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From: rhorn@infinet.UUCP
Newsgroups: comp.dcom.modems,comp.periphs,misc.wanted
Subject: Re: Reliability of Modular Jacks
Message-ID: <625@infinet.UUCP>
Date: Mon, 16-Feb-87 18:09:43 EST
Article-I.D.: infinet.625
Posted: Mon Feb 16 18:09:43 1987
Date-Received: Fri, 20-Feb-87 04:00:27 EST
References: <267@aucs.UUCP> <299@mtxinu.UUCP> <796@fmsrl7.UUCP>
Reply-To: rhorn@infinet.UUCP (Rob Horn)
Distribution: na
Organization: Infinet, Inc.  North Andover, MA
Lines: 35
Keywords: RJ-11, RJ-12, RJ-45, RS-232
Xref: utgpu comp.dcom.modems:266 comp.periphs:218 misc.wanted:539
Summary: Telephone lines may have 150 volts on them

The growing popularity of using the RJ series connectors (aka
`telephone modular jacks') for terminal cabling is exposing a lot of
people to a major risk.  These jacks are directly interchangable with
normal telephone jacks, and you can be sure that people will make
mistakes and plug terminals into telephone equipment.  This can do
tremendous damage, and may even pose a health risk.

When a telephone rings, the ring signals are a pulsed DC that can
reach as high as 150 volts!  In terms of vaporized semi-conductors,
this is just as destructive as plugging your connector into an electric
outlet.  The frequency, voltage, and power don't quite match standard
electric power but they are more than enough to totally destroy any
unprotected electronics.

The health risk arises from the potentially poor grounding of the
digital electronics.  These circuits are not normally designed to be
safe with 150 volts on them.  This risk may be shortlived since the
digital circuit will quickly self destruct.  Telephone extension
cables with RJ connectors pose a greater hazard.  When the phone rings
there is high voltage on that connector.  If a child is chewing on it
when the phone rings there is a real risk of death from electrocution.
(The hazard to adults is lower since they don't normally chew on
cables, and the power levels are low enough that the odds are in favor
of a nasty jolt instead of fatal one.)

Beware of using these connectors in inappropriate circumstances.  (I
was warned quite thoroughly by our Mechanical Design people when I
suggested it.  I learned then for the first time that telephones are
not UL approved, nor will they ever be, because of this 150 volt
risk.)

-- 
				Rob  Horn
	UUCP:	...{decvax, seismo!harvard}!wanginst!infinet!rhorn
	Snail:	Infinet,  40 High St., North Andover, MA