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OfflineSpongiform
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Electrical Hookup - 600 feet?
    #14424065 - 05/09/11 11:09 AM (12 years, 8 months ago)

I'd like to set up a little vacation/hunting camper out in the woods.  The camper has a plugin rated at 220v @ 30 amps.

The nearest electrical pole is about 600 feet away from where the camper would go.  Is it possible to run a buried cable that far?  What size/type of cable would be used?


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Invisiblekoraks
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Re: Electrical Hookup - 600 feet? [Re: Spongiform]
    #14424161 - 05/09/11 11:28 AM (12 years, 8 months ago)

Apparently, it's possible, although you're probably going to experience some problems with blackouts when a thunderstorm passes. According to the table here, you'd need 7AWG or heavier (about 11mm2). At 7AWG, you would dissipate about 250W in the cable if you draw 30A through it.


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OfflineSpongiform
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Re: Electrical Hookup - 600 feet? [Re: koraks]
    #14424500 - 05/09/11 12:48 PM (12 years, 8 months ago)

Thanks.  That helps a lot.


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OfflineSeussA
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Re: Electrical Hookup - 600 feet? [Re: Spongiform]
    #14425451 - 05/09/11 04:28 PM (12 years, 8 months ago)

Your local codes may require a heavier gauge wire, conduit, minimum depth, work permit, inspections, installation by a licensed professional, etc.  Failure to follow local codes may invalidate you homeowners insurance, which could really suck if your improper installation causes your house to burn down.  I'm not saying that you are incapable of doing the work, but there are other considerations to worry about.


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Offlineargg
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Re: Electrical Hookup - 600 feet? [Re: Seuss]
    #14426345 - 05/09/11 07:12 PM (12 years, 8 months ago)

yeah what he said but even if you do not pull a permit look up local code and do it to it anyway. You might need bigger then 6 gauge wire on that if its that far maybe 4 or 2 but I don't have the charts in front of me. The heater want 30amps so you have to size 20% bigger then that so you really need to run it for 40 but is there anything else you are going to add?

you need to look at the resistance of the wire and calculate the voltage drop from the distance. I was just used to using a little chart I had in the truck so I forgot the resistance numbers of wire size per foot. If I can find the cheater chart that just says on it what to run for that under local rules.


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InvisiblePrisoner#1
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Re: Electrical Hookup - 600 feet? [Re: Spongiform]
    #14427616 - 05/09/11 11:51 PM (12 years, 8 months ago)

what you want is 2ga quadruplex, it's a direct burial line, 4 conductors,
aluminum, it should carry 60 amps with absolutely no issue, I paid a little
over $1/foot, much cheaper than copper

try and find a supplier that can provide 1000' rolls or you'll end up doing a
bit of splicing like I did, it just runs the cost up with connectors and heat
shrink tube


http://buyawg.thomasnet.com/viewitems/ruplex-conductor-type-urd-cable-mobile-home-feeder/v-secondary-type-urd-cable-aluminum-conductor-1041


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Invisiblekoraks
Registered: 06/02/03
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Re: Electrical Hookup - 600 feet? [Re: Prisoner#1]
    #14428177 - 05/10/11 03:17 AM (12 years, 8 months ago)

Using the cable Pris indicated, which has a 0.403" conductor diameter, the resistance of 600ft would be about 0.059Ohms. At 30A, the cable would dissipate 302*0.059=53W, and the voltage drop would be 1.77V. Both values are far below the levels where you would have to worry about anything. It'll work like a charm.


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OfflineSeussA
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Re: Electrical Hookup - 600 feet? [Re: koraks]
    #14428258 - 05/10/11 04:25 AM (12 years, 8 months ago)

> voltage drop would be 1.77V

For 2awg aluminum over 600ft at 30amps at 60Hz 1-phase 240v, my cheat table claims just under a 12V drop, which is still fine.  As pris said, 2awg can carry 60amps (to 70amps) over the distance without any issue and is probably a good choice in case a few 120v/20a circuits are added.  If the OP is absolutely certain nothing else will ever be added to the circuit, he _should_ be able to get by with 6awg, but if it were me, I would drop down to 4awg just to be safe, especially given the distance of the run.  Again, check local codes, as they are usually more strict.


