DC Main Overcurrent Protection Requirements
ABYC standard E11.12.1.1.1 states that each ungrounded conductor connected to a battery charger, alternator, or other charging source, shall be provided with overcurrent protection within a distance of seven inches (175mm) of the point of connection to the DC electrical system or to the battery.
The exceptions to this are:
• When the conductor is enclosed in a sheath or enclosure such as conduit in addition to its insulation the 7" dimensions can be increased to 40".
• If the conductor is connected directly to the battery terminal and is enclosed in a sheath or enclosure such as conduit in addition to its insulation the 7" dimension can be increased to 72".
• The conductor connects to the starter for the engine.
Figure 1 below shows the location of the circuit protection devices per ABYC standard E11.12.1.1.1
Figure 1
Any devices connected directly to the battery such as bow thrusters and windlasses are required to have a circuit protection device installed per the same guidelines above.
ST (Screw Terminal) Blade Fuse Block
The ST (Screw Terminal) Blade Fuse Block was designed with screw terminals to comply with ABYC Recommended Practices and built with tin plated copper components for improved conductivity and lower operating temperatures. A cover comes standard with each model to protect the conductive surfaces from accidental shorting, label each circuit and store spare fuses.
The ST Blade Fuse Block is ideal for use as a sub-panel in the DC distribution system. This solves the problem of large and expensive circuit breaker panels used to provide circuit protection for electronics and other branch circuits. With most circuit breaker panels a circuit breaker is used as well as an inline fuse for most electronic devices.
Below is a diagram of a typical panel installation.
By using the ST Blade Fuse Block as a sub-panel the space used is reduced and fuses more appropriate for electronics can be used. This provides up to 12 branch circuits and does away with the inline fuses while using only one position on the panel. This allows the use of a smaller panel and the system has a lower overall cost per circuit.
A 12 circuit DC circuit breaker panel costs 10 times more per circuit on average and takes up 3 times as much space. The example below illustrates this.
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