Mr. Electricity is your guide to saving energy in your home.
Rebates & Tax Credits
for U.S. consumers
Rebates. For buying energy-efficient appliances like refrigerators, washing machines, and air conditioners.
Tax Credits. For installing things like high-efficiency water heaters, air conditioners, heaters, roofing, insulation, doors & windows, solar panels, etc.
We're recommended by the government of Berks County, PA.
Related sites:
Watt Watt. News about efficiency and conservation, written by readers of the site.
Home Power Magazine. All about renewable energy for the home.
No-Impact Man. Blog about a family striving to have no net impact. (i.e., What little they use, they offset.) Inspirational.
Off-Grid. News and resources about living without being connected to a utility company.
Ask Mr. Electricity in the news:
Cold, hard cash, Kansas City Star, June
22, 10
Stretch your dollar, not your budget, Globe
and Mail, May 18, 10
Energy-saving schemes yield ยค5.8m in savings, Times
of Malta, Dec. 20, 09
Four ways to reduce your PC's carbon footprint, CNET,
Dec 2, 09
Enjoy the mild weather, low electricity bills, Detroit
Free Press, Jul 18, 09
The most energy-efficient way to heat a cup of water,
Christian Science Monitor, Jun 16, 09
Ten ways to save energy, Times of Malta,
Jan 3, 09
Measuring your green IT baseline, InfoWorld,
Sep 4, 08
The Power Hungry Digital Lifestyle
(PDF), PC Magazine, Sep 4, 07
Net
Interest, Newsweek, Feb 12, 07
Going Green, Monsters and Critics, Jan 6,
2007
A hunt for energy hogs, Wall Street Journal
Online, Dec 18 06
|
|
|
|
How
much electricity can you get from an outlet or
circuit?
I've heard that it can be a
potential hazard to plug a power stip directly into another
power strip and that you should rather plug the power strip
directly into a wall outlet "only", it this true? Along
those same lines, I also heard that you should only plug
"one" item into an extension cord even if they have several
plugs available. What are the facts?
--
Cincy Ward, Berkeley, CA, Feb. 2005
For some reason, UL (the group which evaluates
the safety of electrical products) says that you
shouldn't daisy-chain multiple power strips, and that you
shouldn't plug a power strip into an extension cord. Any
instructions that came with your power strip would
probably tell you the same thing.
That said, I can't see what the problem would be in
doing so, as long as you don't plug in so much stuff that
you exceed the capacity of the circuit (see the next
question), and as long as the power strips have nice
thick cords to handle all the electricity you're pulling.
Seems to me that several power strips chained together
would be no different than using a single thick orange
extension cord.
But the officials and manufacturers recommend
otherwise, so if you want to daisy-chain multiple power
strips together, you do so at your own risk.
Regarding a three-outlet extension cord, why would
they put multiple outlets on the cord if you weren't
supposed to use them? As long as the total of the devices
you're plugging in doesn't exceed the wattage or amperage
of the cord (look for the label on the cord) or the
circuit the cord is plugged into, you should be fine.
How many
watts can a standard outlet deliver before it's overloaded?
I ask this because occasionally when I'm using a lot of
electronic appliances, electricity shuts off in parts of my
home. I have to switch the fuse in order to restore power.
What am I doing wrong?
-- Mark Lee, Mar.
2003
You're not overloading an outlet,
you're overloading a circuit. First understand
that each circuit usually supplies power to several
outlets and lights. For example, Circuit A might supply
power to the four outlets in the master bedroom plus the
ceiling light, Circuit B might supply all power to the
bathroom, etc. Each circuit is controlled by a breaker or
a fuse. So you don't really overload an individual
outlet, you overload a whole circuit.
You can't tell which circuit an outlet's on just by
looking at it. The only way to tell is to plug
something in, turn it on, and keep turning off breakers
(or removing fuses) until the appliance turns off. You
can make a circuit map of all outlets and lights in your
home this way. Once you know which outlets are on the
circuit that's being overloaded (and which are not), you
can plug some of the offending appliances into outlets on
different circuits. That way the overloaded circuit won't
have to try to supply so much power.
