Re: wire gauge

Christopher Erickson

You just have just a few basic choices for 100'.  #14, #12, #10.
I would run 3 #12's (hot, neutral and ground) if it really is just a scope, PC, dew heaters, etc.  Terminate it into a 20A breaker in your main electrical panel or a sub panel.
If you want to run electric motors (dome motors) space heaters (bad idea that would hurt local seeing) then you would want to run 4 #12's (h1, h2, n, g).  Terminate the hots into two unbridged 20A breakers in your main electrical panel or a sub panel.
The code requires that #14 is terminated into a 15A breaker, #12 into a 20A and #10 into a 30A.
Every watt of power that you use in your observatory is a watt of heat radiated by your equipment.  And that radiated heat harms local seeing.  That pesky "conservation of energy" thing.
Run two 3/4" or 1" plastic electrical conduits in the same trench.  One for power and one for data.  Do NOT use water pipe.
It is a (USA) National Electrical Code violation to put power and data in the same conduit. 
Avoid direct burial cable.  Impossible to upgrade without digging if your needs ever increase.
For data, use multimode fiber-optic cable and media converters if you are in a lightning-risk area.  Transtectors, Polyphasers, a ground ring and a Faraday cage might not be a bad idea either.  I would not install copper Ethernet unless your particular area has almost zero chance of ever suffering lightning damage.  Multimode fiber is more robust and fault-tolerant that Single-mode.  Single-mode is intended more for 1km and longer applications anyway.
And FWIW, most modern switching power supplies have no problems operating all the way down to 90VAC, which means that even #14 wire would work for the telescope, PC, dew heaters and such, although the code recommends #12.
I hope this helps.

Christopher Erickson
Consulting Observatory Engineer (and certified electrician)
Summit Kinetics
Waikoloa, HI 96738


From: Christopher Erickson [mailto:christopher.k.erickson@...]
Sent: Sunday, June 29, 2014 7:34 AM
To: ap-gto@...
Subject: Re: [ap-gto] wire gauge


-Christopher Erickson

On Jun 29, 2014 1:03 PM, "rjblack67@... [ap-gto]" <ap-gto@...> wrote:

I am building a new observatory 100 ft. from AC source.

would someone please help me figure the guage of wire I should use to allow for voltage

and amperage loss.

Using  AP 900 - plus lights camera dew heaters etc. I think I would like to run 3 wire to get 2 

separate circuits?

Sorry if this is not an appropriate post for this forum but don't know where else to ask.

Thank you for any help I might receive, bob

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