T&T: Galvanic Isolator and ABYC standard
Jim Gano via Trawlers-and-Trawlering
All the units I could find that say "fail safe" in their literature were on the high price side.... yet most had the same basic design as the Newmar product I was investigating... I was advised to ask Newmar directly about their product so I did....
My question to Newmar:“are the GI-50 galvanic isolators failsafe... that is, if the internal components (diodes) of the unit fail, will theunit basically connect the ground wire in the boat and the ground wire on shoretogether (and no longer act as an isolator)?”Answer from Newmar:“The galvanic isolator has for additionalsafety, all units feature a large capacitor, providing a secondary lowimpedance path for sending AC current to ground.”My follow-up question to Newmar:“Thanks.. so the safety capacitor is big enough tosupport 135% of rated current even if one of the diodes has malfunctioned?”Answer back from Newmar:“Yes it will support that rating. It wasoriginally designed around the spec for ABYC standards but they were thenchanged to have something that also monitored the system periodically. So wedecided to not peruse the certification.”This latter statement from Newmar confusesme. The DEI, the Guest, the Prosafeand DEI Galvanic isolators do not have “something that also monitored the systemperiodically”. The only way to test ALLGalvanic isolators that I can find is to disconnect shore power and then testthe diodes with a multimeter… Manually… Please correct me if there is an isolatorwith a status light,,, meter,,, whatever… to tell me it is functioning.. That is, when I am on my boat I want to lookat a light or meter that tells me the unit is “Galvanically” protecting my fiberglassboat’s metal components AND providing a safe ground so I will not electrocutemyself or my guests onboard.I have no financial interest in Newmar andhave never owned one of their products. Newmar at $215 price… versus $325 for Guest… versus $345 for Prosafe.. versus $430 for DEI They all seem to have the same specs andoperational capabilities…So I am now leaning toward Newmar..
Jim Gano
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AnnMarie--- via Trawlers-and-Trawlering
connection to underwater metal in the event of a diode failure so that
swimmers in the vicinity won't get electrocuted. The worst case
scenario, which is not uncommon, is a mis-wired boat that is using the
ground instead of the neutral for the AC return path. It is this
scenario that influences the 135% of rated current specification by ABYC
for galvanic isolators.
A voltage trasient of just 2 volts AC per foot in fresh water can
deliver sufficient current to kill a swimmer who bridges it. (REF a good
BoatUS article worth reading at
http://www.boatus.com/seaworthy/assets/pdf/electric-shock-drowning-explained.pdf.)
To keep the voltage safe if the diodes have failed the voltage should be
less than 2 * distance to dock, boat or other in-water ground. For an
assumed current path distance of 10 feet the AC leakage on the boat
should be less than 20 volts. Worst case could be even closer than 10 feet.
For a capacitor on a 50 amp isolator to keep underwater metal below 20
volts at ABYC specification of 135% rated current its impedance would
have to be 20/67.5 = 0.3 ohms.
Using the formula for capacitor impedance at 60 Hz to produce a
resistance lower than 0.3 would require a 10,000 uF capacitor rated at
120 volts AC minimum.
For example, a motor starting capacitor at 25 uF is about the size of a
can of Coke. To have a 10,000 uF capacitor in a Galvanic Isolator it
would have to be the size of 400 cans of coke. The heat generated in
the capacitor would be over 1,250 watts.
There is no way the capacitors in Galvanic Isolators make them fail
safe. They contain a "token" capacitor so they can be advertised as
complying. Again I challenge you to get the capacitor size
specification in ANY brand of galvanic isolator and do your own
calculations.
Ann-Marie
On 6/6/2016 4:55 PM, Jim Gano via Trawlers-and-Trawlering wrote:
> <SNIP”My follow-up question to Newmar:“Thanks.. so the safety capacitor is big enough tosupport 135% of rated current even if one of the diodes has malfunctioned?”Answer back from Newmar:“Yes it will support that rating. It wasoriginally designed around the spec for ABYC standards but they were thenchanged to have something that also monitored the system periodically. So wedecided to not peruse the certification.”<SNIP>
Jim Healy via Trawlers-and-Trawlering
Comments imbedded below, indicated by --> or IN ALL CAPS...
All the units I could find that say "fail safe" in their literature were on the high price side.... yet most had the same basic design as the Newmar product I was investigating...???
--> True! Technology-wise, not a huge change; liability-wise - device lives in the AC Safety Ground circuit - much more exposure and risk. Just my supposition, but how many product-liability stories have you seen in your adult life? Look what happened to McDonald's over a hot cup of coffee and an extraordinarily stupid human being...
