricity consumers, but in fact, hybrids that require both 115V and 230V to run. A Dryer needs 230V for the heating element, but 115V for the control timer and the drum motor. Larger A/C units require 230V for their compressors, but may require 115V for their fans, pumps and controllers. Since in this configuration, there could be a fault in either one of, but not both, legs, both legs must be simultaneously protected. The mechanical linkage on the breaker does that. Secondly, true 230V devices require both hot legs, but no neutral; think of electric space heaters and deep well pumps. If one leg were to fault, the other would still be delivering 230V to heaven-only-knows-where downstream. So, a double pole breaker is used to simultaneously disconnect both legs. The first case, above, results in a very complex interplay of circulating currents flowing, respectively, in L1, L2, and the Neutral. An interesting theoretical observation is that with only 115V loads distributed equally (balanced) across both sides of the center tap, you may actually have no current flowing in the neutral at all. The Neutral provides the circuit's reference voltage, but all of the current flows only in L1 and L2. The more unbalanced the loads, the more current flows in the neutral. Again, not *two phase*; the current flowing in the neutral is single phase. This is all predicted and described by Kirchhoff's Laws. Another poster mentioned 208V 3-phase power. In marinas, many "mega yachts" require 3-phase shore power, often for large pumps and A/C compressors. So it is possible to encounter a marina wired for 3-phase power. HOWEVER, 3-phase shore power connectors are quite different from single phase connectors, 3-phase circuit breakers are obviously different from single phase breakers, and connectors are generally 100A or more, so physically very different. It's inconceivable that you could encounter one to which could actually plug a 30A or 50A single phase connector. And if you did, you would almost certainly have a shower of sparks in you hand as you tried (a good reason to make sure the breakers are "off" when you attach them). When 3-phase circuits are used to source downstream single phase circuits, 3-phase circuits should always be interconnected via single phase transformers that correct the characteristic voltage differences between the two. In my experience, I have never seen 3-phase "accidentally" delivered into a residential service. I HAVE SEEN LOW SHORE POWER VOLTAGE AT THE PEDESTAL, THAT WAS SUPPOSED TO BE 230/115. IF YOU ENCOUNTER THAT CONDITION, DO NOT STAY CONNECTED TO IT. THAT IS EQUIVALENT TO A SERIOUS BROWN OUT, AND WILL DAMAGE EQUIPMENT BY OVERHEATING (again, predicted by Ohm's Law). Another post said: >SNIP "Both ABYC and the Canadian Standards Association require that separate shore power inlets _must_ be isolated - the neutrals must not be connected together on board. This is, I think, primarily a safety precaution to protect against incorrectly wired dock outlets, where hot and neutral may be reversed." >ENDSNIP I think this is actually related to a concept other than reversed polarity. If the neutrals were connected together on the boat, you'd be "paralleling" the two neutral wires into one, single conductor. If one of the shore power lines/connections had a high resistance anywhere along it's run, the current from the high resistance line would transfer (predicted by Ohm's Law) to the line with lesser resistance. The theoretical worst case would be that both 30A services were maxed on a hot summer day with A/C and refer/battery charger/hot water heater/washer/dryer all running, and the single functioning neutral would now have to handle 60A. If it's #10 AWG, it's ampacity is seriously exceeded and poof, fire or worse. The concept here is, *never* NEVER parallel two or more individual wires to achieve ampacity; always, always, always install a larger diameter, single piece of wire rated in excess of the design point ampacity requirement!!! Finally, (well, I said this was a humongous, long post) one poster said that reverse polarity circuits would result in the absence of overload protection. That is not correct. The circuit would still be fully protected in the "overload" sense of the word, but yet, *very dangerous* to human life. The danger is because the hot line of the service would be feeding the neutral line(s) on the boat, and the neutral line of the service would be connected to the hot side of the boat circuits; i.e., reversed. That would possible raise the exposed metal parts of all attached appliances (pumps, electronic enclosures, washer, dryers, stoves, etc, etc) to 115V. So, touching the metal part of the stove and the sink at the same time could be a shocking - potentiall lethally shocking - experience. Double-insulated tools are designed specifically to accommodate this condition, but home appliances as frequently found on boats are generally not. I have been following this list for some months now, and am constantly impressed with the knowledge and experience I find here. My thanks to all who contribute so much. I didn't create this post (a couple of hours, now) to embarrass anyone or impress anyone. Here's my basic point: There are lots and lots of ways to "make things work;" There are only a couple of ways to "do it right." So, in all matters like this, AFTER YOU GET THE INPUT FROM THE LIST that enables you to talk intelligently to professionals, I urge everyone to never, never "just trust the input," mine included. I urge one and all to always, always, always, always "check-it-out" with professionals when dealing with electricity, low temp/pressure flammable fuels, (gasoline, propane, CNG), etc. This stuff, done wrong, however innocently, can kill you, your family, and your marina neighbors. I apologize if I'm preaching. I've seen a boat fire that cost several lives, and I don't want that to happen to anyone, ever again. Jim Healy aboard Sanctuary, currently at Rock Creek, Pasadena, MD

