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C8 Grounding question

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#26 rmollise

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Posted 09 January 2013 - 09:19 AM

Maybe someone knows if running it offer a battery pack reduces any shock or electrocution risk?


No it does not. How could it? 1 amp of inverter produced AC is exactly the same as 1 amp of AC coming out of the wall and will kill you just as pea-picking dead. ;)

#27 actionhac

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Posted 09 January 2013 - 11:45 AM

I was reading its difficult to get the heart beating again once it stops.
A defibrillator is really only to correct an abnormal rhythm.
I guess it doesn't matter no one I know has a defibrillator anyway.
The key though is not to provide a path for the electricity to flow across your heart to ground, like touching the mount with one hand and having the opposite foot in a puddle of water. Or making a easier path using your body than going through the mount legs. The electricity will take the path of least resistance.
In other words probably put one hand in your pocket if you are fiddling with your mount or cords and everything is wet with dew. And wear shoes.

Robert

#28 kansas skies

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Posted 09 January 2013 - 01:14 PM

Grounding equipment doesn't necessarily make it safe. While grounding the chassis or case of a piece of equipment can remove the possibility of having voltage levels present on the chassis, it also provides a very effective return path to ground for voltages that might be present elsewhere (on some other piece of equipment that is in use). The most effective protection would probably be to install an inline ground fault interrupter (GFI) (in addition to the ground) as was mentioned above.

Bill

#29 DAVIDG

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Posted 09 January 2013 - 01:29 PM

Let remember that issue with the grounding is for the very old C-8 that had the mounts that used the two prong Jones plug, that was on the side of the mount. There most likely were less then 200 of these style mounts made before Celestron changed the design to use the three prong grounded plug located on the back surface of the mount and used the oval type "HP" power cord.
So with a typical vintage orange tube C-8 or newer units, the danger has greatly been reduced. Also if one looks at the construction of typical syn. motor used to drive a telescope, the coil windings are insulated from the body of the motor. So some how a winding would need to break free, go thru the insulation around it and come in contact with the motor housing. Not impossible but pretty low odds. What the real risk comes from is the extension cord used to power the scope. This is were most problems occur from the use of one that is damaged and having exposed wires and/or one that is not a three wire grounded type and/or plugging it into a non grounded outlet. So anyone using a AC powered scope should double check the cord they use, use a three wire grounded one and be sure that it is plugged into GFI outlet.

- Dave

#30 dgreyson

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Posted 09 January 2013 - 01:55 PM

2. I do not recall ever hearing, over the past 43 years, of anyone being electrocuted by a dadgum C8. :cool:


Richard Feynman in his dissent to the Rodgers commission report on the Challenger space shuttle disaster, Appendix F, cites this very logical fallacy:

"It appears that there are enormous differences of opinion as to the probability of a failure with loss of vehicle and of human life... We have also found that certification criteria used in Flight Readiness Reviews often develop a gradually decreasing strictness. The argument that the same risk was flown before without failure is often accepted as an argument for the safety of accepting it again. Because of this, obvious weaknesses are accepted again and again, sometimes without a sufficiently serious attempt to remedy them, or to delay a flight because of their continued presence... The acceptance and success of these flights is taken as evidence of safety. But erosion and blow-by are not what the design expected. They are warnings that something is wrong. The equipment is not operating as expected, and therefore there is a danger that it can operate with even wider deviations in this unexpected and not thoroughly understood way. The fact that this danger did not lead to a catastrophe before is no guarantee that it will not the next time."
Report of the PRESIDENTIAL COMMISSION on the Space Shuttle Challenger Accident

In other words, the O rings had never caused the shuttle to explode, despite obvious evidence of hot gas blow by and burn erosion thru the ring wall so therefore nothing is a problem and the Shuttle is Safe to fly. :foreheadslap:

All activities come with a certain amount of risk, one has to manage risk by taking steps to increase safety and minimize danger.

The impression is being given that all c8's are unsafe, which is not true indeed. the three prong double insulated ones are not what we are talking about. Rather, I mean any classic telescope made before the UL code mandated three prong grounding and double insulation of electrical devices. Cave Astrolas & etc, are just as dangerous. Worn extension cords are indeed a more likely hazard, the takeaway point here is that there is a very good reason undgrounded electrical devices are prohibited by code.

