How much Voltage Drop is acceptable for computers? Outdoor Desktop Office

[Dubs]

Hello, I'm not very good with basic electricity, but I'm interested in
running a 200 - 250 ft cable, probably Underground UFB cable as
opposed to an extension cord. I want to run a 17" monitor, a desktop
computer, and 2 or 3 flourescent bulbs. I'm not really to concerned
about the lifespan of my computer's power supply or my monitor. That
stuff is next to free for me. What I'm more worried about is the
money to buy the cable. Is 12 guage cable acceptable? Do I have to
use 10 guage? Are there any fire risks involved if this is all
plugged into a circuit breaker? Does anybody know about any good
deals on cable?

Thanks Folks

 

[Michael A. Covington]

You need a licensed electrician for this.

Voltage drop should not be a problem, but this is the kind of high voltage
project that I would leave to a professional.

 

[Robert Baer]

Hello, I'm not very good with basic electricity, but I'm interested in
running a 200 - 250 ft cable, probably Underground UFB cable as
opposed to an extension cord. I want to run a 17" monitor, a desktop
computer, and 2 or 3 flourescent bulbs. I'm not really to concerned
about the lifespan of my computer's power supply or my monitor. That
stuff is next to free for me. What I'm more worried about is the
money to buy the cable. Is 12 guage cable acceptable? Do I have to
use 10 guage? Are there any fire risks involved if this is all
plugged into a circuit breaker? Does anybody know about any good
deals on cable?

Thanks Folks

First you need to know (measure) the total current drawn by all of the
loads.
10 AWG wire is about 1 ohm per 1000 feet and 12 AWG wire ia about 1.6
ohms per 1000 feet.
For a 250 foot run, that is a total of 500 feet.
Say you used 12 AWG, that would be about 0.8 ohms; at 2 amps current
(crudely 250 watts) that would give a drop about 1.6 volts - which is
not enough to worry about.
You should use wire rated for underground useage, and have zero
splices anywhere outside (or underground).
Do not buy used wire, the cost savings is not important; *safety* IS
important and well worth a few dollars.

 

[Winfield Hill]

Robert Baer wrote...

Say you used 12 AWG, that would be about 0.8 ohms; at 2 amps
current (crudely 250 watts) that would give a drop about 1.6 volts
- which is not enough to worry about.

BUT, most computer and monitor power supplies are not PFC, not
power-factor corrected, and draw their current in a short pulse
in the middle of the sine wave. With a stiff source impedance
they draw about 10x the rms current, so that'd be 20A and a 16V
drop. Of course we'd not call 0.8 ohms a stiff source, so the
pulse wold be spread out some and the drop a bit less severe.

 

[John Woodgate]

I read in sci.electronics.design that Winfield Hill
about 'How much Voltage Drop is acceptable for computers? Outdoor
Desktop', on Sun, 29 Aug 2004:

Robert Baer wrote...

BUT, most computer and monitor power supplies are not PFC, not
power-factor corrected, and draw their current in a short pulse
in the middle of the sine wave. With a stiff source impedance
they draw about 10x the rms current, so that'd be 20A and a 16V
drop. Of course we'd not call 0.8 ohms a stiff source, so the
pulse wold be spread out some and the drop a bit less severe.

Considerably less severe. I don't have data for 120 V mains, but this
issue is important for IEC 61000-3-2 and -3, and 0.8 ohms strongly tends
to turn 'rapacious' rectifier loads into pussy-cats.

 

[Paul Burridge]

Robert Baer wrote...

BUT, most computer and monitor power supplies are not PFC, not
power-factor corrected, and draw their current in a short pulse
in the middle of the sine wave. With a stiff source impedance
they draw about 10x the rms current, so that'd be 20A and a 16V
drop. Of course we'd not call 0.8 ohms a stiff source, so the
pulse wold be spread out some and the drop a bit less severe.

"Stiff source impedance"? I know what you mean, but have never
encountered that curious term before...

 

[~Dude17~]

X-No-Archive: Yes

Hello, I'm not very good with basic electricity, but I'm interested in
running a 200 - 250 ft cable, probably Underground UFB cable as
opposed to an extension cord. I want to run a 17" monitor, a desktop
computer, and 2 or 3 flourescent bulbs. I'm not really to concerned
about the lifespan of my computer's power supply or my monitor. That
stuff is next to free for me. What I'm more worried about is the
money to buy the cable. Is 12 guage cable acceptable? Do I have to
use 10 guage? Are there any fire risks involved if this is all
plugged into a circuit breaker? Does anybody know about any good
deals on cable?

Thanks Folks

Computer power supplies are often rated for 90 to 132V and usually
exactly twice that with switch in 230V position. Many monitors are
rated for full range 90 to 264V. Use a good power supply though.
Cheap power supplies often have a narrower tolerance and when you go
out of the band, your PC will crash or reboot. Because of the way
computer draws current, power factor is about 0.6. Because it's crest
factor is so high, peak current can be over 3 to 1. Thin wiring will
result in high harmonic distortions at the line end making the top and
bottom of sinewave closer to a shape of mesa.

 

[Ken Taylor]

X-No-Archive: Yes


[email protected] (Dubs) wrote in message

Computer power supplies are often rated for 90 to 132V and usually
exactly twice that with switch in 230V position. Many monitors are
rated for full range 90 to 264V. Use a good power supply though.
Cheap power supplies often have a narrower tolerance and when you go
out of the band, your PC will crash or reboot. Because of the way
computer draws current, power factor is about 0.6. Because it's crest
factor is so high, peak current can be over 3 to 1. Thin wiring will
result in high harmonic distortions at the line end making the top and
bottom of sinewave closer to a shape of mesa.

Not sure where the OP is but assuming he has a 110VAC supply, even with 10
gauge cable, at 250 feet length and assuming a 500W load (which seems about
right for what he's saying), there'll be of the order of 10 volts drop along
the cable. It doesn't sound much but that also means that there'll be about
1W per foot of cable being dissipated 'somewhere': this is a recipe for
disaster.

That length of extension is a job for someone who knows their stuff and can
do it properly - they will probably even be able to source the cable cheaper
than the lay person.

Ken

 

[scada]

Hello, I'm not very good with basic electricity, but I'm interested in
running a 200 - 250 ft cable, probably Underground UFB cable as
opposed to an extension cord. I want to run a 17" monitor, a desktop
computer, and 2 or 3 flourescent bulbs. I'm not really to concerned
about the lifespan of my computer's power supply or my monitor. That
stuff is next to free for me. What I'm more worried about is the
money to buy the cable. Is 12 guage cable acceptable? Do I have to
use 10 guage? Are there any fire risks involved if this is all
plugged into a circuit breaker? Does anybody know about any good
deals on cable?

Thanks Folks

You did not mention where you are from. Here in the US, as a general rule of
thumb if you go with a run larger than 50' you should use the next wire
size. A run of 200 - 250' I would go with a "Sub Panel". A 40A Sub Panel,
with 20A circuits should fit your needs.Check with your local codes and the
NEC code book, or better yet confer with a licensed electrician if you've
never done this work.

 

[Walter Harley]

"Stiff source impedance"? I know what you mean, but have never
encountered that curious term before...

Art of Electronics.

 

[Paul Burridge]

Art of Electronics.

I don't think so... "stiff signal source" might be a better term.