knotflying
Well-known member
- Joined
- Jul 25, 2010
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- Fluid Motion Model
- C-28
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- Non-Fluid Motion Model
- 25' Parker & 246 Robalo Cayman
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- http://illusionsmikeandjess.blogspot.com
Here is a copy from a post on the American Great Looper site. I found it informative and important so I figured I would share it on this site.
Introduction:
Long post. I apologize in advance for the length. It's long because I've tried to be clear and thorough. I know most will not diagnose problems like this themselves, but periodically checking your own boats for this condition is something we can all do. I hope many on the listserv will benefit from what I've learned.
Executive Summary:
Some of you will remember that the ABYC offered a free "webinar" by Kevin Ritz on "Electric Shock Drowning" earlier in the season. When Sanctuary returned from cruising this summer, I took my hand-held clamp-on ammeter and walked the docks at our yacht club. I found that the clamp-on meter worked very, very well for the purpose of tracking down boats that are leaking current into the water.
Detail:
I have a Sears Model 82369 hand-held clamp-on meter. I like that particular meter because it has the capability to measure both AC and DC amps. The typical Lowes/Home Despot/ACE hdwr clamp-on meter versions are intended for home use, and usually do not have the capability to measure DC amps. The Sears unit is about $70, and competes with professional meters costing 3 times that amount. Even if you never used it to track down AC leakage currents, I find it extremely useful as a DC circuit diagnostic tool aboard the boat. Clamp-on meters are most usually used on both AC and DC to clamp around a *single conductor* to measure the current flowing in that one conductor. But when clamped over *all* of the wires in any one triplex AC cable ("Romex," etc), or any other configuration of AC or DC circuit, what happens is that the current returning to the source cancels out the current flowing out to the load. Thus, with everything working normally/correctly, the meter will read "zero" amps. Any non-zero meter reading indicates there is a "leakage" current; i.e., current going out in the hot wire that is not coming back to the source as it should. On a boat, in AC shore power lines, that means AC current going into the water.
The aforementioned ABYC webinar quoted a technician that in his experience as many as 10% of boats could have AC leakage problems. To test that statement, I walked the docks at our yacht club. After I zero'd the meter, I found most boats measured at less than about 0.06 - 0.08 amps, so 60 - 80 milliamps. I can't comment on the accuracy of the meter at that low current level, but since I saw a large sample size of different boats fit into that range or lower, I concluded it's OK. I will investigate that assumption further. Of about 80+ boats on our docks, I found four that had leakage currents of 0.25 amps AC or more. I found one with a leakage current of 2.5 amps, and the owner of that boat also told me his diver had reported that he'd gotten a "tingle" while cleaning the bottom and changing zincs. No one was hurt; thank heavens! We're in salty, brackish water on the Chesapeake Bay. But in fresh water, that could easily have been a lethal situation. The message is, my inexpensive Sears hand-held clamp-on meter had definitely identified, and confirmed, that there was a problem aboard that boat.
The boat itself is a 1970s vintage that has had a lot of modernizing work done over time. The modernization included adding a heat pump and a net-new AC shore power inlet circuit to power it. We could see on the clamp-on meter that when the heat pump came on, the leakage current was 2.5 amps, but when the heat pump cycled off, the leakage current went to "zero." So, armed with my meter, I clamped-on the cable supplying the circulator pump, but found no leakage. Then I checked the entire heat pump at the device: again, no leakage. That told me the leakage was occurring at an earlier point in the circuit, and not in the equipment itself. Next, we checked back at the inlet disconnect breaker, immediately aboard the boat: sure enough, 2.5 amps of leakage. Then we checked at the branch circuit breaker on the new AC panel that feeds the heat pump.
And there it was... Viola...
The hot line to the heat pump is served by a 20A circuit breaker, and the neutral and the safety ground were on adjacent, but separate, buss bars on the back of the panel, just as they are supposed to be. The original crimp of the terminal on the neutral wire was not made-up tight enough, and the neutral wire had vibrated out of the crimp terminal. Normally, that would just cause power to be lost to the heat pump, and the symptom would have been that it didn't work. But as amazing as these things can be, by coincidence, the loose neutral had come to rest lying on the adjacent safety ground buss bar. Thus, the heat pump and circulator ran normally, and no one aboard was aware there was any sort of problem. No circuit breaker blew. No loss of cooling/heating performance. Simply, no symptoms. But, the diver got zapped. Because the heat pump was running via the safety ground buss bar, current was also being dumped into the water. I repaired the bad crimp and presto, no more leakage.
And btw, if this boat had been fit with an ELCI (Equipment Leakage Circuit Interrupter), or if the dock had been fit with a marine-compliant GFCI protecting it, this problem could not have existed past it's inception, and an obvious potential shock safety problem would have been foreclosed, with appropriate warning to the boat owner and the marina.
The yacht club plans to have the maintenance crew carry a clamp-on meter with them when they do the monthly electric meter readings, and check every boat connection. Yes, this works on 120VAC and 240VAC shore power cord cables. We will do this until the shore side infrastructure is eventually upgraded. And for those who doubt the value of the work they do, it seems to me, at least, that what the ABYC is advocating with regard to ELCI devices is right on the money!
