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Power runs to observatory, type of wire, placement, boxes?

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#1 markm75c

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Posted 18 July 2019 - 12:15 PM

I have my main build thread (documentary thread) at that location, but had a few specific electrical requirement things i still need to work out.

 

My nexdome/deck sits about 120 feet from the garage where i have a breaker box, which i think still has one free slot for a new breaker (strangely the whole box was wired as 30 amp, though i guess its ok, the one breaker powers the pool at about 9amp total pull at any given time).  I'm guessing i need to buy just a standard breaker 15amp to put in the box in the garage.

 

I was going to rent a ditch digger and dig the ditch up to the deck area (still in construction).  I plan on using separate pvc for both the electric and data in another.

I'm thinking 3/4" conduit for the power and 1.5-2" for the data (3 cat 6 ethernet runs).  Ill leave a string in each pull for future use if need be.

 

Things im unclear on..

How to figure out the type of electrical wire i need for this run.  I assume 10-12 gauge of some variety (i use lowes as my source so ill go there for things and there was a certain type i bought before, certain color i think too).

I also assume a 15 amp breaker will be good enough to power the cem120, a laptop (or nuc one day with lcd), the various other things that might be in there like a dehumidifier (still to tbd) and/or small exhaust fan on a timer and web camera.

 

Does the electrical pvc have to be the grey conduit variety (i think electrical type?)?

For the data 1.5" ill just use standard pvc and glue them together as i go along.

 

At first i thought i'd bring the two conduits up near the edge of where the inner side of the dome wall will be, but since i dont know that, i'm thinking ill route it to the pier location, next to it, on a vertical piece of pvc coming up.

 

Here i cant recall as its been years, would i just have that come to a "breakout box" of some type, i guess weatherproof for now to be safe though in 2 months it wont matter.  I figure from there i can leave some boards up on the floor or make removable and have a the data/electric pvc go from the pier to an outer wall, which again i wont know exactly where, but i can probably estimate or leave a board removable near where the wall should be.  Actually, i guess this first breakout box area needs to be GFI, or the first outlet after it, rather, would need be a two port GFI outlet.

 

Any thoughts on this?

I guess if need be i can hire an electrician, but i had a friend help run a shorter run to the pool/deck we have and it worked out fine.'

Thanks in advance

 

 



#2 Garyth64

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Posted 18 July 2019 - 01:00 PM

Plan for the future.  I would at least have maybe two circuits out there.  One for lights, and the other for accessories.

 

I would go with #6 or #8 wire because of the distance, and pull it thru about 1/1/4" pvc.  For any data lines, yes,  I think it would be good to run them in their own conduit.

Just keep the elbows, 45s or 90s to a minimum,  it gets harder to pull thru the bends.

When I ran power to my garage, I only had to go 50 feet.  My conduit was too small, and I had to many turns.  I almost couldn't pull the last few feet of cable.  I also wired it for 220.

 

Maybe even have a 40 amp breaker box in the observatory, and one in the house.

 

It is a very good idea to ask advice from a real electrician.


Edited by Garyth64, 18 July 2019 - 04:12 PM.


#3 Chucke

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Posted 18 July 2019 - 01:08 PM

I have a 140' run.  I went with #6 wire and used 1 1/2" PVC conduit.  Didn't need conduit that large but I figured why not.  It doesn't cost much more and makes pulling easier.  I used L-boxes where the wire entered buildings.  They take care of the issue of number of bends and act as pull points.



#4 markm75c

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Posted 18 July 2019 - 01:44 PM

I have a 140' run.  I went with #6 wire and used 1 1/2" PVC conduit.  Didn't need conduit that large but I figured why not.  It doesn't cost much more and makes pulling easier.  I used L-boxes where the wire entered buildings.  They take care of the issue of number of bends and act as pull points.

Is it something like this 12/2 uf-b type at lowes?

https://www.lowes.co...he-Roll/3129375

 

I assume the first number is the gauge?  So it should be 6-2?

