UPS for power regulation?

[Seth Gordon]

(Posted and emailed.)

On Tue, 2002-12-31 at 08:57, Billy SG McCarthy wrote:
> My parents have a fairly old house, such that there is
> only 1 outlet in the room where they have 2 computers
> (and some lights, etc).  The computers are never both
> running at the same time, but it still makes me a bit
> uneasy, 2 full power strips, 1 plugged into the other.
>  
> 
> I was thinking they should get a UPS and plug
> everything into that.  Does this make sense?  If it
> does, how powerful a UPS should they get?  If not, any
> suggestions aside from getting an electrician to put
> in more plugs?

Short answer: If your parents actually have a power problem, then
getting a UPS is unlikely to solve it.

The number of plugs and power strips doesn't strictly matter; what
matters is the amount of current going through the power strip and then
through the circuit breaker in the house.

For example, if you turn on a 100-watt bulb, that will draw about 0.83
amperes (100 W / 120 V) of current.  The wiring inside your walls, and
therefore your circuit breaker or fuse, can take up to 15 amperes.  A
power strip or extension cord will probably take less than that: look
for a label or tag with the number.

So you need to add up the maximum amperage of all the things that are
plugged into each power strip (for example, the AC converter on the
laptop that I'm using now is labeled "1.5 A"), *including other power
strips*, and make sure that the sum isn't greater than what the power
strip can take.  If it's too high, and your power strip has some kind of
circuit breaker, then it will trip the circuit breaker when too many
things are turned on at once.

Then find out what outlets are connected to the same circuit breaker as
the power strips, find out the sum of the amperages of everything that
is plugged into all those outlets, and make sure that the sum isn't over
15 A.  If it's too high, then you risk tripping the circuit breaker of
your house when too many things are turned on at once.

If everything is running within those limits, then your parents don't
need a UPS (although they do need a good surge protector).  If you do
have too much current going through one place, then a UPS will buy your
parents time while they turn things off, but it won't fix the real
problem, which is that too many things are plugged into the same
circuit.  Even if an electrician adds more outlets to the room, if those
outlets are all connected to the same circuit breaker, it still won't
fix the real problem.

> 
> Kindly yours,
> Billy S G McCarthy
> 
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-- 
"Computer security policy is expressed in a language such as Spanish
or English or Japanese."  --Rita C. Summers, _Secure Computing_
// seth gordon // sethg at ropine.com // http://ropine.com/sethg/cv.html //