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Equipment Discussions >> Classic Telescopes

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Brian RisleyModerator
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Re: C8 Grounding question new [Re: orion61]
      #5614681 - 01/09/13 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


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Geo.
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Re: C8 Grounding question new [Re: orion61]
      #5614760 - 01/10/13 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.

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Rich (RLTYS)Moderator
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Re: C8 Grounding question new [Re: Brian Risley]
      #5615402 - 01/10/13 12:11 PM

Brians right lets keep this thread on subject.

Rich (RLTYS)


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Joe Cepleur
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Re: C8 Grounding question new [Re: Rich (RLTYS)]
      #5626008 - 01/16/13 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/cpscpub/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?

Edited by Joe Cepleur (01/16/13 02:58 PM)


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dgreyson
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Re: C8 Grounding question new [Re: Joe Cepleur]
      #5626113 - 01/16/13 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.


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Joe Cepleur
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Re: C8 Grounding question new [Re: dgreyson]
      #5626235 - 01/16/13 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.


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dgreyson
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Re: C8 Grounding question new [Re: Joe Cepleur]
      #5626290 - 01/16/13 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.


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Joe Cepleur
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Re: C8 Grounding question new [Re: dgreyson]
      #5626339 - 01/16/13 02:56 PM

Quote:

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!


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dgreyson
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Re: C8 Grounding question new [Re: Joe Cepleur]
      #5626421 - 01/16/13 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.

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Joe Cepleur
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Re: C8 Grounding question new [Re: dgreyson]
      #5683072 - 02/16/13 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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apfever
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Re: C8 Grounding question new [Re: Joe Cepleur]
      #5683123 - 02/16/13 10:09 AM

Plug in your GFI extention cord as close to the supply as you can. You want to run other extention cords, or anything else out into the field, off the GFI being close to the supply.

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Joe Cepleur
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Re: C8 Grounding question new [Re: apfever]
      #5683331 - 02/16/13 11:48 AM

Quote:

Plug in your GFI extention cord as close to the supply as you can. You want to run other extention cords, or anything else out into the field, off the GFI being close to the supply.




Thanks! Upon hearing your answer, it makes sense. If we're going to walk through a puddle in which the connection between two extensions happens to be submerged, we want that connection to be protected by a GFI between it and the supply.


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Joe Cepleur
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Re: C8 Grounding question new [Re: orion61]
      #6155019 - 10/24/13 08:56 AM

The thread re-opens! A question about grounding any older telescope, or an Orange Tube C8 in particular, arose in another thread about an RV-8, so rather than hijack that one, I have moved the issue here. Picking up with a quotation from that thread:

Quote:

Quote:

Thanks, Norm. So, in theory, we can rewire any old scope. How would the new ground wire fit into the case? These old C8s use oval-ended Belden cords (if I recall the name correctly).



Joe,
If you have a C-8 that uses the Belden oval shaped cord then it is already a three wire grounded type and the middle prong on receptacle on the base is the ground prong. Here is a picture that shows both the cord and plug on the base of a C-8, with the ground pins indicated.
If you have the first generation of the orange C-8 that used the mount that used a two prong Jones plugs, then you need to add a ground. The Jones type male receptacle on the base of the mount is located on the side of the mount and not underneath and is round in shape and about 5/8" in diameter.

- Dave




DavidG to the rescue again! Thanks, Dave. You are an angel to we electrically challenged.

Part of the trouble is that, for me, a "two prong Jones plug" is something I'd find in a bin with a left-handed monkey wrench. Googling did not help much, because I can not see where this type of connector fits on the Orange C8's mount. I am currently miles from my C8, and will inspect it as soon as I can. My recollection is that the Belden cord is odd, in that there is a hole in the plug where a ground would go, yet there is no metal in the hole.

Are you saying that the mount is already grounded, if only I had the correct cord; or, that there is a way to ground it, if I could find this "Jones type male receptacle on the base of the mount," and wire it to... to what; one of the motors?


