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Replacing Main AC Breaker

Jan 11, 2014
4,649
Sabre 362 113 Fair Haven, NY
Over the past few years the main breaker on the AC panel has been acting up. Often, when shore power is first plugged in the breaker trips. Reset the breaker and all is fine until the next unplug/plug-in cycle at which point it may or may not trip. This happened regardless of any AC load.

This week an ELCI was installed and now the breaker no longer works at all. As soon as shore power is plugged in, the breaker trips, but the ELCI breaker does not trip. I suspect the timing of its failure is simply coincidental and has nothing to do with the ELCI installation.

The new breaker will be a Blue Sea 30 A DPDT breaker (7237). Looking at the existing breaker and wiring, I'm puzzled by a couple of things. First, there is neutral line side is connected to a stud on the panel which is connected to the AC Ground. This connects the Neutral and Ground which I thought was poor practice on the AC system. Bill Bishop seems to agree (http://themarineinstallersrant.blogspot.com/2013/12/the-reverse-polarity-light-ac-leaking.html).

Second the line side of the breaker has 2 connectors on each side of the neutral breaker, line and load. In between the 2 connection points on the load side is a capacitor. What purpose does this serve?

In the photo, the line side is on the left, load on the right. The left meter is a voltmeter, the right an ammeter. The small wires go to the polarity indicator and an AC power indicator.


IMG_1695.JPG
 
May 27, 2004
1,285
Hunter 30_74-83 Ponce Inlet FL
So I understand the situation: Your main AC breaker switch trips when you connect the power cord?
That implies that the switch is in the "ON" position when you plug in the shore power?
 
Nov 16, 2012
866
Catalina 310, 2000, #31 Santa Cruz
So I understand the situation: Your main AC breaker switch trips when you connect the power cord?
That implies that the switch is in the "ON" position when you plug in the shore power?
I leave the AC breaker on the boat on almost always, but turn the AC off at the dock pedestal before removing or inserting the cord at the boat. That way the cord is fully de-energized (and minimizes damage if somebody accidentally drops it in the water-not naming any names here...).
 
Jul 7, 2004
6,181
Hunter 30T Cheney, KS
I leave the AC breaker on the boat on almost always, but turn the AC off at the dock pedestal before removing or inserting the cord at the boat. That way the cord is fully de-energized (and minimizes damage if somebody accidentally drops it in the water-not naming any names here...).
I can think of 1 situation where this might not be a good idea: You left your A/C (air conditioning) power on but the intake valve is closed.
It's always more wise to power down at the control panel first. That ways there's no surge when you plug shore power in again.
 
Nov 16, 2012
866
Catalina 310, 2000, #31 Santa Cruz
I can think of 1 situation where this might not be a good idea: You left your A/C (air conditioning) power on but the intake valve is closed.
It's always more wise to power down at the control panel first. That ways there's no surge when you plug shore power in again.
No A/C on this boat.
How is the surge any different whether you turn it on at the dock pedestal, or at the AC panel in the boat? Unless you shut off the individual breakers at the boat panel and turn them on one at a time?
 
Jul 7, 2004
6,181
Hunter 30T Cheney, KS
How is the surge any different whether you turn it on at the dock pedestal, or at the AC panel in the boat? Unless you shut off the individual breakers at the boat panel and turn them on one at a time?
Exactly. You may have either a weak main breaker or some high initial load. Could be a battery charger. I struggled with a similar problem until I replaced mine. It's hard to guess without knowing your setup.
 
Jan 11, 2014
4,649
Sabre 362 113 Fair Haven, NY
Exactly. You may have either a weak main breaker or some high initial load. Could be a battery charger. I struggled with a similar problem until I replaced mine. It's hard to guess without knowing your setup.
The intermittent shut off occur regardless of the load on the panel. It will trip when all breakers are off, or some on. I don't have AC so that's not a culprit. I do have a battery charger but the current draw is pretty low, it is a 50 amp 12 v charger max output is 600 watts that's only about 5 amps AC. I think the circuit breaker was just ready to retire at 25 years.

The other question is perhaps more important, tying the neutral and AC ground together at the breaker.
 
