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Old 09-11-2019, 06:04 AM   #1
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A 240V danger.

Reading on the RV boards there are sad comments of electrical failures from low quality or miss wired 240v plugs.

Seems that if the supply line looses the white neutral all heck breaks loose with electrical devices.

Checking the plugs connections would seem a worthwhile task.

Boat plugs are different , and perhaps made for more abuse , but why not take a look?
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Old 09-11-2019, 07:34 AM   #2
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True, and even homes without main "plugs" have this issue sometimes.
The rest of the world doesn't have this issue of split-phase plus flaky neutral. A boat with a 240V iso transformer also gets rid of the bad plug neutral connection.
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Old 09-11-2019, 08:11 AM   #3
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Have seen a few marine pedestals where the neutral on a 50A 125/250 circuit was toast/loose.... and a lot of expensive TVs, Sat tel, stereos, etc were all fried.
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Old 09-11-2019, 08:23 AM   #4
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On my motorhome I have a Progressive Industries EMS voltage protector. There are a couple other brands. These protect from open neutral, accidental 240v, etc. I've had it prevent problems when the neutral blade on my 50 amp cord broke off and at campgrounds where the pedestal was wired wrong.
Should not be difficult to install one of these in a boat.
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Old 09-11-2019, 09:41 AM   #5
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Have seen a few marine pedestals where the neutral on a 50A 125/250 circuit was toast/loose.... and a lot of expensive TVs, Sat tel, stereos, etc were all fried.
Can someone explain why a neutral in a 50A 124/250 circuit is any different than any other AC connection.

If a neutral is loose then it affects the 120V circuits and they flicker or won't have power. But how is that any different than the hot leg being loose. In other words, what is unique about the neutral?

And how does flickering destroy appliances?

David
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Old 09-11-2019, 10:36 AM   #6
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An open or loose neutral will upset the voltage on both sides of the line. L1 to L2 will be stable at around 240V, but L1 to N and L2 to N will seesaw; worse case is zero volts on one 120 side and 240V on the other side. Application of 240V to most 120V loads will be very bad for them.
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Old 09-11-2019, 10:54 AM   #7
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Reading on the RV boards there are sad comments of electrical failures from low quality or miss wired 240v plugs.
So, if one has high quality plugs and the vessel is wired correctly is there a problem?
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Old 09-11-2019, 11:03 AM   #8
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So, if one has high quality plugs and the vessel is wired correctly is there a problem?
only if the dock wiring has issue, or if your flex cable has issue. Or, the connection to the upstream dry transformer has an issue. Beyond those, no issue.

HOpefully, you don't have a 3 wire fed 240/120 V clothes dryer on board.

Mostly, only N. America has this issue where just an OPEN connection can cause a significant shock issue.
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Old 09-12-2019, 07:07 AM   #9
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Reading on the RV boards there are sad comments of electrical failures from low quality or miss wired 240v plugs.

Seems that if the supply line looses the white neutral all heck breaks loose with electrical devices.

Checking the plugs connections would seem a worthwhile task.

Boat plugs are different , and perhaps made for more abuse , but why not take a look?


Itís the thought I had as well. The problem occurs when not connected also. Example: Genset running and not connected to the shore power.
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Old 09-12-2019, 07:13 AM   #10
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Can someone explain why a neutral in a 50A 124/250 circuit is any different than any other AC connection.

If a neutral is loose then it affects the 120V circuits and they flicker or won't have power. But how is that any different than the hot leg being loose. In other words, what is unique about the neutral?

And how does flickering destroy appliances?

David

I hope Diver Dave answered your question.


I am an operator, not an engineer so my brain only goes nto so much detail.


But I have a lot of experience and not reason to BS about what I have seen along the way.


I just lost an inverter/charger to what I think as a loose connection on a 30A power post outlet feeding my smart Y.


It won't charge any more and the auto pass though is intermittent (the whole reason I got rid of 30A shore powerbut am screwed where I am).


Not sure exactly what all the problems are...but the loose connection, possible arcing, rapid off/on, etc...etc...is never good. Have seen it take out electronics in many occasions.
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Old 09-12-2019, 07:23 AM   #11
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So, if one has high quality plugs and the vessel is wired correctly is there a problem?

In my opinion, old style 30A plugs are an accident waiting to happen.


After 2 weeks away from my boat, a loose end of my 2X30 to 50A smart Y to dock pedestal had one loose side and seems to have cooked my inverter/charger.


For any number of reasons a 30A twist lock can work loose (partially loose). Sure, so can a 50A...but I haven't seen that problem ever....except in CMS posts which I can respect.


But I have seen burnt up 50A connectors which I have no explanation for, but if it's the neutral from being overloaded and cooked, then your 110V appliances aboard can be at risk as Diver Dave points out and I have seen cooked appliances. Whether the issue started with the dock receptacle or boat issues including unbalanced load and overwhelmed neutral...ya got me.
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Old 09-12-2019, 07:43 AM   #12
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Sometimes it is worthy to go into the WHY of a situation, and not just the WHAT.

