Editing Multimeter (section)

=== Safety ===
[[File:Fluke 28 Multimeter Input Protection.jpg|right|thumb|An example of input protection on a multimeter]]
Most multimeters include a [[fuse (electrical)|fuse]], or two fuses, which will sometimes prevent damage to the multimeter from a current overload on the highest current range. (For added safety, test leads with fuses built in are available.) A common error when operating a multimeter is to set the meter to measure resistance or current, and then connect it directly to a low-impedance voltage source. Unfused meters are often quickly destroyed by such errors; fused meters often survive. Fuses used in meters must carry the maximum measuring current of the instrument, but are intended to disconnect if operator error exposes the meter to a low-impedance fault. Meters with inadequate or unsafe fusing were not uncommon; this situation has led to the creation of the [[measurement category|IEC61010 categories]] to rate the safety and robustness of meters.

Digital meters are rated into four categories based on their intended application, as set forth by IEC 61010-1<ref>{{cite web|url=http://www.gossenmetrawatt.com/english/seiten/newsafetystandardiec61010-1since0.htm|archive-url=https://web.archive.org/web/20061202071525/http://www.gossenmetrawatt.com/english/seiten/newsafetystandardiec61010-1since0.htm|url-status=dead|archive-date=2006-12-02|title=Safety Standard IEC 61010-1 since 1.1.2004}}</ref> and echoed by country and regional standards groups such as the [[European Committee for Standardization|CEN]] EN61010 standard.<ref>{{cite book|title=Safety requirements for electrical equipment for measurement, control and laboratory use. General requirements|isbn=0-580-22433-3|year=1993|publisher=B S I Standards }}</ref>

* Category I: used where equipment is not directly connected to the mains
* Category II: used on single phase mains final subcircuits
* Category III: used on permanently installed loads such as distribution panels, motors, and three-phase appliance outlets
* Category IV: used on locations where fault current levels can be very high, such as supply service entrances, main panels, supply meters, and primary over-voltage protection equipment

Each Category rating also specifies maximum safe transient voltages for selected measuring ranges in the meter.<ref>{{cite book|page=285|title=Survey of Instrumentation and Measurement|year=2001|last=Dyer|first=Stephen|publisher=Wiley |isbn=0-471-39484-X}}</ref><ref>{{cite web|url=https://electronicshacks.com/how-to-check-240-voltage-with-a-multimeter |title=Anatomy of a high-quality meter |access-date=2015-11-05 |url-status=live |archive-url=https://web.archive.org/web/20061018221940/https://electronicshacks.com/how-to-check-240-voltage-with-a-multimeter |archive-date=18 October 2006 }}</ref> Category-rated meters also feature protections from over-current faults.<ref>{{cite book|last = Mullin|first = Ray|title=Electrical Wiring: Residential|publisher=Thompson Delmar Learning|year=2005|page=6|isbn=1-4018-5020-0}}</ref> On meters that allow interfacing with computers, [[Opto-isolator|optical isolation]] may be used to protect attached equipment against high voltage in the measured circuit.

Good quality multimeters designed to meet Category II and above standards include high rupture capacity (HRC) ceramic fuses typically rated at more than 20&nbsp;A capacity; these are much less likely to fail explosively than more common glass fuses. They will also include high energy overvoltage MOV (Metal Oxide [[Varistor]]) protection, and circuit over-current protection in the form of a [[Polyswitch]].{{Citation needed|date=February 2022}}

Meters intended for testing in [[electrical equipment in hazardous areas|hazardous locations]] or for use on [[blasting machine|blasting circuits]] may require use of a manufacturer-specified battery to maintain their safety rating.{{Citation needed|date=February 2022}}