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DAVIDG
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Re: C8 Grounding question new [Re: Joe Cepleur]
      #6155208 - 10/24/13 10:29 AM Attachment (5 downloads)

Joe,
If you have a C-8 that has the plug for the power cord on the bottom of the mount, it is using the Belden oval shaped cord. Both the cord and the plug on the base are the three wire types with the center pin grounded. So your scope is ground IF you plug it into a grounded outlet in your house and you use a three wire Belden power cord. I'm pretty sure your C-8 is the type with the oval grounded plug located on the bottom of the base.
When Celestron first introduced the orange model units, they did not use the Belden cord and oval plug on the bottom of the base. Instead the receptacle for the power cord was location on the side of the base of the mount and not on the bottom. The type of plug they used were Cinch Jones type.
Here is a picture of the power cord I made for my old C-8 that has the Jones plug and shows what the plugs look like. The Jones plug has only two prongs, so no ground prong. So if you have this type of mount and the original power cord then the base is NOT grounded
If you look at the end of my cord were the Jones plug is attached you can see the Green ground wire coming out. I attached it to metal frame of the plug. To have the telescope grounded I would need to attach a wire to the mount and then attach it to the green ground wire AND be sure to plug the cord into outlet that is grounded.

- Dave


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orion61

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Re: C8 Grounding question new [Re: DAVIDG]
      #6155241 - 10/24/13 10:42 AM

His C8 is not a Sand Cast mount Dave. He has 2 C8s.
Both are the oval cord series.

Edited by orion61 (10/24/13 10:44 AM)


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DAVIDG
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Re: C8 Grounding question new [Re: orion61]
      #6155353 - 10/24/13 11:42 AM

Quote:

His C8 is not a Sand Cast mount Dave. He has 2 C8s.
Both are the oval cord series.




If that is the case, then the mount should be grounded. To test that it is, plug the power cord into the base of C-8 and test the resistance from the center ground pin on the plug on the power cord to some bare metal on the base of the mount of the C-8. The resistance should be be very low.

- Dave


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Joe Cepleur
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Re: C8 Grounding question new [Re: DAVIDG]
      #6155670 - 10/24/13 02:24 PM

Quote:

His C8 is not a Sand Cast mount Dave. He has 2 C8s. Both are the oval cord series.




Larry, my other guardian angel! Exactly correct.

So, my C8s were grounded all along! Nice to know my fears were ungrounded. No wasted effort, though; this is the sort of information that should be found on these forums. Maybe I'm not the only dazed, confused astronomer who thought his Orange Tubes were not up to modern safety standards. Someone else will need to know. Besides, I now know to always supply my own GCFI when using unfamiliar outlets at viewing sites. Then even if it's not grounded, that's a good safeguard.

Testing the ground sounds like a job for an electrical meter, which I don't have, but may soon. I have a habit of buying whatever tools I need, because I always need them again once I know how to use them.

Thousand thanks,

Joe


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Joe Cepleur
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Reged: 03/18/10

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Re: C8 Grounding question new [Re: Joe Cepleur]
      #6155681 - 10/24/13 02:32 PM

This arrived in a private message:

Quote:

The post-sand cast C8s have the 3 conductor cord which includes a ground pin so they should be OK. But I seem to recall a post where someone found the ground wire was not connected internally in the base of the scope, so that's really not good.




I also have a vague memory of such a thread, which may be the origin of my concerns. Sounds as though Dave's test for the grounding is indeed in order, so I'll find an electrical tester.


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DAVIDG
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Re: C8 Grounding question new [Re: Joe Cepleur]
      #6155713 - 10/24/13 02:53 PM Attachment (5 downloads)

Quote:

This arrived in a private message:

Quote:

The post-sand cast C8s have the 3 conductor cord which includes a ground pin so they should be OK. But I seem to recall a post where someone found the ground wire was not connected internally in the base of the scope, so that's really not good.




I also have a vague memory of such a thread, which may be the origin of my concerns. Sounds as though Dave's test for the grounding is indeed in order, so I'll find an electrical tester.




It is correct that there is no ground wire from the center pin on the oval plug connecting to the telescope BUT the ground pin is attached to a metal band. That Band is attached to the metal housing of the plug and the metal housing is screwed to the bare metal base of the telescope. See the attached picture. So in theory the ground pin IS electrically in contact with the telescope base and grounding it. BUT you need to test the resistance from the grounding pin on the CORD when the cord is plugged into the telescope to the bare metal base to be sure that the resistance is very low. You can have a break in the wire in the cord or poor electrical connect between the metal housing of the plug in the base to the base of the telescope.

- Dave


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ColoHank
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Re: C8 Grounding question new [Re: DAVIDG]
      #6155756 - 10/24/13 03:17 PM Attachment (5 downloads)

Here's the Belden #17280 cord for my ca. 1983-84 Super C8. I ordered it from Hands-On Optics. The scope has a Byers drive, and I've never opened it to see if the ground circuit inside is intact. Neither have I been electrocuted...

...yet.

Belden #17952 will also work, but polarity is reversed.

Edited by ColoHank (10/24/13 03:19 PM)


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