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Old 05-20-2019, 06:29 AM   #1
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Best overcurrent protection device for Charles isolation tranformer?

Going over the install instructions for my isolation transformer, and wondering what overcurrent protection device (between shorepower inlet and IT) has been used by those who have installed the Charles unit- breaker, ELCI, none, or?

Thanks!
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Old 05-20-2019, 09:57 AM   #2
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Well, since ABYC standards specify a breaker near the shore power inlet although older boats don't often have one, I would install one if you don't have it. Put in a 30A single pole, 50A single pole or 50A double pole depending on what kind of shore power inlet you have.


Blue Seas makes one that will work.


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Old 05-20-2019, 10:03 AM   #3
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For boats it is required to break both the hot and neutral on the 120V line. So it requires a 2 pole breaker. This would go between the shore power inlet and the transformer. Preferably as close as possible to the shore power inlet.



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Old 05-20-2019, 10:25 AM   #4
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The breaker is supposed to be installed within 10 from the inlet measured along the wiring.
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Old 05-20-2019, 12:05 PM   #5
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Asking, not challenging, but about that breaker within 10’ of the inlet by wire travel. That’s a new wrinkle to me. If the shore power stand is properly wired, and the isolation transformer is properly installed, why would there need to be an additional breaker?
For instance, my 1988 Bayliner 3818 was built with two 30amp inlets just forward of the cockpit. Since I don’t have air conditioning, 30 amps is all I need. The inlets are 15’ from the distribution panel as the wires are run. Are you suggesting that I need to install a double pole breaker in that system? My plan is to disconnect one of the inlets, add a new inlet on the transom then use an automatic transfer switch to open the unused inlet when the other closes and combine the two panel wires so the transfer switch acts as a Y cable. I want to do this correctly, but it seems like the configuration would be GFI at the dock, outlet, cord, inlet, GFI, transfer switch, isolator, panel rotary selector, buss breaker, circuit breaker, load.
Have I got this right?
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Old 05-21-2019, 05:59 PM   #6
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Essentially, the breaker at the pedestal is considered iffy, at best.

The requirement for a breaker within 10' of the shore power inlet, measured along the conductor has been in the ABYC Standard for at least 10 years. About 5 years ago, the requirement was for an ELCI to be installed within 10' of the shore power inlet, unless there is an isolation transformer in the circuit.
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Old 05-21-2019, 06:02 PM   #7
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The breaker within 10 is there to protect the wiring and the boat in case of a short in the wiring. It is an arbitrary distance but you have to pick a distance and 10 is it.
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Old 05-21-2019, 06:09 PM   #8
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I installed a Blue Seas 2-pole breaker with my Charles isolation transformer. Works fine. I'm within the 10 ft limit.
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Old 05-23-2019, 05:21 AM   #9
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The breaker on the power pole is to protect the power pole , and the wire to the boat and the plug and socket on the boat.

An internal breaker is to protect the wire to the first user a transformer or panel to feed the rest of the boat.

The CB in the panel is to protect the feed wiring to the multiple users on the circuit.

A fuse or CB protects each individual user on the feed wire..

This is how I understand the usual recommendations.
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Old 05-23-2019, 06:12 AM   #10
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Quote:
Originally Posted by Ken E. View Post
I installed a Blue Seas 2-pole breaker with my Charles isolation transformer. Works fine. I'm within the 10 ft limit.
Ditto. I was able to get a two-pole, 50-amp breaker within two or three feet of the shore power inlet.
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Old 05-23-2019, 06:21 AM   #11
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Originally Posted by kchace View Post
For boats it is required to break both the hot and neutral on the 120V line. So it requires a 2 pole breaker. This would go between the shore power inlet and the transformer. Preferably as close as possible to the shore power inlet.

