Multimeter input protection - Page 1
Forum section: electronics / beginners

author: IO390
author_rank: Regular Contributor
timestamp: January 16, 2014, 01:23:03 am
content: I've noticed that one of the most common concerns about multimeters is the input protection.So is this basically the chances of a spark jumping out of the casing and zapping you? Or what? And what normally constitutes good input protection?

author: IonizedGears
author_rank: Regular Contributor
timestamp: January 16, 2014, 01:34:12 am
content: From watching EEV blog videos, MOV's, polyswitches, routed spaces in PCB's between possibly HV traces, plastic shields between HV traces that sometimes poke through the routed spaces for even better isolation, HRC fuses, Etc are great indicators of quality input protection. There is no more of a chance for you to get shocked just by holding a meter than you having your hands on the probes measuring something that could even supply enough voltage to shock you from a distance(Unless you have a meter that was horribly designed which even then what I said stays true for the most part)

author: Wytnucls
author_rank: Super Contributor
timestamp: January 16, 2014, 02:07:57 am
content: Severe burns and electrocution are the main dangers associated with measuring high power circuits with unprotected or defective meters. Accidents can also happen with the best equipment, if the user exceeds the instrument CAT ratings or mishandles meter selections. The most common mistake is trying to measure high voltage with the probes plugged in the amps jack, shorting the voltage supply.Input protection has to comply with ever more restrictive regulations requirements.The best protection usually require current limiting resistors, MOVs, crowbar circuits, PTCs and HRC fuses. Physical dimensions are also regulated, like trace and component separation. The probes also have to meet minimum safety requirements.

author: AG6QR
author_rank: Frequent Contributor
timestamp: January 16, 2014, 03:54:50 am
content: A big danger is arc flash, but not everyone needs to worry about it. It requires a high energy power supply to sustain an arc flash. An electrician dealing with power distribution, or someone in a factory dealing with the circuits that drive high power motors should always be aware of and careful about arc flash. An electronics tinkerer dealing with devices that use batteries or a bench power supply for their power doesn't have nearly as much to worry about, and may be able to get away without much input protection. But if you are ever tempted to use the meter to check a household circuit breaker box, it's something to consider.Protection against arc blast doesn't just involve using a good meter, but also using the right procedures and protective equipment.http://www.geararcsafety.com/working_480-600_volts.pdfA proper meter will safely handle the full rated voltage, plus expected transients according to the CAT rating, across any of its terminals at any setting of the meter's switches. It will blow a fuse if you put low-impedance high voltage across it in current mode, but it won't blow up or create an arc flash hazard.When in doubt, it never hurts to have more input protection than strictly needed. I certainly don't NEED a 600V CAT IV rated meter to check the AA batteries of my kid's toys, but the meter does an excellent job on low- as well as high-energy circuits.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 16, 2014, 07:19:33 am
content: Quote from: IO390 on January 16, 2014, 01:23:03 amSome videos where Dave talks about input protection.

author: IO390
author_rank: Regular Contributor
timestamp: January 16, 2014, 01:12:43 pm
content: Thanks for the replies. Very informative