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Swarf&Sparks
06-28-2011, 12:39 PM
I've seen a number of posts here lately, relating to electrical problems with machines.
My immediate response would be "learn how to use a multimeter!"

but I have to re-think that knee jerk
I even have to remind myself sometimes

what is the first thing you test when using a multimeter?

1 toaster
2 missus' hairdryer
3 meter leads
4 beer fridge
5 car battery

the first correct answer will win a holiday in lovely Information Bay, which has better weather than Elsewhere

Rammed
06-28-2011, 12:42 PM
I would have to say number 3.:D

Swarf&Sparks
06-28-2011, 12:59 PM
well done rammed!
you win the holiday, just send me your visa card details and I'll deposit the fare and accomodation details will be sent to you by PM
:D

seriously, I've seen a trade sparky touch live gear cos the "no contact" voltstick sorta tester didn't glow!
he survived, but wasn't a happy camper

point I'm trying to make is, it's not hard to check faults on mains equipment, but observe some basic safety rules which even those in the trade forget sometimes

DougA
06-28-2011, 04:20 PM
Basic electrical safety I was taught was check your meter in a live 115 v outlet. Then check the equipment you are going to work on to see if the power is off then check to make sure your meter is still working properly by testing it in an outlet again. I have never seen any one else do this and have worked with electricians a few times.

Dr Stan
06-28-2011, 04:32 PM
Even though some have commented the following site has some errors I still find it useful

http://www.make-my-own-house.com/diagram-electrical-wiring.html

BTW, I too am one of the few who checks his meter before use.

Iraiam
06-28-2011, 05:14 PM
I check my meter before use, it's a Fluke 177, a very good meter. But if the 9 volt battery gets too low it will lie to you, you can usually tell because the readings won't make sense, but it's something to keep in mind.

To test the leads I usually just set the meter to read ohms and short them together and verify 0 ohms, or darn close to it (0.3 usually). I'll check incoming power to verify it's presence and then I'm sure my 0 volt readings are the truth, if I lock it out or something. That can be important if a particular machine has multiple power sources.

macona
06-28-2011, 05:48 PM
I check my meter before use, it's a Fluke 177, a very good meter. But if the 9 volt battery gets too low it will lie to you, you can usually tell because the readings won't make sense, but it's something to keep in mind.

To test the leads I usually just set the meter to read ohms and short them together and verify 0 ohms, or darn close to it (0.3 usually). I'll check incoming power to verify it's presence and then I'm sure my 0 volt readings are the truth, if I lock it out or something. That can be important if a particular machine has multiple power sources.

I had a fluke that did the same thing. I thought it was bad until it hit me to change the battery.

MaxHeadRoom
06-28-2011, 06:46 PM
Unfortunately the low battery symbol on the Fluke does not come on until its too late.
I had a very confused electrician ask my advice about his Fluke, he was reading 210vac on what should be a 120vac circuit.
Battery cured it.
Max.

deltaenterprizes
06-28-2011, 06:54 PM
In the old days before cheap meters the electricians tested for power by grounding their pinky and lightly touched the wire to "get a feel for things" !
Glad we have cheap meters today.
I do like the others and short the leads while on the Ohms scale.

Black_Moons
06-28-2011, 07:11 PM
Car battery. On the amps setting. Thats what most people test with thier new multimeter.
Or maybe a plug socket.. Again, on the amps setting. Or maybe ohms. :)

