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Old 02-26-2013, 10:03 AM   #1
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Gen/shore Power Switch Guard
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Old 02-26-2013, 10:15 AM   #2
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Gen/shore Power Switch Guard
Probably. Trying to use both at the same time would cause problems and there would be no good reason to use both at the same time.
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Old 02-26-2013, 10:25 AM   #3
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Gen/shore Power Switch Guard
It is because the boat is not equipped with the type of generator control that would allow parallel operation with shore power.

When boats equipped with multiple generators which are not fitted with paralleling controls, there is usually a similar mechanical interlock to prevent them from being online at the same time.

Many installations allow for "splitting the buss" so that one generator can run one side of the distribution panel, and the other can run the other side.

This type of installation is not restricted to large ships and there are many good reasons to wire the switchboard this way. Few houses incorporate this feature.
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Old 02-26-2013, 10:36 AM   #4
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Gen/shore Power Switch Guard
Walt, I had that set up on my last boat, and liked it very much. Too many things can go wrong with a rotary generator/shore power switch. It has never happened to me, but I have seen the results of them shorting out. I check mine for loose connections frequently.
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Old 02-26-2013, 02:54 PM   #5
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Walt, I am pretty sure, connecting the generators most of us use directly to shore power would damage at least the generator controls, maybe more.

The sliding switch covers prevent that from ever happening. They are simple and effective. I too like them better than a rotary switch.

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Old 02-26-2013, 05:30 PM   #6
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I can think of 4 things, all of which are very bad, that the interlocked switch prevents. Switching both on at the same time can result in:

1) If you are connected to shore power and have the generator running and join the two together: unless the shore power and generator just happen to be exactly synchronized, which is pretty unlikely, you will be creating a short circuit between the two. How bad it is will depend on how our of phase the two are, but it's a very anti-social thing to do. Breakers will likely trip all over the place.

2) If you are connected to shore power and have the generator running and join the two: in the freak situation where the two happen to be in phase and the join doesn't trip breakers, your generator will potentially be trying to power the entire community around you.

3) If just your generator is running and you are not connected to shore power: Joining the two will place live power on the plug end of your shore power cord and/or power inlet. Touching the exposed plug blades will kill you. The male and female ends of power connections are carefully chosen so the energized end is female. By joining the two you are reversing that and creating an serious hazard.

4) If you are on shore power and your generator is not running: Joining the two will energize your generator and turn it into an electric motor, attempt to start your generator, and do all sorts of other unexpected and dangerous things.

There is a really good reason for the interlocked breakers, or rotary selector switches, both of which ensure that only one power source is connected at a time.
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Old 02-26-2013, 05:43 PM   #7
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I can think of 4 things, all of which are very bad, that the interlocked switch prevents. Switching both on at the same time can result in:

1) If you are connected to shore power and have the generator running and join the two together: unless the shore power and generator just happen to be exactly synchronized, which is pretty unlikely, you will be creating a short circuit between the two. How bad it is will depend on how our of phase the two are, but it's a very anti-social thing to do. Breakers will likely trip all over the place.

2) If you are connected to shore power and have the generator running and join the two: in the freak situation where the two happen to be in phase and the join doesn't trip breakers, your generator will potentially be trying to power the entire community around you.

3) If just your generator is running and you are not connected to shore power: Joining the two will place live power on the plug end of your shore power cord and/or power inlet. Touching the exposed plug blades will kill you. The male and female ends of power connections are carefully chosen so the energized end is female. By joining the two you are reversing that and creating an serious hazard.

4) If you are on shore power and your generator is not running: Joining the two will energize your generator and turn it into an electric motor, attempt to start your generator, and do all sorts of other unexpected and dangerous things.

There is a really good reason for the interlocked breakers, or rotary selector switches, both of which ensure that only one power source is connected at a time.
I agree.

Some of the "experts" on this board do not seem to understand these things so it's important that those folks who do speak up.
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Old 02-26-2013, 07:07 PM   #8
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I agree.

