Xref: utzoo comp.dcom.lans:989 comp.dcom.modems:1326
Path: utzoo!mnetor!uunet!husc6!cfa!wyatt
From: wyatt@cfa.harvard.EDU (Bill Wyatt)
Newsgroups: comp.dcom.lans,comp.dcom.modems
Subject: Re: Fluorescent lights and data cables
Message-ID: <866@cfa.cfa.harvard.EDU>
Date: 29 Jan 88 14:57:22 GMT
References: <1769@saturn.ucsc.edu>
Organization: Harvard-Smithsonian Ctr. for Astrophysics
Lines: 57

in article <1769@saturn.ucsc.edu>, eshop@saturn.ucsc.edu (Jim Warner) says:
> Xref: cfa comp.dcom.lans:1025 comp.dcom.modems:1506
> 
> In article <865@cfa.cfa.harvard.EDU> wyatt@cfa.harvard.EDU (Bill Wyatt) writes:
>>
>>I can't actually comment on the above question, but I have a warning
>>that may not have occurred to you: Make SURE you have separate
>>circuits for your computers and other quiet power units (including
>>separate GROUND at the outside water main or whatever) that isolate
>>from the lights and other noisy equipment. 
> 
> I disagree that computers are electrically quiet.

Right. But I really meant *other* sources of noise that pollute the
computer's power. 

>  But more important,
> DO NOT ASK FOR SEPARATE GROUNDS.  The purpose of grounding electrical
> equipment is primarily for safety.  Separate "isolated" ground systems
> are a violation of the NEC. 

All grounds are supposed to terminate at the outside water main. I was 
asking for sepaarate CIRCUITS, not GROUNDS. I should have said `separate
ground wires' to make that clear.

> If you are responsible for spec'ing the
> power for a new installation, be sure to get a copy of "Guideline
> On Electrical Power for ADP Installations", FIPS Publication 94,
> U.S. Dept of Commerce, National Bureau of Standards.
> 
>>In our building, built in 1972-3, the fluourescent lights leak a
>>voltage into the neutral wire, so that there's 1.5 volts between the
>>neutral and ground. This is usually OK, but can apparently affect the
>>life of our computers. Since DEC specifies a limit of 0.7 volts, we've
>>sometimes had hassles with field service over the issue.

> I'm not sure I believe this.  The resistance of 12 gauge copper wire
> is 1.6 ohms/1000 ft.  At its rated load (20 Amps), DEC's 0.7 volt
> rule would require your circuits to be no more than 21 ft from the
> panel.  

What don't you believe? That fluorescent lights leak voltage? I'm quoting
the building electrician on that. That DEC's specification is 0.7v?
I'm quoting the head of DEC's F.S. for Boston on that.

> One thing you should ask for is dedicated outlets for the custodians
> to use for their floor waxers and vacuum cleaners.  [...]

Absolutely. Also, we buy noise filter/surge supporessor power strips to
plug in to *all* our computers. At ~$100 per, it's worth it.
-- 

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