Al Thomason

Tue, Jul 29, 2008 6:00 PM

Jim,

Good post and good summary. One correction with regards to 208v. It is
common to see 120v feed taken off of different legs of 3 phase power.
Mostly you will see this in commercial and/or larger residential condos.
You are totally correct that the 'right' way to do it would be to
install an additional single phase, center tapped transformer, but this
is rarely done. When the 120v is taken of a 3-phase feed, there is no
difference to the end application. But when '240v' is called for,
because of the phase shift between the 3 phase one gets the equivalent
of 208v. This is why you can purchase 240v equipment as optional 208v.

It is known for larger marinas to bring in 3 phase power, mostly cause
it is cheaper to configure and install. Except for large yachts and
ships, there is no need for 3-phase power to be brought out to the boat.
But they do it to save money. What they do is bring in power to the
marina on 3 'hot' lines, and a neutral. (1 hot wire for each 'phase').
Between any hot wire and the neutral, you will measure 120v. So, if you
slip is wired for 120v, they only bring one of those hot wires along
with the neutral to your slip. To keep things balanced, you neighbor
will get his slip wired to a different hot wire (everyone shares the
same neutral), and the one next to him get the last hot wire of the
three. Then it starts repeating. If you have "240v" at a slip, then they
will bring 2 hot wires to your slip, but in this case you only get 208v
across the two hots because of 'phasing' issues. 120v is still not a
problem, it is only the '240'v that is different. So, they bring
3-phase to your marine, but not all the way to the slip.

My marina is wired this way, the prior one was not. And I 1st noticed
this approach many years ago while working on a high rise Condo, where
all the 240v was really two legs of 3-phase, and hence we had special
ordered 208v dryers, heaters, ACs, etc...

Issue is there is no real way to tell how your marine is set up, other
then measuring with a good meter. If you are using heavy amp 240v with
a 240v motor(ala larger AC's), and they expect 240 but are only getting
208 that can cause issues. 240v heaters do not care if they see 208,
they will just put out less heat. And anything that uses 120v
(including many smaller to mid sized ACes) will also not care. As Jim
pointed out, even some '240v' items which are actually mixed will not be
a problem. take a dryer: Mostly the motors and controls are 120v, only
the heating element is 240v. So in that case, the dryer will be OK, it
will just dry a little slower running the heater on 208v vs. 240v. It
is really only a problem for you if you have items which use motors that
are expecting to get a full 240v.