 

Would 6-4 mean 2 pair (240 volt, to run 2 circuits if need be)?

 

Not seeing anything lower than 10 at lowes site at least.

 

EDIT : maybe this southwire by the foot $2 or so per foot (so 2x as expensive as the 12-2 above) https://www.lowes.co...e-Foot/3345386 

 

Did you use grey electrical pvc at that size 1.5" i assume?


Edited by markm75c, 18 July 2019 - 01:47 PM.


#5 CharlesW

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Posted 18 July 2019 - 02:00 PM

Are you saying that you have a total of 30 amps to your entire house, or that every breaker is 30 amp and you have a 100 or 200 amp service?

 

If you have a total of 30 amps, if the pool, microwave, obs, and a vacuum are all going at the same time you are going to be looking at your own personal blackout. It sounds you me like you need to get your service upgraded before you add anymore load to it. 


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#6 spacemunkee

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Posted 18 July 2019 - 02:17 PM

I assume the box you're speaking of is a sub- panel off the main which I'm sure it is.

In any case save yourself some cash and throw in at least 1-1/2" conduit(pipes cheap) and run you a #4 aluminum URD 4 wire feed(good for at least 60 amps if you ever needed up upsize things, don't see you ever coming close and should be big enough to not worry about voltage drop) to give you the option of having 240 out there. Save a chunk over copper. Install a small sub-panel out there to run circuits out of. Small subs are cheap. And just be sure that the wire is USE-2 which is approved for running inside a structure. It usually always is. And don't forget oxide inhibitor to apply to terminations.

Verify that this panel you speak of is wired correctly as a sub-panel with separate ground wire fed to it bonded to the enclosure and separate neutral isolated. If you need an extra space to get a 2 pole breaker in there buy a half size to combine 2 into one breaker slot.

Edited by spacemunkee, 18 July 2019 - 02:20 PM.


#7 markm75c

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Posted 18 July 2019 - 02:28 PM

Are you saying that you have a total of 30 amps to your entire house, or that every breaker is 30 amp and you have a 100 or 200 amp service?

 

If you have a total of 30 amps, if the pool, microwave, obs, and a vacuum are all going at the same time you are going to be looking at your own personal blackout. It sounds you me like you need to get your service upgraded before you add anymore load to it. 

Im not sure what the main breaker is (in house) but 30 amp is hand written on the box outside, the line going out, in the main box in house does have a 30amp breaker on it, then each one appears to be 15amp (3 of them in there in garage).

 

haha not 30 amp total.. pool at 9amp and whatever pull from the observatory on that 30 amp line from house (which could be upgraded if the wire was thick enough i suppose, its underground)



#8 physics911

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Posted 18 July 2019 - 02:29 PM

There are calculators on the web which will tell you the size you need for a given load and distance. I can tell you that 12 gauge isn't going to cut it for that length.

I ran 8 gauge for a 15 amp service at 150 feet.
And be prepared for sticker shock on the bigger wire.

#9 markm75c

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Posted 18 July 2019 - 02:31 PM

I assume the box you're speaking of is a sub- panel off the main which I'm sure it is.

In any case save yourself some cash and throw in at least 1-1/2" conduit(pipes cheap) and run you a #4 aluminum URD 4 wire feed(good for at least 60 amps if you ever needed up upsize things, don't see you ever coming close and should be big enough to not worry about voltage drop) to give you the option of having 240 out there. Save a chunk over copper. Install a small sub-panel out there to run circuits out of. Small subs are cheap. And just be sure that the wire is USE-2 which is approved for running inside a structure. It usually always is. And don't forget oxide inhibitor to apply to terminations.

Verify that this panel you speak of is wired correctly as a sub-panel with separate ground wire fed to it bonded to the enclosure and separate neutral isolated. If you need an extra space to get a 2 pole breaker in there buy a half size to combine 2 into one breaker slot.

Yep its a subpanel at 30amp overall, so should be ok.

 

We plan on moving in 5-10 years, just a nexdome, i guess the only upgrade might be to add an AC unit (or dehumidifier) if needed, probably just dehumidifier.

