Galvanic Corrosion

How about studying Kirchoff's law untill you can write a book about it. (Just please don't publish it). Before writing first page you will be able to answer your question. S.M.

With the generator not running (and assuming it is an isolated ie not grid connected) generator.

I don't see the voltage source except as you said the galvanic.

The other sources would be too negligible to measure (eg the thromocouple effects etc). But your post indicate you are getting some. How much?

The generators I'm referring to are on aluminum offshore work boats with a system voltage of 120/208v, 3 ph, 4 w. What I'm trying to determine is how many mv are generated from the neutral to the switchboard ground to determinine if I should put a galvanic isolator in the neutrals. I don't know how much voltage as I have no way to measure it at this time.

Thanks,

Here is my take on this thread..... From what I can understand, you have a 3 phase 4 wire system, and, I am assuming that your neutral is not earthed? It is usual on a ship to then use a 4 pole circuit breaker, which is open when the generator is stopped, isolating the 3 phases, and the neutral. With the generator stopped, there would be no voltage between the generator centre tap (neutral point) and the ship's hull (earth). However, I have seen a 4 wire system with only a 3 pole CB, the neutral line still connected when the generator was stopped. If an earth fault develops on this system, between one phase and earth, the neutral voltage could "float" up above zero, and there would be a current path from your recently grounded centre tap, and back down the neutral cable to the running generator.

For info, and I am sure BV Rules would be similar, Lloyds Register Rules state "No fuse , non linked switch, or non linked circuit breaker is to be fitted in an earthed conductor. Any switch or circuit breaker fitted is to operate simultaneously in the earthed and non earthed conductors"

Also, " A means of isolation is to be fitted in the earthing connection of each generator so that the generator can be isolated for maintenance".

This would read to me that you need to use a 4 pole circuit breaker in you generator, but I could be wrong....?

No, the neutral is grounded at the neutral bus and is used to monitor grounds as well. My question is can a generator copper windings, without power, induce a stray current to ground in order me to determine if I need to put a galvanic isolator on the neutral ground.

The reason I'm curious is BV punched me on making sure the gen. neutral disc. switches are open while on shore power.