Do I need to switch both positive and negative feeds from solar panels to SCC?

[corn18]

I was in a discussion on an RV forum and the topic of whether to disconnect both positive and negative wires from the solar panels to the SCC is required. I guess it is per NEC code for houses, but not for RVs. While I'm all for codes, I would like to understand why it would be a good idea to break both wires in an RV application. Right now, I just break the positive wire from the panels to the SCC.

 

[pollenface]

Switching one or both will have equal effect.

 

[12VoltInstalls]

it is per NEC code for houses, but not for RVs. While I'm all for codes, I would like to understand why it would be a good idea to break both wires in an RV application.

Codes are created for a reason. Safety.
100% disconnected isolates any panel-based fault or battery backfeed. A DC double breaker does both.

 

[corn18]

Codes are created for a reason. Safety.
100% disconnected isolates any panel-based fault or battery backfeed. A DC double breaker does both.

Why do I only disconnect the positive cable coming from the batteries? Should I disconnect the positive and negative battery cables?

 

[12VoltInstalls]

Why do I only disconnect the positive cable coming from the batteries? Should I disconnect the positive and negative battery cables?

There’s no self-perpetuating circuit for one thing. For another, 12- or 24V batteries probably won’t or can’t even zap you, whereas solar panels could be 88VDC or 150VDC and that can actually kill you.

 

[Zil]

In my van. All the dc negatives are common. 12V/500 W solar panels, 45 ampere/12 volt Morningstar CC. There is no reason to switch the negatives. If there was some kind of strange fault that energized the panel negative. CCs would shut down, fuses would blow, or, rather, nothing muchs would happen.
It is not the practise in the USA to switch both negative and positive of dc circuits. Most often it is the positive that is switched, but some circuits, such as the interior lights, switch the negative. The USA fuse is on the positive.

 

[corn18]

I am replacing my single pole switches with double pole breakers. Better safe than sorry.

 

[Zil]

Oh well. We tried.

 

[corn18]

Oh well. We tried.

For $47 total for 2 breakers and a box, it seems like a no brainer.

 

[kenryan]

It's good for the economy.

 

[Zil]

Low amperes from panels should be ok with low cost dc breakers.
I use Blue Sea DPST disconnect. Both battery and panel from SCC. It was $45+. But I know it will not fail.
I'm that guy that doesn't like dc circuit breakers. There are many that do.

 

[HRTKD]

I have double pole DC rated breakers between my PV panels and the solar charge controller. Not a big deal. They weren't that expensive.

 

[12VoltInstalls]

They weren't that expensive.

And I wanted the occasional disconnect anyway. Nothing wrong with bluesea switches, just the added feature of self disconnect feature in case of something I can’t imagine happened was a bonus.

 

[HRTKD]

The double pole DIN mounted breakers were half the price of the Blue Sea single pole breakers. I saved the Blue Sea breakers for after the solar charge controller.

I really warmed up to the DIN mounted breakers when I realized they took up a lot less real estate in my compartment than did the Blue Sea breakers.

 

[12VoltInstalls]

took up a lot less real estate in my compartment than did the Blue Sea breakers

The bluesea are designed to solve a single layer problem reliably. The din rail breakers are designed to provide incorporated systems with an expected component. They can do any one thing of multiple applications in a designed enclosure. The rails are just a handy way of using them in applications that do not have panels built to accept them- although it bothers some people due to NEC when they aren’t enclosed. But I sorta feel better about selecting DC breakers and surface mounting over buying a generic $130 combiner box and just running with whatever they put in them.

 

[corn18]

Finally got out to the camper and installed the dual pole disconnects for the solar panels. Also chassis grounded the SCCs.

 

[Paul_R]

2P breakers make for a cleaner install and are less money than a quality switch.

 

[andrewgokart]

Resurrecting an old thread about DC breakers... I was trying to find a decent answer to why most DC breakers are for the Poz and Neg. Couldn't find a solid answer, but my logic is this: In a DC circuit, if you break one of the leads/lines, then that is only 1 point that an arc has to jump. But if you break 2 points, that's TWICE as far that arc has to be able to jump to maintain continuity (assuming the breakers are COMPLELTELY physically separated by some non-conductive material). So, if both the Poz and Neg break at the same time, that is helping to ensure the connection is broken and the arc extinguishes as quickly as possible.

 

[12VoltInstalls]

was trying to find a decent answer to why most DC breakers are for the Poz and Neg

Depending on application, NEC wants both PV cables to disconnect. One reason.
Another is that both pos and neg will be protected if the battery wants to dump

 

[JoeHam]

Resurrecting an old thread about DC breakers... I was trying to find a decent answer to why most DC breakers are for the Poz and Neg. Couldn't find a solid answer, but my logic is this: In a DC circuit, if you break one of the leads/lines, then that is only 1 point that an arc has to jump. But if you break 2 points, that's TWICE as far that arc has to be able to jump to maintain continuity (assuming the breakers are COMPLELTELY physically separated by some non-conductive material). So, if both the Poz and Neg break at the same time, that is helping to ensure the connection is broken and the arc extinguishes as quickly as possible.

I only use double pole in my systems as a matter of choice, it’s only a few bucks more usually and a negligible part of system expense.

IF someone only wanted to break one side I would always break the positive in a mobile setup since the chassis is often a potential return path as commonly wired in vehicles. That could circumvent the negative side breaker.