I was advised to ask Newmar directly about their product so I did.... (I DID; I'M GLAD YOU DID.)
My question to Newmar:?are the GI-50 galvanic isolators failsafe... that is, if the internal components (diodes) of the unit fail, will theunit basically connect the ground wire in the boat and the ground wire on shoretogether (and no longer act as an isolator)??Answer from Newmar:?The galvanic isolator has for additionalsafety, all units feature a large capacitor, providing a secondary lowimpedance path for sending AC current to ground.? (DID YOU NOTICE, THEY DON'T SAY "YES" AND THEY DON'T SAY "NO?" DID YOU NOTICE, THEY DIDN'T ANSWER THE QUESTION YOU ASKED? WEASEL WORDS; ALLOWS YOU TO THINK YOU'RE GETTING WHAT YOU WANT. NON-ANSWER TO THE QUESTION YOU ASKED. DID THEY SAY IT COMPLIES TO ABYC, A-28, JULY, 2008? NO, JIM, THEY DID NOT). My follow-up question to Newmar:?Thanks.. so the safety capacitor is big enough tosupport 135% of rated current even if one of the diodes has malfunctioned??
--> I never did find that 135% language in the current ABYC standard. The tests I posted yesterday are what it contains. Still own the to-do to search that one further...
Answer back from Newmar:?Yes it will support that rating. It wasoriginally designed around the spec for ABYC standards (GENERATION ONE GI DEVICE STANDARD, AS DEFINED IN MY PREVIOUS EMAIL) but they (MEANING "ABYC") were thenchanged to have something that also monitored the system periodically (REFERRING HERE TO THE GENERATION TWO GI DEVICES). So wedecided to not peruse the certification.? (THAT'S BECAUSE THE PRICE-POINT WENT FROM $75 TO $600; ONLY PROMARINER MADE THAT INVESTMENT THAT I KNOW OF; DEI AND GUEST DID NOT. NEWMAR DID NOT. CLEARLY, GUEST, DEI & NEWMAR MADE A BUSINESS DECISION THAT THERE WAS NO ROI AT THAT PRICE-POINT TO RECOVER THEIR INVESTMENT, AND THEY CHOSE NOT TO ENGAGE THAT MARKET. THEY ARE NOW SELLING THEIR ORIGINAL - NOW NON-COMPLIANT - UNITS, WITH CAPACITOR ADDED, INTO THE MARKETPLACE. BUYER BEWARE).
--> Small point further to the term "certification." "Certification" is not a term that applies to ABYC. ABYC does NOT "certify" products or manufacturers. What the ABYC standards do is refer to UL testing standards. So "certification" for marine devices electrical and electronic devices really means, complies to UL-xxx.
This latter statement from Newmar confusesme.? The DEI, the Guest,?the Prosafeand DEI Galvanic isolators do not have ?something that also monitored the systemperiodically?.? (ONLY PROMARINER THAT I KNOW OF; THE PROSAFE 1 COMPLIES TO THE ABYC GENERATION TWO STANDARD. PERHAPS ANN-MARIE KNOWS OF OTHERS). The only way to test ALLGalvanic isolators that I can find is to disconnect shore power and then testthe diodes with a multimeter? Manually? (CORRECT.) Please correct me if there is an isolatorwith a status light,,, meter,,, whatever? to tell me it is functioning..? (YES; THE PROMARINER PROSAFE1 IS A GENERATION TWO DEVICE THAT DID THAT. IT APPLIES A GROUND FAULT THAT MAKES IT INCOMPATIBLE WITH THE NEW SHORE POWER SYSTEMS, WHICH IS WHY YOU DO NOT WANT IT TODAY). That is, when I am on my boat I want to lookat a light or meter that tells me the unit is ?Galvanically? protecting my fiberglassboat?s metal components AND providing a safe ground so I will not electrocutemyself or my guests onboard.I have no financial interest in Newmar andhave never owned one of their products.?Newmar at $215 price? versus $325 for Guest? versus $345 for Prosafe.. versus $430 for DEI They all seem to have the same specs andoperational capabilities?So I am now leaning toward Newmar.
--> My opinion: you are squeezing the buffalo too tightly on this one. Get a UL tested, compliant, THIRD-GENERATION fail-safe certified device. Make your insurance carrier happy. Make your next surveyor happy. It will never be any less expensive than it is today.
All those question marks in your post, above, are punctuation and/or special characters the T&T list couldn't interpret correctly. Apparently including your "return" key...
Peg and Jim Healy aboard Sanctuary, currently at Charlotte Harbor, Punta Gorda, FL
http://gilwellbear.wordpress.com
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