-al-

Jim, Good post and good summary. One correction with regards to 208v. It is common to see 120v feed taken off of different legs of 3 phase power. Mostly you will see this in commercial and/or larger residential condos. You are totally correct that the 'right' way to do it would be to install an additional single phase, center tapped transformer, but this is rarely done. When the 120v is taken of a 3-phase feed, there is no difference to the end application. But when '240v' is called for, because of the phase shift between the 3 phase one gets the equivalent of 208v. This is why you can purchase 240v equipment as optional 208v. It is known for larger marinas to bring in 3 phase power, mostly cause it is cheaper to configure and install. Except for large yachts and ships, there is no need for 3-phase power to be brought out to the boat. But they do it to save money. What they do is bring in power to the marina on 3 'hot' lines, and a neutral. (1 hot wire for each 'phase'). Between any hot wire and the neutral, you will measure 120v. So, if you slip is wired for 120v, they only bring one of those hot wires along with the neutral to your slip. To keep things balanced, you neighbor will get his slip wired to a different hot wire (everyone shares the same neutral), and the one next to him get the last hot wire of the three. Then it starts repeating. If you have "240v" at a slip, then they will bring 2 hot wires to your slip, but in this case you only get 208v across the two hots because of 'phasing' issues. 120v is still not a problem, it is only the '240'v that is different. So, they bring 3-phase to your marine, but not all the way to the slip. My marina is wired this way, the prior one was not. And I 1st noticed this approach many years ago while working on a high rise Condo, where all the 240v was really two legs of 3-phase, and hence we had special ordered 208v dryers, heaters, ACs, etc... Issue is there is no real way to tell how your marine is set up, other then measuring with a good meter. If you are using heavy amp 240v with a 240v motor(ala larger AC's), and they expect 240 but are only getting 208 that can cause issues. 240v heaters do not care if they see 208, they will just put out less heat. And anything that uses 120v (including many smaller to mid sized ACes) will also not care. As Jim pointed out, even some '240v' items which are actually mixed will not be a problem. take a dryer: Mostly the motors and controls are 120v, only the heating element is 240v. So in that case, the dryer will be OK, it will just dry a little slower running the heater on 208v vs. 240v. It is really only a problem for you if you have items which use motors that are expecting to get a full 240v. -al-

Jim Boyd

Tue, Jul 29, 2008 6:30 PM

All
Sorry to add to this already confusing (at least to me) subject but I have a
situation that I have received at least a dozen different answers to and I'm
not sure which, if any, is correct.

When I purchased Lark it came with two 50A cables and a 50A splitter that
hooked to a 50A shore power source. Each of the 50A cables attach to a
separate receptacle on the boat. I have been told the following...

Due to the splitter I have 50A on each leg
Due to the splitter I only have 25A on each leg and would be better off
buying 2 30A cables so I would have 30A on each leg
I could eliminate the splitter and go with one 50A cable and still have
50A as both legs share one incoming source (now I am really confused at this
point)

Hopefully I have supplied sufficient background to receive an answer that is
correct and that I could understand.

Thanks for any assistance

Jim Boyd
Lark

All Sorry to add to this already confusing (at least to me) subject but I have a situation that I have received at least a dozen different answers to and I'm not sure which, if any, is correct. When I purchased Lark it came with two 50A cables and a 50A splitter that hooked to a 50A shore power source. Each of the 50A cables attach to a separate receptacle on the boat. I have been told the following... 1. Due to the splitter I have 50A on each leg 2. Due to the splitter I only have 25A on each leg and would be better off buying 2 30A cables so I would have 30A on each leg 3. I could eliminate the splitter and go with one 50A cable and still have 50A as both legs share one incoming source (now I am really confused at this point) Hopefully I have supplied sufficient background to receive an answer that is correct and that I could understand. Thanks for any assistance Jim Boyd Lark

Mark Richter

Tue, Jul 29, 2008 9:22 PM

I have a hard time understanding why a boat would be wired this way, unless
it was kept at a Marina with only 50A 120v service, which is now quite rare.
But you do have 100 total amps available at 120v. Depending on how the boat
is wired internally, you may or may not have 240v available for heavy
appliances.

Yes, a single 50A 240v cord could provide the same amount of power, but your
boat's inlet receptacles and possibly part of the main panel would have to
be rewired.

Mark Richter, Mark's Mobile Marine, Ortona, FL
Electrical system design, installation and repair
m/v Winnie the Pooh, mobile electrical workshop lying Brockport, NY

Jim, It's not entirely sure from your post, but it sounds to me like you may have a pair of 50A 120v cords. The splitter would then split the 50A 240v available at the marina post to 50A 120v for each of the two cords. You can test this theory by plugging the cords and splitter into the marina power and checking the voltage at each cord from each terminal to ground with a multimeter. If only 120v is found, then my guess is correct. If there is 240v on the cords... I have a hard time understanding why a boat would be wired this way, unless it was kept at a Marina with only 50A 120v service, which is now quite rare. But you do have 100 total amps available at 120v. Depending on how the boat is wired internally, you may or may not have 240v available for heavy appliances. Yes, a single 50A 240v cord could provide the same amount of power, but your boat's inlet receptacles and possibly part of the main panel would have to be rewired. Mark Richter, Mark's Mobile Marine, Ortona, FL Electrical system design, installation and repair m/v Winnie the Pooh, mobile electrical workshop lying Brockport, NY

Ken Bloomfield

Wed, Jul 30, 2008 2:45 PM

Jim,
It is a bit hard to be definative without looking at your cables and
splitter, but I suspect what you are running into is as follows:

(a) There are two types of "50A" cables out there, with respective
connectors. These are 50A @ 125 VAC, and 50A @ 125/250 VAC.

