Is it safe to stick my multimeter probes in the wall socket ?

[openthomas]

If I set to measure AC voltage , can I probe ground to neutral safely from a wall socket ? Never worked with mains voltage unsure on this.

[fozzyvis]

Shouldn't be a problem.

[c4757p]

Honestly, if you have a reasonably good meter and it's set to measure voltage, you can pretty much stick it anywhere. Most of them are OK up to 1000V - though I'd recommend for reasons besides multimeter safety that you avoid one kilovolt unless you really know what you're doing.

My best meter (Fluke 8050A) will take 1000V on the 200mV range (exceeding the range "maximum" by a factor of 5000) for up to ten seconds, and 500V on the resistance and conductance ranges. It's pretty hard to blow it up. (Stick it on the mains set to measure current and you'll be short a rather expensive fuse, though)

[alm]

Make sure the meter is at least rated for CAT II 300 V (assuming residential installation not connected to overhead power cables) and that the manufacturer can be trusted to take safety seriously. VC99 would be out, for example, and I wouldn't trust any random Uni-T meter without checking either. Also check that the probes are at least CAT II 300 V and the insulation of the probes and leads is not damaged.

[Psi]

The main thing you need to check is make SURE the probes are in the voltage position.

If you accidentally connect it to mains with the probes in the current (Amps) position it will...
On a good DMM: Vaporize a chunk of metal off your probe tips and blow the HRC fuses. Maybe $80 to replace the fuse plus buy a new set of probes
On a bad DMM: Probe damage, plus the meter may melt, catch fire and perhaps explode (depending on household fuses/breakers). Maybe kill or burn yourself and completely destroy the meter.

As long as the probes are connected correctly to the voltage terminals and the meter range switch is set to volts AC you shouldn't have any problems.
Be very careful not to touch one probe end while the other is connected to mains.
While it's highly unlikely to kill when configured for volts (as there is 1M or 10M in series) when the probes are set for current they're essentially shorted so it can kill instantly if you touch one probe while the other is live.
So always treat both probes as live if one is live.

[c4757p]

So always treat both probes as live if one is live.

This. A thousand times this. Any time you are anywhere near lethal voltage, assume there's a voltage across your probes at all times. Never ever touch them.

If you're working on an entire circuit with high voltages instead of just mains outlets, I'd recommend clamping one probe to a solid ground, then always probing with one hand off the desk (behind your back if possible). That way you avoid having a conductive path from one side of your torso to the other.

[samgab]

I'm of the opinion that if someone needs to ask this question, then the answer is most likely "no" as it reveals a lack of knowledge about electricity and electrical safety. But that's just my opinion. Certainly no electrician would be asking the question.

[AndyC_772]

One major problem with electrical safety - or safety in general, I guess - is that very few people are ever willing to take responsibility for saying what is is OK to do. I've lost count of the number of times I've read things which boil down to "if you need to ask, then the answer is no" - and whilst that no doubt keeps someone safe on that particular occasion, it doesn't advance anyone's knowledge.

It's almost as though proper techniques are some kind of secret black magic that engineers aren't allowed to know until they've served their apprenticeship along side one of the privileged inner circle, and have finally proved themselves worthy of being entrusted with "the knowledge".

There's a pretty comprehensive guide to working with mains voltages here:
http://openbookproject.net/electricCircuits/DC/DC_3.html

If it were me, I'd pick one of my Fluke meters (rather than the crappy cheap one that lives in my toolbox), check the probes are plugged into the right sockets, then go right ahead and shove them in the socket. But then again, I'm not a member of the inner circle.

[peter.mitchell]

I think it is more of an intuition thing, rather than a "secret black magic this", eg, if it feels RIGHT/OK to stick the probes in with the meter you have you probably have enough experience to judge if it is right or not

[HackedFridgeMagnet]

I realise this doesn't apply to probing a wall socket, but the other thing to watch as well as the voltage, is the likely fault current of the equipment you are working on.

It might only be a 230v circuit but if there are busbars involved (low source impedance) then any mistake on your part could ruin your day.
So if you ever have to do any high power work, think first about what is going to happen if you do slip with your probes, and plan accordingly.

[kg4arn]

Here is an interesting publication, from the CDC in Atlanta, on Electrical Safety.
There is a table on page 7 showing current vs. injury level.

http://www.cdc.gov/niosh/docs/2009-113/pdfs/2009-113.pdf

A sobering quote from the document (emphasis is mine):

According to the Bureau of Labor Statistics Census of Fatal Occupational Injuries Research File for 1992–2005, electrocution is the fifth leading cause of work-related deaths for 16- to 19-year-olds, after motor vehicle deaths, contact with objects and equipment, workplace homicide, and falls. Electrocution is the cause of 7% of all workplace deaths among young workers aged 16–19, causing an average of 10 deaths per year.

