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Old 29-07-2014, 18:31   #16
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Re: Popping the marinas GFI

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Originally Posted by capngeo View Post
Fairly simple actually... first you need to understand a GFI and how it works; A GFI measures the power coming from the hot side, going to the neutral, when the values become unequal, the GFI assumes there is a fault and current is going to ground (possibly through a human), which trips the GFI and shuts down power.

Because all neutrals are bonded together in a 120VAC system, a TWO GFI circuit will you suddenly have TWO paths to neutral on the same circuit.. this confuses the values and one or both GFIs will trip.
No!

First, you are correct in stating a GFI monitors for an imbalance between the current flow on hot and neutral. But where your theory falls apart is the assertion there are multiple points where neutral and ground are bonded. All codes require that neutral and ground are bonded at the source only, hence a boat without an isolation transformer should never bond neutral and ground. Second, regardless of multiple neutral to ground bonds, that by itself won't cause a GFI to trip (without the imbalance between neutral and hot). If there is a neutral ground bond downstream of the GFI, it renders the uplink GFI unable to protect a ground fault, but won't cause it to trip.

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Read up on NEC, Underwriter's and ABYC..... NONE of the codes allow more than one GFI on a circuit for the above reason.
Please cite the codes.

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That said, you CAN have one GFI protect multiple outlets by connecting them THROUGH the GFI. The latter is how many smaller boats are wired. For instance, say the OP boat has 3 outlets wired after the GFI on ONE breaker: all is good. Now put a GFIC on the pedestal and plug into it... you now have two: bad.

Most small marine electric systems are designed to be plugged into either a single 30A 120V, two 30A 120V, or a single 50A 220V... NOT into a typical household 15 or 20 amp receptacle. Those (the 15-20A receptacles) are included in a pedestal for tools run direct to the pedestal independent of a marine (boat) system. With that in mind, and the possible shock hazard of nearby water (within 4' by code), a GFI is installed in the pedestal..... IT WAS NEVER INTENDED TO HAVE A BOAT PLUGGED INTO IT!
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Old 29-07-2014, 19:40   #17
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Re: Popping the marinas GFI

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Because all neutrals are bonded together in a 120VAC system, a TWO GFI circuit will you suddenly have TWO paths to neutral on the same circuit.. this confuses the values and one or both GFIs will trip.

Read up on NEC, Underwriter's and ABYC..... NONE of the codes allow more than one GFI on a circuit for the above reason. That said, you CAN have one GFI protect multiple outlets by connecting them THROUGH the GFI. The latter is how many smaller boats are wired. For instance, say the OP boat has 3 outlets wired after the GFI on ONE breaker: all is good. Now put a GFIC on the pedestal and plug into it... you now have two: bad.

Most small marine electric systems are designed to be plugged into either a single 30A 120V, two 30A 120V, or a single 50A 220V... NOT into a typical household 15 or 20 amp receptacle. Those (the 15-20A receptacles) are included in a pedestal for tools run direct to the pedestal independent of a marine (boat) system. With that in mind, and the possible shock hazard of nearby water (within 4' by code), a GFI is installed in the pedestal..... IT WAS NEVER INTENDED TO HAVE A BOAT PLUGGED INTO IT!
Almost all of this is wrong (the swimmer hazard is right). It is quite common to have GFI type devices in series at marinas. A GFI in the pedestal and a whole boat RCD on-board is very common these days. This violates no code at least in the US and I doubt it does anywhere.

Neutral and ground are not connected together by a GFI. That happens at one place only and nowhere near the boat or dock pedestal. A GFI works by running both the hot and neutral circuit through a magnetic sensor. So long as there is no path from hot or neutral to ground down stream from the GFI then the hot and neutral currents will be equal and opposite thus cancelling one another and the GFI does not trip. If any leakage is present from either hot or neutral to ground then the two currents will not be equal and the GFI will trip. You can put 10 GFI's in series with one another without causing one of them to trip but there would be no point in doing so. If there is a leakage path then one or more might trip.

