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Larry wrote:
"Glenn Ashmore" wrote in news:l_2kg.112247$Ce1.77235 @dukeread01: http://www.bluesea.com/Article_detai..._ID=290&id=299 What this manufacturer of diode isolators DOESN'T tell you is that their product does NOT protect your underwater metal parts from AC LEAKAGE caused by connecting this wire. These "isolators" are simply two rows of silicon diodes in series with the boat's ground wire. Like this: |--|-|-|-------| ac gnd--| |----boat gnd |--|-|-|-------| Each diode has a forward breakover voltage of around .6V. By having two rows in parallel, either a positive or negative voltage over, in my example, 1.8V (AC or DC it matters not) across the device will make it conduct. 120VAC will make one row conduct on one half cycle, the other on the other half cycle, a virtual short if there is any kind of short OR AC LEAKAGE in any appliance. Any leakage that will trip a GFCI, for instance, will make this device ALWAYS conduct, rendering it useless, a fact Blue Sea will never tell you, of course. Once it is conducting the AC leakage current from the hot water heater's leaky element to the grounded cabinet of the hot water heater, all the DC electrolysis currents it blocked destroying your prop and zincs now pass through it as if it never existed. The AC current through it provide the breakover voltage that was supposed to block the electrolysis currents...either way. GFCI protection at the pedestal of the neighboring boat causing the problem would have prevented the problem at the source if it were a 125 volt circuit. The solution to THIS malady is an isolation transformer of sufficient power to isolate the boat without overheating, itself. Big yachts have them in the bilge. They're beasts humming away in my bud's Hat 56 FBMY. The only connection between the power company and a boat protected by an isolation transformer is magnetic power in the core. NO DC current can pass between the windings, at all, even if the hot water heater leaks like a sieve. By the way, if the boat had had an isolation transformer, the only way the kids would have gotten shocked is if TWO appliances connected to the water had a short on L1 on one of them and L2 on the other. The whole AC power system on the secondary of the isolation transformer has NO PATH to earth. The only way you can get shocked is if you get right across the AC power leads, L1 to L2. Too bad the whole power grid doesn't simply have NEUTRAL isolated from ground, making it impossible to get a shock by touching one of the wires and ground. ABYC and common sense would have you ground the neutral of the isolation transformer secondary and use that as your equipment grounding conductor. That way you remain isolated from the AC systems of the rest of the world, but you maintain the safety benefit of equipment grounding. Even GFCI protection on the secondary wouldn't work without that ground. You don't need the green wire for GFCI to detect a ground fault, but you DO need a connection to "ground" for a ground fault to occur. So if you leave off a secondary ground, you prevent ground faults by allowing the hot wire to short to an equipment cabinet undetected! Not likely to be very popular, Larry. Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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