#31 rmollise

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Posted 09 January 2013 - 02:19 PM

Astrolas & etc, are just as dangerous. Worn extension cords are indeed a more likely hazard, the takeaway point here is that there is a very good reason undgrounded electrical devices are prohibited by code.


Which is why I said, yeah, that grounding these things is probably a good thing. But, the awesome Feyman not withstanding, I know of no one succumbing to death due to C8 or from Colonel Mustard in the library.. :lol:

#32 dgreyson

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Posted 09 January 2013 - 02:58 PM

But, the awesome Feyman not withstanding, I know of no one succumbing to death due to C8 or from Colonel Mustard in the library.. :lol:


People dying by electrocution trying to use a telescope you say? Sure, it happens. ok, they really do not say whether it was a C8 or not, but:
Man dies of electrocution trying to watch meteor shower

#33 PiSigma

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Posted 09 January 2013 - 03:17 PM

My 1976 C8 has the two prong Jones plug so I think it is a lot more than 200 units. Didn't the change to the 3 pin HP plug occur when they went from sand cast to die cast forks?

And didn't someone here have a picture of the three prong HP socket and internally the ground pin wasn't even connected to anything in the base?

#34 DAVIDG

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Posted 09 January 2013 - 04:04 PM

But, the awesome Feyman not withstanding, I know of no one succumbing to death due to C8 or from Colonel Mustard in the library.. :lol:


People dying by electrocution trying to use a telescope you say? Sure, it happens. ok, they really do not say whether it was a C8 or not, but:
Man dies of electrocution trying to watch meteor shower


The article say that the person removed the cover plate on a street light and cut the live wires trying to turn off the light to get a better view thru their telescope.

" Millett was killed when hit by an electrical charge of 4,000 volts after he cut the light's main power cord."

Failure of the electrical system of the telescope had nothing to do with the electrocution but it was a willful act of the person who didn't understand what he was doing to cut thru live wires.

- Dave

#35 dgreyson

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Posted 09 January 2013 - 04:18 PM

Actually he didnt even need the telescope to see a meteor shower, but as you saw, he did indeed die by electrocution. That it wasnt the telescope that electrocuted him is an important detail, but he was certainly trying to use a telescope in the incident. so therefore: He was electrocuted while trying to use a telescope.

My question is: did the street lamp have a 3 prong cord? a GFI? I rest my case.

#36 kansas skies

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Posted 09 January 2013 - 05:46 PM

Maybe it's just me, but I worry more about tripping over the extension cord than getting shocked or electrocuted.

Bill

#37 rmollise

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Posted 09 January 2013 - 06:27 PM

But, the awesome Feyman not withstanding, I know of no one succumbing to death due to C8 or from Colonel Mustard in the library.. :lol:


People dying by electrocution trying to use a telescope you say? Sure, it happens. ok, they really do not say whether it was a C8 or not, but:
Man dies of electrocution trying to watch meteor shower


Uh...eletrocuted because he cut the wires of the a streetlight. The telescope was innocent.

NOT GUILTY, YOUR HONOR! :lol:

#38 rmollise

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Posted 09 January 2013 - 06:31 PM

Actually he didnt even need the telescope to see a meteor shower, but as you saw, he did indeed die by electrocution. That it wasnt the telescope that electrocuted him is an important detail, but he was certainly trying to use a telescope in the incident. so therefore: He was electrocuted while trying to use a telescope.


He was standing next to a Dodge Neon when he shimmied up the light pole, so I SAY THE DODGE WAS AT FAULT, COUNSELOR! WE WILL SUE CHRYSLER! :lol:

#39 actionhac

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Posted 09 January 2013 - 06:48 PM

My neighbor has "hot wires" in the cattle fences out in the valley.
The intensity of this wire is adjustable and right now they are set to a relatively mild shock, mild if your a 1200lb cow!
Well it definitely will wake you up. I'm not sure how it works because we usually have knee high thick rubber boots on when we get ZAPPED.
It must be going through body tissue and exploding outward in the form of radiation into the atmosphere seeking a ground or something. I'd should see what it looks like in the dark.
Not very dangerous because very little amperage just a massive amount of voltage.

