[clug-talk] OT: Computer safety

Peter Carless pcarless at carless.com
Wed Dec 8 21:39:03 PST 2004


Hi there,

My $0.02 worth on the subject.

All computers that we are likely to be using plug into a standard 15 amp 
110 volt ac circuit. This would mean that if you had too many computers 
plugged into the same circuit and they were drawing excessive power then 
the circuit breaker (or fuse if you have older wiring) would trip and power 
to the computer would be killed.
Keep in mind, that even if the computers are plugged into different wall 
outlets they could be still on the same circuit breaker, as I believe that 
the electrical code allows  up to 10 to 15 outlets to be fed from the same 
breaker,

One 15 amp circuit should supply approx. 1700 watts (115 x 15). This does 
not take power factor into account but it should be close enough approximation.

If the electrical wiring is up to standard and you plug too many computers 
in it should just pop the breaker or fuse and should not start a fire.

There are a few safety considerations that should be taken into account 
however.

If you have an older house with fuses instead of circuit breakers make sure 
that there is a 15 amp fuse in the circuit  and that some one has not 
replaced the 15 amp fuse with a 20 amp or higher capacity. In this case you 
could be drawing more than 15 amps through wire that was designed to carry 
15 amps causing over heating and a fire.

Make sure that your outlets are wired correctly and are properly grounded. 
You can purchase testers for less than $10 that plug into an electrical 
outlet and let you know instantly that  your wiring is correct.

If your house was built in the early to mid 70's it may have aluminium 
wiring. At that time the price of copper was sky high and aluminium wiring 
became popular as a cost saving measure.  Aluminium wiring is apparently 
quite safe if it is wired correctly and that receptacles approved for 
aluminium were used. However aluminium wiring can cause receptacles to 
overheat if it was not installed correctly and apparently at the time this 
was not uncommon. If you suspect  you have aluminium wiring it would not 
hurt to feel the receptacles and see if they are warm.

If your house is 70 years old or more and the wiring has not been upgraded 
you may have knob and tube wiring. If this is the case I would strongly 
suggest that you consult an electrician.

If you are a bit  paranoid there is a relatively new device available 
called an arc fault circuit interrupter. This would be used instead of the 
standard circuit breaker in your breaker panel. These will trip if there is 
any arcing in the circuit, even when the current draw is less than 15 amps. 
I have heard that they are required for circuits supplying bedrooms in some 
provinces. These devices do not come cheap. The price of $70 to $80 comes 
to mind compared to $10 to $15 for a standard circuit breaker.

Another device that you may want to consider is a GFCI (ground fault 
circuit interrupter) These are the devices that are required to supply 
outside and bathroom circuits. You can get these devices to replace a 
circuit breaker (cost about $70.00) or devices that replace standard duplex 
receptacles (cost about $10)
  These devices can be identified by the little "test" button. These 
devices will trip if there is any leakage to ground. If your basement 
floods and your power supply gets wet they will trip instantly. If you have 
old wiring with ungrounded receptacles placing one of these in the circuit 
will provide protection almost as good as having a grounded receptacle. 
These devices provide very good protection against electrical shock.
If your power supply has even a very small electrical leakage these devices 
will trip, which could prevent an electrical fire. A standard circuit 
breaker will not provide this level of protection.


Please note IANE (I am not an electrician).

Before proceeding with any electrical work consult with a licensed 
electrician or apply to the City of Calgary for an electric permit and have 
the work inspected by the city inspector.

Peter




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