To the OP, you need to find the reason your boat trips the pedestal GFI. It is a serious safety hazard to people in the water. There are a few possibilities. Some AC panels have lights that show when the marina power is wired "wrong". If these fail they can cause the pedestal GFI to trip. Someone suggested the inverter/charger but I doubt that is the issue. If the device is working correctly it should not trip the marina GFI. A qualified electrician should be able to find the offending circuit very quickly.
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Old 29-07-2014, 22:26   #18
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Re: Popping the Marinas GFI

I have spent some time and money chasing marina ground faults. The reasons are to resolve personal safety hazards, and protection of equipment. The personal safety limits are lower than equipment protection limits so you really only need to be concerned with what is safe for people. A person can feel electric currents in the 1 to 3 mA range. One mA is 1/1000 of an amp. At 10 to 30 mA's a person looses control of muscles. Equipment damage can occur at 30 mA and above. Around the water the greatest hazard is not electrocution, but drowning of a person in the water due to loss of muscle control.

At one time I had a lease at what was a "hot" marina. I purchased an expensive Fuke clamp meter that could measure fractions of a mA. I dropped a wire into the water, and measured 50 to 1500 mA's near my boat that was going to ground. To find where it was coming from I made up two short shore power cords, a 30 amp 120 volt, and a 50 amp 120/240 volt with the conductors separated from the ground wire so that I could measure them separately using the amp clamp meter. One at a time, I powered each boat through the pigtail with the amp clamp meter checking for leakage current. This process led to two boats with serious ground faults. One had a portable electric heater with a mis-wired plug that connected to ground instead of the neutral, and the other had an insulation failure causing leakage currents.

Such conditions a rare. These arose from uniformed people doing their own wiring, and poor maintenance of equipment.

A 30 mA ground fault device at the shore power connection does little to provide safety. It is far better to use 2 to 5 mA GFI's on the branch circuits. Also, it is worth having a simple outlet polarity tester to let you know that your boat is wired properly, and that you are not plugged into a marina with a polarity error.
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Old 30-07-2014, 05:57   #19
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Re: Popping the Marinas GFI

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I have spent some time and money chasing marina ground faults. The reasons are to resolve personal safety hazards, and protection of equipment. The personal safety limits are lower than equipment protection limits so you really only need to be concerned with what is safe for people. A person can feel electric currents in the 1 to 3 mA range. One mA is 1/1000 of an amp. At 10 to 30 mA's a person looses control of muscles. Equipment damage can occur at 30 mA and above. Around the water the greatest hazard is not electrocution, but drowning of a person in the water due to loss of muscle control.

At one time I had a lease at what was a "hot" marina. I purchased an expensive Fuke clamp meter that could measure fractions of a mA. I dropped a wire into the water, and measured 50 to 1500 mA's near my boat that was going to ground. To find where it was coming from I made up two short shore power cords, a 30 amp 120 volt, and a 50 amp 120/240 volt with the conductors separated from the ground wire so that I could measure them separately using the amp clamp meter. One at a time, I powered each boat through the pigtail with the amp clamp meter checking for leakage current. This process led to two boats with serious ground faults. One had a portable electric heater with a mis-wired plug that connected to ground instead of the neutral, and the other had an insulation failure causing leakage currents.

Such conditions a rare. These arose from uniformed people doing their own wiring, and poor maintenance of equipment.

A 30 mA ground fault device at the shore power connection does little to provide safety. It is far better to use 2 to 5 mA GFI's on the branch circuits. Also, it is worth having a simple outlet polarity tester to let you know that your boat is wired properly, and that you are not plugged into a marina with a polarity error.
I find it interesting that you state 30ma ELCIs do little to provide safety but yet if the shore power feeding the 2 boats you found to have faults would have had ELCIs at the pedestal, those 2 boats would have been denied power until they fixed the faults.

