From: John Woodgate
Subject: Re: PA (Public Address) Systems
Date: Sun, 8 Dec 2002 21:35:23 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Mon, 9 Dec 2002 03:49:50 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that ntl user
wrote (in ) about 'PA (Public Address) Systems', on Sun, 8 Dec
>"Michael A. Terrell" wrote in message
>> John Woodgate wrote:
>> The National Electrical Code classes 25 volt systems as low voltage,
>> and some places are required to use them. Both 70 and 100 volt are used
>> elsewhere, with 70 volt being the most used of all three types. It is
>> simple, if you're used to it. :)
>In the UK 400V 3-phase distribution (or old 415V that everybody uses) is
>classed as low voltage.
>Less than 50V is something like Safe-Extra-Low-Voltage SELV, which would be
>good for putting speakers in your bathroom!
The NEC is a law unto itself in these matters. It isn't consistent with
international standards, and I don't suppose its authors see any
pressing need to make it so, in spite of the new bid by the USA to take
over the IEC. http://www.iec.ch/online_news/etech/spotlight.htm#usnc
SELV isn't all that safe *in general*. It's OK for connections between
boxes in one room, but extended systems can fail dangerous. PELV
(Protected Extra-Low Voltage) is preferable; this is 'double-insulated'
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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