That said, iv got a nice multimeter that I learned the "Battery low" indicator means "Readings incorrect, Change battery NOW" not "Warning, Device may stop working sometime later"

boslab
06-28-2011, 07:51 PM
my own expirience indicates that multimeters should be kept out of most folks hands, it is a valuable tool in the hands of the initiated, that is those who know what they are dooing but the rest form a liability to themselves and others, electricity is a dangerous thing.
as i was told as a child about fire, it is a good slave but a bad master, same applies to electricity.
for most people i would recoment a fluke dipole tester if they have the urge to fiddle, no numbers just a series of leds, reverse polarity not a problem, easy to use no confusion.
if your not properly trained its worth getting someone who is to do your electrical work, or at the very least check your work before juicing it up
I had the pleasure of spiking a 11Kv phase yesterday and the thing nearly got me, also fatigue and electricity dont mix [as i found out].
however with the appropriate training in safety i'm sure anyone of average intelligence can master basic electrical work, but, get trained on a course preferably.
how many self taught pilots, surgeons, astronauts, pipewelders etc do you know [live ones]
mark

rohart
06-28-2011, 08:01 PM
The way I test for live mains is to flick my finger over it fast. I assume a dry finger. I assume that I am not standing in a bath full of water at the time. I assume the wire I am testing is not sticking up and sharp and likeluy to catch or impale and part of me. I wouldn't call the results of a positive test a jolt. I would call it a tingle.

Now that's one finger allowing the body to get alternating charges. It's not the same as holding a failing lead in each hand and jamming them solidly into the live and neutral terminals. That is really going to be terminal.

There's absolutely no substitute for being aware all the time. Take anything for granted, and you're toast. But that doesn't mean you stick to monotonous rules.

If I have pulled the fuse, switched off the distribution box, and I'm about to mess with what I think is a length of cable I've just cut off the reel, I'll still flick my finger over it. And that's a dam**d sight safer than the rules ask for.

darryl
06-28-2011, 09:16 PM
I've never been terribly fond of the flick-the-finger method. My old boss used to do that- he'd lick a finger, then carefully wipe across what might be a live wire- he'd either say 'there's nuttin there', or he'd say 'yup, ders juice der'.

I've had more than my share of shocks, but I always follow a set of rules which to me are now second nature. One of them is to look down at my feet to judge how much insulation potential I have at that moment. If my shoes are dry (inside as well as outside) and I'm standing on a dry wood floor, linoleum, or tile, then I consider it safe to touch a live wire if I have to- or if there's the potential to slip with the pliers or side cutters. I don't trust concrete even if it's dry, and if there's water- even on linoleum, I don't trust that. If I'm working in a live electrical box, I keep my hands touching together. I always look around me to see if anyone else would get in my way if I suddenly jerked because of a shock, or maybe they would contact me and either cause a circuit for juice to flow or become part of my 'connection'.

Often enough it's kids I have to look out for. I don't just tell them to stay clear- I tell them exactly what might happen and why, and almost all the time they get it.

I always check the meter and its leads before trusting any other measurement. First thing I want to see is the resistance of the leads giving a stable reading. Usually that's anywhere from about .1 ohm to about .3 ohm. If the reading is a bit high or jumping around, I find out why and correct the problem. Sometimes I repeat this test after taking a reading, just to feel a little more assured that the reading I took was good. It's not uncommon for a meter to fail this test- it may seem good at first, but then develop a bad connection just as you go to use it. Anyone who's used a meter lots knows how this can be. In most cases, this is a connection going bad inside the probe or the banana plug on the meter.

One of the more dangerous aspects of using a meter and checking voltages, etc, is if you're afraid of what you're about to do- that either says you're not sure of what you're doing, or you haven't taken enough safety precautions. If you have no fear at all, ie a lack of respect for the potential danger, then you shouldn't be touching a meter or any wiring- and you probably shouldn't be driving a vehicle or using any power tools, and you probably shouldn't even open a cutlery drawer. Common sense goes just as far in electrical matters as it does in any other field where one is required to be cognizant.

Dawai
06-28-2011, 10:36 PM
High voltage meter? ya take a cresent wrench, stick it in the end of a fuse stick and hold it up next ta the power lines.. if the line is HOT and drawing a current the wrench will rattle.

Walking by the electric generators in Chickamauga TVA power plant.. The small 4" cresent wrench I carry to save steps started twitching in my pocket.. working with some real jokers expected to see something "live" come out of my pocket. It was the magnetic fields rolling by..

