Some DC dry relays use a magnetic field to pull the arc to the side and extinguish the arc that forms when the contacts open. There is also the term "dry switching"- this refers to switching dry relays at such a low current that an insulating film develops over time.
Dave Cuthbert Micron Technology From: [email protected] [mailto:[email protected]] On Behalf Of Chris Maxwell Sent: Monday, February 23, 2004 11:49 AM To: Cereceres, David; [email protected] Subject: RE: dry circuit questions David, Dry contact relays are named because of what they don't have. Many high current relay designs feature contacts that are wetted with Mercury in order to prevent damage from arcing during make/break cycles. Dry contact relays have no such protection. As such, they are usually rated for lower currents than wet contact relays. Dry contact relays are prone to having their contacts weld together if they are used in situations where there is either: excessive in-rush, excessive steady state current and/or excessive inductance in the load (causing showering arcs during opening). For either type of relay, you must read the specification sheet thoroughly and understand the switching curves (many spec sheets provide a curve which shows the maximum switched current versus voltage for the relay). Be sure that your application is within the relay's specs. Otherwise, you will end up with welded contacts. Some types of dry contact relays have extra wide contact gaps in order to extinguish the arcing and prevent damage and/or welding without the use of wet contacts. American Zettler used to have some good information in their catalogs which explained this in better detail. Chris Maxwell Design Engineer Nettest From: [email protected] [mailto:[email protected]] On Behalf Of Cereceres, David Sent: Monday, February 23, 2004 1:26 PM To: '[email protected]' Subject: dry circuit questions Hello Group, I was forwarded the following question from a fellow engineer. I was wondering if anyone knows of any reference material pertaining to Dry Circuits and what constitutes a Dry Circuit. "When you see a reference to either 'dry contact' or 'dry circuit' as far a relay goes, what does this mean the relay is designed to handle?" As always, your guidance is always appreciated. Regards, David Cereceres Product Safety Engineer Pelco Phone:559-292-1981 ext.3493 Fax: 559-294-3707 mailto:[email protected] <mailto:[email protected]> http://www.pelco.com/ <http://www.pelco.com/> This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [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.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [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.ieeecommunities.org/emc-pstc
