dbeckstrom
super member
Reged: 10/29/06
Posts: 169
Loc: Andover, MN
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Hi guys,
This is a good thread on electrical. I have a question and I thought I'd add it to this thread (as a good single source of info) rather than start a new topic.
My observatory is about 200 feet from my house. Total run from the main panel in the house to the observatory will be about 250 feet. I have 2" schedule 40 buried between the house and the obs.
My plan was to run 12-2 and a 20 amp circuit. Do I need to be concerned about running different wire given the distance or will 12-2 work just fine? I'm assuming 20 amps will be all that I need? I'll have a couple of lights, a computer, a small electric space heater and then whatever the telescope needs for power.
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My Observatory build with photos http://www.observatorycentral.com/index.php?showtopic=435
Domed 12/17/2006
12.5 RCOS
Paramount ME Mount
Pilot's Cross Observatory
45° 15'48.85"N, 93° 21'30.91"W
"Time is the fire in which we burn" - Star Trek
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John Fitzgerald
In Focus
Reged: 01/04/04
Posts: 2709
Loc: AR
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I would run #4 aluminum URD wire that distance for a 20 amp load. You will need the larger wire to cover the voltage drop. 12-2 would have too much voltage drop at full load, but would work OK for less than 5 amps.
Edited by John Fitzgerald (12/22/06 10:53 PM)
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Achernar
Postmaster
Reged: 02/25/06
Posts: 7805
Loc: Mobile, Alabama, USA
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For temporary use, that would probably be fine. But I wouldn't do it for a permanent set up. It's be better to bury PVC conduit 18 to 24 inches under the ground, and run #12 or #10 wiring through it to your observatory. That could either be household ROMEX or individual wires pulled through the condiut. If the power draw of everything is going to be well under 20 Amps of 110V current, #12 gauge wiring is more than adequate. Alternatively, bury direct burial cable that has #12 gauge or #10 gauge conductors if you're drawing up to 20 amps to the same depth. Two conductor cable is used for a single circuit, and three conductor cable allows for two circuits because it has two hot wires, one neutral and one ground wire. Also, make sure your outlets are grounded correctly, GFI outlets that are in weather resisitant boxes would be ideal. Once inside the observatory, ordinary ROMEX wiring is adequate. Your best bet would be to disucss this with a local electrician who can wire your observatory to meet both national and local electrical codes.
Taras
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15-inch F/4.5 Homebuilt truss-tube Dob with Sky Commander digital setting circles.
10-inch F/4.5 Discovery Dob with JMI digital setting circles.
6-inch F/8 Homebuilt Dob
24, 18, 14, 11, 8.8, 6.7, 4.7mm ES 82 degree eyepieces.
21, 13, 8, 5 and 3.5mm Orion Stratus eyepieces.
Two Televue T-1 Paracorrs with tunable tops
Orion and Lumincon Deepsky, Ultrablock, O-III and H-beta nebula filters.
Three curious and needful cats
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oldsalt
Astro Philosopher
Reged: 02/12/05
Posts: 8806
Loc: Pa - between starparties
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I'd stay away from mixing aluminumwire with copper. It is best to consult the local code, as if anything nasty happens, insurance will not cover the loss if it is deemed out of spec.
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There are no winners in war, only bigger losers.
"Duty is the most sublime word in our language. Do your duty in all things. You cannot do more. You should never wish to do less.” Rober E Lee
"It is well that war is terrible-otherwise we would grow to fond of it" Robert E Lee 13Dec1862 Battle of Fredricksburg
Jim
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Galaxyhunter
Carpal Tunnel
Reged: 01/02/06
Posts: 2315
Loc: Northern Illinois
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I used to be on a volunteer fire department when the aluminum wire was starting to be used wide spread, One of the biggest problems with alum wire is the expansion & contraction due to heat. You MUST be sure the connecter clamps are tight!! Check them often, they can become loose & start to ark, That is the main fire hazzard with Alum. Other than that, Alum wire is O.K. Around here, that is what's used for overhead service from the pole to the house.
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Carl
Observatory temperature experiment
Weather Station @ Hawkeye Observatory
My lousy skies at Hawkeye Observatory H52
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LateViewer
Pooh-Bah
Reged: 11/17/05
Posts: 1009
Loc: Manhattan
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Using a schedule 40 PVC that is not listed for use with electrical equipment is not permitted. Don't do it.
Also. Installing phone or coax in a conduit with your power cables is also a code violation. It you would want to have phone and power run separate conduits.
As for voltage drop. I could give you formulas for voltage drop or you can us this.
Voltage Drop
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Chance favors the prepared astronomer.
Yeah I have some stuff.
