What Do CAT Ratings Mean?

There are many different types of meters available for us electricians to use. Multimeters, Amp Clamp meters, Hot Sticks, etc. But what are the different CAT ratings for on these meters? In the latest episode of Electrician U, Dustin discusses what the different CAT ratings are for as well as talk about a few different Multimeters available from Klein Tools.

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Each meter is designed to work on a specific voltage range and have a specific amount of current run thru it. If you choose the wrong meter to work on a different range other than intended, it can cause damage to the meter. Think about electrical services and available fault current. The closer you are to the source (transformer) the more available fault current there is, as there is less impedance to stop it. If the service conductors are short, there is less wire to offer any impedance. Also, on the service conductors, there are no loads yet (motors, devices, etc.) to provide impedance. Meters work in much the same way. Each has a certain amount of impedance built into the meter to be able to have its functions work at a certain range of voltage and or amperage.
So, the CAT rating is simply the voltage/amperage category environment it can be used in. The lower the CAT rating, the lower the voltage/amperage it can be used to test for. Something to keep in mind is that you CAN use a higher CAT rated meter to test in a lower CAT rating environment. So, you could use a CAT 4 rated meter to test in a CAT 2 environment, you just shouldn’t go the other way, or you could risk damage!
CAT 1 meters are the lowest rated meter, with about 30 ohms of impedance and a low voltage range, but these probably won’t be something that you would find readily available, so let’s start with the CAT 2 rated equipment. CAT 2 meters have a bit higher impedance with around 12 ohms and able to handle a bit higher voltage. An example of this is a plug tester that is rated at 300v max. CAT 3 meters are the most common category of meter most electricians have; whether it’s a standard tester, a multimeter, or an amp clamp type of meter. These meters are rated at 600v and has an impedance of about 2 ohms. The lower impedance allows more current to flow thru them and at a higher voltage. These types of meters at this CAT rating should work well for most applications that most of us electricians run into daily. Three phase distribution, lighting panels, and the like are things these meters are made for. CAT 4 meters have roughly the same impedance as CAT 3 (around 2 ohms) but allows you to use them up to 1000v.
Meters can also come with several different options depending on which meter you select. Some have backlit displays (so it’s easier to see the readings), some allow you to HOLD the reading, some are even auto ranging. Amperage testing is another option as is temperature readings.
Always choose a quality meter and TAKE CARE OF IT as your life depends on it. Meters should be kept separate from your other tools (preferably in a good case or bag) and do NOT belong in the bottom of the toolbox or rolling around in your van! Same with the leads of the meter. They should be inspected regularly, batteries should be changed frequently, and always test on a KNOWN source before attempting to use them on what you are attempting to test.

[brianbeasley]

Good info. I was amused by your illustrators light bulb illustration at 5:00 where the leads were connected in a dead short across the ground terminal!😁

[theteenageengineer]

I noticed at 6:40 you had the leads in the current measurement. A top tip especially for the young people, if you’re going to store your meter with the leads in it, put the leads in the voltage measurement configuration because that way if you aren’t paying attention before you use the meter you don’t short the circuit and damage the current shunt, pop your fuse, and possibly destroy your meter.

[dustinboyce]

I hope nobody tries to use a light bulb as a multimeter now, especially if they connect it as a dead short like the picture 🤣

Great video and explanation, hopefully it helps some people understand their meter and the importance of the correct selection

[waynecostanza]

Category ratings are based on the meters ability to withstand transient voltage spikes and not have the meter fail internally and become a short or point of arc fault on system. The closer you are to the utility the more robust your meter input protection needs to be to prevent dielectric failure causing a dangerous fault condition in the meter. The more equipment a transient such as a lightning strike has to go through the more it is attenuated. The industry has broken buildings into category’s. Category 1 being the farthest from the utility with the least residual transient voltage and Category 4 being at the utility interface with little drop in transient voltage. The impedance you are talking about is not in the meter it is the impedance from the source to your location. IE. your service connection will have less impedance including all the connections and length of wire, by the time you get to an outlet in an upstairs bedroom you may have much more. So a transient spike traveling through these environments will have less energy as it travels through the building. The input protection is designed accordingly. There is nothing wrong with using a category 1 meter on your service wire connections unless a voltage spike hits the system and creates a fault in the meter that is connected to your mains power, which could create a real short circuit condition with lots of current available. The issue is you don’t know when that transient is coming so don’t do it.

[jesstreloar]

Meters save lives. Any time I opened something up I checked for voltage, breaker is open, locked and tagged out, the switch on the wall is open, and there was still 115VAC present. The local switch was labeled with the wrong panel, but the panel was labeled for that circuit so the panel was labeled improperly also. And the local switch was wired backwards, breaking the white wire, instead of the black wire!