 

Im clearly not searching on the right parameters at lowes to find this lower gauge wire, unless its an in store only thing.

 

What sort of box would i want as the first "junction" by the pier to split the connections in the dome, is that just called a gang box, again its been awhile and I had some first hand help last time around?  I'm also going to triple check with my contractor contact on things before i finalize.



#10 Chucke

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Posted 18 July 2019 - 02:32 PM

I used  6 AWG THHN individual copper wires (black, white, green) I bought from http://wireandcableyourway.com and not direct burial cable.  I have had good luck with that company and you can get from them pretty much any type of wire there is.  You always want to use the water resistant wire for any type of underground runs because conduit can fill with water from condensation or leakage in the conduit if you didn't glue it well.

 

I used standard grey PVC electrical conduit 1.5".  I used larger than required conduit to ease pulling the wires.  Don't forget the wire lube if you have a long run or tight conduit. Note that the glue for grey conduit is different than the glue for white conduit.

 

I used the direct burial cable (uf-b) from my service to my garage.  In retrospect I wish I had used conduit and individual wires.  Pulling a 1"+  thick cable bundle with the heavy plastic coating that is on direct burial cable was not fun at all.  The stuff doesn't bend well.  Also, if I ever decide to increase the current capacity to the garage I will have to re-excavate the trench vs just pulling new cable through conduit.


Edited by Chucke, 18 July 2019 - 02:32 PM.

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#11 Chucke

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Posted 18 July 2019 - 02:38 PM

Get a book about electrical wiring.

 

There are codes about the depth of trenches.



#12 Rich V.

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Posted 18 July 2019 - 02:45 PM

Consider that compensating for voltage drop, whether a 15 amp or 20 amp circuit, it will require #8 THHN copper wire or #6 aluminum for your 120' distance. Don't forget a ground wire.

 

1" minimum conduit and wire pulling lube will make pulling the wire easier.  Aluminum wire requires an anti- oxidant compound on the splices.  Use a GFCI outlet at the observatory.

 

I highly recommend you use the gray PVC schedule 40 electrical conduit, not white PVC water pipe. Make sure you also use gray electrical sweep elbows, not plumbing fittings.  If an excavator digs near your conduit, he'll know that gray means electrical; I've seen bad outcomes with white pipe used for electrical...

 

A gray steel 6"x 6" SC (screw cover) box is a good landing point for your conduit.  You can use the knockouts pre-punched in the box to install the necessary conduit connectors.

 

Rich


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#13 jgsstars

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Posted 18 July 2019 - 02:59 PM

Hello Markm,

First let me qualify that I am a Master electrician.I have a similar situation that you do as my garage has only a 40 amp service.You should run at least #10 wire for voltage drop at 120' distance,and that is for a single 20 amp circuit. I would recommend 10/2 UF without the conduit for the electric circuit. That is what I have in my observatory. I went to a j-box inside the observatory and branched out for the other receptacles. It controls a  12" ota and Celestron cgem dx and misc receptacles . It also takes care of the computer and lights. Unless you plan on trying to run an air conditioner an or a heat pump or astro cameras which I don't think they require a lot of current,but I'm not sure because I am only  visual only observer.  It will be sufficient.I also have a permanent mount that I mount my Ar6 at the same time. After you get the #10 into the observatory you can step down to # 12/2 romex to the other duplex Receptacles.I have at least 6 other receptacles also.     

 

I also run a fan during the summer. Its great for keeping the mosquitoes at bay. 


Edited by jgsstars, 18 July 2019 - 03:04 PM.

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#14 spacemunkee

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Posted 18 July 2019 - 03:29 PM

Look up an electrical supply house near you. Sure to be a few around and will have someone there that knows what they are talking about. Tell them what you want to do. They can help you out and will have what you need.

Been in Depot or Lowe's many times and overheard an employee "helping" someone only to jump in there and help them myself.

