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Old 05-09-2014, 10:49 AM   #1
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How dangerous was this?

I'm not super experienced with marine electrical systems, so I'm posting this to try to learn more. We trailer our boat, so we do use shore power and our generator occasionally, but not as much as many here do. Regardless, the generator worked fine for the three years I've owned the boat until late last year, when it suddenly was only showing about 45-50 volts of output at the electrical panel meter. I assumed it was the voltage regulator, and I had my mechanic look at it during my spring commissioning.

He told me that after checking the generator output directly and finding nothing wrong, he traced it back to the electrical panel. He found that the PO had rewired both the shore power main breaker and the genset main breaker. Specifically, a post had broken off each of them (both 30 amp dual pole), so they simply wired everything to the remaining post.

I've borrowed a diagram from our friends at Bluesea to show what I'm talking about. The lower 30 amp is for the genset.

I've marked this file up to show how the post was broken off, and the wiring rerouted.

All of this has been replaced now, but I still would like to learn something. This setup worked while I owned it. I assume that the circuit switch worked because the hot was still connected properly and would be broken by the switch. So was the circuit protection missing? And would that be true just with the mains? Or would it apply to the individual circuits that come off the bus?

A second question would be why did the volt meter start showing 45-50 volts?

Thanks for your input.
BD
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Old 05-10-2014, 06:58 AM   #2
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Just a guess at the voltmeter question.... bad surviving connections in those breakers.

As for the rewire, the PO knew houses, but not boats. On a boat, AC power sources should have both their neutral and hot lines run through the breaker, like BlueSeas shows. It's an added measure of protection in case of reversed polarity at the dock post outlet, or your generator, and in case of wire or device shorts developing over time in the boat. Additionally, as the PO wired things, the exposed neutral prong on your show inlet wire wired directly to the generator, so energized when the gen is running. As long as that neutral is floating or tied to ground it's OK, but if any fault developed it could be quite dangerous.

The concept behind proper grounding and good wiring practices is that the grounding system provides a protective "shell" around the active wiring. If a fault develops in the active wiring, the shell still protects you. Most "creative" wiring solutions like the one you found on your boat work functionally, but defeat the protective shell. Once the shell is gone, and single fault creates a dangerous situation.
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Old 05-10-2014, 10:23 AM   #3
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I agree with everything said above. The potential for a dangerous condition to occur was there if any single fault resulted.
As far as your voltage meter anomaly I'm thinking a poor connection to the meter was a coincidence. Did the PO use the proper butt splice connectors or were wire nuts used?
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Old 05-10-2014, 06:39 PM   #4
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Quote:
Originally Posted by twistedtree View Post
As long as that neutral is floating or tied to ground it's OK, but if any fault developed it could be quite dangerous.
.
Just a little clarification on that point ... Neutral/ground should only be connected at the generator when the generator is running (most are automatically switched). With the generator circuit open, the neutral and ground should never be connected. If the boat DC negative and AC ground are bonded as they should be, an AC neutral/ground bond will send AC current to many places it should not be when plugged into shore power.
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Old 05-10-2014, 09:15 PM   #5
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On a muliple earth neutral system the ground and neutral are tied and circuit breakers will be single pole. On an above earth system the earth and neutral are seperated and the breakers will be 2 pole. MEN systems are becoming more the norm in many areas now. Regardless of all that, your PO did wrong.
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Old 05-10-2014, 09:58 PM   #6
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Quote:
Originally Posted by Nightcap View Post
On a muliple earth neutral system the ground and neutral are tied and circuit breakers will be single pole. On an above earth system the earth and neutral are seperated and the breakers will be 2 pole. MEN systems are becoming more the norm in many areas now. Regardless of all that, your PO did wrong.
ABYC E-11
11.5.5.2 Grounded Neutral - A grounded neutral system is required. The neutral for AC power sources
shall be grounded only at the following points:
11.5.5.2.1 The shore power neutral is grounded through the shore power cable and shall not be
grounded on board the boat.
11.5.5.2.2 The secondary neutral of an isolation transformer or polarization transformer shall be
grounded at the secondary of an isolation or polarization transformer. (See DIAGRAM 6, DIAGRAM 7,
DIAGRAM 8 and DIAGRAM 9. See EXCEPTION.)
11.5.5.2.3 The generator neutral shall be grounded at the generator. (See DIAGRAM 2 or DIAGRAM
4.)
11.5.5.2.4 The inverter output neutral shall be grounded at the inverter. The inverter output neutral
shall be disconnected from ground when the inverter is operating in the charger or the feed-through
mode(s).
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Old 05-10-2014, 11:25 PM   #7
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I guess ship builders in the rest of the world don't follow ABYC. I've got one vessel in port now going through its four year survey check of bonding points. Japanese built.
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Old 05-11-2014, 08:35 AM   #8
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I believe you experienced a classic back feed through an unswitched neutral wire. The neutral wire needs to be switched at the generator / shore power selector switch.
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Old 05-12-2014, 10:35 AM   #9
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Quote:
Originally Posted by twistedtree View Post
Just a guess at the voltmeter question.... bad surviving connections in those breakers.

