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cinnr

Shore power gfi tripping

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I need help understanding the best way to find my wiring problem that is causing the newly installed gfi on my shore power to trip.

Here's my current state: with battery switch in "off", I can connect shore power and run the battery charger and AC outlets without a problem.  Bilge pump works no problem.  All DC switches on the panel are in the off position.  When I turn the battery switch to "1", "2" or "both", the gfi on the shore power will trip after about 10 seconds (not immediately).  This is with no power being supplied by the DC switches on the panel.

I'm looking for advice on where to start looking, and perhaps a method/procedure for identifying the specific problem.  This is my first time diving into the back side of the electrical panel, and don't have much experience with electronics and electrical systems, but I'd like to get to the bottom of this.

Thanks!

Tom

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Hmmmm - this is a weird one.

The GFCI will trip when the current through a coil in the breaker from the hot is not balanced by the return current through the neutral. That creates a force that flips the breaker. Ergo, you have hot current that is returning via ground and not via the neutral.

That's a boat no-no because it means you're sending current through your bonding and into the marina, so you have a good chance of your keel paint falling off, or your prop vanishing mysteriously. Also, you can zap your diver if it's fresh water (and clean).

Since this happens when you connect the battery charger, I'd guess that your charger is connected to your boat DC ground, but boat DC ground is not connected to the neutral or is connected, but through a corroded contact that has so much resistance that the current prefers to go via ground than by the wire. Typically a GFCI will permit a certain amount of leakage current - spec that we work to is 500uA - which is nothing. But maybe your GFCI is set up to trip at >100mA or something like that and so you are not drawing enough current under normal circumstances through the HOT to trip the GFCI. When the charger is connected that takes a decent whack of power, now you have enough current flowing in HOT but not in Neutral to flip the breaker.

My recommendation is to check that your connections between boat ground, mains ground and neutral are correct and not corroded.

You can check if I'm right by putting your multimeter in AC current mode in series with HOT and later in series with Neutral and measure the current with and without the charger on. My guess is that there will be a more or less linear relationship of HOT current to Neutral current, which speaks to a resistance (corrosion). If the Neutral current is zero, you probably have a wiring error - fuse placed on neutral and blown, disconnected entirely or something like that.

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On 8/28/2018 at 12:12 PM, cinnr said:

I need help understanding the best way to find my wiring problem that is causing the newly installed gfi on my shore power to trip.

Here's my current state: with battery switch in "off", I can connect shore power and run the battery charger and AC outlets without a problem.  Bilge pump works no problem.  All DC switches on the panel are in the off position.  When I turn the battery switch to "1", "2" or "both", the gfi on the shore power will trip after about 10 seconds (not immediately).  This is with no power being supplied by the DC switches on the panel.

I'm looking for advice on where to start looking, and perhaps a method/procedure for identifying the specific problem.  This is my first time diving into the back side of the electrical panel, and don't have much experience with electronics and electrical systems, but I'd like to get to the bottom of this.

Thanks!

Tom

Clarification - When you run the charger with the battery switches off, your charger can be wired up to the batteries directly or through the cutoff switches. 

Which way is it set up? If its through the switches that means that the batteries are not drawing current, and thus no load to the AC side of the system.

To me, the problem is something on the AC side of the system, that only becomes noticeable when DC current load goes up. That makes sense if you got a current leakage issue with the battery charger.

Also, are your AC outlets, a direct feed from the AC side of the system, or are they powered from the batteries through an AC inverter?  To sort this out need to know what's connected to the AC side of the system and then start eliminating those items.

My first guess is that the battery charger is leaking current to ground.

 

 

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Posted (edited)

@jerryj2me - the charger is not connected through the switches - i.e. when the battery switch is in the off position, the batteries still charge. That part seemingly works fine.

Oh and also there is no inverter involved for AC.

Edited by cinnr

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2 hours ago, cinnr said:

@jerryj2me - the charger is not connected through the switches - i.e. when the battery switch is in the off position, the batteries still charge. That part seemingly works fine.

Oh and also there is no inverter involved for AC.

If you disconnect power to the charger(pull the fuse or trip it's breaker on the AC side) but do everything else the same, do you still have the same issue?  

EDIT: If the problem goes away, then reconnect this time pull the fuse on the DC side of the charger, at the charger end of the DC circuit(you should be fused both ends of that one). 

If the problem goes away when you disconnect the DC side, then hook the charger up to an isolated load on a short set of test leads(spare battery or load tester) and run it again with fuses/breakers back in.

 

   If it goes away when you pull the AC side, but not the DC side, you should be looking at the charger itself or the AC wiring, if it goes away when the DC side is disconnected and doesn't occur when you are testing to an isolated load, look at the DC wiring/charger.  If it happens when the isolated load and AC are live, but not when DC is disconnected, look at the charger only. 