I would still look into running aluminum to a small panel, even a little 4 spacer, not big at all. Can get a higher amp capable size wire at a significant savings over copper when you start getting into the larger sizes. Though admittedly a little harder to work with when you start getting pretty big.

In all my years of electric, depending on the job requirements, I'll run a good size sub-panel to a certain place to handle certain things in a heartbeat vs. pulling those copper circuits back to the main panel. Cost and time savings.

And before someone says "No! Not aluminum!" Not like the danger aluminum is when it was used for circuits in a house. What's that feeding from the pole through the meter and into the panel. Likely aluminum.

#15 Rich V.

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Posted 18 July 2019 - 03:40 PM

 

You should run at least #10 wire for voltage drop at 120' distance,and that is for a single 20 amp circuit. I would recommend 10/2 UF without the conduit for the electric circuit. After you get the #10 into the observatory you can step down to # 12/2 romex to the other duplex Receptacles.I have at least 6 other receptacles also.    

 

#10 wire at a 20A load would have a 5% voltage drop which per the NEC applies to feeders, not branch circuits.  Branch circuits should not exceed 3% which would require #8 copper at a minimum for that distance.



#16 jgsstars

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Posted 18 July 2019 - 04:04 PM

This is not a feeder its a single circuit he also said he only had a 30 amp circuit feeding his garage. it does no good increasing the size wire greater than the wire feeding his garage service.

It works regardless of what the NEC says.

Edited by jgsstars, 18 July 2019 - 04:07 PM.


#17 Rich V.

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Posted 18 July 2019 - 04:28 PM

This is not a feeder its a single circuit he also said he only had a 30 amp circuit feeding his garage. it does no good increasing the size wire greater than the wire feeding his garage service.

It works regardless of what the NEC says.

Yes, it's a branch circuit, not a feeder as I pointed out above.  3% VD max per NEC. Sure he can fudge it but it's not up to code, that's all.  Voltage drop over the distance still applies and wire size must increase.  The wire size feeding the sub panel in his garage makes no difference.  It's about the resistance of the 120' long 20A 120v branch circuit to his observatory only.  Even # 8AWG works out to just over 3%.  At a 15A load the #8 VD drops to only 2.34%; well within the 3% NEC requirement.



#18 spacemunkee

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Posted 18 July 2019 - 05:52 PM

I'll agree on at least just increasing the size on that distance to be covered on drop, regardless of what is supplied to garage.

I see where you both are coming from, but Mark here just wants to know what to do, not bust out the NEC book and dig through equations.

But we're talking about 120' feet here. Over size a bit and forget voltage drop existed. Bet there's the end of 15 amp circuits in the house have more distance than that on them. Any problems? We're talking minimal and probably within tolerances of what your running.

I still go with aluminum. Quick check on Home Depot, without digging up receipts to see what I've paid at supply house.

If #8 copper thhn(which would need pipe), 3 runs of 120' at $1.25 a foot=$450.

Didn't readily find #4 aluminum URD on there(they don't carry much of a selection of aluminum), but even #2 URD that they show(even larger), gets you 2 wires #2 and a #4(for ground) paired up for $1.15 a foot=$138.

Talking almost twice the ampacity and less resistance at well less than half the cost.

By the way, I do nothing without pipe anymore, even if rated for direct burial.
Toned out and fixed enough wires in the past due to a rock finally biting through direct buried wire or some other occurrence. Never would have happened with pipe...

Oh, and of course just talking of a branch circuit. 240v sub-panel would need that fourth wire.

Edited by spacemunkee, 18 July 2019 - 05:59 PM.

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#19 Rich V.

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Posted 18 July 2019 - 06:32 PM

I see where you both are coming from, but Mark here just wants to know what to do, not bust out the NEC book and dig through equations.

But we're talking about 120' feet here. Over size a bit and forget voltage drop existed. Bet there's the end of 15 amp circuits in the house have more distance than that on them. Any problems? We're talking minimal and probably within tolerances of what your running.

