The ABYC standards say that a battery switch is required for all DC systems. One of the main reasons is that if a fault such as an electrical fire is discovered the system can be turned off quickly and easily. Another reason is so that the systems can be turned off when the boat is laid up or not in use.
The exact wording is as follows:
So what about the exceptions? Some circuits are exempt from this requirement. The paragraph above mentions the first exception; if the battery has a rating of less than 800 CCA you can omit the battery switch. This would exempt most small systems with a single Group 24 size battery or smaller.
The circuits that are exempt from the requirement to have a battery switch are items that are normally required to be on all the time. These include Bilge Pumps, Carbon Monoxide detectors, Bilge Blowers and other safety equipment. It also includes battery charging equipment. This might include solar panels, battery chargers and alternators. Finally it also includes electronics that are required to have a continuously powered memory, such as a car stereo which needs to remember the stations.
So these exempted circuits are allowed to be connected directly to the battery or to the supply side of the battery switch so they are not interrupted if the battery switch is turned off. There is one other exception for dedicated trolling motor batteries that I am not going to go into here.
Are there any noted items that are specifically NOT exempted? Inverter/chargers cause some confusion with regard to this rule. Inverter/Chargers ARE required to have a battery switch. Although the charger part would be exempt the inverter part would not. You need to be able to turn off the inverter at the battery switch if something goes wrong of if you want to work safely on the AC system
This is an interactive blog so feel free to add your questions or comments.