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Re: How much light on a circuit?

> Here is another question.  My  house was wired in 68. My fish-room and
>  a couple of other rooms are all on the same 15 amp circuit.  Is there a
>  way to know how much light I can plug in back there before I have to
>  call either an electrician or the fire department? (Either one would have

Watts are calculated by multiplying voltage times current.  Your 15 amp 
circuit can therefore handle a maximum of about 115 x 15 = 1725 watts.  
Naturally, you would not want to run the circuit at the very maximum wattage 
available.  For safety's sake, it would be wise to derate the outlet to 
approximately 1500 watts maximum.  Now you must go around and calculate all 
the wattage of everything plugged into that circuit, including the loads in 
the other rooms that are on the same line.  Add them all up, and that's how 
much load is being drawn.  Whatever is left over is what's available for your 
aquarium.  Be sure to take into account that fluorescent ballasts are 
inefficient, so that a 40 watt tube, say, will actually pull about 80 watts 
due to losses in the ballast.  (That's not precisely correct, but includes a 
safety factor.)  After adding everything up, you'll know whether you're 
within limits or not.  If not, perhaps you can move some of the loads in the 
other rooms to different circuits?  By the way, 15 amp circuits no longer 
meet the National Electric Code, with 20 amp circuits being "standard."  I'm 
trying to remember back, but I seem to recall that was the rule back in 1968 
as well.  If you can look at the actual wire running to the circuit, see if 
you can read the size of the wire.  There will be something stamped on the 
wire that will look like "14/3" or "12/3" or similar.  If the wire is 14 
gauge (the 14 in 14/3), then that circuit is indeed limited to 15 amps.  If 
the wire is 12 gauge, it can actually handle 20 amps, and you could safely 
change the fuse or circuit breaker from 15 amps to 20 amps.  You may also 
have to upgrade the socket itself if it's only a 15 amp socket.  If there's 
any doubt in your mind about how to interpret any of this, hire a licensed 
electrician.  He can run a larger line for you.