|Topic Review (Newest First)|
|09-16-2008 08:25 PM|
|GaryHLucas||If there are a large number of failures, then I'd autopsy one of the ones that failed. It should be easy to cut the connector apart and see how the connection to the wire is made, terminal screw, crimped, or soldered. You probably also can tell where the failure started, because that is likely to have been the hottest part. Charring as opposed to just melting and dis-coloring.|
|09-16-2008 05:33 PM|
|ebs001||Gary, the cord ends are only failing on the female cap and only on the neutral. In CDs case he isn't in salt water. Cam, mentioned, that he has seen a large number and it's only on the 30amp cordsets; not the 50amp cordsets. I think still the problem is a mechanical one as I've stated above - the design of the cordset does not allow sufficient surface area contact. I have written ti Marinco. If I cannot get a satisfactory answer from them I will be contacting CSA (the Canadian equivelent of UL).|
|09-15-2008 07:20 PM|
I'm an electrical guy. The way those cord ends failed is exactly the way I would expect them to fail. The exposed ends pick up salt and other contaminents and increase the resistance. They heat up a little and the resistance increases even more until they burn up. Keeping them very clean is about all you can do. A stainless steel wire brush is the best thing for cleaning the male ends. It would also be good ide to put a little penetrox antioxidant on the male prongs. It'll slow down the corrosion and lubricate the contacts making it MUCH easier to plug them in and twist lock.
Second thing. This is called a high resistance fault, which means the current will be low. Thus it will never trip the breaker, and there is no device that will detect the problem unless it is actually arcing.
|09-13-2008 11:04 PM|
|sailaway21||SemiJim's point can be made, I think, by noting that if 240V is normally supplied to a circuit panel and one leg of the 120V is interrupted, the other leg of 120V will back feed the dead 120V leg through either any 240V appliance or any appliance on the live 120V leg that has the polarity reversed in it's wiring (commonly the plug). Note that the neutral now carries the current to the dead leg. We run into this during lightning storms when one breaker trips at the street power pole and the house is getting only one leg of the 240V service yet everything in the house on 120V is working. Separate the contacts to the 240V water pump pressure switch and half the house goes out. I'm not sure of the significance of this to the current discussion though.|
|09-13-2008 08:24 PM|
Littlewing---Generally voltage drop does not become a factor until distances greater than 100' are achieved (120volts). At that point for every additional 100' an increase in wire size of one gauge will take care of VD (not the disease). And yes I am familiar with the VD formula, and so are the students I taught long ago. I strongly doubt that many posters here are using Marinco cordsets nearing the 100' distance. Nor do I think that solid wire is being used in the shore power cords. Keeping those facts in mind...Ebs is correct in stating that the #10 wire used in the cords is rated for the full 30 amps. I disagree with him on the 80% rule on breakers though.
The harmonics theory is interesting except that does not explain the more recent cord end failure unless newer battery chargers or some other piece of equipment is creating increased harmonics.
Maybe it is designed failure so we can all go out and buy more cord ends.
|09-13-2008 02:32 AM|
|ebs001||Littlewing, the length comes into place because of voltage drop, not heat. Regardless we are looking at the failure in the female cap of the cord sets and my feeling is the problem occurs because of the mechanical connection and not because an electrical problem ie the surface area contact on the neutral is simply not large enough. I asked earlier if anyone has encountered similiar problems with the 30a/125v receptacle because it appears so far that they are able to manufacture a receptacle where this is not a problem and therefore should be able to produce a female cap that also will not fail at the rate it is now.|
|09-12-2008 11:52 PM|
LittleWing, Wire is rated to handle the full load, in this case #10 is rated to handle 30 amps. Breakers are subject to the 80% rule. The shear numbers indicate something other than simple overloads or running near the maximum. I think you'll find that at least one of CD's powercords was used for his A/C unit which probably draws about 15 amps well below the 80% rule and still he had failure. It appears we are basically talking about failures under conditions which should not cause a failure.
The thought of harmonics intrigues me but it I think it would only be a consideration for a neutral carrying the unbalanced load and not a branch circuit although I'm not 100% sure on this. In buildings the neutral on the power panels feeds are now double the size of the line wires to handle the harmonic increase in amperage flowing through the neutral. It sure would explain a lot - now you have a neutral carrying twice as much current as your expecting. Just musing I think, though.
|09-12-2008 06:41 PM|
|ebs001||I have just sent an email to Marinco asking about this problem. I'll let everyone know once I get their answer.|
|09-12-2008 06:07 PM|
With AC circuits a max load is about 80% (24 amps on a 30)
The breaker should be tripping pretty close to 30 amps on a 30 amp circuit
Depending on how the dock is wired i would venture to guess a lot of the feeds are on the LONG side buy the time you go through the shore power cord, you should really be checking what kind of voltage drop you getting under your peak load at the panel in the boat
We run a lot of 500/1000/1500 watt heat bands to warm chemical drums and you can buy the best Hubble 115 volt 20 amp plugs they make and if use the 1500 watt setting the plug life will shorten dramatically
|09-12-2008 05:09 PM|
Jazus the Dock Monitor sure did open a can of worms with this one.
Can we just call this "Solar Stick 2"?
And by the way, don't you have a hurricane to duck from?
Make sure you unplug the boat before she hits!
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