May 20, 2016
2,864
Catalina 36 MK1 94 Everett, WA
I leave the AC Main breaker off when connecting and disconnecting shore power. If it’s on when plugged in you may be surging and you’ll won’t see the polarity light before putting crew in danger.
 

JRT

.
Feb 14, 2017
1,597
Catalina 310 211 Lake Guntersville, AL
I was also told to shut my AC breaker off at the panel also, in fact I shut all the AC breakers off first then the main then disconnect shore power. I follow the same in reverse to, verify AC break is off, connect shore power, and turn on charger, then AC if staying at the dock.
 
Nov 16, 2012
866
Catalina 310, 2000, #31 Santa Cruz
Dave, not to hijack your thread, but I guess the question I’m asking is if it makes any difference if you shut off the AC (power) at the dock pedestal, or at the boat panel, when plugging/unplugging the shore power cord. Leslie’s point about the polarity light is valid, but I still like the idea of the cord not being live at that point. Doing both seems excessive.

On your question: Seems to me that the ground and neutral should not be connected at the boat breaker. There are a lot of articles out there that tell you why it’s a bad idea.
 
Mar 20, 2016
287
Beneteau 351 WYC Whitby
On all my boats the neutral is not grounded, if you had a case of reverse polarity this would be a direct short to ground and trip breaker and your reverse polarity leds would never work ,so the neutral should not be to ground.
DC uses a shunt to measure amps .A/C uses a CT(current transformer) to measure amps and is that a capacitor?? or CT, they can go bad and cause problems and so can capacitors . I have an rdc breaker too (elci) before main breaker ,with main off and rdc on you should be able to measure 120 volts at main breaker.If not your rdc is bad.
If you have 120 ,unground the neutral ,shut off all breakers and turn main on , it should not trip if it does ,CT or Cap is bad ,I see no reason for a capacitor. The only time the neutral should be grounded is when a transformer is used on the secondary side only or breaker and fuses may not blow as there is no path to ground if that makes sense.
 
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Jan 11, 2014
4,649
Sabre 362 113 Fair Haven, NY
The devil, as they say, is in the details.

Having convinced myself that the root of the problem with the main breakers was the breakers and their age I replaced the mains only to find the problem, the breaker tripping, was unresolved. The breaker tripped as soon as I connected to shore power. :(

Out came the digital voltmeter and it showed a short between hot and neutral. How could that be? Everything worked well before I started the project and the only part of the AC system I touched was on the panel. After much hair pulling (good thing I'm not bald) and some sailor speak, I finally found the problem.

The AC breakers are all tied together with a copper bus bar connected directly to the terminals on the breakers. In order to install the ELCI it was necessary to remove this bus bar and shorten it. When I reinstalled it, I inadvertently flipped it 180° which placed the end of the bar just 2 copper atoms away from the neutral terminal. This infinitesimally small contact between the hot and neutral was enough to trip the breakers. This small flaw was clever enough to hide behind the terminal ends so that it was not readily visible to the naked eye.

Apparently I made 2 small errors. When I shortened the bar, the cut was not a precise right angle. Thus, when the bus bar was reinstalled there was a gap at the top and visible section of the bar however, at the bottom it was a little too close. We're talking a distance of a millimeter or two between the top of the bar and the bottom. Second, if I had not inadvertently rotated the bar the crooked cut would not have made a difference.

All is good now, and every thing works as it should with a shiny new main breaker properly installed. It is the little details that will get you every time.
 
Oct 22, 2014
11,131
CAL 35 Cruiser Portland OR, moored EVERETT WA
Good recovery Dave. It goes to show it it’s the little things that can really foul us up.

Good problem solving. When all else fails, go back to the beginning and retrace your steps. We so often want a quick and easy solution.

Thanks for the post.
 
Feb 6, 1998
11,094
Canadian Sailcraft 36T Casco Bay, ME
Dave,

What you had originally was a reverse polarity trip breaker. If it sensed reverse polarity situation it would automatically trip, not just illuminate a dash lamp. Just to be clear, with this type of breaker, it needs to be turned on after shore power is already connected or they could nuisance trip.