Leakage current on shore power cord question

[jackrabbit59]

Thanks for all the help. The electrician is coming tomorrow I hope.

[Jammer]

Originally Posted by jackrabbit59

Thanks for all the help. The electrician is coming tomorrow I hope.

You may find you're chasing ghosts


Some sort of inductive coupling maybe. Averaging or RMS algorithm in the meter distorting the results of the inductive/capacitive load presented by the transformer primary or sensing some wires in the bundle with more gain than others.


I would confirm findings using other instruments and techniques before deciding how concerned to be and would certainly not replace an expensive component solely on the basis of a single measurement especially one from an instrument as ambiguous and imprecise as a clamp on ammeter

[lateral]

No CM I’ve used will give a meaningful reading on multiple conductors at the same time of the same circuit. Should be zero.
As stated above if integrity of insulation of input winding to earth is intact you have no problem.

[jackrabbit59]

Just to be clear, I have walked up and down the dock numerous times with the clamp meter and checked every power cord attached. All of the other ones read a stable 0.04 Amps. I mean everyone of them. Some are 30 amp and some are 50 amp service. I am at dock 41 to give you an idea of how many other boats I have checked. I have plugged my cord into 3 other dock posts and I still get 4 to 7 amps floating around. There is definitely something wrong with my boat. I just want to know if I should replace the transformer or not.

[GordMay]

As others have noted, never clamp around two [or more] conductors, at the same time, as the current passing through them will cancel each other out, and the resultant reading, if not "zero", will be completely erroneous.
Clamp-ons measure current in a circuit, by measuring the strength of the magnetic field, around a single conductor. When measuring current, center the conductor in the current probe [clamp jaws].
To be clear: always use a clamp meter on a single conductor.

There are three types of clamp meters:
1. Current transformer clamp meters: measure only alternating current (AC).
2. Hall Effect clamp meters: measure both alternating current and direct current (AC & DC).
3. Flexible clamp meters: employ a Rogowski coil; measure AC only; good for measuring in tight spaces.

[Jammer]

Originally Posted by jackrabbit59

Just to be clear, I have walked up and down the dock numerous times with the clamp meter and checked every power cord attached. All of the other ones read a stable 0.04 Amps. I mean everyone of them. Some are 30 amp and some are 50 amp service. I am at dock 41 to give you an idea of how many other boats I have checked. I have plugged my cord into 3 other dock posts and I still get 4 to 7 amps floating around. There is definitely something wrong with my boat.

How many of them have isolation transformers?

I just want to know if I should replace the transformer or not.

Well, if you decide to replace it, send it to me. I'll, uh, make sure it's properly disposed of.


Seriously though, you don't replace expensive components like that unless you confirm that there is something wrong with them. There are ways to test isolation transformers that are reliable and trustworthy. Putting a clamp-on meter over the shore power cord isn't one of them.

[lateral]

Before replacing it I would first check the output and make sure it is isolating ie that either output leg has no polarity relative earth.
Then disconnected from dock and with open circuited secondary (output) Megger primary legs (either) to earth wire or case of Charles.
If either fails has a fault.
Also, clamping in the proximity of a magnetic field (near isolating trans) for some type clamps will surely confuse the issue will have you looking for things that ain’t there.
You can disconnect one leg & check with 10A probes if you don’t believe your clamp is lying.
Of course anything done live mains voltage you need to be licensed.

[CharlieJ]

First of all, a properly wired and properly functioning isolation transformer will not allow stray current into the water. The test laid out by smac999 #15 will indicate whether the isolation xfmr is properly wired and is the first test to determine if is operating properly and has not been damaged.

A compliant iron and copper isolation xfmr has the shore side safety ground connected to the shield, and only the shield, between the primary and the secondary windings. N and G are developed at the secondary of the xfmr and are bonded together. The #15 test will determine if your installed isolation xfmr is wired and functioning properly. FWIW, I don’t think it is.

For those without a functioning isolation xfmr installed:
The testing for stray current leakage by clamping the entire cable, although absolutely counterintuitive, is the very valid first testfor AC current leaking into the water. The National Electrical Code (NEC) now requires marina owners to have an appropriate clamp meter to perform this very test.

