Why solenoid?

Convenience for the non-mechanically/electrically inclined. It's like why have an auto-switchover for propane?

because the switch can be placed in a much better place then a mechanical.

LittleBill wrote:
because the switch can be placed in a much better place then a mechanical.

This ^^^^^^^^^^^^.

With a manual disconnect switch, you have to place it between the battery and the electrical panel, making it very inconvenient to access. Using the solenoid lets you place it anywhere, and place its switch right by the door, where it is extremely convenient.

It is actually a Latching Relay!
As others said it is for ease of installation.

And you can install multiple convenience switches throughout the rig. Similar to one pump switch in the kitchen and another in the restroom.

That makes a lot of sense. I have a truck camper and the solenoid and switch are right over the battery compartment/generator. So for me, it’d be easy to use a switch, but for larger RV’s I can see the advantage.
Thanks for the info!

The solenoid for mine is not a latching relay. It is a continuous use design.

PT, I'm surprised you didn't replace the continuous current draw disconnect relay with a latching type. You seem to be very efficiency minded.

The Solenoid, basiclly a big and I mean BIG relay. can easily pass 100 amps or more. The wires that run a great distance to the switch. just a couple amps.
You are asking why they use a fairly low cost remote switch with low cost 20-22 ga wires instead of oh say 50 feet of something between 4ga and 00ga.

Way cheaper. and way better electrically as well. (less voltage loss in the line).

AS other have mentioned, There are 2 types. LATCHING relay(soelnoid) takes current to engage and disengage, but once either is done it requires NO current to keep closed or open. Yes, this type system is more expensive, which you usually only see it on Motorized due to access to the battery banks. The other requires continuous 12 volts to keep engaged. These types are cheap because all you need is a simple ON/OFF switch. Also these type solenoids also build up heat when you have a load and constant power to them to keep closed.
COST? Well, when you factor in the cost of most Motorized and the fact that RVer's want bells and whistles, they make it standard. Now, the drawbacks to Latching type. Some OEM's do NOT run all Coach 12 volt loads thru the disconnect. Some, wire the CO and LP detectors direct to the batteries for liability reasons. So, with Batteries OFF, they can still be drained in 2 to 4 weeks. Inverter/Chargers are NEVER wired thru a Latching disconnect and are wired direct to the Coach batteries. Doug