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Invisiblekoraks
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Re: Electrical Hookup - 600 feet? [Re: Seuss]
    #14428335 - 05/10/11 05:30 AM (12 years, 8 months ago)

Quote:

Seuss said:
> voltage drop would be 1.77V

For 2awg aluminum over 600ft at 30amps at 60Hz 1-phase 240v, my cheat table claims just under a 12V drop, which is still fine.



Your table might be correct, but I can't reproduce the number they quote. In the post above, I calculated the resistance of a single 600ft 2AWG conductor using a web page I cannot find right now.

If we do it manually, not compensating for phase shift/balance (this is where the real difference is with more sophisticated methods) and temperature issues, it comes out something like this:
Aluminium has a resistivity of 2.82*10-8Ohm*meter. 2AWG has a diameter of 6.54mm, which means a cross section of 33.6mm2 (= 3.36*10-5m2). The length of the cable is some 600ft, so that's roughly 183m. The resistance of the conductor is therefore: 2.82*10-8 * (183 / 3.36*10-5) = 1.54*10-2 Ohm. At 30A (RMS), this means a voltage loss of 30* 1.54*10-2 = 0.46V. If you take the return path into the equation, then it would be a drop of 0.92V

However, if I use this nifty calculator for voltage losses in cables, then I get about 9.5V drop using an aluminium 2AWG single phase, single conductor per phase at 30A and 220V input voltage. They provide a link to a good description of how a voltage drop can be calculated, taking into account the load factor of different types of devices: http://www.electrical-installation.org/wiki/Calculation_of_voltage_drop_in_steady_load_conditions

Four methods, four different answers. One conclusion: 2AWG is plenty heavy enough for this purpose.


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InvisiblePrisoner#1
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Re: Electrical Hookup - 600 feet? [Re: Seuss]
    #14429040 - 05/10/11 09:45 AM (12 years, 8 months ago)

Quote:

Seuss said:
> voltage drop would be 1.77V

For 2awg aluminum over 600ft at 30amps at 60Hz 1-phase 240v, my cheat table claims just under a 12V drop, which is still fine.  As pris said, 2awg can carry 60amps (to 70amps) over the distance without any issue and is probably a good choice in case a few 120v/20a circuits are added.  If the OP is absolutely certain nothing else will ever be added to the circuit, he _should_ be able to get by with 6awg, but if it were me, I would drop down to 4awg just to be safe, especially given the distance of the run.  Again, check local codes, as they are usually more strict.





I have 550' of #2 on a 100 amp box, voltage at the meter base is 241v,
voltage at the breaker box is 239v, I've not loaded it, still running wire


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InvisiblePrisoner#1
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Re: Electrical Hookup - 600 feet? [Re: koraks]
    #14429048 - 05/10/11 09:49 AM (12 years, 8 months ago)

Quote:

koraks said:
Your table might be correct, but I can't reproduce the number they quote.




this the book I use

http://www.uglys.net/


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OfflineSeussA
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Re: Electrical Hookup - 600 feet? [Re: koraks]
    #14430894 - 05/10/11 05:25 PM (12 years, 8 months ago)

> Your table might be correct, but I can't reproduce the number they quote.

The table value is 11.2.  I did the math by hand and came up with 11.52V, so the table is pretty close.

600ft of 2 awg aluminum has a resistance of 0.1536 ohms.
30A, given NEC guidelines for feeders, should be calculated at 37.5A (x1.25)
Voltage drop = I x R = 37.5 * 0.1536 = 5.76V
240V circuit uses two conductors 180 out of phase = 5.76 * 2 = 11.52 V
NEC guidelines recommend a maximum voltage drop of 3% for feeders or 5% for feeder + branches.
2 awg aluminum over 600 feet has a 4.7% voltage drop (for single phase 240v)
So really, 2 awg aluminum isn't considered large enough by NEC guidelines.
My guess is local code would require (at least) 1/0 awg aluminum, giving a 3.0% voltage drop over 600 feet.

My background is in electrical engineering; I'm not an electrician, so again, I would recommend consulting with a local professional to be safe.


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OfflineSeussA
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Re: Electrical Hookup - 600 feet? [Re: Prisoner#1]
    #14430926 - 05/10/11 05:32 PM (12 years, 8 months ago)

> I have 550' of #2 on a 100 amp box, voltage at the meter base is 241v

Under full load (of 30A) I would expect to see around 10.5V drop (241-10.5=230.5)...


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Invisiblekoraks
Registered: 06/02/03
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Re: Electrical Hookup - 600 feet? [Re: Seuss]
    #14433122 - 05/11/11 02:05 AM (12 years, 8 months ago)

Quote:

Seuss said:
> Your table might be correct, but I can't reproduce the number they quote.

