Size breaker for device or wire?

[JDBoston]

I am thinking this is a dumb question and most people know that the circuit breaker is there to protect the wire rather than the device.

So why is it that I still see small breakers for individual devices (for example 1 or 2 amp breakers) when using 22AWG wire. Why wouldn't you use a 5 amp every time for more versatility in the future? For example if you choose to add something else into that circuit.

Thanks

 

[gkochers]

Because the Garmin manual, or other manufacturer, says to use a 2 amp breaker.

 

[Pdp7427]

I’d assume that by going smaller than required for the wire, now both the wire AND the device are specifically protected. But that’s just a guess.

 

[kirkbauer]

The breaker should be both small enough to protect the wire and small enough to protect the equipment. So, if you have a wire that could theoretically carry 5 amps but the equipment specifies that it should have a 2-amp breaker, then you have a 2-amp breaker. Arguably you might be able to save a tiny bit of weight and money by using a smaller wire that would more closely align with the 2-amp breaker.

 

[ariel_arielly]

I’d assume that by going smaller than required for the wire, now both the wire AND the device are specifically protected. But that’s just a guess.

In general, Fuse (or CB) does not protect the device but the wire feeding the device. If there is a problem inside an electronic equipment, that problem might consume currents higher than what it was designed for and some traces on the PCB might burn. In this case there is no need to replace fuse or reset the CB because it is too late... The fuse protects the wires against too hi currents or short circuit. It is recommended that the wire size will be as such as it same as what the equipment consumes according to the number of the manufacturer recommended the fuse shell be used. In this case there will be good protection. It must be considered that in most cases more than one instrument is fed through one wire. In that case, the wire should carry the total currents of all the instrument and it should be protected respectively by the correct fuse (CB).

 

[DanH]

I am thinking this is a dumb question and most people know that the circuit breaker is there to protect the wire rather than the device.

So why is it that I still see small breakers for individual devices (for example 1 or 2 amp breakers) when using 22AWG wire. Why wouldn't you use a 5 amp every time for more versatility in the future? For example if you choose to add something else into that circuit.

I don't think it's a dumb question.

We generally wire using 22AWG as a minimum size, for durability. A 1 or 2 amp breaker is thus for shutting down the circuit if something bad is happening inside the driven component. So...

Because the Garmin manual, or other manufacturer, says to use a 2 amp breaker.

Yeah, but why? What physical process can take place inside a component using 5 amp protection that won't happen with 2 amp protection? A little more smoke? Burns a bit larger gap in the circuit to ground?

Side note....design around fuse blocks, and it becomes easy to swap for a larger fuse at any time.

 

[penguin]

I've often wondered the same thing. The only conclusion I have come to is that equipment manufacturers have an equipment centric view, understandably so! But we are building airplanes, not equipment, and have to take a whole airplane view. Breakers or fuses protect the wire from burning the airplane. By all means follow the equipment maker's recommendation but there is nothing wrong in using a 5 amp cb or fuse on a 22g wire. In general the smallest breaker or fuse I use is 5 amps unless I have something smaller in my parts box to use up, no point in spending $20 on a cb if you don't have to. The smallest wire I use is 22g and the smallest breaker/fuse I buy is 5 amp. Pete