Ohh.. ya mean a "low voltage" meter.. A engineer at dupont tried to check 14,600 with a fluke. The safety committee wanted to outlaw them... Everyone came back from lunch and wondered who the dead black man laying there was.. (he was white before lunch) I've accidentally checked 1250 volts with my old 77... still working today.. (twas scratching my head that day) It was one of them surprise circuits, running in thhn wire off the secondary of a miswired transformer.

Tesla coil voltage? Purple lightning about a foot long.. how much is that? I guesstimated 1 million volts.. I was experimenting with pulsing ultra high frequency voltage in synchronization of the brain waves. (don't ask)... but it was in one of them 80s science magazines as a way the Russkies were creating mind-control experiments and I thought I'd try.

It'd not hurt everyone who "owns" a machine to learn the basics of trouble shooting with a meter.

J Tiers
06-28-2011, 11:24 PM
So long as you have AC, the handiest thing to have is a "squeaker"..... One of those gizmos that squeaks when it sees an AC voltage field.

No need to touch anything.

Really easy to check if it is working, stick it near a lamp that is on. Adjust level of sensitivity as desired.

Gives a decent indication of "there's nothing much here" vs "this is live" vs "this is live with something you ought to stay out of". You first clue on that last one will be that it is already squeaking when you are still a meter or two away from the wires......

I know people who don't trust "squeakers", but I like them.... if you stick one near a box you plan to work in, they don't care WHAT is live, they will warn you about the OTHER two live circuits that you may not know are there.....

Evan
06-29-2011, 01:11 AM
There's two ways to work, working hot and working cold. If you are working hot then you KNOW what you shouldn't touch because you don't work hot unless you know what to do. I usually work cold and the thing that I do after tuning of the power is to short hot to ground. No flash/bang? It's cold. I short the other wires too just to be sure.

I have worked around power and high voltage for most of my working life. The only bad jolt I got was from a cracked high voltage lead on a colour TV. 25,000 volts from that giant leyden jar that lept several inches along a spider web to the screwdriver I was holding, through the buttion on the end of the handle, up my right arm and across the back of my neck, to my ear and jumped into the telephone to ground.

I was talking to a friend while working on the TV. He heard the CRACK on the phone and asked if I was ok. For about 30 seconds I couldn't remember how to speak or what my name was.

boslab
06-29-2011, 01:39 AM
i can remember quite a few little shocks, never really bad though, bit of a kick off a 415v isolater, while as evan points out working dead, even though the isolator was switched off, locked tagged and permited [work permit] the door it was on swang shut behind me and terminals on the back of an ammeter on the door stuck me like a cattle prod!
major investigation later showed the isolater mechanism to be broken, the handle was off and locked but the shaft inside had fractured so the contacts were still made.
the end result was now we have a scheme where before any work on electrical kit you must phsically prove it dead with a combination of meter and or dipole terster, both of which must have been checked on a live source daily.
thre is also another scheme called orange stripe, isolaters that fitters can use have an orange stripe painted accross them, these also have a window so you can shine a torch in and see the contact position, again due to an isolator failure resulting in the motor/hyd pump the fitter was working on to start ripping his fingers off in the coupling.
trust no switch! PROVE the abscence of electricity, go home intact
regards
mark

jugs
06-29-2011, 02:07 AM
I have worked around power and high voltage for most of my working life. The only bad jolt I got was from a cracked high voltage lead on a colour TV. 25,000 volts from that giant leyden jar that lept several inches along a spider web to the screwdriver I was holding, through the buttion on the end of the handle, up my right arm and across the back of my neck, to my ear and jumped into the telephone to ground.

I was talking to a friend while working on the TV. He heard the CRACK on the phone and asked if I was ok. For about 30 seconds I couldn't remember how to speak or what my name was.


That could explain a lot



john
:)

Evan
06-29-2011, 02:28 AM
I figured you would take the bait.

Dawai
06-29-2011, 06:32 AM
Power line voltages.. ONE mistake is enough.
Met several people with stubs instead of arms over the years. They lived.

In the beginning, they were hiring people as electricians with no training on how to live, the working conditions were awful. If they lived long enough they could then proceed to learn to be a electrician. The IBEW stepped up with bartering a better workplace, decent payrate and training with saftey.
the best way to learn how to test with a meter is from someone who has done it a long time, not from a book.

High voltage is nothing to mess around with. The charge inside a VFD, old television, or "electrical display toy" is enough to kill you quite dead. My buddy Doc, his hands are dry callus.. one day he was telling the "young" boys standing around he was immune to electricity. He plugged a wire in and held it with his fingers.. (dry=no conductivity).. I thought, one of these stupid boys is going to die.. so I suggested.. "lick your fingers".. When the DA did, I thought I would have to pry him off that wire..
Perhaps he thought he really was immune?

It is all about conductivity, while riding in a bucket truck with a fiberglass boom, on a dry day.. you feel no shock when you get close to a power line.. There is a chain and a metal plate there in the bottom of the bucket, throw the chain across the line and you and the wire are at the same potential, no conductivity to ground.. like a bird sitting on the wire.. THOU, let a wire you are stringing touch or come close to the ground and it's dying time. OR get between them??

http://www.youtube.com/watch?v=TVD0vWg3Kgo Helicopter linemen.. (not me thank you)

Swarf&Sparks
06-29-2011, 09:22 AM
thanks for the input guys, pretty much what I had in mind when I started this this thread, user testing of electrical equipment can be safe, given the ground rules from experienced people, many mentioned above
another worth including is to always keep one hand in your pocket

don't want to scare HSMers with HV horror stories, but let me mention one from a mate of mine in the HV trade (you don't get 2 mistakes!)

new subdivision with a lot of construction going on, bored kids wandering the streets at night.
Got the picture?
A few decided it would be fun to throw metal pack strapping (bricks, timber, etc) over the 440V feeders and watch the light show.
Also annoyed the residents who had to wait for emergency crews to test and restore power.
One "bright spark" decided to go one better, stole a chain from a truck
He figured it would make a bigger bang
Sure did, he managed to get it over the 66 Kv distribution lines near a pole transformer
The resultant explosion of molten metal and boiling oil severely burned him and his cretin mates
To add insult to injury, the parents then tried to sue the power company!
:(

danlb
06-29-2011, 09:38 AM
Voltmeters are a great tool. Like all other tools, you need at least SOME understanding of what you are doing with it. It's not rocket science folks.

Having said that, I will admit that I'm paranoid about live voltages above 24V, and anything that carries a lot of current*. So I'm extra cautious.

Dan

*24V is not deadly, but have you ever seen what happens to a screwdriver dropped across the 1000 amp buss bars of a 24 volt battery string? Flying molten metal is not fun either.

Stuart Br
06-29-2011, 09:46 AM
I've had a few "belts" in my time. I can can say that every one was down to pure carelessness. Mostly 240V UK mains power, from when I thought, but didn't prove the circuit was dead. Luckily nothing more serious than a curse and an aching arm.
The other one one that comes to mind was when I used to be a computer engineer and we were allowed to open up and adjust CRT's in the field.
I was adjusting an alignment pot and caught the live heatsink of the line output transistor with the back of my hand. That one really did hurt.

Black_Moons
06-29-2011, 10:02 AM
Haha, I once took 30kv at 6nF right into my hand/arm, Home made saltwater+tinfoil cap around a 2L popbottle, charged up with a tv flyback.. I think I got a little to close to the discharge lead

Boy did THAT ever hurt. Much like smashing my hand with a hammer, or door. Rest of my arm hurt pertty bad too.

Other bad one would be working on my PC... Unpluged.. Except the phone line. Happened to poke myself on the pins in the back of the modem. 48v. Not a big deal, Just jerked my hand back and... RRRAAAKKKEEE. about 50 slices on my hand from all the pins on the back of the modem, and a half pound of flesh left on the modem. now THAT hurt.

Bob Fisher
06-29-2011, 12:28 PM
Glad to hear about low batteries in a Fluke. I used mine the other day to check a 220, got 430v, wondered WTF.I know there is no 440 in the house. Just the same,you know something is there. Going to change the battery and recheck.just to see. Thanks, Bob.

Dr Stan
06-29-2011, 01:09 PM
I've had a few "belts" in my time.


My worst one for me was from tuning up my old '72 Ford PU. I had one of the old inline timing lights (plugged into #1 spark plug) and was checking the timing when it shorted out. Good Lord that hurt. :(

Dawai
06-29-2011, 01:42 PM
I discovered something? I had a motorcycle frame, front end picked up "over" my tig welder carrying it out of the way. My flip flop rolled over and I fell with the frame hitting me mid chest..

My calf hit the welder plug as the weight hit me. It plugged into my muscle on the back of my leg.. I had to pull it out before I could stand on it.

I learned two things, one, It is stupid to do stupid things alone in the shop with no chance for a valuable funny video, two, I do not possess the energy to turn on a tig welder and supply it even when plugged into it.

I now have a neato scar on the back of the leg. Kinda a peace sign... Nema 6 plug.

rohart
06-29-2011, 01:48 PM
Thanks for the link, Dave. Now I know what IBEW means.

When I was squatting with my brother, in my early twenties, we were in the next door basement hot wiring our mains. Now I'm the can-do one, and he's the economist. But all of a sudden he says, "I'd be careful of that one !" Blow me down if he hadn't spotted a live wire I'd missed. Increased my respect for his practicality enormously.

Rosco-P
06-29-2011, 01:48 PM
So long as you have AC, the handiest thing to have is a "squeaker"..... One of those gizmos that squeaks when it sees an AC voltage field.

No need to touch anything.

Really easy to check if it is working, stick it near a lamp that is on. Adjust level of sensitivity as desired.

What is the real name of the device referred to as a squeakers in the trade? A link to a manufacturer would be nice. Have tried a voltage tic, didn't find it all that useful.

Evan
06-29-2011, 01:59 PM
I have a very similar device. It's like a stud finder with the same type of lights but it finds AC wiring instead.

They are called "live wire finders"

http://www.jasontools.com/product/251-ac-live-wire-finder-130832-9fef/

http://www.altex.com/Velleman-Live-Wire-Detector-Stud-Finder-VTMVS2-P147552.aspx

boslab
06-29-2011, 03:13 PM
I have a very similar device. It's like a stud finder with the same type of lights but it finds AC wiring instead.

They are called "live wire finders"

http://www.jasontools.com/product/251-ac-live-wire-finder-130832-9fef/

http://www.altex.com/Velleman-Live-Wire-Detector-Stud-Finder-VTMVS2-P147552.aspx
try using one with a flat battery and see how long you live!
positive test, no finger flicking madness, if you want to play with electricity watch the green mile first
we got 11KA, thats righ 11000 Amp drive motors on our rolling mill, they will kill you without touching them, even the cables are oil cooled, and truthfully they havent killed anyone yet.
electricity is like being a pedestrian, everyone is aware of crossing a buisy road [HV] but more people are killed on the quiet backroads if you get what i mean.
If your in your shop and your tinkering with wires how many people in your house know how to [a] safely remove you from the current source and[b] administer CPR til help arrives.
You have a responsibility to your family to not put them in that position.
Be safe and dont get killed its easier!.
if you do make a habit of playing with wires then a pair of hv gloves hanging up, and a length of nylon rope, and teach the other half how to use them.
I know i sound over the top but ive had the pleasure of seeing a dead electrician, he only had 35 years experience! [flashover in a carbon contaminated motor drive pack]
regards
mark

Paul Alciatore
06-29-2011, 03:22 PM
AROUND THE HOUSE, the best tester for a live circuit is the neon bulb indicator. Totally simple and ALMOST nothing that can break. It is about as reliable as you can get. Many things can go wrong with a meter: battery, leads, internal fuse, bad switch, etc. I have seen them all.

But no matter what you use, DO test it FIRST every time you will use it on a circuit that is potentally lethal. Check it in a working socket. Wiggle the leads to be sure they aren't intermittant. If it is a meter, check it on the same scale you will be using: switch to another scale and back again and check again. Be SURE it is working. Then test the circuit.

Every piece of test equipment has a Voltage rating. Know what that rating is and DO NOT EXCEED IT. EVER!

boslab
06-29-2011, 03:25 PM
+1 on that paul
mark

Evan
06-29-2011, 04:21 PM
try using one with a flat battery and see how long you live!


Try drilling holes in a wall without one.

jdunmyer
06-29-2011, 05:43 PM
I was a checkout technician at one of my first jobs, back in 1967 or thereabouts, working on fairly complicated relay/step switch control systems. Some of them had dozens or even hundreds of relays, and a cabinet that you'd walk inside of. Nearly everything was 120 VAC. My boss told me, only partly in jest, that "if you don't get bit once a day, you aren't working hard enough". It was about the truth, actually.

However, I'm a lot less complacent about such stuff today.

Dawai
06-29-2011, 06:25 PM
80s.. My triplett RF probe started beeping in my toolbox checked as luggage on a aircraft.. Got me took off plane In Nashville Tn. and questioned.. I got rid of it soon afterwards..

I have a greenlee RF pen here in the cup.. Good for detecting the Radio waves that come off Ac power.. it will detect a wire in a conduit with a hot wire.. Radio noise..

Lay one in front of the television.. gee.. it stays on.. is the screen electrically hot? No.
They are not adequate for troubleshooting circuits, only the advance-no contact alert that voltage may be present..

and voltage checking?? Look to the old wiggy... a solonoid voltage detector.. some even have a battery and way to ohm out circuits for continuity..

J Tiers
06-30-2011, 12:18 AM
try using one with a flat battery and see how long you live!


The squeaker" is so easy to test that there is no excuse for not testing it before and after checks. Just wave it near a known hot wire..... lamps are great, since you can SEE they are on, and therefore hot.

boslab
06-30-2011, 02:56 AM
Try drilling holes in a wall without one.
sorry Ev i was on one about the voltage finder, it does have a place of that i'm certain and upon reflection our walls are different mostly and the wires cant run at silly angles, the only thing that will happen in the uk if you dril a wire is the Earth leakage trip an RCD will drop out, its law to have them, nearly all drills are printed with the double square logo [double insulated] so i suppose my argument was not as well thought out as i thought [normal for me i'm afraid]
i drill holes all the time but usually in brick! iwas on about pulling electrical equiptment apart and relying on a magic wand [as sparks over here seem to call them, i do have one for the occasional job, but they can lie to you, trust me on that one.
regards
mark

boslab
06-30-2011, 03:12 AM
The squeaker" is so easy to test that there is no excuse for not testing it before and after checks. Just wave it near a known hot wire..... lamps are great, since you can SEE they are on, and therefore hot.
you are right and for most householders thats a good idea as i said to Evan, i was getting my industrial work [tomorrow change out the high voltage generator on a phillips xray spectrometer, sheel go 100kv 100Ma with ease] merged with what i would call domestic, it has a good place for finding wires in walls an things but if you got yourself into a bundle of wire where some are live and have to be for you to fault find then they would not be the choice to me
i have a non contact fluke multimeter for that which probably works the same and saves shoving needleholes in the insulation.
your comments regarding the fact that there is no excuse for not checking before and after is correct, but you can forget to do it and if i have maybee 100+ wires to check proximity is an issue, if you had 6 core lives do you know which one will bite you, bear in mind in industrial we usually work hot [in twos with radio, one dooing the tests the other holding the torch/whatever] both cpr trained rubber gloves[ god the fingers are stiff, VDE tools and neoprene mats so if you do go live then it wont hopefully ground out and kill you, still dangerous with all those precautions, but thats not the same as domestic.
thats whare most of the fatalities occur according to our safety gurus
regards
mark