DC Switch for lights, switch positive or negative leg of circuit?

[seprintz]

This may be a silly question, but I'm new to wiring the DC load side of the house.

In the past I retrofitted a travel trailer with 24v LiFePO4 batteries and an inverter, but all of the house wiring from the 12v distribution/fuse box to all the switches and lights were stock from the RV manufacturer.

I'm currently building a DIY travel trailer from scratch. When installing a switch, do I switch the positive, or negative side of the circuit? I bought this switch, and it's a single pole, single throw switch:
https://www.amazon.com/dp/B08CZ9BTNZ?ref=ppx_yo2ov_dt_b_product_details&th=1

I would have assumed switch the positive side, but I recently did some work on my van (tow vehicle), and noticed that the door switch for the dome lights actually switches the circuit to ground (which in a mobile application, I understand to be the same as the negative).

 

[TomC4306]

In a mobile application, negative battery is typically tied to chassis. And so, it saves on wire switching negative.

 

[Lorenzo90]

I would always switch the positive.. switching negative you have the chance that if for any wacky reason the appliance grounds itself to ground(all the chassis if grounded is negative), it will complete the circuit..
Another reason it that if you have to do any maintenance on the appliance, you would still have a live positive (unless yous switch off the main circuit), and more chances to go to ground.
Instead if the positive is switched off, you could smash the thing onto the chassis without worries of completing the circuit.
I don't get what tom is saying about saving on wire switching the negative.. I may have a different approach to wiring..
Actually I'm using almost all wireless relays on my campervan, so I don't have wires all over the places and I can decide at the end where to put the switches..

 

[Rednecktek]

Gotta vote for positive. If you break the negative and short to ground/frame/negative it'll tickle/hurt.

If you cut the positive and touch the frame nothing happens.

 

[Checkthisout]

This may be a silly question, but I'm new to wiring the DC load side of the house.

In the past I retrofitted a travel trailer with 24v LiFePO4 batteries and an inverter, but all of the house wiring from the 12v distribution/fuse box to all the switches and lights were stock from the RV manufacturer.

I'm currently building a DIY travel trailer from scratch. When installing a switch, do I switch the positive, or negative side of the circuit? I bought this switch, and it's a single pole, single throw switch:
https://www.amazon.com/dp/B08CZ9BTNZ?ref=ppx_yo2ov_dt_b_product_details&th=1

I would have assumed switch the positive side, but I recently did some work on my van (tow vehicle), and noticed that the door switch for the dome lights actually switches the circuit to ground (which in a mobile application, I understand to be the same as the negative).

Dome light receives constant power so that it can be switched on at dome light, dash switch or door switch without having to do 3-way wiring nonsense.

 

[TomC4306]

I don't get what tom is saying about saving on wire switching the negative.

You have negative available everywhere. Chassis nearby to switch to fixture. No need to run 2 conductors all the way from battery or fuse box.

 

[seprintz]

Thanks for all the advice, I think you guys all shed good light on the situation, and why the dome lights in the van are wired the way they are.

 

[Rednecktek]

Just to throw this out there, but all the DC fuse blocks I've seen put the fuse on the Positive wire to break the connection...

 

[Browneye]

For a vehicle, like a van with a metal body, you only need a pos wire from a fuse block to a switch to the light. The ground wire can be attached to the body, at or near the lamp itself.

For RV's without a metal body, generally there's a negative bus system that attaches the frame to connect dc fixtures. Switches still go on the pos side.

 

[HRTKD]

All the switches in my RV use the positive leg. Everything also has a negative wire that goes back to the same source as the positive wire (the main distribution panel). In other words, none of my devices get their negative from the chassis, except for the generator but that's a different situation.

 

[Lorenzo90]

You have negative available everywhere. Chassis nearby to switch to fixture. No need to run 2 conductors all the way from battery or fuse box.

Ohh I see what you mean! I eliminated that problem, all my switch are RF 433mz wireless switch.. so positioning them is just an afterthought.. and no messy wires ??

 

[seprintz]

Ohh I see what you mean! I eliminated that problem, all my switch are RF 433mz wireless switch.. so positioning them is just an afterthought.. and no messy wires ??

Do you have a link to your switches? That sounds neat.

 

[12VoltInstalls]

don't get what tom is saying about saving on wire switching the negative.

Some people who have not spent years correcting dumb things people do in boats and campers do not homerun their neg(-) circuit. I always homerun or (rarely) busbar-to-homerun the neg(-) and that never has been an issue.

none of my devices get their negative from the chassis

And some technician down the road won’t be writing you a bill with 9 hours of diagnose and repair on it?

TV

Just to throw this out there, but all the DC fuse blocks I've seen put the fuse on the Positive wire to break the connection...

bevsuse these days nearly everything is a negative aka neg(-) ground system.

People get worried about spending twice as much cash on wire which is a lot by % whereas in real dollars it could just be the cost of a couple of pizzas- not so significant when thought of in reality terms.