In article <telecom24.280.16@telecom-digest.org>,
Howard S. Wharton <yhshowie@acsu.buffalo.edu> wrote:
> Pat,
> By daisy chaining your power strips, you are causing the first ones in
> the chain to be overloaded and possibility the circuit it's plugged into.
> And it is a fire waiting to happen.
> Howard S. Wharton
> Fire Safety Technician
> Occupational and Environmental Safety Services
> State University of New York at Buffalo
If the first power strip has a circuit breaker, then everything
downstream of that strip is limited to the current available on that
single power strip. It dosen't matter how many strips are plugged
together, the current limitation will stay the same, unless there are
smaller circuit breakers downstream, in which case the limitation will
decrease at that point.
I do note your concern about overloading, and I will note that it's
not so much that the circuit will be overloaded, as it is that the
single outlet on either the first power strip, or the wall may become
overloaded.
What matters most is the condition of the wiring, including the power
strips, and it is for that reason that I suggest using quality power
strips, from a known vendor, and avoiding the generic plastic strips
made in the third world.
Keep your power strips in good condition, and dispose of them when
they show signs of abuse or wear. Strips that have broken ground pins
should be disposed of, or have the plugs replaced.
Large loads such as laser printers or copiers, should be plugged into
wall circuits if at all possible.
Wall outlets that are worn, or otherwise abused, should be replaced by
a electrician, or other qualified person.
I prefer not to daisy chain strips together, but instead pick a high
quality strip to be the master, and use that to feed the other strips,
thus distributing the load across multiple outlets on the power strip.
It would also be a good idea to mount your power strips to a board,
desk, wall, or other fixed object to keep the wiring from becoming a
tangled mess.
Try to keep your wall warts separated enough so that cooling does not
become a problem. Do not pile stuff on top of power strips. Do not let
wall warts get buried in the carpet.
Your typical wall wart is going to draw between .1amp and 2amps,
although some may draw more, check the nameplate rating.
A quick sampling of the wall warts in my office comes up with the
following: radio charger 24w(0.2amp), ethernet switch 18w(0.15amp),
cellphone charger 6w(0.05amp), wireless bridge 30w(0.25amp), dsl
bridge 18w(0.15amp), Palm charger 18w(0.15amp), etc ... Total load of
the 6 wall warts in this example = 108w = 0.9a
A generic power strip is normally protected with a 15amp circuit
breaker. Since many of the power strips available today are cheap
plastic junk, I would advise that those be derated even further, to no
more than 10amps.
Your normal wall circuit is going to be either 15 or 20amps.
A circuit should not be loaded to more than 80% of it's rated capacity
under normal usage, which says that the maximum load on a 15amp power
strip should be no more than 12 amps, assuming that nothing else is
plugged into the same circuit. In a house, there may be 1-12 (or more)
outlets on a single circuit depending on when the home was built, how
cheap the builder was, and if the homeowner/handyman/etc has added
outlets without proper capacity planning.
P(watts) = I(current)*E(voltage), so:
2400w @120v = 20a
1800w @120v = 15a
1440w @120v = 12a
1200w @120v = 10a
600w @120v = 5a
120w @120v = 1a
12w @120v = 0.1a
As you can see, it takes a lot of your typical wall warts to overload
a normal household circuit, or even a cheap generic power strip.
-- Welcome My Son, Welcome To The Machine --
Bob Vaughan | techie @ tantivy.net |
| P.O. Box 19792, Stanford, Ca 94309 |
-- I am Me, I am only Me, And no one else is Me, What could be simpler? --
[TELECOM Digest Editor's Note: I changed my setup today to use the
three outlets on the back of a UPS to connect the three power
strips each separately. Then I used the two newly gained outlets on
the power strips (where strip 2 was fed from 1 and where strip 3
was fed from strip 2) to plug in the two devices which lost their
home when the plugs on the back of the UPS were taken over. It
seems to have balanced the load a little better. PAT]
Bob Vaughan (techie@tantivy.tantivy.net)