Date: Fri, 6 Mar 1998 21:35:59 -0600 From: Karl Denninger <karl@mcs.net> To: Chuck Robey <chuckr@glue.umd.edu> Cc: shimon@simon-shapiro.org, Terry Lambert <tlambert@primenet.com>, dmlb@ragnet.demon.co.uk, wilko@yedi.iaf.nl, julian@whistle.com, hackers@FreeBSD.ORG, lada@ws2301.gud.siemens.at Subject: Re: SCSI Bus redundancy... Message-ID: <19980306213559.63726@mcs.net> In-Reply-To: <Pine.BSF.3.96.980306214647.438u-100000@localhost>; from Chuck Robey on Fri, Mar 06, 1998 at 09:51:41PM -0500 References: <19980306194939.58793@mcs.net> <Pine.BSF.3.96.980306214647.438u-100000@localhost>
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On Fri, Mar 06, 1998 at 09:51:41PM -0500, Chuck Robey wrote: > On Fri, 6 Mar 1998, Karl Denninger wrote: > > > On Fri, Mar 06, 1998 at 05:49:17PM -0800, Simon Shapiro wrote: > > > Telcos run equipment on 48VDC. In most switching rooms, not only you are > > > not allowed (and do not have) power grid AC, you cannot even generate it > > > inside your own cabinet. > > Unless it's changed in the last 5 years, that's not true. The telco's > test equipment is made by companies like HP, and runs on AC (not to > mention the technicians stereos!). Of course they have AC in their > office, and on every single equipment bay. > > Of course, their equipment does largely run on 48V nominal (which usually > means around 55-56 V in fact, else the battery plant'd not ever get > charged). Getting buzzed with 48V is nothing, even with 1500 Amps behind > it, I've been bitten countless times. Ringing battery is _much_ more > painful! Old style teletype, at polar +- 130V, would _really_ wake you > up (thank god that was interrupted). I'm not talking about getting buzzed. I'm talking about bridging it with something near-zero resistance (say, a metallic object). People discount lower-voltage circuits because they *think* they're safer. They're not really if there is what amounts to a near-infinite current source behind them. 110V is perfectly safe if you provide no path to ground through yourself and never bridge hot and neutral (or ground). 48V is perfectly safe under the same conditions. Violate those conditions and you find out how unsafe either can be. -- -- Karl Denninger (karl@MCS.Net)| MCSNet - Serving Chicagoland and Wisconsin http://www.mcs.net/ | T1's from $600 monthly to FULL DS-3 Service | NEW! K56Flex support on ALL modems Voice: [+1 312 803-MCS1 x219]| EXCLUSIVE NEW FEATURE ON ALL PERSONAL ACCOUNTS Fax: [+1 312 803-4929] | *SPAMBLOCK* Technology now included at no cost To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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