(b) In the first case, these are 3 wire cables, each with neutral, hot, and
ground wires that carry 125 VAC with 50 ampere current capability. A lot of
the older Bluewater boats in our marina were originally equipped this way.

(c) In the second (now more common) case, the cable has four wires
internally, and they are neutral, hot #1 aka L1, hot #2 aka L2, and ground.
Each of the hot wires is capable of carrying 50 amperes and the AC waveform
relationship is such that the voltage differential between them yields a
potential difference of 250 VAC.

If you have a splitter, I suspect that if you examine it carefully, you will
find that it is rated (at the shorepower socket end) as 125/250 VAC at 50A
and has the four wires internally. It is likely wired such that on the
outlet ends that mate with your shorepower cords it has the 3 wire outlet
sockets that are rated 125 VAC at 50A and I further suspect that if you
examine the connectors on the cables closely that you will see that they are
rated 125 VAC at 50A as well. If my suspicions are correct, then you will
in fact have 50A on each leg, since the HOT#1 in the four-wire splitter is
carried on on one of your three-wire cables and the HOT#2 in the splitter is
carried on the other three-wire cable.

It is always interesting to watch the owners of the 125 VAC/50A cord sets
trying to find a shorepower socket to fit into. As someone else posted in
the last few days, I hate the term "a 50 amp cable" since either of these
cases could apply. That poster suggested something like "a 50A dual cable"
or some such nomenclature, and I wholeheartedly agree. I am sure your prior
owner ran into this scarcity of 125 VAC/50A shore-sockets and purchased or
had made up the splitter you have.

Hope this is of some help and potentially understandable.

Ken.

Ken Bloomfield
MTOA# 2062
AGLCA# 3529
M/V Tellico Lady, 50' Marine Trader-Walkaround
Maryville, TN

All
Sorry to add to this already confusing (at least to me) subject but I have
a
situation that I have received at least a dozen different answers to and
I'm
not sure which, if any, is correct.

Due to the splitter I have 50A on each leg
Due to the splitter I only have 25A on each leg and would be better
off
buying 2 30A cables so I would have 30A on each leg
I could eliminate the splitter and go with one 50A cable and still
have
50A as both legs share one incoming source (now I am really confused at
this
point)

Hopefully I have supplied sufficient background to receive an answer that
is
correct and that I could understand.

Thanks for any assistance

Jim Boyd
Lark

Jim, It is a bit hard to be definative without looking at your cables and splitter, but I suspect what you are running into is as follows: (a) There are two types of "50A" cables out there, with respective connectors. These are 50A @ 125 VAC, and 50A @ 125/250 VAC. (b) In the first case, these are 3 wire cables, each with neutral, hot, and ground wires that carry 125 VAC with 50 ampere current capability. A lot of the older Bluewater boats in our marina were originally equipped this way. (c) In the second (now more common) case, the cable has four wires internally, and they are neutral, hot #1 aka L1, hot #2 aka L2, and ground. Each of the hot wires is capable of carrying 50 amperes and the AC waveform relationship is such that the voltage differential between them yields a potential difference of 250 VAC. If you have a splitter, I suspect that if you examine it carefully, you will find that it is rated (at the shorepower socket end) as 125/250 VAC at 50A and has the four wires internally. It is likely wired such that on the outlet ends that mate with your shorepower cords it has the 3 wire outlet sockets that are rated 125 VAC at 50A and I further suspect that if you examine the connectors on the cables closely that you will see that they are rated 125 VAC at 50A as well. If my suspicions are correct, then you will in fact have 50A on each leg, since the HOT#1 in the four-wire splitter is carried on on one of your three-wire cables and the HOT#2 in the splitter is carried on the other three-wire cable. It is always interesting to watch the owners of the 125 VAC/50A cord sets trying to find a shorepower socket to fit into. As someone else posted in the last few days, I hate the term "a 50 amp cable" since either of these cases could apply. That poster suggested something like "a 50A dual cable" or some such nomenclature, and I wholeheartedly agree. I am sure your prior owner ran into this scarcity of 125 VAC/50A shore-sockets and purchased or had made up the splitter you have. Hope this is of some help and potentially understandable. Ken. Ken Bloomfield MTOA# 2062 AGLCA# 3529 M/V Tellico Lady, 50' Marine Trader-Walkaround Maryville, TN > All > Sorry to add to this already confusing (at least to me) subject but I have > a > situation that I have received at least a dozen different answers to and > I'm > not sure which, if any, is correct. > > When I purchased Lark it came with two 50A cables and a 50A splitter that > hooked to a 50A shore power source. Each of the 50A cables attach to a > separate receptacle on the boat. I have been told the following... > > 1. Due to the splitter I have 50A on each leg > 2. Due to the splitter I only have 25A on each leg and would be better > off > buying 2 30A cables so I would have 30A on each leg > 3. I could eliminate the splitter and go with one 50A cable and still > have > 50A as both legs share one incoming source (now I am really confused at > this > point) > > Hopefully I have supplied sufficient background to receive an answer that > is > correct and that I could understand. > > Thanks for any assistance > > Jim Boyd > Lark