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dbeckstrom
super member
Reged: 10/29/06
Posts: 169
Loc: Andover, MN
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Aluminum loses a lot more voltage over the distance (according to a voltage drop calculator that I found) than copper does. Copper seems to be a better choice from what I can glean but there may be some reason for aluminum that isn't obvious so I'm open to suggestions.
After some research, I am now thinking about running AWG 8 copper. If I run an 8-3 with ground, I believe that could get two circuits out of it. Since neither circuit would likely need the full 20 amps, I think the #8 would be enough. Does that seem reasonable?
--------------------
My Observatory build with photos http://www.observatorycentral.com/index.php?showtopic=435
Domed 12/17/2006
12.5 RCOS
Paramount ME Mount
Pilot's Cross Observatory
45° 15'48.85"N, 93° 21'30.91"W
"Time is the fire in which we burn" - Star Trek
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LateViewer
Pooh-Bah
Reged: 11/17/05
Posts: 1009
Loc: Manhattan
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Read the above threads if you plan on installing 8-3. You will need to provide a disconnect in your observatory.
Al
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Chance favors the prepared astronomer.
Yeah I have some stuff.
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dbeckstrom
super member
Reged: 10/29/06
Posts: 169
Loc: Andover, MN
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Quote:
Read the above threads if you plan on installing 8-3. You will need to provide a disconnect in your observatory.
Al
Al,
If I install a subpanel with a breaker in it, the breaker would serve as a disconnect, correct?
I'm aware I would need to separate the nuetral and grounds on different terminal bars, too.
--------------------
My Observatory build with photos http://www.observatorycentral.com/index.php?showtopic=435
Domed 12/17/2006
12.5 RCOS
Paramount ME Mount
Pilot's Cross Observatory
45° 15'48.85"N, 93° 21'30.91"W
"Time is the fire in which we burn" - Star Trek
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LateViewer
Pooh-Bah
Reged: 11/17/05
Posts: 1009
Loc: Manhattan
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Yes, to the breaker acting as a disconnect.
And yes to not bonding the ground and neutral in subpanel.
You will also need to establish a grounding electrode, ground rod, that bonds, connects, the grounding conductor (from your feed) with the grounding electrode conductor, from you ground rod, on a ground bar in your observatory breaker panel. This is separate from you neutral bar.
NEC 250.32 (A) and (B)(1).
Al
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Chance favors the prepared astronomer.
Yeah I have some stuff.
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John Fitzgerald
In Focus
Reged: 01/04/04
Posts: 2709
Loc: AR
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I ran #2 aluminum triplex to my dark site building 230 feet to serve a maximum 40 amp load. I used a glob of "inhibitor" on each connection and it does very well. The aluminum is in 1.25" sch 40 PVC electrical conduit. There is nothing wrong with running aluminum wire as a service entrance conductor as long as it is terminated properly and the lugs are rated for aluminum (most are). Aluminum is pretty much the only conductor that electric utilities use, and these days it is mostly trouble free if installed properly.
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Manny Myles
Postmaster
Reged: 11/29/05
Posts: 6284
Loc: Far South of the flyover city ...
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Michael,
First thing I'd do is find out what and how many other things are on that circuit, then find out what size breaker is controlling that circuit.
If this GFI where you plan on tieing into is a ways from the breaker panel you might want to pull new and a heavier gauge wire to that point and then run #10 the rest of the way.
No sense over taxing the existing circuit if its a # 14 from breaker panel to GFI and 6 things are running at the same time, not counting the stuff you intend to run.
If its feasible I'd run a seperate circuit dedicated to the GFI and then off to the place you want the power.
Manny
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Light travels faster than sound. This is why some people appear bright until you hear them speak
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Achernar
Postmaster
Reged: 02/25/06
Posts: 7805
Loc: Mobile, Alabama, USA
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Not only that, but aluminum wiring has a way of loosening connectors over time. Periodically checking and tightening the connectors is a good idea. I know electricans who found all sorts of problems caused by this tendency aluminum wiring has. The wiring must be in the correct type of conduit specified by the local and national electrical codes, the gray PVC type is usally permissible under the ground if buried deep enough. However, you might be required to use rigid steel conduits where they come out of the ground to protect them from damage. I ran conduit recently for an emergency generator, the buried portion was PVC, the portion that runs from the ground to the main breaker and transfer switch was rigid steel. As the others have said, do not run data or telephone wiring through a conduit that also contains electrical wiring. That is very dangerous and illegal too. A lightning strike or a problem with the electrical wiring could result in electric shock, fire, property damage or even explosions.
Taras
--------------------
15-inch F/4.5 Homebuilt truss-tube Dob with Sky Commander digital setting circles.
10-inch F/4.5 Discovery Dob with JMI digital setting circles.