 

 

Mark, the OP, hasn't said what his line voltage actually measures; if it starts out at 120V and he's pulling say, a 15A load, #8 copper or #6 aluminum will give him 117.2V at his observatory.  If he goes with #10 copper, it's down to 115.5v.

 

What voltage delivered at the observatory will be adequate for his equipment?  I can't say.  There are online calculators that figure this anymore; not like when I was an electrician apprentice many years ago and we had to do it manually.  wink.gif

 

http://wiresizecalcu...voltagedrop.htm

 

The original line voltage matters a lot; take your pick; I did the hypo calculations for Mark-

 

A 20A load @ 120V with #8 cu would deliver 116.25V or with #10, 114V.

- 15A load: 117.2V or 115.5V, respectively

- 10A load: 118V or 117V

 

If the line voltage is only 115v, though:

- 20A load: 111.25V or 109V

- 15A load: 112.2V or 110.5

- 10A load: 113.1V or 112V

 

You see there is a real potential to have significantly low voltage but there are a number of variables; line voltage, load and wire size matter.

 

I agree that using aluminum wire in the larger sizes saves a lot of money as long as the wire is terminated properly.


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#20 kathyastro

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Posted 18 July 2019 - 06:51 PM

I used 10 gauge wire for my 200' run.  I have a split 240v circuit, so effectively two 120v circuits isolated from each other.  I ran the electrical in a 1.5" PVC conduit, and data in a 1" conduit, both in the same trench.

 

Keep bends to a minimum.  It is better to bend a couple of 10' lengths of conduit into a sweeping curve than to use an elbow.  When pulling cable, use lots of cable lube.

 

I pre-planned the building location, and brought the cables up in one corner of where it would be.  Inside the observatory, I have a fused cutoff switch, after which the circuits branch out to to various outlets.  I have a quad outlet on each wall, and one on the pier.


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#21 spacemunkee

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Posted 18 July 2019 - 07:11 PM

I'm absolutely with you. Just didn't add what your supply is giving you as far as voltage which affects the end of things.
Tested voltage on many mains over the years. Sometimes may be hitting around 110, sometimes 125+.

I did one job a few years ago where upon coming back for some things the homeowner said with this and that going(good draws), and the AC kicks on we get a quick dim, our neighbors have the same problem.(well there's a clue..).

Well service I installed is all good and required load calculation for inspection bureau came in well below required.

"Historic neighborhood" and upon checking things out, 1 transformer(obviously old), 2 poles plus 2 riser pole away was feeding 4 homes to get there. 1 directly off transformer, with the other three spanned off probably 250' I'd say at the very least, with two homes mid-spanned off that run before their house at the end.

Well my work is fine. Better call the power company..

They did come put there permanent crimps on my 4/0 at the wheather head to their inadequate wire to that point, but nothing else...

Edit: But yes I see your point. But what is called significant will likely still fall within the tolerance of what is being ran. Though I'll admit, when you're cutting it close, can be hard on equipment.

Edited by spacemunkee, 18 July 2019 - 07:36 PM.


#22 John Fitzgerald

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Posted 18 July 2019 - 07:19 PM

Hello Markm,

First let me qualify that I am a Master electrician.I have a similar situation that you do as my garage has only a 40 amp service.You should run at least #10 wire for voltage drop at 120' distance,and that is for a single 20 amp circuit. I would recommend 10/2 UF without the conduit for the electric circuit. That is what I have in my observatory. I went to a j-box inside the observatory and branched out for the other receptacles. It controls a  12" ota and Celestron cgem dx and misc receptacles . It also takes care of the computer and lights. Unless you plan on trying to run an air conditioner an or a heat pump or astro cameras which I don't think they require a lot of current,but I'm not sure because I am only  visual only observer.  It will be sufficient.I also have a permanent mount that I mount my Ar6 at the same time. After you get the #10 into the observatory you can step down to # 12/2 romex to the other duplex Receptacles.I have at least 6 other receptacles also.     

 

I also run a fan during the summer. Its great for keeping the mosquitoes at bay. 

I agree with the above post.  You can see my quals in my profile.