[Psi]

Some pretty gruesome burn pictures in that pdf.

[Lightages]

One helpful tip for measuring higher voltages. Do not use both hands. If at all possible clip one lead to one side of the circuit and use one hand to probe with the other. If probing a wall socket, hold both probes in one hand and insert them that way. This way, if there is a fault the current only flows through your hand and not across your chest.

A good general rule for working on high voltages/unknown voltages, keep one hand behind your back.....

[G7PSK]

Ascertain the neutral first if at all possible and connect to this first  then put the other probe to the live with one hand and if at all possible withe meter resting on something and not in your other hand.

[Neilm]

Another tip is to remove any rings from your fingers or wear gloves if you have to put your hand in a restricted space. One of the worst injuries I've ever seen (thankfully in a picture not real life) was the remains of a guys finger who had a ring on when it shorted out a bank of batteries.

Neil

[peter.mitchell]

If you're working on mains, never be alone, safety first, never rush, ignore the deadline, it doesn't matter if you're dead.

[AndyC_772]

electrocution is the fifth leading cause of work-related deaths for 16- to 19-year-olds, after motor vehicle deaths, contact with objects and equipment, workplace homicide, and falls. Electrocution is the cause of 7% of all workplace deaths among young workers aged 16–19, causing an average of 10 deaths per year.

Hang on a minute... not only am I much more likely to be killed in a car crash going to or from work than they are to be electrocuted while working - I'm actually more likely to be murdered by a co-worker...?!

OK, I'm not in that age bracket any more, and don't live in a country where ordinary citizens carry guns, but even so it seems like a good reason to have a lot of confidence in electrical safety procedures. Maybe I should overcome my general fear and apprehension when it comes to working with the mains after all?

[ciccio]

Another tip is to remove any rings from your fingers or wear gloves if you have to put your hand in a restricted space. One of the worst injuries I've ever seen (thankfully in a picture not real life) was the remains of a guys finger who had a ring on when it shorted out a bank of batteries.

Neil

Agree.
And another one is to never wear metal bracelets or all metal wrist-watches...
You can lose an entire hand if the metal touches a live part.
I always wear an cheap all plastic wrist-watch when working on mains circuits.
Best regards

[alm]

Do you really take all those safety precautions just to measure the voltage of a wall outlet? It's important to be aware of the dangers, but decent probes should be fine as long as you keep your fingers behind the finger guard.

[c4757p]

alm, I work with high-ish voltages a lot (vacuum tube audio equipment), and when you're used to doing that, yeah, those safety precautions become second nature. I would never wear metal jewelry or a metal watch around anything high-energy (so car batteries are right out, too - I've heard horror stories from my nurse mother about metal jewelry completing a circuit on one of those). I avoid putting both hands at once near the device, I use a clamp probe to attach to ground if possible to free a hand, and so on. I've been shocked many times at voltages much higher than 120/240 and I'm all right, but I'll be damned if I put unnecessary electrodes on my skin and touch unnecessary voltages because I can't be bothered to move a hand away and take my jewelry off.

[ivan747]

I heard from one electronics teacher that one of his friends was tightening a nut on a lead-acid battery with a wrench when he touched both contacts. The wrench welded into the contacts and they had to hit it with a hammer to separate it. Lesson: be careful with high energy circuits not just high voltage ones. 12V at hundreds of amps can produce nasty stuff like this.

[Psi]

When dad worked at the airport someone dropped a small wrench in the 120V ILS backup battery bank (entire room of batteries.)
(We assume it landed across the full 120v bus bars.)

After the flash no amount of looking could find the wrench and everything around the area was plated with metal.

[SeanB]

Wrong spanner for the application. There are regulations for battery room tools, which include full insulation of the tool with only one end of the metal at the working face exposed. I wear a metal banded watch, and always take it off when working with the car, not only for the battery, but to keep it clean and not to have anything that can catch. Rings have the same warning as well. I have met mechanics with piercings and studs, but none of them work with them in.

[amyk]

I heard from one electronics teacher that one of his friends was tightening a nut on a lead-acid battery with a wrench when he touched both contacts. The wrench welded into the contacts and they had to hit it with a hammer to separate it. Lesson: be careful with high energy circuits not just high voltage ones. 12V at hundreds of amps can produce nasty stuff like this.

This is also why the negative lead should be the first to come off and last to go on when working with a car battery, to reduce the chances of shorts to the grounded chassis. (Positive-ground vehicles should have the order reversed).

[alm]

No argument that these precautions are necessary when working on high-energy circuits. I'm aware that vaporization is a perfectly normal failure mode for metal tools when working on large battery banks. But assume you use suitable probes and DMM and plug the probes into a wall socket. What would it involve to get these kinds of failures? Depending on the plug your country uses, it's barely more dangerous than plugging in a real plug: make sure you keep your fingers away from the metal parts.