The table value is 11.2.  I did the math by hand and came up with 11.52V, so the table is pretty close.




Your calculation is a lot more accurate than mine, even if the 1.25 factor with which the current is multiplied seems like an approximation of something; what's it for exactly?

Quote:

My background is in electrical engineering



I never made it that far; gave up on EE right in the first year, mucked about for a bit and then switched to management science / information management. I thoroughly respect the people who have finished a 'proper' education.


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OfflineSeussA
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Re: Electrical Hookup - 600 feet? [Re: koraks]
    #14433400 - 05/11/11 04:55 AM (12 years, 8 months ago)

> if the 1.25 factor with which the current is multiplied seems like an approximation of something; what's it for exactly?

The 1.25 is the safety factor recommended by the national electric code (NEC) to use when doing maximum amperage calculations.  (The safety factor varies for different applications.)  The safety factor is to help compensate for things such as temperature changes, continuous vs nominal ratings, short duration current spikes when motors start, manufacturing slop, unanticipated resistances (connectors, breakers, etc), power factor losses, etc.

> I never made it that far; gave up on EE right in the first year,

I started out in comp sci and added electrical engineering as I went, which looking back was a lucky "mistake".  The first year of our EE curriculum was designed to weed people out.  Getting all of the math (calculus, differential equations, linear/matrix algebra) out of the way before diving into EE saved my rear.  Even then, I was only interested in digital and continually had problems in the power/analog classes (due to disinterest).

> switched to management science / information management

I took a handful of engineering management classes on a whim.  Of everything I have done in life, the management classes are the ones that paid dividends.  If I had it to do over again, I would skip the other stuff and go straight into engineering management.


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Invisiblekoraks
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Re: Electrical Hookup - 600 feet? [Re: Seuss]
    #14433466 - 05/11/11 05:39 AM (12 years, 8 months ago)

Quote:

Seuss said:
> if the 1.25 factor with which the current is multiplied seems like an approximation of something; what's it for exactly?

The 1.25 is the safety factor recommended by the national electric code (NEC) to use when doing maximum amperage calculations.  (The safety factor varies for different applications.)  The safety factor is to help compensate for things such as temperature changes, continuous vs nominal ratings, short duration current spikes when motors start, manufacturing slop, unanticipated resistances (connectors, breakers, etc), power factor losses, etc.



I suspected this, thanks for clearing that up.

Quote:

I started out in comp sci and added electrical engineering as I went, which looking back was a lucky "mistake".  The first year of our EE curriculum was designed to weed people out.



Same here, and it worked for me :wink: I did get to see a lot of movies in that brief period though. One of my classmates worked at a local cinema, so we got free admission. Having to choose between Calculus and the latest from Hollywood proved disastrous for my EE eduction.

Quote:


I took a handful of engineering management classes on a whim.  Of everything I have done in life, the management classes are the ones that paid dividends.  If I had it to do over again, I would skip the other stuff and go straight into engineering management.



You'll never regret having a solid foundation underneath those management classes, and that's a guarantee. Enjoy being able to combine the best of both worlds :thumbup:


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OfflineChuangTzu
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Re: Electrical Hookup - 600 feet? [Re: Seuss]
    #14445665 - 05/13/11 01:55 PM (12 years, 8 months ago)

Quote:

Seuss said:
If I had it to do over again, I would skip the other stuff and go straight into engineering management.




What does engineering management involve, exactly?  I read the wikipedia article and, while I'm not a retard and get the gist of it, an example would be nice...


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OfflineSeussA
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Re: Electrical Hookup - 600 feet? [Re: ChuangTzu]
    #14446137 - 05/13/11 03:37 PM (12 years, 8 months ago)

> What does engineering management involve, exactly?

It is an "basic" engineering degree with a focus on management and business.  (By basic, I mean all of the courses that are common to all of the fields of engineering.)  At my college they also focused a lot on production and design.  The engineering management guys were the ones designing the systems to produce aluminum cans, or wrap candy, etc.  They also take a lot of business courses and in industry act as a liaison between the engineering teams and the owners, understanding both sides (engineering and business).  Plant managers, etc...  Most of the people I knew would get a specialized BE (electrical, mechanical, civil, petroleum, chemical, etc) and then engineering management for a masters (MEM).


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