[NSRCA-discussion] Question.
Ron Van Putte
vanputte at cox.net
Fri Aug 20 09:36:39 AKDT 2010
Yeah, but things might be wet if I feel a shock, no matter how dry
the conditions.
Ron
On Aug 20, 2010, at 12:09 PM, Atwood, Mark wrote:
> From Underwriter Lab documents….
>
>
>
> Testing in 1950s determined that a
>
> shock and let-go value of not greater than 42.4 volts was
>
> an acceptable level in most dry locations and would not
>
> be lethal to a person in contact with the circuit. This
>
> value of 42.4 volts peak would not be acceptable in a wet
>
> location since the resistance of a person’s body would be
>
> much lower in a wet condition.
>
>
>
> It’s extremely person to person dependent. Our skin resistance
> varies wildly and the difference between Dry skin and Wet skin is
> something like 100,000 ohms to 1,000 ohms. Sort of a wide range.
>
>
>
> But again, the “generally accepted” safe low voltage is 40V, or in
> the case of UL Listing, 42.4.
>
>
>
> I have to believe that played a big role in the FAI guideline
> initially of not exceeding 42V.
>
>
>
> AC current is different, both more and less lethal. More because
> it fibrillates the heart, but less because you have a chance of
> letting go. Very situation dependent.
>
>
>
>
>
>
>
> Mark Atwood
>
> Paragon Consulting, Inc. | President
>
> 5885 Landerbrook Drive Suite 130, Cleveland Ohio, 44124
>
> Phone: 440.684.3101 x102 | Fax: 440.684.3102
>
> mark.atwood at paragon-inc.com | www.paragon-inc.com
>
>
>
> From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-
> discussion-bounces at lists.nsrca.org] On Behalf Of Bob Richards
> Sent: Friday, August 20, 2010 12:01 PM
> To: General pattern discussion
> Subject: Re: [NSRCA-discussion] Question.
>
>
>
> >>>The voltage in a battery is not the lethal element, current of
> Amperage is.<<<
>
>
>
> So are you saying that a 1 cell 5000mah pack is dangerous enough to
> kill 1000 people? :-)
>
>
>
> A 12v car battery can put out hundreds of amps. It does not kill
> anyone from electrocution since the human body is a terrible
> conductor (high resistance) and 12v is not enough voltage to cause
> a significant current to flow through human tissue. So, it takes a
> high enough voltage to overcome the resistance of the human body
> before enough current flows to cause problems.
>
>
> On the other hand, a Tesla coil can produce over a 100k volts, but
> a person can touch it because there is so little current produced -
> not enough to hurt someone.
>
>
>
> It takes a source with a high enough potential (voltage) to
> overcome the human resistance, along with enough current capacity,
> before harm can be done.
>
>
>
> The exact values that can be considered dangerous can be debated.
> 50ma will not always be dangerous - it won't feel good, however.
> OTOH, less than 20ma under the right circumstances can be lethal.
>
>
>
> Bob R.
>
>
>
>
> --- On Thu, 8/19/10, Randall Bearden <rbearden56 at bellsouth.net> wrote:
>
>
>
> The voltage in a battery is not the lethal element, current of
> Amperage is. I believe the voltage is to limit the number of cells
> that can be used for the power source. Each will have 3.6 volts so
> you can see that 11 cells in series can will have 39.6 volts.
> The number of cells in parallel will add up to the current you need
> for the engine to produce power. Letha current is about 50 mA or
> 0.05 Amps of current.
>
> On 8/19/10 3:22 PM, "Atwood, Mark" <atwoodm at paragon-inc.com> wrote:
>
> I can’t answer the “checking” question, as I have never had mine
> checked, but I “think” I was told they did at the worlds. As to
> why the limit on voltage, that’s simply a safety issue. 40V dc is
> generally accepted as the threshold for non-lethal dc voltage.
> Your skins natural resistance will prevent enough current from
> going through you at that voltage to kill you (though as many have
> experienced, it can burn the crap out of your fingers). That
> said, if you had electrodes poked through the skin, it could still
> toast you.
>
> There has been talk about raising that limit to accommodate 12s
> batteries which FAI has done for the Heli F3C competitions. I
> doubt you’ll see it go above that. I’m actually surprised that
> the AMA hasn’t put an upper limit (or maybe they have and I’m
> unaware) for the same safety reason.
>
> I can only imagine what a good old fashioned electrocution would do
> for our image. Big bird fun fry…
>
>
>
> Mark Atwood
> Paragon Consulting, Inc. | President
> 5885 Landerbrook Drive Suite 130, Cleveland Ohio, 44124
> Phone: 440.684.3101 x102 | Fax: 440.684.3102
> mark.atwood at paragon-inc.com <mailto:mark.atwood at paragon-inc.com>
> | www.paragon-inc.com <http://www.paragon-inc.com/>
>
>
> From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-
> discussion-bounces at lists.nsrca.org] On Behalf Of Tim Taylor
> Sent: Thursday, August 19, 2010 3:13 PM
> To: nsrca-discussion at lists.nsrca.org
> Subject: [NSRCA-discussion] Question.
>
>
> 4. Model Aircraft Requirements:
> 4.1: Propulsion source limitations: Electrically-powered model
> aircraft are limited to a maximum of 42.56 volts for the propulsion
> circuit, measured prior to flight while the competitor is in the
> ready box.
>
> I see Electrics have a "Displacement" limit, why are they limited
> and the IC engines not?
>
> I also see they must be checked in the ready box prior to each
> flight, anyone ever have this check done? Even at the worlds?
>
> Or is this another ignored rule?
>
> Tim
>
>
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