electric shocks

[sellers]

Just something I've thought about beforem, wondering if anyone can explain why it works in this way.

Electric shocks are all about you becomming the fault path. So if you touch a live cable with your 1000v insulated screwdriver your safe. Even if you put your work boots over your hands and touch them on the cable you would be safe, but once they're on your feet and you touch with your bare hands how does the circuit all of a sudden become complete?

 

[steptoe]

it took me 2 reads, but it all makes sense now,

and if you dont know how this all works by now then you should get a job in a chippy,.



what was that sir, cod & chips twice??!!?!

:C

I dunno,

 

[Phoenix]

Simply put, it doesn't!, with yourself insulated from the floor (and work boots are unlikely to be seen as effective isolation), then your body will simply go to the potential of whatever metalwork you are touching and no shock is felt as the circuit is not complete (unless you brush against earthed metalwork with your other hand for example)

Its why they put rubber matting down in switchrooms sometimes, to give additional protection, and there are ols school folk out there with tails of standing on this, one arm round their back gripping the back to their belt (so they knew it wasnt straying to anything earthed), and using back of hand to feel for excess heat at busbar connections.... not considered safe working practice anymore though

Back in college I had a lecturer who would demonstrate this by standing on a wooden floor, removing the cover of a DB and grabbing hold of one of the busbar tabs while it was live!, that was only a few years back and I strongly suspect the health and safety dept. would have had a heart attack if they'd witnessed it...

 

[sellers]

i can undertsand that I will be there at 0v about to touch something 240v, so there is potental difference, but when I'm touching it why can't I be at 240v, with the boots insulating me from the ground at 0v. Just something I've never asked or been taught.

---------- Post Auto-Merged at 18:50 ---------- Previous post was made at 18:48 ----------

Phoenix I'm 90% sure I've had a shock with the fault path through the boots? I do agree with you though to me it doesn't seem possible?

 

[Phoenix]

Boots are unlikely to effectivly isolate you from the earth (but are likely to limit the severity greaty over bare toes!) , especially if you have just walked across a muddy site to the work area, also on their own i suspect they might be somewhat capacitive due to there being a layer of non conductive material either side of the metal that protects you from upturned nails!. Switch gear matting is designed to provide the correct insulation and standing on this while touching metalwork at 240v would not result in a shock

 

[kerching]

to get a belt you need current flow. current only flows when there is a difference in potential. L1 in one hand and L2 in the other...415V PD and good morning Vicar. L1 on 1 hand and the rest of you isolated form a phase or earth or neutral, then no PD so no current flow. HOWEVER Should any part of you touch ground, other phase or neutral then 'Good Morning Vicar. I am old school and tend to have one hand in my pocket when 'rooting about'...simples

not sure how much sense that makes having read it back again......... :coat

 

[Sidewinder]

kerching,

It does make sense.

This is the same way birds can perch on 400kV lines and survive.

i.e. they sit at 400kV with no earth path.

I've never had the bottle to prove the theory though, not even @ 110V CTE!

I have with 12V d.c. though.

Think about it...

 

[Evans Electric]

Think of the reasons for equipotential bonding , while you are at the same potentional you are safe . As with the dickie birds sitting on the high tension grid system.

I too remember being told to put one hand in pocket when in the DC Subs at local steel works .

 

[Doc Hudson]

Just something I've thought about before, wondering if anyone can explain why it works in this way.Electric shocks are all about you becomming the fault path. So if you touch a live cable with your 1000v insulated screwdriver your safe. Even if you put your work boots over your hands and touch them on the cable you would be safe, but once they're on your feet and you touch with your bare hands how does the circuit all of a sudden become complete?

Out of curiosity have you tried doing an insulation test through the soles of your boots to the inside? maybe they have some deterioration. I know many brands are supposed to be insulated up to 1000v. But some of the cheaper brands are just oil & slip resistant, without any specified insulation levels.

Doc H.

 

[ProDave]

I was on a new install last week on the day the DNO came to connect the supply.

Overhead feed.

The guy goes up the pole in a cherry picker thing with a fibreglass (insulated) man basket, and with his insulated gauntlets on, makes the connection live.

All good stuff.

Except he didn't have his safety harness on, so if he had got a belt, he might have fallen from his perch (literally)

 

[Andy™]

i can undertsand that I will be there at 0v about to touch something 240v, so there is potental difference, but when I'm touching it why can't I be at 240v, with the boots insulating me from the ground at 0v. Just something I've never asked or been taught.---------- Post Auto-Merged at 18:50 ---------- Previous post was made at 18:48 ----------

Phoenix I'm 90% sure I've had a shock with the fault path through the boots? I do agree with you though to me it doesn't seem possible?

if your boots really are insulated, then you will be at the voltage your touching, but isolated form earth

many boots many have some resistance, but they will probably still let power through. but you can get boots specifically designed for live working, and have adequate insulation

 

[steptoe]

my boots are insulated to 1000v apparently, and metal free,

but,

the ubiquitous neon still works, as does my new Di-Log tester(thank you all ) which also does a single contact test,(more on that later),

I havent done a finger test yet and am not about to just to prove a theory. !!!!!!

 

[Sidewinder]

Yes Steps quite!

Thing is how many nano amps via a few Op Amps does it take to drive an LED, the current could be miniscule, though the whole LED current has to return to "earth" somehow, but, taking say 5mA @ 3.5V d.c. even with losses in the conversion from 230V a.c. would be not a lot!

Plus @ 3.5V d.c. you would not feel the tingle.

 

[Apache]

The guy goes up the pole in a cherry picker thing with a fibreglass (insulated) man basket, and with his insulated gauntlets on, makes the connection live.All good stuff.

Except he didn't have his safety harness on, so if he had got a belt, he might have fallen from his perch (literally)

Read that back Dave, and then tell us why he couldn't get a belt!

:|

---------- Post Auto-Merged at 22:41 ---------- Previous post was made at 22:39 ----------

Testing my immersion heater with a neon screwdriver a few years ago felt noting until my elbow touched some heating pipework and I quickly dropped the screwdriver.

Your shoes [even if not specifically 'insulated'] provide a good degree of insulation and only allow a small current through.

 

[sprocketflup]

Yes Steps quite!Thing is how many nano amps via a few Op Amps does it take to drive an LED, the current could be miniscule, though the whole LED current has to return to "earth" somehow, but, taking say 5mA @ 3.5V d.c. even with losses in the conversion from 230V a.c. would be not a lot!

Plus @ 3.5V d.c. you would not feel the tingle.

So how much juice do you think someone would get when they put a PP3 on thier tongue?

 

[Sidewinder]

Dunno Sproc, chuck an IR tester across it & tell me the resistance?...

]

ROTFWL :innocent:slap:tongue in cheek:run

 

[Apache]

For those that don't get it

https://www.youtube.com/embed/-n1pSHzdahc?feature=oembed

 

[sprocketflup]

**waits for one of the sprogs to ask "WTF is a PP3??" **

:^O

 

[Apache]

**waits for one of the sprogs to ask "WTF is a PP3??" ** :^O

9V square battery?

 

[Sidewinder]

Well my 11yr old calls them pp3's!