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Ten Deadly Conditions to Check for in Your Boat's Electrical System
~ Part 1
Blue Sea Systems’ engineering department has identified 10 conditions that, when present in your boat’s electrical system
, can cause serious problems. Five of these conditions are presented here. The second five will be presented in the October newsletter.
1. Incorrectly sized wire
There are several problems that occur when sizing wire for a boat’s electrical system
using the ABYC 105̊C tables:
• Using wire with less than 105̊C insulation
• Bundling wires together or burying them in thermal insulation
However, usually wire size isn't a problem because:
• Most DC large loads are short term.
• Most DC wire is chosen for voltage drop and is therefore larger than the minimum recommendations from the ABYC tables.
2. Running fuses continuously at full ratings
When matching circuit protection to the wire it protects, two facts contribute to the complexity of this task:
• The amperage at which fuses
actually blow, and circuit breakers actually trip, is considerably higher than their nominal ratings, the rating usually marked on the unit.
• Wire and circuit protection devices heat up dramatically when they carry 100% of their rated value for several minutes or more.
3. Not using the shore power cord locking ring
The shore power
cord locking ring maintains a solid connection between the power cord plug
receptacle. When this connection isn’t secure, motion can cause the plug
to wiggle back and forth in the receptacle, compromise the electrical
connection, and result in dangerous heating
4. No “Green Wire” or poor-quality connection between DC negative and AC safety ground
Without a good connection between DC negative and AC safety
ground, stray AC current
may enter the DC ground system. When this happens, AC current
may enter the water
around a boat and injure or kill swimmers near the boat.
The green wire can be tested and indicate continuity but be unable to safely carry enough current to trip a circuit breaker during a fault. There are ways to check the quality of the connection.
5. Using ordinary plug-in AC receptacle testers to check ground integrity
Ordinary plug-in AC receptacle testers are so sensitive that they will indicate a good ground even if the only connection is through a prop shaft or thru-hull fitting to water
. A better way to test for ground integrity is to connect the shore cord to the boat and bring the shore plug back to a position near the electrical panel. With all on-board AC sources turned off, use an Ohm meter to check that the ground prong is solidly connected to the boat’s safety ground system. Check to the “U” ground at each receptacle by dragging around the shore cord end and meter to test at each receptacle.
Avoiding these deadly conditions will make your boating
experience far more safe and pleasurable. Take time to check your boat’s electrical system and look for these conditions. Contact your local ABYC electrician.