Robert

#40 orion61

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Posted 09 January 2013 - 08:10 PM

I grew up on a Farm and we ran those electric fences. Trust me they will wake you up!
FUNNIEST thing I ever saw in my life, was when our old dumb Farm dog lifted his leg on one of those Metal Fence posts!
I just happened to look back at him when he did it.
There was a big YELP and he took off running faster than I'd ever seen him run, Amd as God as My witness the tip of his tail was curled up under him and touched his chin as he ran.. Front end WAY in the air, back end WAY down low as he was running...
Next day we were walking up the lane again, he looked at that post paused and GROWLED at it.... This is a true story..

#41 Brian Risley

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Posted 09 January 2013 - 11:10 PM

Ok, I think this has been beaten to death and wandered off course a bit. I will say, if you use a drive corrector, better check inside on what they did with the grounding on the AC input and output, it may surprise you!
Brian

#42 Geo.

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Posted 10 January 2013 - 12:22 AM

Electric fencers operate at very high voltages, 10-20K, but very low amps. Circuits can easily run a mile. My dad would grab the wire to test them. If he got a good contracton of his arm then the fence was working well. If not, I got to patrol the line looking for weeds grounding it.

#43 Rich (RLTYS)

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Posted 10 January 2013 - 12:11 PM

Brians right lets keep this thread on subject.

Rich (RLTYS)

#44 Joe Cepleur

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Posted 16 January 2013 - 11:10 AM

Please could someone confirm that I understand how to prevent electrocution when using at AC powered telescope?

(1) If the scope lacks at three-prong plug, have one installed by an electrician.

(2) If an older scope has a three-prong plug, consider having an electrician check that the ground is actually properly connected.

(3) Use only heavy-duty, three-prong extension cords in perfect repair.

(4) Use only three-prong, grounded outlets. (Corollary: If only two-prong outlets are available, do not use the electric drive!)*

(5) If the available three-prong outlet is also GFI, great! If not, plug a GFI extension cord into the outlet, and the longer three-prong extension into that.

(6) Be smart. Especially when joining several extension cords together, protect the joined plugs from puddles, melting snow, or excessive dew.

And, Larry: You presumably know how to test the wiring on that orange tube's base?!

-=-=-=-=-=-

*Edit:

At http://www.cpsc.gov/...ub/pubs/099.pdf, I just read that "a GFCI works even on two slot receptacles." Does this mean that I do not need to worry whether the outlet is three prong or two slot, or is a three prong still better?

#45 dgreyson

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Posted 16 January 2013 - 12:33 PM

Yes, to be reasonably safe all of those statements are valid.

GFI devices work by comparing the current going out to the current coming in. If more current is going out than coming back, the device knows that electricity is flowing to ground somewhere (a ground fault) and opens the circuit. So yes GFI affords protection even on two prongs.

The difference, is that with a three prong, the gfi trips immediately when you plug it in. On a two prong, it will trip when someone grounds themselves or a stepstool against an electrified casing and provides the missing path to ground. A three prong without GFI will hopefully trip the house breakers or fuse if the hot wire shorts to the case.

When all you have is a two prong wall outlet, do not use a 3 to 2 prong adaptor and assume the cover screw is grounded.
It likely is not. Also, just to be paranoid, just because an outlet is three prong, it doesn’t necessarily mean its grounded. Sometimes previous handyman owners will swap out the old outlet for convenience. A decent receptacle tester can be had from amazon for $7 bucks and shows by lights if the outlet is good or improperly wired when you plug it in.
If your outlet is ungrounded, use a GFI or the battery or have it fixed.

The important idea to take away with you, is that in the past, any sort of safety was not something that was much worried about. In the 1920's, it was not uncommon to see exposed conductor knife switches. If you were feeling around in the dark for the switch and put your fingers across the switch lever, you would know it immediately.

In today's lawsuit ready environment, electrical safety is considered more important. Over time, as commercial products kill and maim their customers, product designs have evolved from mortality data to reduce the manufacturer’s chance of monetary loss.

But besides taking care of your own personal safety, you really have to consider the financial ramifications from electrocuting the barefoot neighbor’s kid who runs up and wants to look through your scope and touches the frame in admiration. And it looks really bad at Outreach demonstrations when that happens.

