On 4/30/2008 8:32 PM Tony Hwang spake thus:

David Nebenzahl wrote:
On 4/30/2008 6:46 PM Tony Hwang spake thus:

Boden wrote:



The purpose of the breaker is to protect the wire from excessive
current. So long as the wire gauge and breaker capacity are matched
properly the size of the load is immaterial.

Hmmm,
Really? wire is link between breaker and the load. Current flowing on
the wire is depending on load. You are trying to say breaker only
protects wires, nothing to do with the load? Does not make sense to me!


The point is that the tripping point of the breaker depends on the
maximum capacity of the wires, *not* the load. Think about it and you'll
see why this is so. I suppose you could say that it's more important to
protect the wires, since they're what can cause fires if overloaded.

So if you have a device that normally draws, let's say, 1 amp on a
20-amp circuit, and the device overloads and draws, let's say, 10 amps,
that device is going to burn up without tripping the breaker. No way to
avoid it, unless the device itself is fused.

Hmmm,
Who in right mind would configure/install a wire/load like that? All 3
is on a closed loop. They all interact together.

You would. I would. We all do.

Think about it: you've got a 20-amp circuit in your house connected to a
run of baseboard outlets. You've got various things plugged into that
circuit: let's say one of them is a device that draws half an amp
maximum. Then let's say that device overloads and draws, let's say, 10
amps: enough to blow the device, but not enough to blow the breaker. (Of
course, it's far more likely that an overload will cause a direct short
which *would* trip the breaker, but this scenario is possible.)

If I understand your logic correctly, then yes, we could set things up
so that each load is perfectly matched to its wires. But that would mean
we'd need a separate circuit *and* circuit breaker for each and every
device in the house. The systems we actually have--branch circuits each
serving a number of devices--is a compromise.


--
The best argument against democracy is a five-minute
conversation with the average voter.

- Attributed to Winston Churchill