Jim, Replacing the switch with a toggle type dimmer will greatly lengthen the service life of bulbs. I have them in bedrooms and the bathroom. The main intent was to prevent being jolted awake by bright lights if it were necessary to get up at night. Because they look like ordinary light switches, visitors have no trouble operating them.
As to using NTC thermistors, I would recommend that you NOT use them inside of an electrical box. They do get quite hot, and even if they did not damage wire insulation, you might be risking your insurance coverage in the event of a fire. I have used them in the past to reduce inrush currents in power supplies, but these were forced air cooled. Without forced cooling, they provide almost no protection if power is re-applied almost immediately after shutoff. By the way, mechanical vibration may be the real culprit. I used to work in a place where the bulbs failed with alarming frequency in our old shield room. Leaving the ventilation blower off reduced the failure rate. Fragile filaments hate to be shaken. Scott Lacey -----Original Message----- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Jim Eichner Sent: Monday, July 10, 2000 2:35 PM To: emc-p...@majordomo.ieee.org Subject: RE: Are NTCs Safe to Use in Electrical Equipment On the subject of NTC's, please allow me a slight detour from the compliance world to the real world. I have a circuit in my house that blows light bulbs far more often than any other. I can't determine any reason for this - the voltage seems normal and there aren't any transient-producers on that same circuit (that I'm aware of). Long life and rural-duty bulbs make little or no difference. Instead of figuring out the root cause, I'm considering resorting to trying to deal with the symptom (blown bulbs) by putting an NTC in series with the light fixture somewhere. My thinking is that the mechanism that blows an incandescent bulb filament is related to the high inrush current into the cold (and therefore low R) filament, and the physical and thermal stresses that that inrush causes. Any comments on how likely this is to help, and whether or not I can safely put an NTC in an junction box full of wires? I'd check the NTC's temperature under load (they get hot) and compare that the the temp. rating of the wires in the box. I'd also insulate the bare legs of the NTC and try to make sure it isn't touching anything else. Anyone familiar with the failure modes of these things? Thanks, Jim -----Original Message----- From: Peter Merguerian [mailto:pmerguer...@itl.co.il] Sent: Monday, July 10, 2000 7:58 AM To: emc-p...@majordomo.ieee.org Subject: Are NTCs Safe to Use in Electrical Equipment Dear All, I have seen some design where NTCs are used to limit inrush currents in motion controllers. Q. Are NTCs safe and reliable as means to limit inrush currents? Q. Are there safety considerations to consider for circuits employing NTCs? Q. Are there any Approved (previously evaluated) NTC components out there? I appreciate all of your comments and/or links regarding the use of NTCs in electrical equipment. Thanks Peter Merguerian Managing Director Product Testing Division I.T.L. (Product Testing) Ltd. Hacharoshet 26, POB 211 Or Yehuda 60251, Israel Tel: 972-3-5339022 Fax: 972-3-5339019 e-mail: pmerguer...@itl.co.il website: http://www.itl.co.il ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