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#23 markm75c

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Posted 18 July 2019 - 08:33 PM

Thanks all for the input.

 

I'm trying to read back through to figure out what might be the best choice.  I might ask locally to, mainly before i do it and then if i run into questions ill get an electrician to check it or finish the wiring.  I'm not up on the terminology unfortunately, though i'm going to try to watch a few videos.. ie: the need for oxide inhibitor on the aluminum wiring etc.

 

I'd like to run the right gauge wire now so if i manage to get an electrician to upgrade the box in the garage later, i can be set.

 

That said, i guess whatever keeps it close to that 3% spec and might work later if i throw a small air conditioner into the mix (i forget how many amps even a small one pulls).  I'm not sure how many amps a small NUC pc would use + lcd + scope + misc.

 

So trying to look back here which gauge/type wire covers that for the future, but also doesnt break the bank?  I was hoping for around $250 or less in the wire at least, but maybe thats not possible given the distance.  And it sounds like some of this isnt found at lowes and home depot that i should look at that online store link from before?  IE: #4 aluminum, or even maybe #8?  (honestly i bet alot of the wiring in my house's main breaker needs upgraded, there are at least 6 runs in there that have very old looking wires, so when talking about being up to current code, yikes, if i sell the house i dont know but some of this could be an issue).

 

It also sounded like 10 gauge would work, but when we start talking about the pairs of wires with a 240v run, i get a little lost compared to the standard wiring.  Ground wise, doesnt the wire come with the copper embedded, that i just screw it onto the ground on the gfi adapter on the other end (i forget how it is in the garage side).

 

Thankfully my cousin is a contractor and can point me to an electrician in the long run if need be.  I was just hoping i'd get the run done with pvc and wire and if i have to have someone finish the boxes on the other end (2 foot deep trench etc and the gray pvc).



#24 spacemunkee

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Posted 18 July 2019 - 08:39 PM

I agree with the above post. You can see my quals in my profile.

Over-qualified! lol.gif Take it away John! smile.gif

My suggestions are vastly overdoing things for sure. But I'm just overdoing things to go with the norm around here, and cover any concerns at a good cost.
Nothing like doing something twice! wink.gif

Been wiring 25 yrs. and no meltdowns yet.
Myself have about 50 feet of 10 wire from main house to shed panel(existing when I got here), and 1 30-40 foot 12 wire circuit running from there to obs.

No power problems for my needs..

Oh, and no matter what, my only disagreement..
Throw it in conduit!
That back filled rock you didn't catch, over time won't care about the direct burial rating!

Edited by spacemunkee, 18 July 2019 - 08:51 PM.


#25 Phil Sherman

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Posted 19 July 2019 - 07:34 AM

One of the things that needs to be considered when running power to an observatory is, "how much power do I need". People doing imaging with a portable rig can easily do a full night's work using an 85AH 12V battery. If we make worse case assumptions, using all of the battery capacity over ten hours, that's 1000W or 100W/hour. Since power will be brought into the observatory at 120V, that's less than 1A! The only things you might use in an observatory that would significantly increase power consumption would be an air conditioner or an electric heater.

 

A simpler, less costly, solution if you will not be using these high current devices would be to run #10 wire to the observatory and install a 10A breaker feeding it. I suspect you'd have enough power to run an 800W electric heater, even with the 10A breaker.

 

An interesting alternative, possible because almost all astronomy gear runs on 12V DC, is to use an RV converter to keep a deep cycle battery charged and provide DC power to the equipment. Use a DC motor for the roof and you'll never have to worry about a power failure interrupting your observing and preventing you from closing the roof. If you have some gear that requires other DC voltages, DC-DC switching voltage converters are available that can provide both higher and lower voltages from a 12V source. These regulators are usually more than 90% efficient which means that a 5V regulator feeding 2A of current to USB devices (10W) will draw less than 1A from the 12V battery. An older style linear regulator supplying the same voltage and amperage would draw 2A (24W) from the battery and have to dissipate 14W of power as heat.




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