Also, if there are any lights on the overloaded
circuit, replace them with compact fluorescent bulbs,
which use 75% less energy than normal bulbs.
So, to rephrase your question, how many watts can a
circuit deliver before it's overloaded? Most
modern residential circuits are 15 or 20 amps, so we're
looking at a max load of either (15A x
120V =) 1800 watts or (20A x 120V
=) 2400 watts before the breaker trips. The
breaker will be labeled either 15 or 20. I'm unfamiliar
with old-style fuse-type circuits but I'm guessing
they're also around 15 or 20 amps.
For continuous loads (on for more than three hours)
the limit is 20% lower. So for 15-amp breaker, you
can't draw more than 12 amps from the circuit for more
than three hours, or 1440 watts (12A x 120V). And what do
you know, the wattage of a huge window-unit AC or a large
electric space heater is... 1440 watts.
(source
1, source
2)
Some people are tempted to swap out a breaker with
a larger one to keep it from tripping. Don't. Your
home's wiring almost certainly isn't thick enough to
handle a higher load. If you put more current through the
wiring than it's capable of handling, it can heat up and
burn your house down. If you keep tripping a breaker,
just plug some of the offending items into different
circuits (or stop using so much electricity to begin
with).
Thanks to Frank Ketchum for
the reference to the National Electric
Code.
We have
about 120 servers running in a computer data center. The
specs on these say that the power supplies are
"Auto-switching 100/240V AC power". Now, if I'm reading your
site right, then the most these should draw would be 2 amps
--however, we have had five plugged into a 15-amp power
strip and the strip has tripped! My question is, how
can these computers be drawing (as they must be) more than 3
Amps each?
--Jessica
Palmer, April
2004
First off, the 15-amp rating is only for an
instantaneous load. For a continuous load,
it's likely about 20% less. So your 15-amp strip is
really a 12-amp strip, if the equipment is on constantly.
Next, the 100/240V label means that the server can
handle any kind of electricity from 100V to 240V, so it
will work with the voltage in any country. (US/Japan is
100-120V, most others are 220V). But your question wasn't
about foreign use, so now that we've taken care of the
100/240V label let's move on.
finally, I don't see where you're getting that your
servers draw a maximum of two amps. That's unrelated to
the 100-240V label. If the maximum number of amps aren't
listed, then the number of watts will be, and you divide
the number of watts by the number of volts (120V, for the
U.S.) to get the number of amps.
So let's say that one of those two things is the case
and you know your servers should be drawing no more than
10 amps, so why is it tripping your "15-amp" (really
12-amp) power strip? There are two possible answers:
The first possibility is that you have a faulty power
strip. Try another one.
The second possibility is that when the final server
or two is switched on the brief power surge when the
equipment is turned on is enough to exceed the 15-amp
rating of the strip. The surge you get when you turn on
equipment is so brief and so small that you'll never see
its effect on your electric bill, but sometimes it's
enough to trip a power strip or circuit breaker.
If swapping out power strips doesn't work, I suggest
getting a cheap watt-meter and
measuring how much electricity each server is using.
Either way, I'd be interested in hearing what you
ultimately discover.
I'm trying to determine how many
amps I'm putting on a circuit so I don't overload it, but
I'm having a hard time understanding the labels. For
instance, my DSL modem adapter says "INPUT: 120V 60Hz 30W"
and "OUTPUT: 12VAC 1.67A" I understand how to convert
watts to amps [Watts / Voltage = Amps], so it looks
like in this case the input (30 watts or .25 amps) is less
than output (200.4 watts or 1.67 amps). But your site
says that input is always higher than output. What am I
missing? -- David
Hylton, Oct.
2003
What you're missing is that the input is 120
volts but the output is only 12 volts. Electricity from
the wall is AC, and is 120 volts. The adapter changes
that to low-voltage DC, usually 3, 6, 9, or 12 volts. So
the output is 12V x 1.67A = 20W, which is less than the
30W input. Output is always less than input, because the
conversion process is inefficient.
|