Circular saw won't ground, safe?

[Don Klipstein]

A few problems with this:

1. Perspiration is salty. A sweaty hand on a metal power tool could have resistance down to about 1k ohms or so.

1. Electric shock can stimulate sweat glands.

2. Electric shock at a few 10's of mA or maybe around 10 mA can stimulate muscles and cause you to involuntarily grip what is shocking you.

1. Most sources say 100-1,000 mA is a range of current that is likely to cause ventricular fibrillation, with a few saying this deadly range starts at 50 mA. (Also a few sources make the upper limit of this "most deadly range" lower.) The changes of death do not decrease to zero at 99 or 49 mA. I have heard of electrocution by 30 mA from a neon sign transformer, although people *usually* survive this.

2. Electrocution is unreliable. With electric chairs, they use enough current to either:

• Cook vital organs * Paralyze breathing muscles long enough to deprive the brain of oxygen to the point that breathing will not restart when the shock ends

Lack of electrocution is simularly unreliable.

1. The low fatality rate of 110-120V shocks lulls people into a false sense of security that leads to this voltage achieving a body count. On US Navy ships, most power circuits are 440V rather than 110V, and most electrocution deaths are from 110V. (Another factor could be that lights and ordinary outlets - where exposure to less-trained people is greater than that of 440V stuff - are 110V.) (Yes, US Navy ships have 110V at least nominally rather than 120V.)

- Don Klipstein ( [e-mail])

[Don Klipstein]

I have been told there are old pilots and bold pilots, but not many who were both. My father said the same thing about electricians.

- Don Klipstein ( [e-mail])

[Leon]

And who says the breaker box was labeled correctly or labeled at all.

[Ed & Sue Beresnikow]

Several of you posters are really scaring me on this topic. If half of you believe even bits that have been posted in this thread I don't expect to read anything more from you within the next several months.

Benton has a chunk of the information in that 120VAC is _DANGEROUS_!! ...and yes at these voltages and frequencies (60Hz) 100mA is almost assuredly deadly. However, under not that unusual conditions fatalities can occur with 120VAC at currents under even 10mA! ..no you don't need to be taking a salt-water bath as there are numerous other items that will drop the skin resistance to permit these fatal current flows including excessive sweating and even more so a break/burn in the skin.

A GFCI will typically cut the circuit at the 5mA ground leakage current that is considered a manageable risk level for most conditions and people but of course not a certainty. When I was involved in the Electrical Safety business in Hospitals in the 70's ICU's & OR's used a

2mA alarm standard that I believe has been dropped since then into well under the 0.5mA range to recognize the increased exposure by the lower resistance seen in open flesh. Death can well occur at less than 100mA at 120VAC and by numerous other factors. Treat with respect.

The GFCI works on the principle that it is able to "detect" any _potential_ current leaks to ground. The fault current does not exist (flow) yet but rather the devices monitors that there are defects in the circuitry that could cause a fatal electric shock should a powered device or line have a person be in contact with the 'failed component'- and the safety device will shut down to prevent the actual shock failure. There are many possible patterns that can make this condition occur not the least being shoddy/worn insulation and broken ground wires.

For all the stories about testing live circuits with fingers and grabbing live wires - they are not impossible nor in many cases even risky _IF_ you fully _understand_ what you are doing and for that reason should never be attempted by the average person.

Urban legends, hearsay and 'best guess' are not to your well being when dealing with electricity. Get facts or leave it alone.

Ed

[Ed & Sue Beresnikow]

....snip...

?? What is the definition here? 'pikey' - don't recognize it as a Canajun term.

Ed

[toller]

Yes, excessive sweating and a break in the skin can allow higher than normal CURRENTS for a given VOLTAGE by lowering the skin RESISTANCE. (though they are unlikely to lower the resistance of your shoes to make you grounded, and without a ground connection, it doesn't matter how low your skin resistance is.) But they will not make 10ma anymore harmful. Exactly what "not that unusual conditions" will 10ma cause fatalities? Being tied up with the wires?

[Dr. Anton T. Squeegee]

Underestimating potential hazards has probably gotten lots of people killed.

Any cord that is frayed and cracking is dangerous. Period. That saw should NOT be used, under any conditions, until it has been properly repaired.

[spudnuty]

For info on how a GFCI works check Sam's , very complete:

please explain why do some modern factory drills, grinders

As above double insulated and more over usually GFCI protected.

Hot to ground short - how big is the spark? 15-20 Amps? Breaker. No spark? - Possibly a GFCI Neutral to ground short - Possibly a GFCI or total miswire And if this is the case can't you ID the GFCI?

Incidently any electrician knows that you can be shocked from a neutral line, especially if you're dissasembling a junction of several neutrals even with the power turned off to the box you're in. One or more of the neutrals can be tied back to another hot or often the other leg through an appliance. Can be a nasty suprise if someone turns on the toaster while you're working on a neutral. There could also be a break in the neutral. I recently rewired a garage where the BX was run along the ground right under the threshold of the door. Salt corrosion rotted the neutral wire out as well as the BX shield. Whoever did this job also tied the neutral to conduit ground so the path was hot to device neutral to box ground to earth through the remenents of the BX. Their son got a nasty shock walking into the garage barefoot on a rainy night and turning on the light!

