What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Circuit Breaker Orientation? Line - Load

DTARM1

Active Member
Does the line - load matter on circuit breakers in a 12v DC application?

All I've ever read or seen is the line side connects to the bus bar - but that's always been in an AC application.

If I emplace the circuit breaker with the line side connected to the bus bar, the amp rating on the stem is oriented upside down.

Why does line - load matter in a DC application?
 
It normally doesn't matter on an old fashion mechanical circuit breaker. It normally does matter on a new fangled solid state circuit breaker.

:cool:
 
Which are these?

This is the CB I'm using. I've got 28 of them replacing old, simple, unmarked CB's.
 

Attachments

  • 20220417_110405.jpg
    20220417_110405.jpg
    534.9 KB · Views: 126
  • 20220417_124535.jpg
    20220417_124535.jpg
    258.3 KB · Views: 115
  • 20220417_124552.jpg
    20220417_124552.jpg
    273.6 KB · Views: 88
Does the line - load matter on circuit breakers in a 12v DC application?

All I've ever read or seen is the line side connects to the bus bar - but that's always been in an AC application.

If I emplace the circuit breaker with the line side connected to the bus bar, the amp rating on the stem is oriented upside down.

Why does line - load matter in a DC application?

I surely hope it doesnt matter, because otherwise my panel is hosed.

I am serious, and dont call me Shirley
 
I would just call the TE customer service line +1 800 522 6752 to get the final word. I looked at the W23 TDS and it had non definitive answer.

They were quite helpful the last time I called . . . .and my labels were falling out. They gave me the plant managers number, called it and they sent me a lifetime supply. A different model, but same company.
 
Last edited:
If I emplace the circuit breaker with the line side connected to the bus bar, the amp rating on the stem is oriented upside down.
Why would they be upside down?
Put the bus bar on the line side as intended. If that is top, so what. Load wire coming off bottom terminal not an issue.
Only hassle comes in mixing different types of switches or switches with circuit breakers. For pilot easy I would not mix those together anyway as I would Group like kind together thus allow a bus bar to connect them with short jumper wire from one group to the next.
 
Not for me

Why would they be upside down?
Put the bus bar on the line side as intended. If that is top, so what. Load wire coming off bottom terminal not an issue.
Only hassle comes in mixing different types of switches or switches with circuit breakers. For pilot easy I would not mix those together anyway as I would Group like kind together thus allow a bus bar to connect them with short jumper wire from one group to the next.

My breakers are in a grid pattern. I wanted to keep the unfused bus and the CB breaker's outputs separated, so the bus input for two rows are next to each other, and the CB outputs for the other two rows are next to each other.

If one does what you suggest, then every row has the unfused input power right next to the CB output (fused) power of the adjacent row. Not the best idea in my opinion. JMHO.
 
That part number is also rated for use as a switch, so is has a diode (like your master relay). If you use it to turn on and off inductive loads, the polarity will matter. If its only use is as a circuit breaker, I wouldn't worry about it.
 
A diode in parallel with a switch does absolutely no good whatsoever protecting the switch from arcing caused by inductive voltage spikes. The diode needs to be across the coil. The diode may be located at the switch provided that it is in parallel with the coil. In other words, connected between the load side of the switch and ground, assuming one leg of the coil is grounded.
 
Mich48041/Joe Gores and Bob Nuckolls are in agreement that Line and Load can be reversed in the OP's case.

I was curious so I asked on AeroElectric List. Link

P.S.
  • Bob Nuckolls shows the internals of three different breakers here.
  • You can pull the breaker open and check with an Ohmeter whether there's a diode inside. I'm thinking no diode in the OP's breakers.
  • A diode across switch contacts is not effective at absorbing an inductor's flyback spike. Bob Nuckolls did empirical testing. Link
 
Last edited:
Down here with the rabbits . . . . . and IRS attorneys . . .

:D
Mich48041/Joe Gores and Bob Nuckolls are in agreement that Line and Load can be reversed in the OP's case.

I was curious so I asked on AeroElectric List. Link

P.S.
  • Bob Nuckolls shows the internals of three different breakers here.
  • You can pull the breaker open and check with an Ohmeter whether there's a diode inside. I'm thinking no diode in the OP's breakers.
  • A diode across switch contacts is not effective at absorbing an inductor's flyback spike. Bob Nuckolls did empirical testing. Link

Holy smoking breakers!! - - if one hooked power to LOAD rather than LINE, that gives me a headache even beginning to think about creating an FMEA for the Potter-Brumfield design with all the intricate little parts!!

But Ya know . . . if 12V+ was hooked to the LOAD side , and that single little screw on the side of the case shorted to ground it would circumvent the breaker function. But if it was covered with a touch of RTV, it could be mitigated by lowering the probability of occurrence to. . . . . .

Good for you, John, those photos/links are fun to see.
 
Last edited:
Re Posts 15 and 17

Re Post #15... I see what you mean Bill re FMEA - screw to the outside of the case is hot depending on B+ to Line or Load and CB open or closed. Looks like hot screw shorting to ground does not trip the breaker if B+ is connected to Line and does trip the breaker if B+ is connected to Load.

But... as pointed out in post #17, the screw is covered with an insulating material as delivered. Ref photo copied here from post #1.
.
.
 

Attachments

  • 81a 2.jpg
    81a 2.jpg
    233.7 KB · Views: 68
  • 20220417_124535.jpg
    20220417_124535.jpg
    308.3 KB · Views: 60
Last edited:
R Unlikely a conductor will come in contact with the screw but of course less likely if the screw is covered with an insulating material.
.

if you look at the second picture of post 3 you will see the screw is buried in a a non-conductive material.
 
Back
Top