My point is that not all faults involve humans and not all faults are on receptacle attached appliances. Main breaker ELCIs provide a huge safety factor to both humans and equipment.
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Old 30-07-2014, 06:18   #20
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Re: Popping the Marinas GFI

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I find it interesting that you state 30ma ELCIs do little to provide safety but yet if the shore power feeding the 2 boats you found to have faults would have had ELCIs at the pedestal, those 2 boats would have been denied power until they fixed the faults.

My point is that not all faults involve humans and not all faults are on receptacle attached appliances. Main breaker ELCIs provide a huge safety factor to both humans and equipment.
Correct! 30mA ELCI devices have been tested and found to be non-life threatening. And they are not as prone to "false" trips thus there is less chance a frustrated user will bypass them. A 5-10mA device that opens at the slightest provocation and so gets bypassed isn't safe at all.
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Old 30-07-2014, 07:03   #21
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Re: Popping the Marinas GFI

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I find it interesting that you state 30ma ELCIs do little to provide safety but yet if the shore power feeding the 2 boats you found to have faults would have had ELCIs at the pedestal, those 2 boats would have been denied power until they fixed the faults.

My point is that not all faults involve humans and not all faults are on receptacle attached appliances. Main breaker ELCIs provide a huge safety factor to both humans and equipment.
Your observation "if the shore power feeding the 2 boats you found to have faults would have had ELCIs at the pedestal, those 2 boats would have been denied power until they fixed the faults" is a fair point.

However, if people believe that they are protected by them alone, and do not have 2-5 mA GFI protection they can be subjected to 10 to 29 mA leakage currents that could cause drownings due to loss of muscle control. Also, the two individuals who's boats had such conditions are not the type to hire professional help without being compelled to do so, and may attempt to bypass the device at the pedestal that they perceive as an inconvenience without consulting the marina management.
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Old 30-07-2014, 08:09   #22
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Re: Popping the Marinas GFI

The "let-go" threshold is between 6mA and 18mA. The maximum trip level of 6mA required, by UL, for personnel-protection GFCIs (Class A) is based on this let-go current threshold.
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Old 30-07-2014, 08:58   #23
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Re: Popping the Marinas GFI

Firstly, I never mentioned neutral and ground bonding.

Secondly, what I was referring to in the codes was having two GFIs in series which was told to me by an electrician...(I'm on a cell phone, I will look up the codes later when on a real computer)... a quick phone call to the electrician confirmed what I said was accurate. He did add that parallel was fine to have more than one. If I am mis-informed, I will gladly eat crow.
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Old 30-07-2014, 13:44   #24
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Re: Popping the Marinas GFI

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I've been in, around, over, and under marinas and boatyards for 40 years; in all that time, I've NEVER seen a GFIC in excess of 20A
Then I must thank you for your post. It serves to demonstrate and confirm my contention that most of those who profess great maritime electrical knowledge in fact possess very little of that knowledge. When dealing with "marine electricians" CAVEAT EMPTOR.

And I need to confess that I mis-typed when I claimed to never have seen a 50 amp GFI. When we were moored at Petersburg a few months ago we were plugged into a 30 amp GFI but the neighbouring pedestal in fact had both 30 and 50 amp GFIs on it.
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Old 30-07-2014, 13:54   #25
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Re: Popping the Marinas GFI

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However, if people believe that they are protected by them alone, and do not have 2-5 mA GFI protection they can be subjected to 10 to 29 mA leakage currents that could cause drownings due to loss of muscle control. Also, the two individuals who's boats had such conditions are not the type to hire professional help without being compelled to do so, and may attempt to bypass the device at the pedestal that they perceive as an inconvenience without consulting the marina management.
It is extremely unlikely that a swimmer could even notice 30mA in the water. The current would be spread over such a large volume of water that a tiny fraction of that amount would pass through the swimmer. In cases where swimmers have drowned the leakage current will be in the hundreds or thousands of milliamps as a previous post described. We need to tell people the right story about ELCI and GFI as there is a lot of misinformation out there. We need to get all marinas (fresh water anyway) fitted with ELCI and if they were set at 5mA trip they would never work and people would bypass them thus negating their benefit.

