Jerry,
I'm glad we had this discussion. It is easy for an amateur radio operator to
become complacent and take a caveliar attitude and forsake safety for cost
saving. Just because a thing will work, does not excuse forsaking safety. Even
you admitted to using an aged extension cord in your rental home. It will
probably continue in service there indefinetly.
I wonder what we should think about having the young man who lives next door,
climbing our 30 year old tower to redo some things up top. At least the tower
owner is not at physical risk...
I wonder how many amateur radio operators or the volunteers helping them do get
injured or die each year as a result of poor safety practices.
Ron
KA7U
Quoting "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>:
> On Sun, 2006-09-24 at 17:26 -0600, Ron wrote:
> > Gary,
> > Looks like we have a discussion going.
> >
> > As I understand it, a ground rod at a secondary panel is usual if the
> > secondary panel is located in a separate building. The ground rod at the
> > secondary panel is more for lightening protection than for electrical
> > grounding and would connect via the safety ground and not the neutral back
> > to the main panel.
>
> A ground rod is acceptable at the secondary panel. It is not acceptable
> as a substitute for the ground wire carried from the main panel and kept
> isolated from the neutral in the secondary panel.
>
> > The neutral and safety ground would be isolated from each
> > other in this secondary panel. In a radio shack this ground rod has use
> for
> > RF ground and equipment case bonding. I think you are correct about the
> 240
> > VAC only on the 3 wire circuit passing code. I think Jerry is correct on
> > everything else and his assumption of ROMEX being the likely cable being
> > considered is well taken.
>
> A three wire romex of black white and bare will pass for a 240 volt
> load, but it ought to not put 120 volts on white but use black, red and
> bare. I looked at a death case where such a circuit left the panel as
> black, white, and bare and reached an outdoor panel with the same colors
> for keeping a cattle waterer from freezing. The 240 volt heater didn't
> heat well. The family complained of high electric bills. One drizzly
> Sunday afternoon the farmer went out to trouble shoot and didn't come
> back in. They found him dead next to that outdoor panel. When I checked
> the circuit, I found 120 volts between the outdoor panel case and the
> earth. I connected a 100 watt incandescent lamp between the panel case
> and a shovel stuck in the ground two feet from the conduit. It was
> bright enough to make a good color picture (slide actually) in bright
> summer sun. I checked the currents in and out. There was a 10 amp
> current in white or black (I forget which, now) in the panel in the
> house and that current was in the bare at the outdoor panel. There were
> two splices between the house and the feed lot. I found one easily,
> where the black white and bare was spliced to black, red, and white
> (without bare ground) from an earlier installation. Tracing the wire
> (helped by the local REC) showed where it should have been but it took
> the farmer's son all summer of digging to find the second splice that
> had been buried about 9 feet down. I should say that the brand of the
> wire leaving the house panel and arriving at the feed lot panel were the
> same. In the second splice, the connections between black white red and
> bare were permuted to that one of the hots ended up hooked to the bare
> which was hooked to the outdoor panel. This was a situation that caused
> a death that if it had been down with a proper four wire circuit it
> would not have happened. My report was very short, but the widow
> complained about the cost per word. I suppose she threatened to sue and
> got a settlement from the person who had made those connections. I heard
> nothing more about it.
> >
> > The NEC has required a safety ground and a neutral for a total of 4 wires
> to
> > 240 VAC subpanels for 2 or 3 decades now. Anybody ever cut the ground lug
> > off of an extension cord to be able to plug it into a 2 wire receptacle?
> Or
> > considered how the chassis ground on your older tube rigs makes it back to
> > the electrical panel...
>
> I had another case involving the death of a siding contractor. Someone
> wired 120 and 240 volt outlets with three wires even though the
> subdivision work panel had a 4 wire outlet. They twisted the pins of a
> three wire 30 amp 240 volt plug to fit and ran three wire with a
> steel/aluminum ground wire, a triplex as used overhead for service
> entrance. At the 120 volt outlets they connected neutral and ground
> together. With the triplex laying on the ground and across a concrete
> street (with concrete truck traffic over it) the ground/neutral broke.
> That contractor was noticing getting tickled while using his Skil saw.
> He even untapped all the twisted splices and redid them making sure the
> ground was good. Working on a damp morning that open neutral let him be
> the ground return for his saw or another tool on the circuit. He didn't
> survive. My report was very short and caused settlement without having
> to file a lawsuit.
> >
> > A little knowledge can be useful but also dangerous. Then again, what is
> > life without some risk. Oh... and never trust a tenant improvement! :)
> > Ron
> > KA7U
>
>
> The risk of shock is pretty good when shortcuts are taken that get
> around what are considered safe practices. The risk of death from those
> shocks is fairly high even though the shocks are only 120 volts because
> a 120 volt shock is enough to put the heart into fibrillation and there
> is nothing but a defibrillator that will get the heart out of
> fibrillation. No pounding, no CPR will do it. The brain lasts 4 to 5
> minutes with the heart in fibrillation, the heart lasts some longer.
> Higher voltage shocks are sometimes safer because they stop the heart
> and a stopped heart can start spontaneously or from the impact of
> falling or from CPR. There are somewhat bad side effects of higher
> voltage shocks, though, there are often burns, one of my clients
> survived 7200 volts but lost two legs, and arm and other body parts.
> Another only lost two hands. Electric burns are often from the inside
> out (like an electric hot dog cooker) and are very hard to heal,
> sometimes the only thing doctors can do is carve away the cooked flesh
> and bone.
>
> I mean this to be gross to be more of a shocker to scare those who would
> take short cuts into not taking those short cuts. Death is permanent.
>
> --
> 73, Jerry, K0CQ,
> All content copyright Dr. Gerald N. Johnson, electrical engineer
>
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