Everyone has heard of someone’s grandpa who smoked tobacco & etc. and died at a ripe old age in perfect health. If you plug in your old scope with the rotten wires flaking off the insulation, you have a good chance of being just fine and nothing ever happening. One has to weigh the risks you are willing to accept versus the benefits and consequences and choose for yourself. No one has to do any of this if they choose not to, it is merely a good idea to do so and one takes one's chances as they like however they fall as in any activity.


#46 Joe Cepleur

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Posted 16 January 2013 - 01:48 PM

Thanks, dgreyson! I like to be careful for myself, but also feel an obligation at star parties to offer only best-practice, safe electrical cords to unwitting guests.

I actually have a receptacle tester. Used to use it in traveling sales to determine whether an outlet was on a GFI protected circuit, prior to plugging in a surge protector. Learned to do that after blowing up a customer's outlet once, while on a call in a fancy loft in the Garment District of New York. Apparently, it's one or the other, not both!

Is there any similar risk to the receptacle in plugging in a GFI extension cord, if the circuit is already GFI protected? I recall an electrician telling me that installing a GFI as the first outlet on a circuit of many protected all the outlets downstream. This opens the possibility that plain-vanilla, three-prong outlet could actually be GFI protected. Any chance I'm going to blow up yet another outlet, by adding a GFI extension where it does not belong? If there is no risk, then I should simply use a GFI extension cord whenever I do not plug directly into a GFI outlet.

Which is better (less harmful), or does it matter? Getting zapped while connected to a properly grounded, standard outlet, or a GFI outlet? It sounds as though the GFI is better, so I may as well always use it.

#47 dgreyson

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Posted 16 January 2013 - 02:23 PM

Sorry Joe, I'm an Electronics Tech not a Master electrician and that question exceeds my level of competence to answer.
I do not know if two GFI in series are more dangerous.

GFI is better than no GFI, I can say that with confidence.

New Hair dryers commonly come with GFI plugs and bathrooms are mandated by the NEC code to have GFI recepticals. I use a hair dryer every day in series like that and it seems to be fine. When I test the gfi by pressing the test button, both trip. So by that I presume that it isnt an issue or the dryer box would have a warning against it. (anyone going to Target or WalMart today? go look and see.)

My best guess is that it isnt any safer to have two in series as they both protect and two in series isnt a signifigant risk. That is just my guess though, your mileage may vary.

One thing to add however, GFI is looking for improper shorts to ground. If you wet your thumb and put it in a
lamp socket, current will flow from hot to neutral and the GFI is perfectly fine with that. It has no way of discerning whether it has a proper load or if someone is touching hot and neutral at the same time. So touching exposed wiring does not automatically mean the GFI will always trip. Thats the reason why you shouldnt use worn and damaged extension cords or cables.

#48 Joe Cepleur

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Posted 16 January 2013 - 02:56 PM

GFI is looking for improper shorts to ground. If you wet your thumb and put it in a lamp socket, current will flow from hot to neutral and the GFI is perfectly fine with that. It has no way of discerning whether it has a proper load or if someone is touching hot and neutral at the same time. So touching exposed wiring does not automatically mean the GFI will always trip. Thats the reason why you shouldnt use worn and damaged extension cords or cables.


Interesting! In this case, the GFI would not help, but a proper ground would, so it would be better always to have both. It sounds as though if there is a problem at the scope, with electricity grounding far from the outlet, the GFI detects that, and cuts the power. But, if the expected amount of power were coursing through the outlet and some unlucky soul's wet thumb in the socket at the same time, only a ground would help, by being more efficient at carrying the power into the Earth than would be the body of the poor fool being electrocuted.

Good to know there is no harm to the household wiring in doubling up on GFIs. Blowing up that outlet was not one of my finer moments!

#49 dgreyson

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Posted 16 January 2013 - 03:42 PM

More is better one would suppose, and that the hapless person who inserts personal parts into energized electrical apparatus is risking an illuminating experience if the gods by chance were to shuffle when they should have cut.

#50 Joe Cepleur

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Posted 16 February 2013 - 09:44 AM

I bought a weather-proof, super heavy-duty, outdoor GFI extension for $30. Does it matter where it is plugged into the circuit? If I am going to run 100 feet of extension cord, is it better to install the GFI at the receptacle, or at the end of the cord just before the telescope -- or does it not matter?

This strikes me as a wise purchase for using a telescope at outreach events, which are often at older buildings with unknown electrical wiring.






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