Date: Fri, 6 Mar 1998 21:43:45 -0600 From: Karl Denninger <karl@mcs.net> To: shimon@simon-shapiro.org Cc: "John S. Dyson" <dyson@FreeBSD.ORG>, tlambert@primenet.com, dmlb@ragnet.demon.co.uk, wilko@yedi.iaf.nl, julian@whistle.com, hackers@FreeBSD.ORG, lada@ws2301.gud.siemens.at, Chuck Robey <chuckr@glue.umd.edu> Subject: Re: SCSI Bus redundancy... Message-ID: <19980306214345.34788@mcs.net> In-Reply-To: <XFMail.980306193157.shimon@simon-shapiro.org>; from Simon Shapiro on Fri, Mar 06, 1998 at 07:31:57PM -0800 References: <199803070316.WAA00278@dyson.iquest.net> <XFMail.980306193157.shimon@simon-shapiro.org>
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On Fri, Mar 06, 1998 at 07:31:57PM -0800, Simon Shapiro wrote: > > On 07-Mar-98 John S. Dyson wrote: > > Chuck Robey said: > >> > >> 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). > >> > > Getting buzzed isn't the problem with 48V and mega-amps. It is any kind > > of metal jewelery melting and burning off skin :-(. > > We knew to take off all jewlery. The killer was the dog-tags. You stayed > for a qhile in the hospital after one of these evaporated around your nexk. > I witnessed the aftermath of a Phillips #2 screwdriver dropping someplace > it should not. Quite a site. > > A switching center here in town is using surplus submarine batteries. > There are sealed and lay on their side, so they are not as sparky as the > old open cells. Uh, sparks around batteries with the kind of capacities being played with in these environments is a seriously bad idea. So is any impairment of the ventilation system. Together they would make for a rather, uh, interesting situation. I have seen a #2 screwdriver *vaporized* by bridging the supply and ground on such a 48V plant. It was quite impressive, and tends to give you really serious respect for the energy levels involved in these things. Don't screw around when you're working near any high energy source. Voltage is *not* a reliable indication of whether you are dealing with energy levels that can be dangerous or even lethal, and in many ways I respect 48V Telco plant far more than I do 110V house current, if for no other reason than that people who don't know these things tend to get complacent around what they consider "low voltage" and therefore "safe" wiring. BTW, not all telcos prohibit 110V in their colocation areas. We have 110V hardware in a telco colocation room in Milwaukee. We *did* have to provide our own short-run UPS to cover generator startup (they don't cover that on the 110V side) and for the hard-wiring of the power and ground to the rack, but that was it. Doing so was far cheaper than buying 48V equipment for that installation, and it means that all our hardware is interchangable. -- -- 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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