Is It Safe to Use a Battery Switch When the Engine Is Running?

Question:

I have a 26 foot powerboat with a single 200hp diesel engin with 1 separate start switch and 1 separate house, plus 1 parallel switch.  

If I need to use the parallel switch to help start a low start battery issue,  is it ok to ‘open’ the parallel switch after the motor is running? I worry about major arching. - Don

Answer:

Great question, if your battery switch is in good shape, you should be able to turn the switch from 1 to both or all and to 2 without losing any contact to a battery. The source selector battery switch does a "make before break" connection when changing from 1 - both - 2. Make sure to never turn switch to off when engine is running.