Measurement Categories (CAT I, CAT II, etc...)

[Jwillis]

Not be an alarmist but not all DMMs are not created equally and should be used in accordance to the Categories they are designed for.This is important for the novice to understand to prevent either damage to your DMM your potential fatal injury to yourself or some one else.
  Always read the Manufacturers Operators Manual.

There has been a few topics on DMM on this forum and I thought it would be a good idea for people that are looking for a DMM to understand what the Measurement Categories (CAT I, CAT II, etc...) mean and the applications they are rated for.

Transients are often referred to as voltage spikes or surges.This can happen on both AC and DC
 

Understanding  Measurement Categories

 As you see each Category has several voltage ratings.Most CAT IV DMMs are rated 600V with transients not exceeding 8000V .So just because your DMM says CAT IV does not mean it will be rated for the highest transients.

Understanding application

DMMs with no rating are CAT I and should never be connected to CAT II,CAT III or CAT IV Circuits

I hope this clarifies and helps when selecting a DMM.
If anyone has anything to add that would be a great help.

[Vtile]

Generally yes. Even more important is to learn to predict the hazards and learn the instrument.

That picture is a bit misleading and mainly apply only small houses, not ie. industrial environments. Energy storage devices are another can of worms. The latter is what beginner might encounter. Not so much the industrial networks.