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Thermal vs. Magnetic Circuit Breakers

Thermal circuit breakers respond to over-current situations, as their name implies, by the circuit generating an inordinate amount of heat causing the bimetal contacts inside the breaker to disengage due to unequal expansion. A magnetic circuit breaker responds to over-current situations by a loading coil inside the breaker lifting the contacts apart when the current flow through the coil is sufficient to overcome the spring force holding the contacts together.

Connecting and Disconnecting from Shore Power

There is a suggested sequence for connecting and disconnecting from shore power and sound reasoning for it. When connecting to shore power, first make sure the main AC disconnect switch is in the “off” position and connect to the boat side inlet before connecting to the...

Double Pole AC Circuit Breaker

Most boats have a shore power inlet to plug into dockside power. The power supplied is AC (alternating current), and it is usually available in 240V/120V, with a 30A, 50A or 100A service offered. Most mid-sized boats (32 to 45 foot) will have a 30A inlet installed, as original equipment...

Fusing Electric Motor Circuits

Generally electric motors have their own over-current device. When this is not the case the fuse or breaker should be rated to the full load potential of the motor (provided that the wires run for the circuit are adequate). These breakers or fuses need...

Improper Fusing: Common Reason for Fires on Boats

Preventing fires in general is very important, but it is even more important while on a boat. The reason for this is that unlike a house, a boat is hard to escape from if it is on fire. And it is important to note that boat fires are commonly caused by electrical issues!

Keeping Clear

We all know storage space on boats is hard to find and easy to fill. When storing gear on boats we need to think about the items we are covering up.

Cover Up!

From time to time we come across situations that scream danger! One of these situations is when we see AC outlets and AC Switchboards that haven't been covered up from behind, or the backing cover hasn't been put back on after being worked on. AC outlets with no backing cover are very dangerous for many reasons.

Getting the Most Out of Your Switches and Breakers

Recently, while I was working on a client's boat, they commented on the battery On/Off switch. They were particularly curious about the labels on the terminals in the back. One terminal said "Battery" and the other was labelled "Load". "If the switch is just on and off does it really matter which side the battery is attached to?" they asked. Yes, it does matter.

Multiple Downstream Fast-blow and Slow-blow Fuses

It is normally necessary to have multiple fuses or breakers downstream of each other. For example, you might have a main battery fuse, a main DC panel breaker, and individual breakers for each circuit on a panel. From one circuit you might have a couple of fuses downstream if you're feeding multiple devices off one breaker, like a chartplotter and GPS.

The Importance of Proper Wire Colours

The other day PYS was sent to troubleshoot a boat that had recently changed marinas. At the new marina, the dockside shore power breaker tripped every time the boat was plugged in; however, they had had no problems at the past marina. The vessel was a small sailboat with only 3 AC circuits so there wasn't a lot to troubleshoot.

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