Some of the "experts" on this board do not seem to understand these things so it's important that those folks who do speak up.
Hence, the reason for restating a question that I already knew the answer to.
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Old 02-26-2013, 08:29 PM   #9
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The big difference is that most people here have the experience to know not to do it on their boat and the run of the mill toy boat but there are a few that have enough experience that know it's done in certain circles plus how and why it's done....

what's so amusing is the one or two that don't even get that!!!!

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Old 02-26-2013, 09:22 PM   #10
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what's so amusing is the one or two that don't even get that!!!!
There are one or two will fight to the death to NOT "get it." They just want simple rules with no variations or exceptions or messy details to confuse or frighten them. It's sad really.
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Old 02-26-2013, 09:50 PM   #11
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There are one or two will fight to the death to NOT "get it." They just want simple rules with no variations or exceptions or messy details to confuse or frighten them. It's sad really.
It's our total lack of qualifications and a lifetime of doing things wrong that have forced our posts to be incapable of providing usefull information...
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Old 02-27-2013, 06:34 AM   #12
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It's our total lack of qualifications and a lifetime of doing things wrong that have forced our posts to be incapable of providing usefull information...
When I think of all those years running an engine room at sea without having a copy of the NEC onboard it makes me shudder when I realize how lucky I was to live through it.

And thank heavens someone finally told me I wasn't really paralleling the generator with shore power. I guess I was splitting the buss and just didn't know it ... I wonder what that thing was with the label "reverse current relay" that went BANG when I wound down the generator field going the other way?

It is a good thing that we have house electricians here who are willing to show us dangerous old sailors how the world is supposed to work.

Now, if they could only learn to read

I think the forum header should include the disclaimer that any boat owner looking for electrical advice should proceed with great caution or go elsewhere because only certain ideas and comments are permitted here.
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Old 02-27-2013, 06:46 AM   #13
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to be fair...both ends of the spectrum were correct.

You can't parallel the genset with shore power on boats without the right setup.

To say it CAN'T be done....well hopefuly that's worked out now.

It's the ones that keep going and don't understand that opposing views may not be discussing the same point that they are trying to make...well...

They are probably the same ones that don't understand the 3 worlds of boating out there....(either commercial or recreational) the haves, have nots and a whole lot of in between. Just like cars, houses, planes, etc...etc...not every object in the world meets every reg, code, etc..etc...but that doesn't mean that the world comes to an end when it's pointed out in some forum and then not adhered too....
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Old 02-27-2013, 07:08 AM   #14
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In the size boats most folks have paralleling the generator with shore power will never be an option.

There is simply no reason to attempt it, on a non commercial boat.

What is far more common is a following INVERTER , that can boost dock power or noisemaker output to start a heavy induction motor load.

Folks can right size the noisemaker so it works harder and lasts longer.
12KW charging a battery set is not a happy diesel.

A second huge advantage is a smart inverter can have limits on power draw , and fill in as required, if desired..

So an old marina with 15A of 120V can start an air cond with out blowing the shore fuse.

Great for folks that travel off the main routes.
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Old 02-27-2013, 07:13 AM   #15
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to be fair...both ends of the spectrum were correct.

You can't parallel the genset with shore power on boats without the right setup.

To say it CAN'T be done....well hopefuly that's worked out now.

It's the ones that keep going and don't understand that opposing views may not be discussing the same point that they are trying to make...well...
The frustrating part for me, as one who is deeply involved in this stuff on a day to day basis, is that while some will go on forever in great detail about airy-fairy fanciful future tech gizmos they might consider purchasing, they won't even acknowledge that there are boat systems that have existed for years on boats of all sizes that allow certain operations - like paralleling generators with each other or even shore power - that are neither dangerous or foolhardy or too exotic to consider.

The house electricians refuse to acknowledge that marine electrical systems are not like house systems and the NEC doesn't apply to a boat any more than an ABYC suggestion applies to the local building codes.

There are a few laughs though ... the one from the guy who told me I haven't really been paralleling power sources was priceless.
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Old 02-27-2013, 07:28 AM   #16
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In the size boats most folks have paralleling the generator with shore power will never be an option.

There is simply no reason to attempt it, on a non commercial boat.

