Circuit Breaker Amperage Question

[ToyDB]

Installing a fuse/relay block and circuit breaker.
Anyone aware of a guide to determine what amp circuit breaker to use? (I've searched the web, forums, you tube to no avail.)

Plan on relatively low load accessories such as a couple of lights, front camera, dash cam, etc.

See plenty of folks using 100 amp breakers so that's my inclination but want to double check.

Thanks!

 

[Dillusion]

Depends on your load from your accessories. Are you making your own relay panel or just looking at one power source for all of the above?

I dont think one relay with lights, camera, dash cam etc is a good idea.

I guess you should decide how much circuits/relays you want. Those should be individually fused. And one big one from the battery feed to all these relays/circuits.

Don't forget to size your wire appropriately.

 

[ToyDB]

Yes, understand it depends on the load which is why was looking for a guide for breaker amp sizes similar to those for wire and fuse sizes.
Will be installing the breaker along with a fuse and relay block.
Thanks,

 

[Dillusion]

Not sure how we can guide you without knowing exactly what equipment.

If you following something like the SPOD.

I believe it is 30A per circuit with a 50A main inline fuse.

 

[gamefreakgc]

You need the circuit breaker to be lower than the max amperage value of the power wire. You also need each accessory to be fused. Here's a simple way to understand it:

Fuses protect the equipment. If say, you dashcam draws a max of 8 amps, a 10 amp fuse will protect it. In case of a malfunction, the fuse blows instead of your dashcam. If you were to install a 5 or 7.5 amp fuse, it'll blow during normal operation though.

Circuit breakers protect the wiring. They are more important than fuses because they protect the wiring from catching fire.. If you have wires with 85 amp capacity, meaning the wire will fail and burn up when it exceeds that capacity, you will want around a 75 amp circuit breaker. That way the breaker trips instead of burning the wire and potentially the entire vehicle.

So to answer the question, you will need to tell use what gauge wire you are using and the max amp load it can handle.

 

[Dillusion]

they are more important than fuses because they protect the wiring from catching fire..

what?

 

[gamefreakgc]

what?

If you exceed the amp load rating of the wire, it overheats to the point of possible combustion. Toyota used fusible links in the engine bay to prevent this from happening. The 100amp fuse for the alternator is a good example. If it ever goes beserk and starts cranking out too much power it trips the fuse and keeps the wiring from melting.

 

[Dillusion]

If you exceed the amp load rating of the wire, it overheats to the point of possible combustion. Toyota used fusible links in the engine bay to prevent this from happening. The 100amp fuse for the alternator is a good example. If it ever goes beserk and starts cranking out too much power it trips the fuse and keeps the wiring from melting.

And a what do you think a fuse does?

 

[ElectroBoy]

If you exceed the amp load rating of the wire, it overheats to the point of possible combustion. Toyota used fusible links in the engine bay to prevent this from happening. The 100amp fuse for the alternator is a good example. If it ever goes beserk and starts cranking out too much power it trips the fuse and keeps the wiring from melting.

... and causing a fire.

 

[gamefreakgc]

And a what do you think a fuse does?

It blows leaving you stranded in the middle of nowhere. A circuit breaker you just reset.

 

[ToyDB]

Thank you for the info.

 

[ToyDB]

Thanks.

 

[Dillusion]

It blows leaving you stranded in the middle of nowhere. A circuit breaker you just reset.

Thats not what you implied above.

You said circuit breakers are more important than fuses because they prevent fires.

I agree a circuit breaker is easier to reset.

And if you don't carry spare fuses when going into the middle of no where sounds like a personal problem.

 

[gamefreakgc]

Thats not what you implied above.

You said circuit breakers are more important than fuses because they prevent fires.

I agree a circuit breaker is easier to reset.

And if you don't carry spare fuses when going into the middle of no where sounds like a personal problem.

Got up on the wrong side of the bed today?

 

[Dillusion]

Got up on the wrong side of the bed today?

No just preventing misinformation.

 

[Bumbo]

Holy hell there is some terrible/inaccurate information in this thread… with no assistance on how to actually apply these products.

First and foremost a breaker is NOT a replacement for a fuse. It never was and never will be. Where a breaker could fail, a fuse would not.

Breakers are thermal devices, and with a dead short, there is a chance the breaker could weld itself closed (aka ON) rending it useless, and with a worst case scenario electrical FIRE. The fuse in turn would be your last line of defense.

Application:

• Breakers are used to manage temporary overload conditions.
• Fuses are used to protect the mains cabling from fire / short circuit.

To answer your question OP. Breakers are sized to protect the LOAD, not the wire. Buy reputable products from companies who publish datasheets regarding their trip curves. Not all are the same, and the application will determine what to use.

Here is a blow delay curve for a breaker and fuse. The trip is NOT instant, and it’s a time vs current relationship.

Fuses on the other hand need to be sized to protect the wire, and also to make sure it can cover the short current interrupt rating. I always use HRC (High Rupturing Capacity) fuses on my battery mains from REPUTABLE brands like Bussman Cooper, MEGA or other. No import garbage.

The operating voltage of the system also matters in both these examples. Failure to do so may result in arcing which would in turn not stop current flow and result in fire. Its a low concern in 12v system, but still worth mentioning.

Consult the manufacturers spec sheet and you need to calculate you actual loads you are trying to protect. Arbitrarily sizing this stuff because some guy on the forum says it's good is how you burn your rig down.

This is a decent video to watch if you want a little more info:
YouTube

 

[ElectroBoy]

Circuit breakers generally are not used in an OEM automotive application. Other than aftermarket lighting where it serves more as an on/off switch.