Ken
Ken, do you mean this to apply for boats without an isolation transformer? With my Charles IsoBoost, the neutral shore power conductor is terminated at the boats inlet and does not come aboard. The two-pole breaker handles the dual hot conductors.
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Old 05-23-2019, 11:32 AM   #12
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As Im going from 2 30A inlets to a 50/250 (split to feed both panels), as part of the isolation transformer install, I found that SmartPlug makes a 50A breaker that (conveniently enough) will fill the hole left by the 2nd 30A breaker.
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Old 05-24-2019, 06:36 AM   #13
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Quote:
Originally Posted by CharlieJ View Post
Essentially, the breaker at the pedestal is considered iffy, at best.

The requirement for a breaker within 10' of the shore power inlet, measured along the conductor has been in the ABYC Standard for at least 10 years. About 5 years ago, the requirement was for an ELCI to be installed within 10' of the shore power inlet, unless there is an isolation transformer in the circuit.

If there's an ELCI, what purpose would an isolation transfomer serve?

Full disclosure: I've been wondering whether we need an isolation transformer, or a galvanic isolator... or now, an ELCI... and if so, which... and why.

-Chris
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Old 05-24-2019, 07:04 AM   #14
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Ranger42C:
I think you misunderstood my post: An isolation transformer negates the requirement for an ELCI. An isolation transformer installation still requires a circuit breaker that breaks all current carrying conductors installed on the primary side if the isolation transformer is >10' from the shore power inlet.

That said, if it was my boat, I would install an appropriate circuit breaker on the primary side of the isolation transformer regardless of its distance from the shore power inlet. I just do not trust pedestal circuit breakers.

As to your larger question:
# An isolation transformer separates the vessel's electrical system from the land based mains.

For 240/120VAC split phase the hot (line) conductors are brought aboard with the safety ground wire. The hots are connected to the primary winding and the safety ground is tied to the electrostatic shield located between the primary and secondary windings.

For 120VAC shore power, all three conductors are brought aboard, and the hot and neutral feed the primary side of the xfmr and the safety ground is tied to the electrostatic shield. The neutral (if needed) and safety ground are derived on the secondary side of the xfmr. Total electrical isolation.

# A galvanic isolator is placed in the safety ground wire aboard the vessel. It is recommended to be physically placed close to the shore power inlet so that it is not inadvertently bypassed by a technician or DIY'er later.

The conducting voltage is about 1.2VDC so it will block galvanic current trying to leave or come aboard the vessel via the safety ground (green) wire. It will not block stray current if the associated potential is greater than 1.2VDC and stray current is usually >>1.2VDC.

It will pass AC fault current so that an upstream breaker will trip.

# An ELCI is similar to the GFCI in your bathroom, it just has different trip characteristics. These residual current devices (RCDs) measure the current flowing in on the hot conductor or conductors and compare it to the current flowing back to the source via the neutral. If the two don't match the RCD trips.

For GFCIs, the tripping threshold is 5mAAC. For ELCIs on boats, the tripping threshold is 30mAAC in 100mS. If less current is coming back to the source via the conductors, the current is flowing through the water path. In fresh water that is deadly
Note: The measurement of 240VAC/120VAC split phase is a bit more complicated but the concept is still that the ins must equal the outs within <30mAAC.
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Old 05-24-2019, 07:19 AM   #15
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Quote:
Originally Posted by CharlieJ View Post
Ranger42C:
I think you misunderstood my post: An isolation transformer negates the requirement for an ELCI. An isolation transformer installation still requires a circuit breaker that breaks all current carrying conductors installed on the primary side if the isolation transformer is >10' from the shore power inlet.

That said, if it was my boat, I would install an appropriate circuit breaker on the primary side of the isolation transformer regardless of its distance from the shore power inlet. I just do not trust pedestal circuit breakers.

As to your larger question:
# An isolation transformer separates the vessel's electrical system from the land based mains.

For 240/120VAC split phase the hot (line) conductors are brought aboard with the safety ground wire. The hots are connected to the primary winding and the safety ground is tied to the electrostatic shield located between the primary and secondary windings.