A clamp meter used for general electrical work does not have the sensitivity or accuracy for this testing. The maximum leakage into the water must be <30mAAC, with the goal being to be as close to zero as is possible. 30mAAC is the trip point for the Equipment Leakage Current Interrupters (ELCIs) now required at marina pedestals by the NEC.

So the clamp meter must be able to measure to 0.1mAAC.

All electrical current will return to its source by all paths available. By clamping the entire cord, a determination is being made of the current that is not returning via L1, L2, N or G (50A service w/o a xfmr) or L, N or G (30A service w/o a xfmr), the only other path available to return by, if there truly is leakage is via the water path and this can be deadly to people in the water.

This full cord test must be performed when all AC equipment is operating, not simply energized, but operating.

The follow up test if the full cord test indicates leakage is to use a break-out adapter so that all the conductors can be individually clamped. This adapter is simply a male and female shore power connection and the appropriate number and size of conductors between the two connections. With the break out adapter in place and all AC equipment energized, clamp L1, L2, N and G (50A service); L1, N and G for 30A service

Any current on the G indicates:
1. that there is an improper N>G bond somewhere on board that must be found and eliminated or,
2. In the case of multiple shore power connections, that the N from one supply has been landed on the N of the other supply causing an imbalance.

I will post some references in another post.

[CharlieJ]

Here are some references that should be helpful:
https://tinyurl.com/v4b85stb
https://tinyurl.com/kvbbra8m

[drdoyle]

Something is not right with the way the iso transformer is wired into the system or the iso is defective. Try bypassing the iso transformer completely out of the circuit and test your cord again for current.

[GordMay]

Originally Posted by CharlieJ

... For those without a functioning isolation xfmr installed:
The testing for stray current leakage by clamping the entire cable, although absolutely counterintuitive, is the very valid first testfor AC current leaking into the water ...

Thanks, for correcting me [& others], Charlie.

You, of course are absolutely correct, and I was wrong.

Technical Bulletin: Understanding AC Leakage Current
In particular, see the 2ND Scenario, illustrated in Figure 7
➥ https://www.marinadockage.com/techni...akage-current/

Beyond the basics: Electrical problems at a boat dock
Leakage currents, Kirchoff's law
➥ https://www.fluke.com/en-ca/learn/bl...at-a-boat-dock

[Nicholson58]

Check the specifications for the transformer. Your short power is connected to the primary. Even if there is zero demand on the secondary there will be current flowing through the primary. This is the parasitic loss.

[col50]

Originally Posted by jackrabbit59

I have a 50 amp 240V shore power cord. The boat has a Charles 12KVA Isolation Transformer. The shore power cord input is directly connected to the isolation transformer, Red Black and ground wires only. If I place a clamp meter over the shore power cord it reads anywhere from 4 to 7 amps!. I have tested other boat power cords and they read around 0.04 amps. I bought a new 50 amp cord, $600 and I get the same 4 to 7 amps. I have tried plugging into other dock posts with the same results.
On the output side of the transformer to the breaker box the clamp meter reads 0.02 amps to 0.03 amps.
I have tried disconnecting the output side of the transformer completely and the input side still reads 4 to 7 amps.
I had the DC leakage tested with a line from the prop shaft to the other electrode in the water. It tests fine. I do not any unusual zinc deterioration.
Anyone have an idea what could be wrong with the isolation transformer? Should I replace it?

The power cable is very thick and could be holding the probe-clamp open slightly. Are you sure the probe-clamp is completely closed? If not, you could be measuring the earths magnetic field. You should also measure individual wires, not the entire cable

[jackrabbit59]

The electrician came by today. We found the stray current in the windings. Even with the neutrals and grounds disconnected from both sides their was still 7 to 9 amps on the wires. The transformer has to be rebuilt or replaced. Less than 2 boat dollars for a new one so I will probably go with replacing it and selling the old one for scrap. The old one weighs 220 lbs so I have to find someone younger than me to take it out. Thanks to everyone for their help.

[MVDarlin]

I recently replaced my very old 10 amp Heart inverter /charger with a 10 amp NOCO genius charger $100, and separate 1,100 watt inverter $75. The Heart charger was causing the shore power dock breaker to trip as soon as it was connected to the boat. It took a lot of time and effort to sort out the problem. I never bothered to troubleshoot the inverter. I did salvage 2 very long 2 awg cables from the unit.