After having been fooled by another bit of wisdom that seemed to be
accepted by all the top authorities (NPT onto NPS through hull
fittings), I'd like to get some real world ground truthing on
another.

Calder strongly recommends galvanic isolators with a monitoring
function to verify that moisture, AC ripple leakage, or other problems
have not disabled the diodes. The epoxy encapsulated units seemed to
be coming on the market just as the second edition of his book came
out.

Has anyone experienced failure or leakage of the new generation such
as the Guest 2433?
Is the extra 70 bucks for the monitoring belt and suspenders?

Calder also recommends and alludes to new ABYC requirements for the GA
capacity to be 1.3 times the shorepower connection. Does that mean
that the Guest unit which is ABYC approved does have the extra margin
or should I spend even more and get the 50A unit?

--

Roger Long

Hello Roger,

I'll defer to others on some of your questions, but I can
offer this.

Silicon power diodes tend to be very reliable, especially if
they are not stressed. The good news is that in normal
operation as a galvanic isolator, they are not likely to be
stressed. The bad news is that while lightning may cause a
diode failure, it can also cause a failure in the monitoring
circuit. So it's not quite belt and suspenders which
presumably have entirely independent failure probabilities.

Isolator failure can be due to a shorted diode, in which
case you get no galvanic current protection, or due to an
open diode, which is a bad thing for safety. Even though
such failures are likely to be extremely rare (you won't get
a reliable estimate of failure probabilities from this
group) they are nonetheless important when they happen.
Maybe even critical. So the issue isn't whether to monitor.
You definitely should. The question is how often, and
whether you do it manually or by machine. Sort of like all
the other safety checks you should be doing at home and on
your boat, except that a diode failure will usually not be a
gradual event like rotting or corrosion that can reasonably
be checked twice a season or so.

Whether it is worth the cost for the built-in monitoring,
you'll have to judge.

Regarding the diode current rating, I simply cannot imagine
what you would be doing to get anything like 50 amperes in
your green wire. If there is leakage to ground on your boat,
your GFI protection (cheap and very important) will trip at
a mere 5 milliamperes! If you're getting 50 amperes due to
some other external problem, I'd sure like to know what that
might be. Galvanic current (which is the main culprit you're
trying to eliminate) will be in the milliamperes unless
maybe your zincs are protecting a nearby, unprotected
battleship in seawater at the same marina.

More important than continuous current carrying capacity is
short-circuit current capacity. Again, your GFI should trip
well before your main AC breaker, but if it doesn't, then
the diode may need to carry as much as 5,000 amperes for a
fraction of a second until the breaker trips. Not a
particularly difficult spec to meet.

Good luck with yet another boating decision for which the
information to support a rational decision is unavailable,
unreliable, or far too expensive.

Chuck






Roger Long wrote:
After having been fooled by another bit of wisdom that seemed to be
accepted by all the top authorities (NPT onto NPS through hull
fittings), I'd like to get some real world ground truthing on
another.

Calder strongly recommends galvanic isolators with a monitoring
function to verify that moisture, AC ripple leakage, or other problems
have not disabled the diodes. The epoxy encapsulated units seemed to
be coming on the market just as the second edition of his book came
out.

Has anyone experienced failure or leakage of the new generation such
as the Guest 2433?
Is the extra 70 bucks for the monitoring belt and suspenders?

Calder also recommends and alludes to new ABYC requirements for the GA
capacity to be 1.3 times the shorepower connection. Does that mean
that the Guest unit which is ABYC approved does have the extra margin
or should I spend even more and get the 50A unit?