For 120VAC shore power, all three conductors are brought aboard, and the hot and neutral feed the primary side of the xfmr and the safety ground is tied to the electrostatic shield. The neutral (if needed) and safety ground are derived on the secondary side of the xfmr. Total electrical isolation.

# A galvanic isolator is placed in the safety ground wire aboard the vessel. It is recommended to be physically placed close to the shore power inlet so that it is not inadvertently bypassed by a technician or DIY'er later.

The conducting voltage is about 1.2VDC so it will block galvanic current trying to leave or come aboard the vessel via the safety ground (green) wire. It will not block stray current if the associated potential is greater than 1.2VDC and stray current is usually >>1.2VDC.

It will pass AC fault current so that an upstream breaker will trip.

# An ELCI is similar to the GFCI in your bathroom, it just has different trip characteristics. These residual current devices (RCDs) measure the current flowing in on the hot conductor or conductors and compare it to the current flowing back to the source via the neutral. If the two don't match the RCD trips.

For GFCIs, the tripping threshold is 5mAAC. For ELCIs on boats, the tripping threshold is 30mAAC in 100mS. If less current is coming back to the source via the conductors, the current is flowing through the water path. In fresh water that is deadly
Note: The measurement of 240VAC/120VAC split phase is a bit more complicated but the concept is still that the ins must equal the outs within <30mAAC.
This explanation should be reference material- thank you!
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Old 05-24-2019, 10:52 AM   #16
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Ranger42C:
I think you misunderstood my post: An isolation transformer negates the requirement for an ELCI.

Heh... very possible. Thanks for the details; I'm still digesting.

Does an ELCI not negate any "requirement" for an isolation transformer or galvanic isolator?

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Old 05-24-2019, 11:06 AM   #17
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Heh... very possible. Thanks for the details; I'm still digesting.

Does an ELCI not negate any "requirement" for an isolation transformer or galvanic isolator?

-Chris
Chris, you can use one of the other:

Isolation transformer:
Iso transformer does exactly that- isolates the boat from shorepower. Think of it this way (this is what helped me to understand the concept)- the shorepower powers the iso transformer, turning the iso transformer into the ship's standalone power supply. Any stray current onboard remains onboard in its own loop. The shorepower cable sees a balance of power fed vs power retuned, and the ELCI on the power pedestal does not trip.

A side benefit is that stray current in the water from another vessel will not attempt to return to ground via your vessel (because you are in an isolated loop) and your anodes will last longer. Ergo- no galvanic isolator needed.

ELCI:
A ELCI onboard the vessel will measure power in vs power out, and if there is leakage of greater than 30 milliamps, it will trip. the next step will be to track down the leakage.

A galvanic isolator can be installed, as it is protecting the vessel from stray current in the water.


Some will correct me if I'm wrong- but this is the way I understand it. Ours goes in this weekend as part of an upgrade from twin 30A to a single 50/250.
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Old 05-24-2019, 11:26 AM   #18
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Put technically, an iso transformer blocks common mode currents. It does very little to differential mode currents.

The long answer from Charlie describes mostly what this means. Blocking a component of lightning surges can also be added.
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Old 05-24-2019, 11:52 AM   #19
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Hmmm... Speak slowly and use small words, guys... I think I understand 90% of the words in Charlie's post, but only maybe 10% of the meaning so far...

Either/or sounds good, especially if one can be significantly less expensive than the other.

Is the main breaker on our boat an ELCI?

Common mode currents? Differential mode currents?

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Old 05-24-2019, 12:08 PM   #20
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We could put a customer value to the use of an iso transformer.
Even a grade of A B C F

Here is my assessment.
A means a qualified install of an iso transformer that has a low line tap if its in a 240v system plus a differential surge suppressor.
B is same with no tap. Or no surge system
C only meets an ABYC minimum spec
F does not meet basic safety specs.
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