Picking the right breaker

Travisfab

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I have been gathering a lot of info on wiring lately and it seems as though the switch/breaker setup is the way to go. My question is, how do I choose the correct amperage breaker for each specific accessory? Do I need to invest in a new tool?

Basically a setup like this is what I am talking about.
 

California MiniTruck

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Im sure other people will post on this soon but yea these breakers work great. I used to work on Helicopters in the Navy and the cockpit was full of these, im going to use them in my truck also. As for the amperage each thing you use i.e. amber light or oil cooler, will have a amperage rating on it so that is what you are going to use for the breaker. If its a 20amp cooler then you use a 20 amp breaker. What ever assy you end up hooking up you should be able to find right on it what amp it is and go by that. The breakers go as low as 5 up to whatever you need. A good place to find these cheep is a air craft salvage yard, there is one in Ontario that I go to all the time called G&J aircraft and they have them for $3 to $5. Its a great place to know any ways they have a lot of cool stuff in there.:D
 

Wilson

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Breakers protect the wiring, not the component. They work great, but you do need to select the capacity carefully. Typically, you need a breaker with more capacity than the actual using unit. There are several reasons for that, one being that some things will draw much more current at start up than at their "running" state. You don't want the breaker tripping due to that start-up surge, but you also don't want the breaker value so high that you have a fire if the using unit "seizes up".

Add up all the "using units" max draw on the circuit you want to protect, then add about 30% - that should give you enough capacity and still protect the wiring (if you've sized it correctly). Also, it's better to have only one item on each circuit - but that's not always practical. Circuit breakers shouldn't be used as switches - if you need a circuit "switched", use a switch!
 

Travisfab

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As for the amperage each thing you use i.e. amber light or oil cooler, will have a amperage rating on it so that is what you are going to use for the breaker.

Is there some place I should be looking to find these amp ratings? I can guarantee that there are going to be a few things that are not going to have an amperage rating on them. I would rather not guess anything, being that this is a race vehicle.
 

Wilson

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You may have to contact the manufacturer to find the power requirements for some things. Most electronic items will have the power requirements listed in the manual, but stuff like fans and pumps may require a call to the manufacturer. You can also measure the "running" current draw with a multimeter, but it'd be more difficult to measure the "start-up" draw.
 

Travisfab

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Well it looks like I need to do my homework. I don't have a manual for anything on my truck. Would this Harbor Freight special happen to have the setting I need to find amperage?
 

Wilson

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Well it looks like I need to do my homework. I don't have a manual for anything on my truck. Would this Harbor Freight special happen to have the setting I need to find amperage?
I can't see the amp ranges very well, but it looks like that one can measure up to 10 amps - most small multi-meters can measure current but are limited to about that amount. Some items in a race car could require more than 10 amps...... Also, a small multi-meter is not going to help much in measuring "start-up" current draws but will be okay for "steady state". Measuring the start-up requirements takes more sophisticated equipment.

Some general statements:

HID lights and fans will have significant starting current requirements, less once they are running. A fresh air pumper will require less current when the filter is clean than when it's dirty, radios will have lower power requirements receiving than when transmitting.

The best way to determine each units needs is to contact the manufacturer or distributor. Or, turn the whole wiring issue over to someone who's got experience in the area (you don't want the car to burn to the ground the first time you try to start it!)?
 

DesertGuy1

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Well it looks like I need to do my homework.
Travis, determining the amperage size of a circuit breaker or fuse will be decided as you start constructing the circuits that you will be using. I'd suggest making a list of all components that you will be running (on paper), then start determining their amperage requirements (ask around/call manufacturers,etc...). That way you will know the components needs, wire gauge required and appropriate circuit protection as well as necessary switches in the circuit. It is a good thing to start looking at circuit protection from the start but you need to figure out the steps prior to get to that answer.

"A very crude example"

As an example, say I bought two schnazzy 100watt Hella AwesomeLights that I wanted to install and run both lights on a single toggle switch. I'd figure the amp draw of each light and for both lights since I want that on the circuit (100watts / 12volts = 8.33amps). Since I want both lights to come on when the toggle is switched, it would be 8.33amps x 2 lights = 16.66amps. (some will also use 13.6 as the volt divider due to charging... but remember, this is a crude example)

Now I know in order for the lights to work I need to construct a minimum of a 16.66amp circuit. Since I have yet to see a 16.66amp circuit breaker, I purchase the next closest size, 20amp.

Since I am now constructing a 20amp circuit, I need to size my wire gauge accordingly to handle that load... I want the circuit breaker to be the "weak link" and not the wire itself. So for 20amps I select a minimum of 12gauge wire. (yes there are other variables... but bear with me).

Then I would look at the switch I would want to use... can it safely and repetitively handle 20amps? If it can, then I could choose to run the circuit with the switch "passing" that load. If I had my heart set on a bling-bling, fancy LED switch from the swap meet.... well, then I would need to consider incorporating a relay into the circuit so the "load" is not passed through the switch and is "controlled" by the relay instead (relay appropriately sized also).

After that, I can start looking at developing that one circuit...

You will need to do that for each and every circuit you plan on running. I left out a few details and other considerations to show the example... but to reply to your statement...... yes, there is homework to do.;):D:D

As with building a rollcage... welding it is the easy part that ends up showing how much preparation you initially took. Wiring is the same way... pulling the wires is the easy part and it is the time you take "developing" your circuits which shows your preparation. Good luck.
 

Travisfab

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I really appreciate everyone's help and I already have a better understanding. I wish I had the budget to have a professional wire it for me. I do like to tackle projects like this to learn, and to be able to fix things in the desert.

My truck is pretty minimal on the electrical accessory bling factor so I shouldn't have too much trouble.

watts/12volts = amperage ------> awesome!
 

Co-Dog

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Most breakers are designed to withstand 80% of the rated current continuously without tripping. Anything from 80% to 125% will not usually trip the breaker instantaneously. That area is for motor starts and surges, which the current drops to a tolerable level rather quickly. Wilson mentioned 30% above, which is acceptable, but if in doubt, always go with the next larger size of breaker. I believe that those particular breakers come in 2, 3, 5, 7.5, 10, 15, 20, 30, 40, and 50.

It is a common misconception that the breaker only protects the wiring. It all depends on where it is located in the circuit. For example, the breakers shown in your picture are protecting the device that they deliver current to. The wiring to those devices must have a rating that is larger than the breaker to prevent voltage drop and to keep the wiring from burning up before the breaker trips. That being said, there must be at least one wire that feeds all those breakers from the battery. That wire will be large enough to carry the current of all the loads fed from those breakers and that wire must have protection in the form of a breaker, fuse, or thermal link. That protection needs to be located as closely as possible to the battery. There are exceptions, but it gets complicated.

As far as current ratings of devices go, most motors will give a current rating on them. As a general rule, if there is no rating listed, it's going to be less than 10 amps. Therefore, that multimeter from harbor freight will be sufficient for most things. Buy an extra fuse or two for it though. Also, if you hook up the leads incorrectly (most people do this at least once), you are going to let the smoke out of the meter. The smoke is what makes the meter work, and once it gets out, the meter don't work no more.:D

The most common mistake made is using too small of wire. That mistake becomes dangerous when the wire rating is less than that of the breaker or fuse that it gets its current from. The concept can be a little difficult to grasp, but don't sweat it. You can PM me if you have any questions, I've been doing this stuff for a long time.
 
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