OK. Long story, I suppose, but it answers the question about the usefulness of a simple clamp-on ammeter. Yes! It works! And it works well!
I hope this is useful!
Introduction:
Long post. I apologize in advance for the length. It's long because I've tried to be clear and thorough. I know most will not diagnose problems like this themselves, but periodically checking your own boats for this condition is something we can all do. I hope many on the listserv will benefit from what I've learned.
Executive Summary:
Some of you will remember that the ABYC offered a free "webinar" by Kevin Ritz on "Electric Shock Drowning" earlier in the season. When Sanctuary returned from cruising this summer, I took my hand-held clamp-on ammeter and walked the docks at our yacht club. I found that the clamp-on meter worked very, very well for the purpose of tracking down boats that are leaking current into the water.
Detail:
I have a Sears Model 82369 hand-held clamp-on meter. I like that particular meter because it has the capability to measure both AC and DC amps. The typical Lowes/Home Despot/ACE hdwr clamp-on meter versions are intended for home use, and usually do not have the capability to measure DC amps. The Sears unit is about $70, and competes with professional meters costing 3 times that amount. Even if you never used it to track down AC leakage currents, I find it extremely useful as a DC circuit diagnostic tool aboard the boat. Clamp-on meters are most usually used on both AC and DC to clamp around a *single conductor* to measure the current flowing in that one conductor. But when clamped over *all* of the wires in any one triplex AC cable ("Romex," etc), or any other configuration of AC or DC circuit, what happens is that the current returning to the source cancels out the current flowing out to the load. Thus, with everything working normally/correctly, the meter will read "zero" amps. Any non-zero meter reading indicates there is a "leakage" current; i.e., current going out in the hot wire that is not coming back to the source as it should. On a boat, in AC shore power lines, that means AC current going into the water.
The aforementioned ABYC webinar quoted a technician that in his experience as many as 10% of boats could have AC leakage problems. To test that statement, I walked the docks at our yacht club. After I zero'd the meter, I found most boats measured at less than about 0.06 - 0.08 amps, so 60 - 80 milliamps. I can't comment on the accuracy of the meter at that low current level, but since I saw a large sample size of different boats fit into that range or lower, I concluded it's OK. I will investigate that assumption further. Of about 80+ boats on our docks, I found four that had leakage currents of 0.25 amps AC or more. I found one with a leakage current of 2.5 amps, and the owner of that boat also told me his diver had reported that he'd gotten a "tingle" while cleaning the bottom and changing zincs. No one was hurt; thank heavens! We're in salty, brackish water on the Chesapeake Bay. But in fresh water, that could easily have been a lethal situation. The message is, my inexpensive Sears hand-held clamp-on meter had definitely identified, and confirmed, that there was a problem aboard that boat.
The boat itself is a 1970s vintage that has had a lot of modernizing work done over time. The modernization included adding a heat pump and a net-new AC shore power inlet circuit to power it. We could see on the clamp-on meter that when the heat pump came on, the leakage current was 2.5 amps, but when the heat pump cycled off, the leakage current went to "zero." So, armed with my meter, I clamped-on the cable supplying the circulator pump, but found no leakage. Then I checked the entire heat pump at the device: again, no leakage. That told me the leakage was occurring at an earlier point in the circuit, and not in the equipment itself. Next, we checked back at the inlet disconnect breaker, immediately aboard the boat: sure enough, 2.5 amps of leakage. Then we checked at the branch circuit breaker on the new AC panel that feeds the heat pump.
And there it was... Viola...
The hot line to the heat pump is served by a 20A circuit breaker, and the neutral and the safety ground were on adjacent, but separate, buss bars on the back of the panel, just as they are supposed to be. The original crimp of the terminal on the neutral wire was not made-up tight enough, and the neutral wire had vibrated out of the crimp terminal. Normally, that would just cause power to be lost to the heat pump, and the symptom would have been that it didn't work. But as amazing as these things can be, by coincidence, the loose neutral had come to rest lying on the adjacent safety ground buss bar. Thus, the heat pump and circulator ran normally, and no one aboard was aware there was any sort of problem. No circuit breaker blew. No loss of cooling/heating performance. Simply, no symptoms. But, the diver got zapped. Because the heat pump was running via the safety ground buss bar, current was also being dumped into the water. I repaired the bad crimp and presto, no more leakage.
And btw, if this boat had been fit with an ELCI (Equipment Leakage Circuit Interrupter), or if the dock had been fit with a marine-compliant GFCI protecting it, this problem could not have existed past it's inception, and an obvious potential shock safety problem would have been foreclosed, with appropriate warning to the boat owner and the marina.
The yacht club plans to have the maintenance crew carry a clamp-on meter with them when they do the monthly electric meter readings, and check every boat connection. Yes, this works on 120VAC and 240VAC shore power cord cables. We will do this until the shore side infrastructure is eventually upgraded. And for those who doubt the value of the work they do, it seems to me, at least, that what the ABYC is advocating with regard to ELCI devices is right on the money!
OK. Long story, I suppose, but it answers the question about the usefulness of a simple clamp-on ammeter. Yes! It works! And it works well!
I hope this is useful!