Scott H.E. Welch

Wed, Jul 30, 2008 3:08 PM

"Jim Healy" gilwellbear@gmail.com writes:

An interesting theoretical observation is that with
only 115V loads distributed equally (balanced) across both sides of the
center tap, you may actually have no current flowing in the neutral at all.
The Neutral provides the circuit's reference voltage, but all of the current
flows only in L1 and L2. The more unbalanced the loads, the more current
flows in the neutral. Ag

Jim,

An excellent post. I have a few other notes that may be of interest:

The non-theoretical corollary is that if you have a high-resistance
neutral and an unbalanced load, the practical effect will be to raise the
voltage on the low-load leg and lower the voltage on the high-load leg. In
plain english, if you notice that when a heavy load (e.g. a fridge) starts up
some of your lights get brighter not dimmer, then you should get to work
right away looking for a loose/dirty/missing neutral connection.
While three phase power is unusual on most boats, it does exist. When I
bought my boat, it had a three-phase 20 KW generator, which fed a three-phase
panel. The shore power cable was 50A, 120 volt, single phase. The shore power
switch fed 120 V into each of the three-phase legs. The genset was the first
thing I took out of the boat, followed by the panel. I now have a nice,
normal 6KW generator and a nice, normal 30A 120V cable.
For those of you heading north to British Columbia and Alaska, talk of
higher amperages is mostly theoretical. At most docks you are lucky to get 30
Amp 120 Volt, and at many docks you get 20 Amp. I've been at several with 15
Amp. Make sure you carry adapters, and make sure you can set your input loads.

Scott Welch
FirstClass Product Manager
www.firstclass.com

Those who make no mistakes rarely make anything.

"Jim Healy" <gilwellbear@gmail.com> writes: >An interesting theoretical observation is that with >only 115V loads distributed equally (balanced) across both sides of the >center tap, you may actually have no current flowing in the neutral at all. >The Neutral provides the circuit's reference voltage, but all of the current >flows only in L1 and L2. The more unbalanced the loads, the more current >flows in the neutral. Ag Jim, An excellent post. I have a few other notes that may be of interest: 1) The non-theoretical corollary is that if you have a high-resistance neutral and an unbalanced load, the practical effect will be to raise the voltage on the low-load leg and lower the voltage on the high-load leg. In plain english, if you notice that when a heavy load (e.g. a fridge) starts up some of your lights get *brighter* not dimmer, then you should get to work right away looking for a loose/dirty/missing neutral connection. 2) While three phase power is unusual on most boats, it does exist. When I bought my boat, it had a three-phase 20 KW generator, which fed a three-phase panel. The shore power cable was 50A, 120 volt, single phase. The shore power switch fed 120 V into each of the three-phase legs. The genset was the first thing I took out of the boat, followed by the panel. I now have a nice, normal 6KW generator and a nice, normal 30A 120V cable. 3) For those of you heading north to British Columbia and Alaska, talk of higher amperages is mostly theoretical. At most docks you are lucky to get 30 Amp 120 Volt, and at many docks you get 20 Amp. I've been at several with 15 Amp. Make sure you carry adapters, and make sure you can set your input loads. Scott Welch FirstClass Product Manager www.firstclass.com Those who make no mistakes rarely make anything.