[abnerdiaz]

Great video, when I was an apprentice my mentor taught me about the CAT levels and the importance of checking each meter prior to using it. This included the checking of batteries and fuses.

[felipea]

As a future Electrician Helper ... I thank you for this video.

[ianbelletti]

Electricians should be using cat 4 meters because we handle testing all the way to the service. He's right that the category number has to do with the environment you are testing. Think levels of protection. Electronics and power limited circuits are category 1. Category 2 would be after sub panels. Category 3 is protected by a main level panel. Category 4 is your service. In most homes electricians will only be testing in category 3 and 4 situations hence an electrician needing a meter rated at least category 4 600v. Industrial electricians may need a higher voltage rating but most commercial and residential work does not exceed 600v.

[JamieStuff]

My EE background makes me call out some of this info, and in researching it, I found even more.

First, what's with this "2Ω of impedance" on a CAT 3 meter? It's certainly not the input impedance of the meter in voltage measuring mode; putting that across 120V would definitely be noticed, as it would (try to) pull 60A through the meter. (Also, Klein proclaims the input impedance in V mode as 50MΩ, but the specs in the manual say 10MΩ.)

2Ω is pretty high for current measuring; on a 1A draw, it would drop 2V. Quite a lot on a 12VDC circuit.

On the plus side, the Klein MM450 looks pretty sweet.

[warmowed]

Super important to note! a lot of meters (even some mid-range brands) do not actually meet their CAT ratings! The eevblog forum maintains a list of meters that do not meet their rating and I'm sure if you do some searching you can find out about any meter you are looking at buying. If I remember correctly Dave Jones got a nasty burn on his hand because a meter exploded while holding it. He wasn't doing anything wrong, but the meter didn't meet its spec and when it failed the plastic case wasn't designed to contain the explosion properly. If you are using test equipment daily then you need to demand the safest possible. If you see a meter have a glass fuse in it then it is very not safe; all meters should have ceramic HRC fuses that resist fragmentation.

[LtKernelPanic]

That poor light Great video even for someone like me who's not an electrician but does the usual homeowner stuff like replacing the occasional switch, outlet, light fixture, etc as well as tinker with other electronics that sometimes deals with mains (or sometimes higher) power. My go to meter is a Fluke 87v which is admittedly overkill for anything I'll probably ever do but can handle just about anything I'll ever throw at it. Before finding a good deal on the 87v I found my Extech 330 to be a good meter for general home use and is Cat III 600V rated. Also recently picked up a Uni-t UT208B clamp meter which so far I'm impressed with but would go with a better brand if I relied on it for my day job.

[JWimpy]

Great tutorial.
I would love to see some armored leads for industrial use. Something with geek strain reliefs at both ends and a Kevlar over-braid wrap with silicone jacket under it.

[allenshepard]

Great explination of "more current at the source" Shorting a car battery is worse than shorting the wires of the break light.
BTW - just a heads up. any metal connected to buss bars at 4MW and above makes a great flash telling everyone where you are (and what was done)
Saw a OSHA documentary where the guy used a CAT-III meter on the HV side of a step down transformer. He did not die but suffered and bleed out for hours as they tried to save him. Not all deaths are quick and painless.
Question - 2 ohms. At 600V two ohms is pretty low and would allow a lot of current to flow. The impedance is for true RMS and spike resolution on switch mode power supplies - right ?

[robertapreston]

so many words...

I'm more of a visual learner... but, I learned none the less. Thx Dustin

[Steve-kgzk]

Also on the MM325 you can turn the selector to your desired functjon and the correct lead position lights will illuminate green then you plug them in correctly

[sween]

Also depending on the environment you are working on/in you will/may need an intrinsically safe meter.

[esthermcgough]

I just got a Klein MM600 Im trying to learn about it to test my car fuses. And old recepticals in my sisters house

[LordSaliss]

I know you promote Klein products on this channel, but I have to say the very best price/performance multimeter I have ever used is the Extech EX570. Available from their website for $250, it is very fast and has very high accuracy. It is up there in accuracy with Fluke's which are 3x the price. Even Klein's best and most expensive are nowhere close to the level of the EX570

[waynegram]

Can you make a video lesson explaining what is "available fault current" giving a bunch of examples. All DVM METERS have a "10 Meg ohm input impedance" so I'm confused why CAT 2 = 12 ohms impedance and CAT 3/4 = 2 OHMS impedance, can you explain this?

[cbeier]

1:04 - you mention that if the two mains were to short it would allow a lot of current to flow due to very low impedance. Makes sense. But how much current would flow if you shorted or touched the two main wires coming from the transformer? Just curious.