[sci.electronics] Flakey Power?

gillies@p.cs.uiuc.edu (06/06/89)

Here's a question I'm curious about:

What can a consistently too low/high-voltage wall socket (100/140
volts instead of 120, for instance) cause a PC power supply to do to
the rest of the computer?  How can erratic frequency control change
the supply, and in turn, affect the computer?

Someone in comp.sys.mac has had 10 separate problems with their Mac/SE
(5 disk drives, 2 system boards, 2 keyboards, 1 mouse).  Many users
have no problems at all.  I'm curious if the power outlet in their
dorm room might be a partial culprit.

Don Gillies, Dept. of Computer Science, University of Illinois
1304 W. Springfield, Urbana, Ill 61801      
ARPA: gillies@cs.uiuc.edu   UUCP: {uunet,harvard}!uiucdcs!gillies

Ploni.Almoni@mailcom.FIDONET.ORG (Ploni Almoni) (06/13/89)

Don -   re your problem of "outlet voltage" varying from 100 - 150 V
  
This is a well known, SERIOUS and DANGEROUS problem.  It is NOT good
for the power supply and will eventually lead to premature and
catastrophic failure.  To say nothing of what the line surges will do
to your data!!
  
It is caused by an ungrounded neutral - a code violation as well as a
safety hazard.
  
In a 120/240 V service, the power utility supplies 120 V each side of
a grounded neutral. This grounded neutral (the "white wire" in the
cable or the "elongated slot" in the outlet) is supposed to be a
solid, reliable connection and extended throughout the installation. 
  
However, if the neutral in the particular circuit (group of outlets,
for instance) becomes isolated from the entrance grounded neutral, the
120 V loads stacked in series between the two "hot" lines will not
receive 120 V.  What they will receive between the "hot" line and the
UNgrounded neutral depends on the balance of the loads between the two
"sides" of the 240/120 circuit - in that case the only "given" is the
240 V "line-to-line".  If the loads are balanced, the line-to-neutral
voltages will be approximately correct.  If the loads are unbalanced,
one side will get a high voltage while the other will get a low
voltage.  And as the balance shifts (as stuff is turned on and off,
for instance), the voltage will go up and down.  90/150 V is not
unusual.
  
This problem has been the cause of an awful lot of "appliance frying"
over the years.  It also results in improper operation ( = failure to
protect) of Ground Fault Interrupters, a specific safety device.  And
it can cause shock hazards on equipment plugged into those lines.
  
QUICK - get the house electrician to check the breaker panels and
entrance equipment to see if a "white wire" has broken or come loose
from the neutral bus.
  
Your computer's life - or YOUR life - may depend on it.
  
          -=Ploni=-  
  
  



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myers@hpfcdj.HP.COM (Bob Myers) (06/17/89)

>This is a well known, SERIOUS and DANGEROUS problem.  It is NOT good
>for the power supply and will eventually lead to premature and
>catastrophic failure.  To say nothing of what the line surges will do
>to your data!!
  
>It is caused by an ungrounded neutral - a code violation as well as a
>safety hazard.
 

While this is a very likely cause, it is not necessarily the only one.  
Problems "upstream" from your service entrance can also cause voltage
fluctuations.  SO - if you check your neutral and safety ground connections
and find everything both hunky and dory, DON'T just resign yourself to
the problem.  Call the utility company, and demand that they get their
act together.  (It may take some convincing - I had an experience with a
P.S. co. in Indiana which flatly denied the problem until shown the charts
from a recording voltmeter (chart recorder) - but you do have a right to 
decent electrical service!)

 
Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
myers%hpfcla@hplabs.hp.com               |  sentient life-form on this planet.