 

 

 

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1 hour ago, jgbrown said:

If you disconnect power to the charger(pull the fuse or trip it's breaker on the AC side) but do everything else the same, do you still have the same issue?  

-- snip--

Yep - if I have shore power connected, but the breaker for the charger off, the gfci will still trip after I switch the batteries from "off" to something else (i.e. 1, 2 or both).  This reproduces with everything on the panel off - both AC and DC sides.  Just connect shore power with the batteries in anything other than "off" and the gfci will trip. Even with absolutely nothing on at the boat's breaker panel.

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Wet spreaders advise is what you need.  I would highly recommend hiring a marine electrician to do some troubleshooting.  As said above stray AC current can be very dangerous for anyone in the water around your boat, it also can do very expensive damage in hurry.  Remember most AC and DC marine panels are only breaking the Hot side and positive side of a circuit.  Lots of possibilities DC ground AC ground and DC negative may be connected.  Also your neighbor may be super hot, in a bad way.  If they are not new you should measure resistance on your shore power cable leads end to end and across each other, the plugs are water resistant not proof.

 

Good luck

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5 hours ago, cinnr said:

Yep - if I have shore power connected, but the breaker for the charger off, the gfci will still trip after I switch the batteries from "off" to something else (i.e. 1, 2 or both).  This reproduces with everything on the panel off - both AC and DC sides.  Just connect shore power with the batteries in anything other than "off" and the gfci will trip. Even with absolutely nothing on at the boat's breaker panel.

I am suspecting a leakage path between "Neutral"  and "Chassis Ground" on the AC side of the charger.   Even if the "Hot" going into the charger is open (switched off) a leakage path will do this. Disconnect all three wires (Hot, Neutral, Ground) on the AC input to the charger and see if the problem then goes away.

Here, something I wrote on this a while back - read the section on AC Power and grounding safety. The rest is not applicable:

https://www.electronicdesign.com/power/essentials-ac-power-safety

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Take the cheap simple step first.  GFCI's can wear out over time.  Replace the GFCI and see if the new one is tripping.  

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9 hours ago, voodoochile said:

Take the cheap simple step first.  GFCI's can wear out over time.  Replace the GFCI and see if the new one is tripping. 

It is new plus is not tripping if DC load side is isolated.

On 8/29/2018 at 5:12 AM, cinnr said:

that is causing the newly installed gfi on my shore power to trip.

 

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I had to re-read this a couple of times to make sure I wasn't missing something..

Are you talking about an on-board GFCI that is tripping or a shoreside GFCI (possibly ELCI?) that is tripping? And- somewhat related in a strange way... is the boat in the water or on the hard?

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Shoreside gfci (or efci?...not sure what that is).

Boat is in the water (fresh water).

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8 hours ago, cinnr said:

Shoreside gfci (or efci?...not sure what that is).

Boat is in the water (fresh water).

Same device but different name used in different countries.

https://en.m.wikipedia.org/wiki/Residual-current_device

My guess is your battery charger is operating with DC side isolated as it as it is isolated from your onboard saftey AC Ground and or DC Ground. Both Grounds may or may not be bonded together depending on AC/DC electrical and galvanic protection design. That is the first thing to establish, though after that with what needs to be done you are probably better off engaging a professional to track the fault.

The introduction of a new GFCI or RCD at the Marina has revealed a potentially dangerous fault on your boat that has been there for some time. For some inexplicable reason the US while having superb onboard electrical regulations were slow to mandate onboard GFCI's compared to other countries. I dont know the current situation. The existence of fresh water only lowers the risk of in water electrocution, it doesn't remove it.

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1 hour ago, jack_sparrow said:

Same device but different name used in different countries.

https://en.m.wikipedia.org/wiki/Residual-current_device

My guess is your battery charger is operating with DC side isolated as it as it is isolated from your onboard saftey AC Ground and or DC Ground. Both Grounds may or may not be bonded together depending on AC/DC electrical and galvanic protection design. That is the first thing to establish, though after that with what needs to be done you are probably better off engaging a professional to track the fault.

The introduction of a new GFCI or RCD at the Marina has revealed a potentially dangerous fault on your boat that has been there for some time. For some inexplicable reason the US while having superb onboard electrical regulations were slow to mandate onboard GFCI's compared to other countries. I dont know the current situation. The existence of fresh water only lowers the risk of in water electrocution, it doesn't remove it.

Fresh water raises the risk of electrocution. You are a better conductor in fresh water as opposed to salt water.

