Galvanic Isolators - SailNet Community
LinkBack Thread Tools
post #1 of 1 Old 08-06-2002 Thread Starter
Contributing Authors
Join Date: Jan 2000
Posts: 266
Thanks: 0
Thanked 11 Times in 8 Posts
Rep Power: 16
Galvanic Isolators

My sailboat has two shore power connects, one for regular house, and the other for air conditioner. Can I use just one galvanic isolator or do I need to order two? Do I order a 30 amp for one 20 amp shore and one 50 amp for a 30 amp shore or do you match 30 to 30?

Tom Wood responds:
For full disclosure, let me begin by saying that I am not a big fan of galvanic isolators. They are nothing more than a set of diodes placed in the ground wire of a three-wire AC line as close to the inlet as possible. The theory is that these diodes can open and close the circuit at a preset electrical potential, usually about one volt. This, again in theory, isolates the AC ground from the DC ground, eliminating the possibility of stray electric current from eating up zincs, shafts, props, and thru-hulls unless there is a major need for grounding, in which case the diodes open the ground circuit.

The reality is that many boats have numerous connections between the AC and DC grounds with generator, battery charger, or inverter installations, rendering the galvanic isolator useless. The systems make a proper lightning protection system impossible. And if the diodes fail one of two things happen: if they fail in the closed position, it's as if the galvanic isolator wasn't there at all, but if they fail in the open position, the risk of electrical shock becomes very real.

If you feel that you absolutely have to have them, you must have a separate galvanic isolator on each incoming power inlet. Each must be sized to be at least 25 percent larger than the maximum capacity of the master circuit breaker on the line, so a 30-amp line should have a galvanic isolator rated at a minimum of 37.5 amps—a 40-amp unit would be the best choice but a 50 would do the same thing. A 30-amp unit would work on a circuit with a 20-amp master breaker.


Tom Wood is offline  
Closed Thread

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Posting Rules  
You may not post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is Off
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome