ARC FLASH investigation

[the blur]

Before clamp on amp meters, the meter was used a dead short with the 2 leads. I remember doing that in school on low voltage DC circuits. So sure, I could see someone blowing themself up phase to phase with an ammeter. I could see the meter exploding, and the leads melting with 20,000 amps of fault current.

 

[hurk27]

Is a wigggy better to use than a cheap meter??

I have have a company issued beckman blow up the battery cover off while checking 480 (good thing i was wearing leather gloves)

Fuses do blow when the knob is on resistance while trying to read 240 volts. OOPS there goes another meter!!!

It is hard to get the dial in the wrong position on a wiggy. but is it better/safer to use for checking 480v???

DENNIS

Yes I use a Wiggy type meter as my normal used meter, it's the first one I grab when go into a house to trouble shoot, Its not a Wiggy as that name is referring to the brand name of the Square D version, I use the Vol-Con by Ideal which gives me both voltage and continuity along with loading down a circuit to expel the ghost voltage, while lately I have had a couple fail it was the smaller version so this time I went back to the larger one and so far no problems, what I do like is the continuity part starts sounding at 600k ohms and is great for finding UF to Earth connections, If you touch the probes with your fingers it will sound very sensitive.

I have seen the batteries explode when someone tried to check voltage in the resistance setting which makes sense since the batteries are some what in series with the meter in that mode.

 

[weressl]

The problem is not that it will read the voltage, it is the person using it fails to pay attention to which setting or banna jack he has installed his leads in to, that is why they came out with cat rated meters as they are protected even if the wrong setting or jack is used, these old meters when the 10 amps jack or setting is used will produce a dead short between the leads and would be very dangerous when someone goes to try to take a voltage reading while in these settings.

Yes I think stupid should hurt but in this case it's killing them, so we have cat rated meters.

Actually the CAT rating serves a completely different purpose. It is designed to protect against overvoltages due to line switching surges and lightning.

http://digital.ni.com/public.nsf/allkb/05D3F9C0F740BC2986256E9A00505421

 

[weressl]

Yes I use a Wiggy type meter as my normal used meter, it's the first one I grab when go into a house to trouble shoot, Its not a Wiggy as that name is referring to the brand name of the Square D version, I use the Vol-Con by Ideal which gives me both voltage and continuity along with loading down a circuit to expel the ghost voltage, while lately I have had a couple fail it was the smaller version so this time I went back to the larger one and so far no problems, what I do like is the continuity part starts sounding at 600k ohms and is great for finding UF to Earth connections, If you touch the probes with your fingers it will sound very sensitive.

I have seen the batteries explode when someone tried to check voltage in the resistance setting which makes sense since the batteries are some what in series with the meter in that mode.

The majority of voltage checks are just what they say, it is a need to verify the presence or absence of potential, not the exact magnitude of the voltage. The Wiggy type meters are a better choice since the V/A connection error is eliminated. A proximity sensor is even better since it does not involve uninsulated and direct contact to conductive parts.

 

[Mike Furlan]

Most common mistake when this happens is by trying to read voltage on Ampere or resistance setting.

Which is why you should always check the meter on a known voltage, before and after, using it to check the unknown voltage.

 

[hurk27]

The majority of voltage checks are just what they say, it is a need to verify the presence or absence of potential, not the exact magnitude of the voltage. The Wiggy type meters are a better choice since the V/A connection error is eliminated. A proximity sensor is even better since it does not involve uninsulated and direct contact to conductive parts.

When I'm grabbing a meter to go into a house its most likely for trouble shooting, so I need a meter that will tell me if I have a true voltage not ghost voltage, the problem with a proximity sensor or as many call them "Tic Tracer" is they like a high impedance meter will also detect ghost voltage and can throw you off thinking a circuit is hot when its not, while I do agree they are a great safety item to alert you of a conductor might be live they can also produce false positives which can baffle the best trouble shooter.

had a guy in our shop change out 15 lamps before he realized that he had a bad dead-end switch that was ghost voltaging his Tic Tracer, I told him to never trouble shoot with a Tic Tracer use a loaded meter, the longest time I ever saw a person take to trouble shoot why a single pole switched light wouldn't work:roll:

 

[Volta]

When I'm grabbing a meter to go into a house its most likely for trouble shooting, so I need a meter that will tell me if I have a true voltage not ghost voltage, the problem with a proximity sensor or as many call them "Tic Tracer" is they like a high impedance meter will also detect ghost voltage and can throw you off thinking a circuit is hot when its not, while I do agree they are a great safety item to alert you of a conductor might be live they can also produce false positives which can baffle the best trouble shooter.

had a guy in our shop change out 15 lamps before he realized that he had a bad dead-end switch that was ghost voltaging his Tic Tracer, I told him to never trouble shoot with a Tic Tracer use a loaded meter, the longest time I ever saw a person take to trouble shoot why a single pole switched light wouldn't work:roll:

Bummer.

Yeah, I use them all the time, but you have to think of the act of trouble shooting with one as more of an art than science, while knowing the whole time that capacitive coupling is all science.

 

[weressl]

Which is why you should always check the meter on a known voltage, before and after, using it to check the unknown voltage.

Your meter would still blow up on the 'known' voltage source.

 

[weressl]

When I'm grabbing a meter to go into a house its most likely for trouble shooting, so I need a meter that will tell me if I have a true voltage not ghost voltage, the problem with a proximity sensor or as many call them "Tic Tracer" is they like a high impedance meter will also detect ghost voltage and can throw you off thinking a circuit is hot when its not, while I do agree they are a great safety item to alert you of a conductor might be live they can also produce false positives which can baffle the best trouble shooter.

had a guy in our shop change out 15 lamps before he realized that he had a bad dead-end switch that was ghost voltaging his Tic Tracer, I told him to never trouble shoot with a Tic Tracer use a loaded meter, the longest time I ever saw a person take to trouble shoot why a single pole switched light wouldn't work:roll:

This is a strawman argument as I've clearly stated to use the alternative tester WHEN only the presence or absence of voltage needs to be verified for safety reasons, not troubleshooting. High impedance digital meters can ALSO read ghost voltages, so in that sense they are the same as the proximity sensors. The Wiggy type detectors will load down the ghost(induced or coupled) voltages, so in that sense they are better than the proximity sensors.

 

[piercent]

Thought you might be interested in a new Eaton article as well about arc flash reduction techniques and energy reducing maintenance switching. It covers their purpose, how they work, benefits, and comparisons. As well as the 2011 edition of the NEC set of solutions for addressing arc flash energy reduction in circuit breaker applications and PPE requirements to keep workers safe.

 

[PetrosA]

CAT rated meters are predominantly designed to safely deal with overvoltages without blowing up in your hand. When you open one up, you'll see that there are cuts in the PCB around the probe jacks and plastic barriers in the case that fit through those cuts which serve to isolate any sparks from jumping from one jack to another. There are also a bunch of MOVs to absorb overvoltages. Further in, there are minimum spark gaps between certain traces on the PCB. The design of the whole meter is such that it should be able to safely withstand a high voltage for some predetermined amount of time. That's also why the probes have ratings, as do tic tracers etc.

To protect against leads being in the wrong terminal during a voltage check, any of the current shunts will be protected by HRC fuses with anywhere from 10kAIC to 100kAIC ratings at at least 600V. There is also protection (usually non destructive) in the better meters on the resistance setting in case it's used on a hot circuit. Some manufacturers have shutters on the jacks that move and close off the openings for ranges that would be dangerous to use with the dial in a given position.

I use Agilent meters and I know I can trust them to protect me in any reasonable situation. I've even checked voltage on a pulse start socket (5000V ) before I realized it was a HID socket with remote ballast and gotten away with it and no damage to the meter. It did make a strange clicking sound from the pulses though

 

[pfalcon]

If Metal vapor were initially conductive,so much heat would not be emitted as the arc is unlikely to form and there would not be the risk of arc blast.But unfortunately, the metal vapor is an insulator and due to electrical breakdown,it begins to conduct current in the form of arc and with large emission of heat.

Contrary to what you state here ionized air and plazma state metal is an excellent conductor.

Is metal vapor and metal plasma the same thing?

Metal vapor and metal plasma are distinctly different. To start an arc requires enough energy to jump the air gap.

Metal vapor creates a series of micro air gaps that reduce the effective air gap size and therefore the energy requirement to start an arc.

Metal plasma is an ionized fluid with no effective air gap and an incredibly high conductivity and high ampacity. An arc-flash will generate plasma.