Electrical safety ground

[Royce]

I read an article in the current CW mag about electrical safety grounds for the AC system. I do not have the AC ground connected to the DC ground or rig bonding grid. I did this to prevent setting up currents with my neighbors boat. I have not had any electrolisis problems in the 10 years I've owned the boat. In the article the author advises against this for saftey reasons. He advocates using an isolation transformer, which I agree would be fine if not for the weight and cost of one. He uses an example of an experience in a boat that had the ground connected, but was not making good connection at the plug, and a defective microwave that had a hot to ground short inside. The shell of the microwave thus became live and a slight shock was felt from it. A isolation transformer would have eliminated the problem of a bad connection on the dock plug. I've delt with this problem in another way and was wondering how some of you have delt with it. First, I have gfi outlets in ALL my outlets on the boat. A shorted microwave should trip that. Secondly, if you connected your dc ground, bonding, and ac ground and you have a bad ground connection to shore power and you have a defective onboard device which results in a hot to ground short, you would end up with everything that was bonded becomeing "live". Maybe I'm wrong on this, but thats how I see it happening. Let me know what you think.Royce

 

[Steve Humenick.]

Galvanic Isolator

What you need is a 'Galvanic Isolator' to connect the DC common and bonding system to the AC shore power ground (green wire). This will block the DC currents that cause electrolosis while safely passing AC current should an AC fault, like the microwave example, occur. A GFI receptacle needs a ground connection since it 'trips' when it senses AC current flow in the ground wire. Boat US and West Marine have 30 Amp galvanic isolators for about $160.

 

[Royce]

GFI

GFI's will work without using the ground, otherwise they would be of no use on a electrical device with only a 2 prong plug. They work by detecting minute differences in current between the "Hot" wire and the "Nuetral" wire. When an electral shock occurs, current is flowing from the hot conductor thru you to a ground. This will cause a difference in current between the hot and neutral (which should be the same) and result in a trip. The article in CW metioned galvinac isolators and claimed they did not eliminate but only reduced the stray currents.I don't see why using GFI's and keeping the grounds seperate isn't a viable solution and still just as safe.Thanks,Royce

 

[chet p]

galvanic isolator

go to www.jackrabbitmarine.com and get a 30A isolator for about $89... it is called a ZINCSAVER II same thing but cheaper (not from west)