Battery main switch: choosing and installing it correctly
A battery main switch disconnects the battery from the on-board network, visibly and without tools: for work on the system, for winter storage and in an emergency. Which one fits depends on the continuous current, the number of battery banks and whether you want to switch directly at the battery or remotely.
What the main switch is for, and what it is not for
The main switch provides mechanical, visible isolation. It does not replace a fuse, and a fuse does not replace it. Every battery bank needs a means of isolation that can be reached without tools and without climbing.
The positive side is switched. Loads that must always stay powered, such as the bilge pump, alarm or gas detector, are deliberately connected ahead of the main switch, but then with their own fuse.
The order at the battery: fuse first, then switch
At the battery, the main fuse comes first, followed by the main switch. Only then is the short, heavy cable to the switch protected as well. The other way round, exactly the piece of cable that can carry the highest short-circuit current would remain unprotected.
How close the fuse must be to the terminal and what breaking capacity it needs is explained in the Academy article on the main fuse.
The right size: continuous and peak current
What counts is the current that can flow through the switch, not the current that usually flows. A bow thruster rarely runs, but when it does, its full current passes through the main switch. Besides the continuous current, the short-term peak current when starting, the permissible voltage and the stud size for the cable lugs all matter.
| Switch | Continuous current | Short-term | Voltage | Connection |
|---|---|---|---|---|
| Quick BH 1000 F / BH 1000 B | 140 A | – | up to 32 V DC | M10 |
| Kissling BH 200 F | 200 A | 500 A / 3 min, 1,000 A / 30 s | up to 32 V DC | M10 |
| Kissling BH 200-80 F | 250 A | 500 A / 3 min, 1,000 A / 30 s | up to 80 V DC | M8 |
| Blue Sea Systems BHS 350 | 350 A | – | – | – |
| EGIS XD1 | 500 A | 1,500 A cranking current | – | – |
| Blue Sea Systems BHD 600 | 600 A | – | – | M12 |
The values are taken from the product information in the shop. The Kissling switches are protected to IP 67, the EGIS XD1 to IP67 and IP6K9K.
Single pole, double pole or selector switch
- On/off for one circuit: the classic main switch, for example Kissling BH 200 F or Blue Sea Systems BHM 300 for outboards and smaller engines.
- Two circuits with one lever: The Kissling BH 220 F 2-pole switches two independent 200 A circuits. The Blue Sea Systems BS 5510e isolates two separate battery banks at the same time and may also disconnect positive and negative together.
- Selector switch: It selects between two battery banks. The BWS 303 keeps both separate in every position, the BWD 504 can also connect them in parallel (Combine).
- Protecting the alternator: The BWS 353 and the BS 11003 have an Alternator Field Disconnect that protects the alternator diodes if the switch is turned off while the engine is running. The BS 11003 is ignition protected for petrol boats.
Remote controlled: the relay at the battery
A mechanical main switch is almost always in the most awkward place. A remote-controlled main switch, by contrast, sits directly at the battery and is switched from the helm via a thin control cable. The heavy battery cables stay short.
Bistable relays hold their switching state without continuous current. The Blue Sea Systems FBR 500 switches up to 500 A and draws no current at rest. The philippi XD1PC also switches 500 A and draws only 1.3 mA when off. The philippi FHR 265 is operated via a control switch with LED indicator. XD1PC and FHR 265 can be operated by hand directly on the unit if the remote control fails. A version with NMEA 2000 interface shows the switching state and battery voltage on the chartplotter.
Frequently asked questions
Does the battery main switch go before or after the main fuse?
After the main fuse. At the battery, the fuse comes first, then the switch. This way the short cable between terminal and switch is also protected. The other way round, exactly the piece of cable that can carry the highest current in a short circuit would remain without protection.
How large does my battery main switch need to be?
It must carry the highest current that can flow through it, including starter motor, bow thruster or anchor windlass. Pay attention to continuous current, short-term peak current, permissible voltage and stud size. In our range, continuous current ratings run from 140 A to 600 A, so plan in some reserve.
When do I need a double-pole main switch?
When two separate circuits are to be switched with one lever, for example starter and service batteries that must stay strictly separate. Double-pole switches such as the Kissling BH 220 F or the Blue Sea Systems BS 5510e switch both circuits at the same time without connecting them.
What are the benefits of a remote-controlled main switch?
It sits directly at the battery and is switched via a thin control cable from the helm or control panel. The heavy battery cables stay short. Bistable relays such as the FBR 500 or XD1PC hold their state without continuous current. XD1PC and FHR 265 can be switched directly on the unit in an emergency.
Which loads may be connected ahead of the main switch?
Only loads that must keep running even when the system is switched off, such as the bilge pump, alarm or gas detector. They are deliberately connected ahead of the main switch, but then need their own fuse close to the battery. All other loads belong after the switch so that it really de-energises the system.