For boats, an ELCI with 30mA trip setting and 100mS trip time is perfectly fine. It will protect swimmers and on-board equipment. If you plug a hand held device into the boat or dock then that device should be on a GFCI circuit with 5mA trip threshold. The GFCI will be down stream of the ELCI (they are in series) and so the GFCI will trip first and not knock out the power to the whole boat. But if you happen to forget to use a GFCI circuit and something does go wrong the 30mA whole boat ELCI will still save your life. You'll feel the shock but you will still be alive.
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Old 30-07-2014, 14:20   #26
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Re: Popping the Marinas GFI

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The "let-go" threshold is between 6mA and 18mA. The maximum trip level of 6mA required, by UL, for personnel-protection GFCIs (Class A) is based on this let-go current threshold.
Gord,

You are right. But that is not the threshold for instant death which is much higher than that. A lot of people look at the U/L limits as an electrocution limit which it is not. It is a safety limit to try to prevent secondary injuries such as falling from a ladder. Many (maybe most) injuries from electrical accidents are not from the shock itself but from a resulting fall, burn or some other injury (e.g. drowning).

I knew a guy that stuck his hand into a 4,160 VAC live circuit. The burns and lacerations he received were more life threatening than the shock itself. He should have died from the shock but he didn't. He nearly bled to death because he involuntarily cut himself on a metal panel.
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Old 30-07-2014, 14:49   #27
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Re: Popping the Marinas GFI

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Firstly, I never mentioned neutral and ground bonding.
Fair enough. I misunderstood when you said neutrals were bonded to mean bonded to ground. Neutrals of branch circuits should only be connected together in one place before any GFCI device. If neutrals are bonded together after (down stream of) a GFCI device then false trips will almost certainly result.

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Secondly, what I was referring to in the codes was having two GFIs in series which was told to me by an electrician...(I'm on a cell phone, I will look up the codes later when on a real computer)... a quick phone call to the electrician confirmed what I said was accurate. He did add that parallel was fine to have more than one. If I am mis-informed, I will gladly eat crow.
I think you may have misunderstood your electrician. It is ok to put as many GFCI devices in series as you want. There is no point in doing so but no harm will be done.
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Old 30-07-2014, 18:36   #28
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Re: Popping the Marinas GFI

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Fair enough. I misunderstood when you said neutrals were bonded to mean bonded to ground. Neutrals of branch circuits should only be connected together in one place before any GFCI device. If neutrals are bonded together after (down stream of) a GFCI device then false trips will almost certainly result.
A much better explanation of what I was trying to convey



I think you may have misunderstood your electrician. It is ok to put as many GFCI devices in series as you want. There is no point in doing so but no harm will be done.
Can someone please pass the salt, this Crow is not tasty. Try as I might, I cannot find any code supporting the position I stated earlier; I will have a chat with said "electrician" in the morning.
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Old 30-07-2014, 21:04   #29
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Re: Popping the Marinas GFI

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Fair enough.

I think you may have misunderstood your electrician. It is ok to put as many GFCI devices in series as you want. There is no point in doing so but no harm will be done.
It can be an asset to have the GFCI's in series. If a false or actual fault happens, then you only kill the portion of the circuit down-line.

Sometimes say you're in an engine room, you would have to remove yourself to the GFCI that tripped upstream, or say that part of the downstream circuit is hard faulted, it would then render the the whole circuit in fault.

Plan your work, then work your plan.

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Old 30-07-2014, 22:00   #30
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Re: Popping the Marinas GFI

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It can be an asset to have the GFCI's in series. If a false or actual fault happens, then you only kill the portion of the circuit down-line.
GFCI's in series have no way to know where the fault is. It is just as likely to trip the farthest upstream GFCI as the one closest to the fault. The ones down stream of a fault won't trip but they will also lose power. It is even possible that all the upstream GFCI's will trip. I don't think there is any advantage in putting them in series.
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