Richard

[Doug Miller]

That's right, you ass, just a little tingle IF YOU'RE NOT GROUNDED.

If you *are*, you're risking your life.

Certainly not a recommended

You ever hear this saying? "There's old electricians, and there's bold electricians. But there ain't no old, bold electricians."

So by that "reasoning", ground fault circuit interrupters (which trip at 20ma) are completely unnecessary. Riiiiiiight.

-- Regards, Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?

[Doug Miller]

Dumbass! Such conditions will cause *much*more* than 10ma to flow! That's why they're dangerous!

And this is why "you're* dangerous: you don't understand electricity, and yet you continue to give "advice" about it.

-- Regards, Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?

[Doug Miller]

Completely false. You *can* get a shock from a neutral that is not open, if you provide a good enough alternate, parallel path to ground. And dryers and stoves with the frames connected to neutral are *not* safe - that's why the NEC now prohibits that on new installations.

-- Regards, Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?

[Doug Miller]

Good point. My breaker box and subpanels are labelled correctly *now*, but they sure weren't when we bought this house. At least a *few* of them were labelled, and most of those correctly - the two previous houses had *nothing* labelled.

-- Regards, Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?

[Doug Miller]

My first guess would be "of, or characterizing, a piker" (i.e. cheapskate).

-- Regards, Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?

[Andy Dingley]

Sure is. The problem is that I'm made of 70% salt water

(and no jokes about 30% tequila and lime juice)

[WillR]

What colour of flowers would you like at your funeral? Best you let us know now. If you believe that shit, you are going to take a chance some day.

Risks are one thing -- chance is another.

[Robatoy]

As a matter of fact I did. Many. And I have a piece of paper to prove it. I went straight from college into a career at Ontario Hydro (the province-wide power company) in operations. During my tenure in operations at a 2000 MW power-station, I received an award for identifying safety problems relating to test procedures in station service electrical distribution. Again, paper/plaque and pictures from a dinner in my honour to prove it. But that's enough about me.

How about you? If you ever DID read anything about electrical engineering, you must now read some material on interpretative skills and memory retention, because, buddy, you do not know what you are talking about.

[WillR]

Aye!!

Good advice Doug. I do triple checks and am used the the rolled eyes from "knowledgeable" people. F** em. It's less stress to do what you suggest, and it's better advice to give.

And I am never embarrassed to have anyone check my work. No one has never found me to make a wiring error, but if someone asked to check my work I would say "thank you" and move over. Getting it right and safe is cheaper than the alternative.

Usually it is the qualified engineers who recognize the value of safety and QA checks and are never embarrassed to do the required checks, and are never embarrassed to have someone check their work. It is part of the training as I recall.

Now now -- jus cause it's true.

[Andy Dingley]

(I'm posting from Europe, your local terms may be different).

All electrical appliances must be insulated, meaning that the live and neutral feeds are not connected to any accessible part of the appliance. However things break, and so we must also design them to be moderately safe even after this insulation fails.

One way it to wrap them in a conducting case and then earth this case. If they're supplied through an appropriate fuse, then the fault current (internal "works" to case) is then enough to blow the fuse and make the appliance safe. For this reason the earth must not only conduct, but it must conduct _well_.

Another approach is an RCD or GFCI. This measures "earth leakage", usually be measuring the difference in current between live and neutral wires. If there's a difference of more than a few mA (i.e. the current has gone _somewhere_ it's not meant to), then something is wrong and the RCD trips.

UK wiring has much better appliance fusing than other systems, so until quite recently (10-20 years) we've been quite lax about using RCDs. US wiring is a shocking abomination by design and so it's only the huge number of GFCIs and arcing-fault breakers (a totally alien concept in the UK) that stop your evil aluminum wiring killing the population of Detroit weekly.

Around the late '60s, a new approach developed. Plastic was the new thing, and plastic cased appliances were everywhere. These allowed the economic use of "double insulated" appliances. They were still insulated (of course) but now they also had to _remain_ insulated, even after an internal fault. If the wire fell out of the switch and hit the case, the case mustn't in turn become "live". Of course with plastics for cases, this isn't that hard to arrange. Once the standards had got sorted out and clever designers knew how to work with them, you could even get such bizarre things as double-insulated hair curlers, where you stick a big metal heating element on your head, without an earth wire. Not something _I'm_ going to trust in a hurry, I can tell you.

You can spot double insulated appliances in Europe by the two nested squares logo. It's also likely that they only have two wire cables, as you describe. The crucial thing is their internal design though, not merely missing off the earth wire!

[toller]

Aside from being an electrical engineer? (or receiving dozens of 120v shocks without any ill-effects?) Without waving your hands and throwing another hissy-fit, dispute one single thing I have said with documented facts. Do so, and I will never post regarding electrical issues again.

Hint; "everyone knows" is not a documented fact.

[Robatoy]

I asked you:

Answer that first.

Sometimes both are one and the same.

For instance:

Everyone knows you don't know what you're talking about AND the group has a documented paper-trail of what you have been posting.

Besides, I never have a battle of wits with an unarmed person.

END of discussion with you.