What is far more common is a following INVERTER , that can boost dock power or noisemaker output to start a heavy induction motor load.

No one ever said it should be done by everyone on every boat. The point is that someone said it could not be done, should not be done, and was illegal to do in any event.

This is patently false and leads readers to believe there is some innate danger in doing so. With the proper governor and reverse current protection there is no danger.

Most toy boat generators are too small (lack inertia) to handle the load swings and remain in parallel so it is uncommon. However as electronic controls become more prevalent this may change. Honda already offers a paralleling kit for their tiny portable gensets.

The NEC rules controlling ground connections do not apply to marine installations, particularly generator wiring. Follow the generator manufacturer's advice and/or that of a professional marine electrician. Avoid house electricians and toy boat surveyors like the plague. They are a curse on the industry and as you have seen here, are the source of bad and even dangerous advice.

The fact that a recreational boat grade inverter can parallel with shore power and provide peaking power to online consumers should light a little bulb in some reader's head ... wouldn't you think?

The simple answer to the rhetorical question tossed out to stir up the board is: The switch guard is there because your boat is not equipped to parallel the generator with shore power. That is all, there is nothing else to read into it and there is no great truth other than that simple arrangement.
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Old 02-27-2013, 07:37 AM   #17
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In the size boats most folks have paralleling the generator with shore power will never be an option.

There is simply no reason to attempt it, on a non commercial boat.

What is far more common is a following INVERTER , that can boost dock power or noisemaker output to start a heavy induction motor load.

Folks can right size the noisemaker so it works harder and lasts longer.
12KW charging a battery set is not a happy diesel.

A second huge advantage is a smart inverter can have limits on power draw , and fill in as required, if desired..

So an old marina with 15A of 120V can start an air cond with out blowing the shore fuse.

Great for folks that travel off the main routes.
Absolutely agree!!!

I'm not sure how it can be done with all inverters...not yet on my project list but probably there next year..

Thus the beauty of internet forums....the many pieces of the puzzle and a few that work interchangeably...

Readers should now be armed with enough information to do a little research and figure out what best suits them. The standard small boat configuration, the paralleling option, the inverter augment option, the use of covered switches or rotary selector or FF's neanderthal but effective multi-plug approach, and there's even more out there with minimal internet browsing.

None are completely idiot proof...so due care is necessary at all different levels...but if certain "rules" whether code, guidelines, or common sense are followed....none are completely wrong either.

But I can't resist...I love the one where if you touch the prongs of a 110 shore power cord you will DIE......man...I giggled myself to sleep last night...
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Old 02-27-2013, 07:51 AM   #18
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I'm not sure how it can be done with all inverters...not yet on my project list but probably there next year..
Not all inverters have that capability. I apologize if my post read as if any and all can do that, I should have made it clear that only certain units have that feature. But what is important, is the fact that recreational level (size and price) units are available with that feature ... that says a lot about how the technology is developing far faster than user education and "standards" writer's ability to keep up.

Quote:
But I can't resist...I love the one where if you touch the prongs of a 110 shore power cord you will DIE......man...I giggled myself to sleep last night...
Darn, missed that one ... could use a few more laughs after reading some of the stuff here.
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Old 02-27-2013, 07:56 AM   #19
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No one ever said it should be done by everyone on every boat. The point is that someone said it could not be done, should not be done, and was illegal to do in any event.
I'm really confused here. Is all this because of the answer I gave a while back explaining the bad things that would happen if you engaged both breakers at the same time?

Or is it in response to something else that I missed?
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Old 02-27-2013, 08:28 AM   #20
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I'm really confused here. Is all this because of the answer I gave a while back explaining the bad things that would happen if you engaged both breakers at the same time?

Or is it in response to something else that I missed?
Can't say for RickB...but my cut on it is... except for the part about touching the prongs ...you are correct about most small boats...

What Rick and I were pointing out that the people who said you CAN'T parallel shore/genset or that there's only ONE way to hook up a marine electrical system just haven't been far enough around the block to know better.

For the one or two that just keep it up for good measure....
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