In N America, unlike most of the rest of the world, we want two different voltages. 240 for "major appliances", and 120V for the rest. This then, is the reason not for a Neutral, but for the two HOT lines on a 240/120V system.
Almost the entire world uses a grounded neutral scheme, but only with a single available voltage. That voltage could be 100, 220, 240V.

The most convenient (cheapest..) way to get two voltages, if they are a factor of 2 different, is to use a center tapped secondary transformer at the utility feed. Voila, now with just 3 wires, I can get two different voltages. In N America, those are 120 and 240. Still have that grounded neutral, and when that particular wire looses its low resistance connection to that center tap, bad things will happen. Not a loss of power, but wildly wrong voltage values. That is the source of the damage, both too high, and too low.

I'll make the bold assumption, that land users started this trend, not boat users. But, you can see that N. American market boats continue the tradition of split phase 120/240 for the larger boats.

Meanwhile, Europe and Asia would have none of this foolishness, and has a simpler, single voltage available for most users. I'm going to exclude industrial users from this discussion, and also 3 phase marine is excluded; since most of the readers here don't use 3 ph for their boat/home service. When a euro 230V boat loses its neutral connection, the voltage simply drops, sometimes all the way to zero. There is no chance for an abnormal high voltage due to neutral loss.

So, that is the madness behind the neutral story.
To the comment I made on the clothes dryer. The rumor is that during/just after WWII, there is a shortage of copper, and it affected home wiring design. Again, to save money, the clothes dryer and usually the electric range wanted both 120 and 240. The safe way to do this is to use 4 wires; L1, L2, N, and safety ground. But no, many installs to this day are still using only 3 wires. L1, L2, and a combined duty N and safety ground. Since this grounded wire carries current (motor and timer), if it becomes disconnected at the source, the frame of the dryer now becomes live with 120V! All other first world countries would not allow such wiring practice. It was about 25 years ago that new installs insist on the 4 wires to any 240/120 appliance.
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Old 09-12-2019, 08:15 AM   #13
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Diver dave, excellent explanation of "why"! I've often puzzled over 3 wire 240 V and wondered how it could be safe?

Another question. Can we use the device folivier uses on his RV on our boats? And if so will it protect those of us still using a single 30 AMP shore power connection should something fail on the marina side of things?

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On my motorhome I have a Progressive Industries EMS voltage protector. There are a couple other brands. These protect from open neutral, accidental 240v, etc. I've had it prevent problems when the neutral blade on my 50 amp cord broke off and at campgrounds where the pedestal was wired wrong.
Should not be difficult to install one of these in a boat.
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Old 09-12-2019, 09:09 AM   #14
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DD
No argument with your euro explanation. Having worked around high and low voltage systems internationally I can rudimentally appreciate the differences.

But with my current boating life being spent in Canada and the US I've no choice as to power sources, appliance and dock pedastel wiring. So this being the case, my question remains. If all is visually and electrically OK and none of the hundreds of boats in my marina have not caught fire, what is the issue?
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Old 09-12-2019, 10:14 AM   #15
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If you are wanting to chase "issues", I'd suggest the Boat US insurance leading cause of boat fires.
Now, Is it a problem for YOU? Obviously, this is a game of percentages. Sample sizes of what you mention are small to make an overall judgment of risk, agree?
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Old 09-12-2019, 10:53 AM   #16
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If you are wanting to chase "issues", I'd suggest the Boat US insurance leading cause of boat fires.
Now, Is it a problem for YOU? Obviously, this is a game of percentages. Sample sizes of what you mention are small to make an overall judgment of risk, agree?
DD
While not ignoring the real world tragedies of improperly wired and maintained E systems for NA boats and docks - I'm not grasping your recommendation other than to presumably check and monitor our individual E systems. As FF said in the first post.
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Old 09-12-2019, 11:23 AM   #17
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Not sure I mentioned any recommendation as yet. But my SAT scores for reading comprehension were low...

However, I will say that on any boat of mine that needs both 240 and 120, I will have a isolation transformer and differential surge suppression. On a 120V boat only, I would reduce that list to only surge protection, both across the line and L to GND.
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Old 09-12-2019, 11:37 AM   #18
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Not sure I mentioned any recommendation as yet. But my SAT scores for reading comprehension were low...

However, I will say that on any boat of mine that needs both 240 and 120, I will have a isolation transformer and differential surge suppression. On a 120V boat only, I would reduce that list to only surge protection, both across the line and L to GND.
Yup, those two items are nice to haves.
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Old 09-12-2019, 05:57 PM   #19
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Is there such thing as a 50A plug tester? One ready-made to plug into a shore power 50A outlet? I know of residential outlet testers, those are handy and compact. I'm not interested in building anything.

I know Hubbel makes ones for 30A connections, but what about 50A?
https://www.hubbell.com/wiringdevice...CM11/p/2296124

And I may be ignoring the obvious, as marine power connectors and their plug genders are always something I get confused. I can't remember which one uses which.
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Old 09-12-2019, 05:59 PM   #20
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I say no DIY because my point of using one would be two-fold. One to make sure the pedestal I'm about to use isn't defective, and two to have something reasonably authentic looking to show marina personnel why I want a different connection. A frankenstein'd box isn't as likely to accomplish the latter.
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