More on Galvanic Isolation...

[Bacchus]

Hi

There is a wealth of information on this site regarding Galvanic Isolation including this (http://www.canalworld.net/forums/index.php?showtopic=6101&page=1) legendary thread from a few years ago for which I am waiting to come out in Kindle format! I have trawled around tyring to find a solution to an issue that I have, but so far to no avail.

The issue is this; I fitted a Galvanic Isolator to my boat last weekend, putting it inline in the earth wire of the incoming shore power lead. I tested it with my good old avo-meter, and it seems to be up and running, BUT when the boat is plugged into a normal domestic RCD, the supply switch trips periodically - maybe after an hour, maybe after several hours.

The shore power on my boat is fairly basic, an incoming lead goes to a fused junction box from which leads are run to two plug sockets, a lamp, and a battery charger, the only thing connected is the battery charger. I have read about Switched Mode and understand that it is possible for some equipment to "dump" current to Earth to suppress RFI, and I think the domestic RCD trips if it detects current on the Earth side (I used to live in a damp old house where this happened quite regularly) so this MAY be a problem, but it never happened before the GI was fitted, and I fail to understand how the GI could cause this??

I was wondering whether any of the forum Physicists or social sparkies are able to explain this? Have I done something wrong? More importantly can I resolve it?

[nicknorman]

Loads of people have GIs and never get an RCD trip, including us. It's hard to see how your problem can be caused by the presence of the GI. SMPS Earth current should be much less than the 30mA or so required to trip an RCD.

I would try disconnecting the earth wires from the GI and connecting them together, the see if the RCD still trips. It is not beyond the bounds of possibility that there is a coincidental fault.

 

It looks like you don't have a conventional narrowboat but do you have a steel hull? I'm just wondering if you have fitted the GI directly onto the steelwork and thus have somehow introduced a connection between hull and earth that didn't previously exist thus highlighting a pre-existing fault. Obviously the hull should be earthed anyway and I don't think the GIs case/heatsink should be connected to either terminal but I can't think of anything else to suggest.

Edited April 10, 2015 by nicknorman

[Bacchus]

Hi Nicknorman

 

Boat is a Dutch Steel Cruiser, not a narrow boat.

 

I am at a bit of a loss with this; the boat is on a home mooring so I have used the same domestic supply (and the same shore-power lead which is a "pukka" metred one) since I bought the boat two years ago, and this has never happened; the only change is the introduction of the GI (which is mounted on a wooden bulkhead behind the saloon seating) - actually not strictly true, I have "scarfed" in an extra metre of cable to run the supply to a convenient point on the bulkhead, but that is connected via normal terminal connectors in insulated junction boxes and also screwed onto wood.

 

It's very bizarre. Also doesn't happen immediately. I did notice it trip yesterday when a large barge went past, which may or may not have been a coincidence. On the first day I fitted it, it happened during the night so at least eight hours after connecting.

 

I can only think that it's the battery charger (which is proper "Sterling" jobbie, not a Christmas cracker one from the market), but I can't think why...

 

[edit]but, yeah, I guess the next step would be to bypass the GI to make absolutely sure that something else hasn't been introduced[/edit]

Edited April 10, 2015 by Bacchus

[smileypete]

It's very bizarre. Also doesn't happen immediately. I did notice it trip yesterday when a large barge went past, which may or may not have been a coincidence. On the first day I fitted it, it happened during the night so at least eight hours after connecting.

 

Could be a loose connection, which can cause nuisance trips.

 

Neighbour had tripping RCD nightmares, turned out to be a loose connection in the bollard. Gently tapping the bollard would make the RCD trip!

 

cheers, Pete.

~smpt~

[Bacchus]

 

Could be a loose connection, which can cause nuisance trips.

 

Neighbour had tripping RCD nightmares, turned out to be a loose connection in the bollard. Gently tapping the bollard would make the RCD trip!

 

cheers, Pete.

~smpt~

 

 

That might be something; the male/boatside connector is "scheduled for replacement", although this wouldn't fully explain why it never happened pre-galvanic isolator (actually, technically, it did trip once when some builders left the loose end dangling in the river...)