As for the rewire, the PO knew houses, but not boats. On a boat, AC power sources should have both their neutral and hot lines run through the breaker, like BlueSeas shows. It's an added measure of protection in case of reversed polarity at the dock post outlet, or your generator, and in case of wire or device shorts developing over time in the boat. Additionally, as the PO wired things, the exposed neutral prong on your show inlet wire wired directly to the generator, so energized when the gen is running. As long as that neutral is floating or tied to ground it's OK, but if any fault developed it could be quite dangerous.

The concept behind proper grounding and good wiring practices is that the grounding system provides a protective "shell" around the active wiring. If a fault develops in the active wiring, the shell still protects you. Most "creative" wiring solutions like the one you found on your boat work functionally, but defeat the protective shell. Once the shell is gone, and single fault creates a dangerous situation.
That's really helpful. Thank you!
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Old 05-12-2014, 10:39 AM   #10
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Quote:
Originally Posted by Billylll View Post
I agree with everything said above. The potential for a dangerous condition to occur was there if any single fault resulted.
As far as your voltage meter anomaly I'm thinking a poor connection to the meter was a coincidence. Did the PO use the proper butt splice connectors or were wire nuts used?
Bill
No wire nuts were used. The connectors seemed proper, but there was not shrink wrap. Would that be required in a dry area like that?
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Old 05-12-2014, 10:44 AM   #11
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Quote:
Originally Posted by Nightcap View Post
On a muliple earth neutral system the ground and neutral are tied and circuit breakers will be single pole. On an above earth system the earth and neutral are seperated and the breakers will be 2 pole. MEN systems are becoming more the norm in many areas now. Regardless of all that, your PO did wrong.
Thanks. I'm going to have to google "multiple earth neutral systems" and learn some more.
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Old 05-12-2014, 10:48 AM   #12
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I guess ship builders in the rest of the world don't follow ABYC. I've got one vessel in port now going through its four year survey check of bonding points. Japanese built.
I found it interesting that they used light blue and brown wires instead of black and white. I guess it's an "international" option?
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Old 05-12-2014, 03:21 PM   #13
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MEN systems are typically used in high voltage (above 1000V) systems on ships but with the advent of reliable RCDs & GFIs are becoming commonplace on lower voltage systems. They reduce the problems of voltage drop on the neutral circuit and also reduce the problem of stray current corrosion between neutraland ground.
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Old 05-12-2014, 03:44 PM   #14
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Quote:
Originally Posted by Nightcap View Post
MEN systems are typically used in high voltage (above 1000V) systems on ships but with the advent of reliable RCDs & GFIs are becoming commonplace on lower voltage systems. They reduce the problems of voltage drop on the neutral circuit and also reduce the problem of stray current corrosion between neutraland ground.

You are now confusing me (not hard to do) stray current corrosion between AC neutral and ground could only occur if the DC and AC grounds are bonded which brings you right back to dumping AC current in the water which is a much more serious problem than corrosion. Please explain how you can bond AC neutral and ground, why you would want to and how "MEN" prevents stray current corrosion and shock potential.

I don't believe I have ever seen such a system on the boats typically owned by members of this forum.
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Old 05-12-2014, 04:04 PM   #15
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Stray current corrosion can occur wherever there is potential (voltage difference) between 2 sources. In a tied system with adequately maintained bonding points there will be no potential between neutral and ground. Therefore, in a single phase system you remove 50% of the source for stray current, in a three phase system 25%.
Because the sea is effectively grounded there is no problem have neutral in contact with it. The problems only occur with stray current. Remove that & your remove the risk.
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Old 05-12-2014, 04:26 PM   #16
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Quote:
Originally Posted by Nightcap View Post
Stray current corrosion can occur wherever there is potential (voltage difference) between 2 sources. In a tied system with adequately maintained bonding points there will be no potential between neutral and ground. Therefore, in a single phase system you remove 50% of the source for stray current, in a three phase system 25%.
Because the sea is effectively grounded there is no problem have neutral in contact with it. The problems only occur with stray current. Remove that & your remove the risk.
USCG & BoatUS have documented 200 cases of what they call "electric shock drowning" in fresh water marinas due to contact between AC ground and neutral on vessels with bonded systems when the vessels were connected to shore power.
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Old 05-12-2014, 04:28 PM   #17
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Did these accidents occur in MEn systems or above ground? It seems above ground is the standard there.
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Old 05-12-2014, 04:39 PM   #18
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The study was contracted to Dave Rifkin on a grant from USCG and BoatUS. The investigation was prompted by the death of Lucas Ritz. You can read more about it on Daves website on his "DOCUMENTS" page. The incident list is a little out of date but the rest of the info is there.

You can view a detailed explanation of the death of Lucas Ritz on this very disturbing
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Old 05-12-2014, 04:43 PM   #19
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Sorry this is the
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Old 05-12-2014, 09:23 PM   #20
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Unfortunately my internet speed here doesn't allow for video. Still, in a properly installed and maintained MEN system the risk of shock is no greater than a properly installed and maintained above earth system both with allowances for appropriate shore power connection. Both have advantages and disadvantages but the reliability & price of GFIs and RCDs for safety is swinging the pendulum to MEN as industry standard.
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