Editing Relay (section)

== Safety and reliability ==
{{Main|Arc suppression}}

Switching while "wet" (under load) causes undesired arcing between the contacts, eventually leading to contacts that weld shut or contacts that fail due to a buildup of surface damage caused by the destructive arc energy.<ref name="electronic-components.com.au" />

Inside the [[Number One Electronic Switching System]] (1ESS) [[crossbar switch]] and certain other high-reliability designs, the reed switches are always switched "dry" (without load) to avoid that problem, leading to much longer contact life.<ref>{{cite web |first=Al L. |last=Varney |url=http://yarchive.net/phone/1ess.html |title=Questions About The No. 1 ESS Switch |date= 1991}}</ref>

Without adequate [[contact protection]], the occurrence of [[Electric arc|electric current arcing]] causes significant degradation of the contacts, which suffer significant and visible damage. Every time the relay contacts open or close under load, an electrical arc can occur between the contacts of the relay, either a ''break'' arc (when opening), or a ''make'' / ''[[Switch#Contact bounce|bounce]]'' arc (when closing). In many situations, the ''break'' arc is more energetic and thus more destructive, in particular with inductive loads, but this can be mitigated by bridging the contacts with a [[snubber]] circuit. The inrush current of tungsten filament incandescent lamps is typically ten times the normal operating current. Thus, relays intended for tungsten loads may use special contact composition, or the relay may have lower contact ratings for tungsten loads than for purely resistive loads.
 
An electrical arc across relay contacts can be very hot&nbsp;— thousands of degrees Fahrenheit&nbsp;— causing the metal on the contact surfaces to melt, pool, and migrate with the current. The extremely high temperature of the arc splits the surrounding gas molecules, creating [[ozone]], [[carbon monoxide]], and other compounds. Over time, the arc energy slowly destroys the contact metal, causing some material to escape into the air as fine particulate matter. This action causes the material in the contacts to degrade and coordination,  resulting in device failure. This contact degradation drastically limits the overall life of a relay to a range of about 10,000 to 100,000 operations, a level far below the mechanical life of the device, which can be in excess of 20 million operations.<ref>{{cite web | title = Lab Note #105: Contact Life — Unsuppressed vs. Suppressed Arcing | publisher = Arc Suppression Technologies | date = 2013 | url = https://arcsuppressiontechnologies.com/wp-content/uploads/2016/07/Arc_Supression_Lab_Note_105_Contact_Life.pdf | access-date = January 21, 2025}}</ref>