Battery cut off switch

69 Avion wrote:

westend wrote:
My vote goes to Cole-Hersee M-750 because it's serviceable and has an O-ring to seal case to back plate.

It looks like a high quality switch. That is the style that I like.

Yup, it is a good piece of gear. I have three of them to distribute 12v in my rig. I have them interrupting power from two banks of batteries to the solar system, the inverter, and the converter.

My blue sea switch has worked well for several years.

If the switch is going to be mounted outside, any marine grade component will do well. The cheapies from WalMart or Harbor Freight may be "iffy" as far as durability and resistance to the elements, but a lot of people claim to have good luck with them. I personally believe in buy quality, buy once. YMMV.

Electrically, it doesn't matter where you put the switch - pos side or neg side. I once considered putting the switch between my 6 volt batteries because the mounting and placement would have made it much easier.

Safety wise, there is a great deal of sense in putting it on the negative, as it is desirable to minimize the amount of exposed metal connected to the pos side. If the installation is done properly I prefer the pos side, as that is the place most people expect it, but if I was selling a cheap switch like this, and I knew many customers would do a poor installation job, and I knew that many of them would not properly prevent inadvertent shorting out by building an insulating shield, I'd probably recommend installation in the negative side.

Where I work we have a number of diesel gensets. 100KW up to 1MW, they are rotated around as needed as emergency units. They all have (with the exception of the 1MW units) a welding cable quick disconnect on the NEGATIVE cable. The 1MW units have a rotary switch that cuts out all the electronics except the maintenance charger.
If you read how to disconnect/replace a battery or jump start a vehicle.. Connect POS first, NEG last. Disconnect NEG first, POS last. As was stated earlier, this is to prevent sparks. If you are concerned about forgetting to connect the battery before towing, hang a flag on the breakaway cable that says "CONNECT BATTERY BEFORE CONNECTING BREAKAWAY CABLE!" Personally, I test the breakaway before moving the rig. Just my .02.
MikeH