6-inch F/8 Homebuilt Dob
24, 18, 14, 11, 8.8, 6.7, 4.7mm ES 82 degree eyepieces.
21, 13, 8, 5 and 3.5mm Orion Stratus eyepieces.
Two Televue T-1 Paracorrs with tunable tops
Orion and Lumincon Deepsky, Ultrablock, O-III and H-beta nebula filters.
Three curious and needful cats
Edited by Achernar (12/26/06 10:36 AM)
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PJ Anway
Carpal Tunnel
Reged: 06/04/03
Posts: 2165
Loc: North Coast
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You really don't have to worry about voltage drop in a branch circuit until you get over 250 ft., a 10% voltage drop is allowed and will not cause any problems. I'm sure 12/2 is fine for a 20 amp circuit at that distance. If it would ease your mind, you can get a voltage conditioner to plug in ahead of any electronics to make up for any small voltage drop.
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Clear Skies,
PJ
http://doublestarobserver.com
Refl.- 203/1420, Refr.- 100/1000, 75/500, 63/840, Bino.- 15X60, 10X50
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PJ Anway
Carpal Tunnel
Reged: 06/04/03
Posts: 2165
Loc: North Coast
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The problem with aluminum wire only applies to solid aluminum wire in small sizes - 10 AWG or smaller. The connectors for these size wires (usually a screw) does not keep a tight enough connection to prevent the contraction and expansion of the wire from loosening and loose connections mean heat. Over my 35 years in the electrical trade, I've seen some very dangerous situations in connection with this wire.
This is not the case with larger sizes of stranded aluminum wire. These terminate in larger connectors (lugs) and with the use of a product like Nolux, the connection will be sufficient to ensure that it stays tight and safe. Though it is a good practice to re-tighten these after the first year.
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Clear Skies,
PJ
http://doublestarobserver.com
Refl.- 203/1420, Refr.- 100/1000, 75/500, 63/840, Bino.- 15X60, 10X50
__________________________________________________
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Achernar
Postmaster
Reged: 02/25/06
Posts: 7805
Loc: Mobile, Alabama, USA
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True, I was refering to the small aluminum wiring, not the big stranded stuff. The loose connections that occur with the small solid wire can not only create a lot of heat, they can also drive up the power bill too. One electrician friend of mine had that sort of wiring in a house, and after he tightened all the connections, the power bill dropped significantly. I wouldn't want aluminum wiring in my house, not for the circuits that fed from the electrical service at any rate.
Taras
--------------------
15-inch F/4.5 Homebuilt truss-tube Dob with Sky Commander digital setting circles.
10-inch F/4.5 Discovery Dob with JMI digital setting circles.
6-inch F/8 Homebuilt Dob
24, 18, 14, 11, 8.8, 6.7, 4.7mm ES 82 degree eyepieces.
21, 13, 8, 5 and 3.5mm Orion Stratus eyepieces.
Two Televue T-1 Paracorrs with tunable tops
Orion and Lumincon Deepsky, Ultrablock, O-III and H-beta nebula filters.
Three curious and needful cats
Edited by Achernar (12/26/06 06:14 PM)
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Pedestal
Post Laureate
Reged: 03/11/06
Posts: 4374
Loc: Smoggy Bottom, Baytown,Texas
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FWIW: I ran about 250' of #8 wire to drive a 1.5hp water pump. I ran 3 wires for 220v service. It works fine. (I also pulled 110v off of it for lighting, occasional power tool use, etc.)
Hubert
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Hubert
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www.smoggybottom.org
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Total
member
Reged: 12/03/06
Posts: 65
Loc: Rhode Island, USA
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You may already know this, but if you want to do it by the book... at least this is by the book in my area...
Use Schedule 40 piping as well as all the proper elbows and boxes.
The pipe should be 18" in the ground (which you already noted). (Ditch Witch rental at HomeDepot around $150)
Use THHWN or THWN (?not sure which is the correct spelling?) outdoor grade cable, usually 15Amp 14/2 or 20Amp 12/2 cable.
If you don't run a line of the more expensive outdoor cable directly to your box, once the line enters the home you could use less expensive indoor cable to the box or splice it into an existing line. Either way you should put all connections into a square metal box, use wire nuts for the connections and wrap them in electric tape. The size of the box depends on the number of and size of the cables being spliced. Keep this in mind if you try and run the outdoor cable into an existing box already holding connections. I don't think it can hurt getting a bigger box than needed?? You should also use a GFI outlet outside at the scope.
I would think that the entire project (without rental) would cost around or under $100, and would be nice and safe.
Someone with more knowledge on this subject may correct me, and it may be different in your area, but I think thats the overall idea 
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