Gary, I like your Sherlock Holmes hat and pipe! The following is purely my personal opinion based on experience and logic.
The NEC wants all electric equipment to have a power disconnecting means. However, they do have to take into consideration certain big equipment (stationary and fixed wiring) that probably may be one of a kind for any particular installation and that will, like my all electric forced air heater, have its own panel with a circuit breaker right next to it. My electric heater is in its own closet. There is a small panel on the wall with a door. Behind the door is a single circuit breaker/overcurrent protection device that is designated for this electric heater. The requirements of the NEC have been met. I agree with Gary that providing equipment without its own disconnecting means is not the best design even if one can "get away with it" per the National Electric Code. When there is a whole lineup of equipment, and in a panic situation a craftsperson wants to shut off a particular cabinet or rack, looking for the specific wall panel to do so is not the most efficient way to be safe. Install the shut-off device in the equipment and be done with it! Your customer will love you. Tania Grant [email protected] ----- Original Message ----- From: Gary McInturff Sent: Friday, May 18, 2001 2:54 PM To: EMC-PSTC (E-mail) Subject: NEC - 1990 version I'm trying to make a decision on this issue right at the moment and here is my thoughts so far. Going through this old copy of the NEC index and looking for Disconnecting means I have a couple of interesting options. Electronic computer/data processing equipment, 645-2(1) and 645-10. The first paragraph literally says go to the second paragraph. 645-10 says that a means shall be provided to disconnect power to all electronic equipment in the same room....they shall be grouped and identified and controlled from locations readily accessible at the principal exit doors. No reference to voltages, although I would assume that they are talking branch circuits. - Tania's note says annex NAB.2 says to treat dc power systems the same. Section 2.3 (UL 1950) allows for a manual statement that requires disconnect device be provided during installation. This matches my experiences with Telecom equipment, that has been accepted and installed. The installations that I have been in have at the top of each equipment rack some sort of power distribution system, that is a series of fuses and/or breakers. They do it for some very practical reasons - there is just a whole lot less chance of the crafts person hitting the wrong switch and bringing down the entire frame. That obviously, would also mean that the craftsperson has less chance of having someone else flip the disconnect back on line while they have their hands inside the equipment. My cynical side says this is only a secondary concern but.... Further down in this section the NEC refers to sections 705-20 and 705-21 Interconnected electric power production sources. While they don't reference it in the index the next section 705-22 (1) is, in my opinion, very pertinent. 705-20 Disconnecting Means, Sources .... disconnect all ungrounded conductors 705-21 Disconnecting Means, Equipment ....from all ungrounded conductors of all sources of supply This would seem to imply having them at both ends !!!?? 705-22 Disconnect device ....manually or power-operable swtich(es) 705-22(1) Located where accessible. Given the other paragraphs this little modifier looks like a pretty interesting "gottcha". I have a couple of interesting locations, tacked onto the outside wall of a building, and on top of a power pole. So this little note convinces me that I will need to provide the disconnect right next to the equipment, and I won't be allowed to rely on the upstream stuff - regardless of a warning in the manual. However, for CO's and NOC's you probably could just put it in the manual. Just ask yourself - beyond the standards allow are you really protecting you users? Gary Please remember that I am using a very old NEC, but I doubt these areas have change much. (The copy I have just has ton's of annotations and page/section markers all carefully put in by the guy I stole this copy from) ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"<br clear=all><hr>Get your FREE download of MSN Explorer at <a href="http://explorer.msn.com";>http://explorer.msn.com</a><br></p>
