Oily Matters Page 2
Q & A — October 2001
By Capt. Ken Kreisler
2: An electrical leak, shore-power cord corrosion
I have a battery that seems to be continually discharging, and I suspect I may have an electrical leak somewhere aboard. How can I check this out? J.W., via e-mail
An electrical leak is when unwanted current flows to ground, often in amounts too small to produce a short circuit. Some common causes include corrosion, a poor connection, dampness, and worn insulation.
To troubleshoot this problem, first turn off all your boat's circuits and remove your battery's positive cable. Set your multimeter to "d.c. volts," and measure the voltage between your battery's positive terminal and the positive battery cable. If the voltage on your meter reads 12 volts, there is still a load on the circuit. If all loads are disconnected and the meter still registers a voltage reading, you've got an electrical leak.
Switch your meter to "d.c. amps" to measure current, and set it to the highest range so it won't be damaged should there be a high-amperage leak. Measure the amperage between the positive battery terminal and the positive battery cable. A reading of more than 1.0 amperes means there is still a load on the circuit. Readings between 1.0 and 0.001 amperes indicate a major electrical leak. A reading of less than 0.001 amperes is a small leak.
If you detect a leak, first check and clean your battery terminals, cables, switches, and connections. Then, one at a time, pull each fuse or shut off each circuit breaker until your meter reading drops to zero. When it does, you've found your leak.
I'm currently living aboard my boat and want to know how to prevent corrosion from accumulating on my shore-power cord. C.P., via e-mail
Corrosion is an ongoing problem with marine electrical equipment and left unchecked can lead to dangerous shock, stray-current corrosion, and equipment damage and failure.
As part of your regular maintenance regimen, you should check all your connections weekly, if not daily. If you are going to be away from your boat for any length of time, have someone make sure your plug is free from corrosion.
One common source of corrosion is the inadvertent dunking. If your power cord is kicked overboard, immediately shut off the power. Wash the cord with fresh water, and let it dry thoroughly. (If you don't have a spare cord, this may be the time to invest in one.) Once it's dry, spray the contacts with contact cleaner. This will also help to remove any moisture. Also, using the cord's sealing collars--especially between an adapter and the cord--will prevent rain water and minor splashes such as when you or your dock neighbor are washing down from getting inside the connector.
While you cannot see inside a properly sealed shore-power cord, you should be aware that corroded terminals may be symptomatic of internal problems such as loose terminals and inferior wire stripping, any of which can lead to overheating and even fire. For this reason periodically check both male and female connections for signs of overheating such as discoloration.
Marinco Phone: (800) 307-6702, one of the industry's largest manufacturers of powercords and connectors, publishes its Boater's Guide to AC Electrical Systems, which will give you some additional information.
Need help with a maintenance problem? Write to Maintenance Q & A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: firstname.lastname@example.org. No phone calls, please.
This article originally appeared in the June 2003 issue of Power & Motoryacht magazine.