Circuit breaker explanation?

[Bryan]

Hey guys, could someone describe to me the wiring of a circuit breaker. I understand it's purpose and how the breaker works but the wiring itself doesn't make sense. It seems it's not on the same loop as what is being powered. It is attached to the switch but not in the same loop as what the switch is powering.

[Geom]

Bryan, I'll take a shot at answering your question. Hopefully it's not overly simplistic.

A circuit breaker is designed, as the name implies, to break a circuit under specific conditions. One type of circuit breaker is the fuse you have in your car. It is composed of material designed to fail, when certain loads are exceeded, by physically breaking; thus preventing the wiring itself from overheating and breaking (or causing a fire) if the high load were allowed to be continued.

Another type of circuit breaker is the one you have in your house (or moving house/RV). Those are resettable breakers. They are spring loaded in such a way that when a certain amount of heat is generated (and electromagnetic force), the spring trips and breaks the circuit. Unlike your car fuse, however, they can simply be reset by reloading the spring mechanism (by flipping the circuit breaker off and then back on).

All circuit breakers are inline with the load. That means that a circuit breaker has to be within the circuit it's monitoring in order to protect that line from overload.

So if you put in a 17amp toaster oven on a 15 amp line, the 15 amp circuit breaker will get hot (just as your wiring will). But at 15 amps, it breaks the connection and doesn't allow the wire to get dangerously hot.

Hopefully that answers your question.

-George

[Cary and Don]

Are you talking 12volt or ac circuit.  They operate a little different. 

Don and Cary

[Seangie]

Bryan - just checking you mean "breaker" and not "relay"

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[mikke60]

Just my opinion here, but your bus is no place to learn about wiring. Playing with a 120 volts is a very dangerous game. Add to that, wiring at some campgrounds is borderline at best, you can be looking at a dangerous situation. I plugged into an outlet last year that was wired wrong, and ended up with a live chassis. Just some food for thought.

[Jon]

I don't even understand the question.

All breakers in my coach are in the line going to the appliance or device. If the breaker opens that line or circuit is dead.

The 120V breakers in my coach serve as master switches to a circuit that might have multiple devices and switches, such as my forward outlets that have a lamp, my computer, and even my shades on the circuit, all of which have their own switches.

What is meant by the CB not on the same loop? What's a loop?

[hatchhome]

Just my opinion here, but your bus is no place to learn about wiring. Playing with a 120 volts is a very dangerous game. Add to that, wiring at some campgrounds is borderline at best, you can be looking at a dangerous situation. I plugged into an outlet last year that was wired wrong, and ended up with a live chassis. Just some food for thought.

Mikke, just thinking of how one might prevent just that. I assume they had the ground incorrect and thus it charged the body. Could a simple light above the plug in on your coach be rigged to light if the body becomes charged?  If so I am doing it for sure as I have seen some interesting wiring at campgrounds.

[Lin]

If I am not lazy, I sometimes test the campground circuits with a multimeter before plugging in.  There are also cheap plug in testers you can get for 120 receptacles.  I keep one plugged in all the time in a visible outlet.  Of course, that merely tells you that you are already connected to a bad outlet; it does not stop you from getting there.

Sorry for the digression.

[Geom]

Mikke, just thinking of how one might prevent just that. I assume they had the ground incorrect and thus it charged the body. Could a simple light above the plug in on your coach be rigged to light if the body becomes charged?  If so I am doing it for sure as I have seen some interesting wiring at campgrounds.

For what it's worth, we'll be installing a device that checks for that (along with under/over voltage, and several other things) before allowing current to flow. It's not cheap, but I think it's good insurance for preventing one of many such possible "interesting wiring" scenarios
This should help protect people, along with equipment (inverter, appliances, etc).

Here it is for reference,
http://www.amazon.com/gp/product/B007O6INSE/ref=gno_cart_title_1?ie=UTF8&psc=1&smid=ATVPDKIKX0DER

They also make a plug-in model, but I think the built-in models don't scream "steal me" quite nearly as loudly, lol!

[mikke60]

Those devices sound like a good idea to me. Getting a tingle through your legs when you kneel against the bus chassis works,but not my favorite method. 

[bevans6]

If you are talking about the 12v wiring on your bus, often the switch controls a relay which turns the load on and off, and the circuit breaker controls the power to the relay.

Brian

[RJ]

Bryan -

George did a pretty good job of describing circuit breakers, but he left out a type commonly found in our OEM coach wiring - automatic reset circuit breakers.

Only found on a few circuits (like headlights), these will trip off when overloaded, then automatically reset when they cool down.  If the overload is still there, they'll trip again, reset, trip again, reset and so forth until the problem has been corrected.  Often heard as an annoying clicking sound in the electrical panel to the driver's left.

FWIW & HTH. . .

[gus]

What RJ said.

Auto-reset breakers used to be on old aircraft also but were finally banned for the obvious reason that they kept re-applying power to a faulty circuit and made some smoke and excitement at a bad time!!

Our older buses have a bunch of these and they are getting to be in pretty bad shape.

[Bryan]

when your circuit breakers go out, where can you get more? or do you have to switch to fuses?

[gus]

Both my buses have numerous unused CB, look inside the elect panel for some with cut wires.

If I ever run out I'll substitute fuses, they're much safer.