Battery disconnect switch

I recently added a 2nd 12 volt battery to my unit, in parallel.  I want to add a battery disconnect switch, using the negative cable.  The unit I bought did not come with instructions.

You should put the disconnect in the positive (ungrounded) cable not the negative (grounded) conductor. Code is to always disconnect the hot line never the grounded one. That leaves all you appliances properly groundcreferenced.

Mountainman, I have tried to hold back and not bother you about it but can't hold back anymore as it might help you down the road...you added a new battery. Is it an exact match for your original battery...same age, manufacturer, size, rating, and a dedicated deep cycle battery?

If the original battery is well used, it is a different size etc, then you may inadvertently shorten the life of your new battery as it will try to do all the work. You want them to charge and discharge as evenly as possible, which is why it is best to change them as a pair. This is true for 12 volt as well as 6 volt batteries.

Andy

The reasoning for placing the switch in the positive/hot/ungrounded conductor is the same as for any other fuse, switch, or circuit breaker in your trailer, house, and any other building. If you leave the negative/neutral/ungrounded conductors intact then you know you have everything safely tied to chassis ground and to your house/campground ground when you are on shore power. The electric code requires this (with very few exceptions) and contrary to a common misunderstanding the code applies to low voltage DC systems.

I think the confusion probably comes from the recommendation to disconnect the battery negative first while doing maintenance. That is done so you don't inadvertently short a tool to the chassis which could happen if you disconnect the positive first. But temporary maintenance and repair activity is not the same as a permanent switch. So disconnect your negative first, then your positive, install the switch in the positive conductor, and reconnect the negative. Or better yet, use tools with insulated handles around batteries. You can tape up a couple of wrenches for that purpose.

No. The smaller is for connecting a solar panel into the system. The heavier battery cables connect to the converter and are used both for powering items when there is no shore power or for recharging the battery.