DIYbanter - View Single Post

John G

josephkk has brought this to us :
On Wed, 12 Sep 2012 17:25:03 -0700, (Dave Platt)
wrote:

In article ,
Dallas wrote:

So, I have a lot of questions:
1) First, why did the computer act like it tripped an overload in its
power supply, most of the load was outside of the computer?

At a guess, the external load may have dragged down the voltage at the
outlet far enough that the computer power supply's "line undervoltage"
circuit kicked in, and shut down the computer cleanly.

Somehow that doesn't sound reasonable.

Why didn’t
the residential breaker trip instead?

Residential circuit breakers are typically of the "thermal" type.
They require some amount of time to react to an overload... the higher
the degree of overload, the slower they trip.

Ummn, i think you meant: The higher the overload the faster they trip.
Every breaker has what is called an (i^2)*t curve. At threshold tripping
current it may take 4 hours to trip, at 10 X tripping current it must trip
within one second.

This allows a circuit to have a momentary over-current (e.g. a
refrigerator drawing a surge of current when it first starts up)
without repeatedly tripping the breaker.

"Magnetic" circuit breakers will trip very rapidly in the face of even
a short overload... but I believe these are rarely found in
residential applications.

2) Can a breaker cut the load for a second without mechanically
flipping to the off position?

Typically, no.

Well, if the circuit breaker trips it must move to the "tripped" position
and stay there until reset.

3) I seem to remember some people just replacing the 15 amp with a 20
amp breaker when things get tight, is that a dangerous/stupid idea?

It is quite possibly both dangerous and stupid, and likely illegal.
The circuit breaker is supposed to be selected to be below the upper
limit of what the circuit wiring and outlets can handle safely.

It is actually all three. If there is a fire and the insurance company
investigator finds such a circuit they won't pay a dime.

If you draw more current than the wiring and outlets are designed to
deliver, you can suffer excessive voltage drop in the wires (lights
dim, motors slow down, and devices with "low line voltage" shutdown
circuits will shut themselves off. The wires can overhead. Also (and
perhaps more of a problem), the outlets themselves can overheat.

Now, it is *possible* that the wiring and outlets in your house are
actually rated for higher amperage (or that the outlets could be
upgraded for this). If so, it *might* be possible for a licensed
electrician to confirm this, and then swap out the lower-rated outlets
and breaker to increase the branch current level. I don't think it's
terribly likely, though.

Very much agreed.

4) Does anyone see a problem running about 13 amps through one
household outlet in a tree of several power strips?

This is probably in the grey zone. A lot of power strips are rather
cheap, and their internal wiring and contacts are designed for
"convenience" loads rather than high-current applications. If you
pull lots of amps through several of them together, you'll probably be
making the voltage-drop and heating problems worse.

I understand that many areas' electrical codes specifically forbid
"daisy chaining" power strips.

Also true.
In Australia Power strips are generally fitted with a breaker so the
first strip governs the total load (10 amps)on a daisy chain and so
ensures (goes a long way) no overload occurs.

I think this has been a requirement for may years now.

Should I increase my fire insurance coverage? :- )

I suggest that you revise your expectations, instead... limit your
circuit use and loads to what they are presently rated for.

Agreed.

--
John G