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Well, ELCIs often will have a higher trip threshold than a common GFCI (I've seen ELCIs with thresholds at 30mA as opposed to 4-7mA for most GFCIs), but, yes, the same general type of device.

Well, I had sort of been hoping that you were on the hard, actually- I have seen some crazy things relating to galvanic isolators setting off a warning light which, in turn, causes enough of an imbalance to trip a GFCI. 

As an ABYC electrician, I love the fact that everyone is recommending a professional look at it, and I ultimately still agree. But these fault tracings have become harder and harder lately. I have had shoreside ELCIs trip from fluorescent light fixtures, indicator lights (usually on galvanic isolators), polarity indicators that suddenly have a resistance of less than 25Kohms, washing machines, and a myriad of things- keeping in mind SOME of these things, in fact, pose no danger to swimmers in the water or, frankly, even shock hazards on the boat. But, until you can verify that, everyone saying to have it traced out is absolutely spot on.

I mean, absolutely check for a neutral-ground issue where ever it's most convenient for you to do so (if access to the panel is easy, that's where I like to do it- right at each buss). With shore power unplugged, depending on the quality of your meter you will see OL or a number above 25Kohms. If it is a smaller number, you need to find the neutral-ground connection. 

I honestly doubt any of what I just will help- and this is an odd fault- I understand. I just want you to know that some of these faults are getting harder and harder to track down so earlier guesses of 'an hour' may not be spot on.

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I really appreciate all the input.  I am hoping to get enough time to get out to the boat soon to dig into this.

Dont know if it matters, but we do have a gfci outlet onboard in our AC outlets circuit. It does not trip when i have the AC outlets on.

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10 hours ago, cinnr said:

Dont know if it matters, but we do have a gfci outlet onboard in our AC outlets circuit. It does not trip when i have the AC outlets on.

Your hardwired Charger and or its wiring appears to be the culpret. If that is a Charger/Inverter combo it is not inconcievable there is AC going to DC side which is obviously super dangerous. 

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54 minutes ago, jack_sparrow said:

Your hardwired Charger and or its wiring appears to be the culpret. If that is a Charger/Inverter combo it is not inconcievable there is AC going to DC side which is obviously super dangerous. 

Maybe, but that is doubtful. The AC side feeds a switching downconverter that is isolated by a transformer, generally a toroid (donut magnet) with an input and an output winding. That donut with the two wires wrapped on it would have to fail to do what you are describing. There's not a lot there to fail. That's the reason I suspect a leakage between neutral and ground on the AC side. That trips the GFCI, and there's a bunch of circuits there that can fail or leak and cause the problem.  That's my motivation for suggesting disconnect all three AC leads into the charger and see if the problem still exists.

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To your original question "I need help understanding the best way to find my wiring problem […]", the answer is simple irrespective of the …

The best way to find the wiring problem is to reverse engineer the wiring, creating an accurate schematic as you go. In other words, until you understand your wiring, you can't  find the wiring problem. Fortunately, once you do understand your wiring, the problem almost always becomes obvious.

Contrary to most posts here, the real risks of danger are rather low. The GFI is tripping because there's a problem with your neutral wire and current is flowing in the ground wire as a result, this is why there is a ground wire. For there to be danger, both the neutral and ground would have to have problems and that's statistically unlikely.

Your best course of action is:

  1. Disconnect the AC input to your battery charger
  2. Carefully trace your AC wiring to your breaker panel to ensure that's looking good
  3. Turn off all the breakers on your AC distribution panel
  4. Check to see whether you have a GFI problem. If you do, then the problem is in this simplified portion of your boats wiring, possibly in the shore power plug/receptacle, possibly within the few wiring connections in the circuit. Find it and fix it.
  5. If you don't have a GFI problem, turn on your AC breakers one-by-one to see whether any of the branch circuits are the culprit. If so, find it and fix it.
  6. If none of the AC branch circuits are the problem, then the problem is in your battery charger. Remove it and replace it.

 

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11 hours ago, Moonduster said:

 

Turn off all the breakers on your AC distribution panel

 

A gentle reminder. The AC breaker switch only opens the Hot line, while ground and Neutral remain connected. This won't isolate any leakage between ground-neutral on those branches. 

What you are suggesting will not hurt, but it does not answer the question where the leakage path is between ground-neutral. An AC breaker switch can be open, Hot is disconnected  on that branch of the system, but the leakage path between ground-neutral within that branch is still tied to all the other Ground-Neutral circuits in the system.  

 

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5 hours ago, Moonduster said:

If there's any current in any branch, the gfi will trip

If there is any current between neutral and ground the GFI will trip. That means that the currents in Hot and Neutral are not equal and opposite.

Most GFI circuits are designed using a current transformer that uses Hot and Neutral to cancel each other out. 

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