Isolation Transformer Question

[Kaptajnen]

After installing a Bridgeport Magnetics Isolation Puck, my ABYC Certified Marine Electrician found that the red Reverse Polarity light on the 120 volt panel was ON. However all 120 volt outlets still had correct polarity and my 120 volt dehumidifier is working.

He spent several hours trying to troubleshoot this, including calls to Bridgeport Magnetics technical guy, but was not able to solve this conundrum.

Any suggestions would be most welcome.

 

[Osprey]

The reverse light comes on if the neutral is isolated from the ground. Normally the neutral and ground are connected at the power (source) panel. The isolation device you are using likely disables the tie in between the neutral and ground. The light is giving a false indication of reverse wiring condition. We commonly see this red light issue when the power source is a portable generator such as a Honda. The Honda does not have the neutral to ground connection. The red light issue is solved by using special plug designed to make the neutral to ground connection.

 

[knotflying]

Just to reinforce the previous post: usually the last thing done is the cause of the problem. If you did not have the reverse polarity before than it is probably has something to do with your issue. See what happens when you disconnect it.

 

[Kaptajnen]

The reverse light comes on if the neutral is isolated from the ground. Normally the neutral and ground are connected at the power (source) panel. The isolation device you are using likely disables the tie in between the neutral and ground. The light is giving a false indication of reverse wiring condition. We commonly see this red light issue when the power source is a portable generator such as a Honda. The Honda does not have the neutral to ground connection. The red light issue is solved by using special plug designed to make the neutral to ground connection.

You are correct. The Marine Puck does disables the connection between the neutral and the ground.
Thanks!

 

[Wee Venture]

Don’t want to unnecessarily complicate things here, but I do think the problem has not been fully pinned down yet.

It is true that portable generators can trigger a reverse polarity light when the neutral (white) wire has not been tied to ground. This is because the light is measuring voltage between the neutral and ground wires: if they are bonded together at the source it should be zero, or very close to it. If it is unbonded and left to float, you can get a voltage differential due to capacitive coupling or leakage.

It is also true that isolation transformers disable any direct connection from the boat wiring to *shore power* ground as well as disabling hot and neutral direct connections to shore power.

However, according to my understanding, the isolation transformer secondary (boat side) should by default bond the neutral and ground wires. This means the voltage differential should still be zero at the panel and the reverse polarity light should theoretically not come on.

I would want to make sure the ground and neutral are actually bonded at the transformer secondary, and that there is no faulty connection or undersized wiring (the white neutral in particular) that could cause a voltage drop. (These are things that I would think the electrician would have checked already.) Beyond that, I would give serious consideration to Brian’s (BB marine) suggestion on your parallel thread. Inverter wiring is the most frequent offender with ground faults on a boat. When neutrals and grounds are connected in the wrong place, you can get ground loops that send current where it shouldn’t be.

John

 

[BB marine]

I agree with John on this subject. First confirm that the boat is wired properly before installing a isolator to fix a problem. Once it is confirmed the boat wiring is 100% ABYC compliant and you want to protect your boat and its electrical system more install a isolation transformer.


This is a copied statement from the ABYC Blog.

The only AC neutral to ground (connecting the white wire to a green wire) connections on board are made at generators or inverters, and then only when they are invert mode. Additionally, if the boat is equipped with an isolation transformer, then the boat side of the transformer becomes a new source of AC power and therefore a neutral to ground link is established.

This is the same thing that is done when using a Honda Generator onboard. The Neutral and ground can be combined by using a special plug that links the neutral to ground at the source (Honda Generator)

I took a Look at the Bridgeport Magnetics Isolation Puck, installation
https://www.bridgeportmagnetics.com/wp- ... scaled.jpg

There is no ground/'neutral connection at the isolator. The new source which is normally done based on the ABYC requirement. Without this bond you will see the polarity light on which as been already concluded by Osprey.

This is the design of this isolation puck. Here is a description from the. ISO-PUCK isolation transformers do not feature output Neutral to Ground Bond. They provide a true floating system (IT Earthing System) for maximum protection against excessive ground leakage current.

He spent several hours trying to troubleshoot this, including calls to Bridgeport Magnetics technical guy, but was not able to solve this conundrum.

I'm surprised that the ABYC certified electrician and the technician from Bridgeport did not realize this. No bond of neutral and ground at the isolator the panel reverse polarity light will be on.

This is because the light is measuring voltage between the neutral and ground wires: if they are bonded together at the source it should be zero, or very close to it. If it is unbonded and left to float, you can get a voltage differential due to capacitive coupling or leakage.

Based on this installation your reverse polarity light will remain on. I would run this by the manufacture and the ABYC electrician that this is considered ABYC compliant. I would assume it is if they make this devise for boats.

 

[Kaptajnen]

UPDATE

After further discussion between my ABYC electrician and the tech guy at Bridgeport, he revealed he had sent the wrong schematic!

This showed a connection between the Puck and the boat’s ground. That solved the issue! Bridgeport also paid the cost of the troubleshooting, which was great news for me.

 

[BB marine]

That is good news that the issue is resolved and Bridgeport stepped up.

Did the original issue you were having get resolved?

"Did confirm a 10mA AC leak coming from customers boat. Appears to be coming from inverter. Customer is having a isolation transformer installed to solve this 10mA AC leak and protect his vessel from other boats or dock."

 

[Kaptajnen]

Yes that was resolved... and it is great to have the boat totally isolated from any stray currents from other boats on the dock.

Presumably, my zincs will last longer thus saving me some $$$

 

[Kaptajnen]

Yes that was resolved... and it is great to have the boat totally isolated from any stray currents.

Presumably, my zincs will last longer thus saving me some $$$