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Old 02-21-2009, 07:50 PM   #1
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Burial wire and a seeming difference of opinion...


A contractor bids my near 300 feet run from the house to an existing 100 amp panel in #2 aluminum wire (burial grade for 190 feet of it). I look up a chart (below) that claims 2/0 (cable?) is good for 250 feet only with a 2% voltage drop. I suggest 3/0 as an upgrade; even though I am only running but a 5 HP 220 volt compressor; 4 flourescents; a few plugs and maybe 5 or 6 500 watt security halogens.

He comes back with around $300 more for 1/0 (or one 'awt') between the garages (190 feet; direct burial also) and the same #2 wire runing from the junctions to the boxes inside.

I am obviously completely ignorant on wire vs cable using the table below; as it seems to indicate 3/0 AWG for a 100 amp service...period.

Is there that many proper ways to run a simple aluminum feeder line this distance on relatively light service...or am I at some crazy length (250-300 feet) that begs this much conflicting info?

One guy would only run the entire thing in pvc pipe...period...(well over a grand more) and claimed that copper and aluminum were within $150 of each other at this point in time. I respect everybody's opinion; yet I received 3 very different ways to do the same job and for some reason don't like the idea of stepping up or down in wire size (?) or type (?) from my background in sizing fluid systems.

Thanks for any help in advance.

See aluminum wire chart: (sorry, I couldn't copy the table properly)
http://www.egr.msu.edu/age/aenewsletter/1_nov_dec_03/surbrook11_03.htm


Last edited by SxS; 02-21-2009 at 07:58 PM. Reason: fix
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Old 02-21-2009, 08:32 PM   #2
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Burial wire and a seeming difference of opinion...


I would suggest you specify what capacity you want and the type wiring method(direct burial, conduit) and let them price that.

All contractors have different ideas, because they're basically being asked to quote a design/build.

I would go no less than 60 amps, direct burial #1. Which would be not quite 4%. To be @ or under 3% You would need 2/0. This is AL btw.

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Old 02-21-2009, 11:45 PM   #3
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Burial wire and a seeming difference of opinion...


Since you have a 100 amp panel, you have the possibility of utilizing that much power. Unlikely but possible. Of course, the correct way to do it would be using 100 amp rated wire and then upsize for the full load but upsizing for 80% would more than likely cover anything you will utitlize. You can do with less but you simply cannot size the wire below the OCPD that protects the wire.

based on my suggestion, it would require 3/0 aluminum or #1 copper. (i think)

somewhere along in life I had heard that copper may be the less expensive way to go, at the moment but it is worth checking.

as to upsizing or downsizing (no way); this is done to reduce voltage drop due to the distance. 300 feet is a considerable distance. You should know, especially being familiar with hydraulics about the increased resistance due to distance and the need to upsize lines to offset the pressure loss due to that resistance. Electricity actually is dealing with the exact same problem.
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Old 02-22-2009, 05:12 AM   #4
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Burial wire and a seeming difference of opinion...


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Originally Posted by wirenut1110 View Post
I would suggest you specify what capacity you want and the type wiring method(direct burial, conduit) and let them price that.

All contractors have different ideas, because they're basically being asked to quote a design/build.

I would go no less than 60 amps, direct burial #1. Which would be not quite 4%. To be @ or under 3% You would need 2/0. This is AL btw.
I should have specified originally, I suppose (gave each bidder the same info offered above; no heavy loads)...yet I wasn't really prepared to discover that much difference of opinion in hooking up a 100 amp service with (imo)normal loading. I used to size my pipe and material as I would do it if I was paying for it and indeed had to live with it afterwards...and always upsized at the end of a scale. Is the chart above somehow 'wrong' and/or why is there no mention of "1 awt" or even "#2 wire" as I have been quoted?

Again, I am having trouble with this "wire" vs "awt" designation quoted above; as I even called my electrical house looking for 3/0 burial...and was told that there was no such thing.

Thanks for your help, wirenut.
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Old 02-22-2009, 05:27 AM   #5
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Burial wire and a seeming difference of opinion...


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Originally Posted by nap View Post
Since you have a 100 amp panel, you have the possibility of utilizing that much power. Unlikely but possible. Of course, the correct way to do it would be using 100 amp rated wire and then upsize for the full load but upsizing for 80% would more than likely cover anything you will utitlize. You can do with less but you simply cannot size the wire below the OCPD that protects the wire.

based on my suggestion, it would require 3/0 aluminum or #1 copper. (i think)

somewhere along in life I had heard that copper may be the less expensive way to go, at the moment but it is worth checking.

as to upsizing or downsizing (no way); this is done to reduce voltage drop due to the distance. 300 feet is a considerable distance. You should know, especially being familiar with hydraulics about the increased resistance due to distance and the need to upsize lines to offset the pressure loss due to that resistance. Electricity actually is dealing with the exact same problem.
Thank you very much for confirming the above chart and my suspicions.

As stated earlier; I have no idea how the capacitance carrying capabilities of "#2 wire" and "2 ought" compare (or any other size for that matter) and cannot locate a chart beyond the one referenced...which seems to indicate both as entirely different monsters.
As to up/downsizing on the same run (as you mentioned) this was always the mark of a vendor 'getting by' in my former business...somewhat akin to sizing fluid handlers using the motor service factor. If it's code...fine...yet I just don't feel right about it and am glad to hear you express the same (especially when the line 'numbers' don't make sense in terms of the chart or #2 'wire' changing to 1/0 burial and then back to #2 wire).

I guess that I'm back to conduit and 3/0 in a pipe if they don't make it in burial...yet this guy claims that getting 3/0 into my box (basic Homeline model)...is yet another hastle yet!

What is this basic barn feeder line stuff, rocket science?

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Old 02-22-2009, 06:16 AM   #6
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Burial wire and a seeming difference of opinion...


Check out this chart. It does not allow for drops over distance.
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Old 02-22-2009, 02:01 PM   #7
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Burial wire and a seeming difference of opinion...


Quote:
Originally Posted by SxS View Post

Again, I am having trouble with this "wire" vs "awt" designation quoted above; as I even called my electrical house looking for 3/0 burial...and was told that there was no such thing.

Thanks for your help, wirenut.
the aught (proper spelling) (as in 1/0, 2/0, etc. ) is merely part of the wire size notation. Wire sizes most people are familiar with use just numbers (#12, #14, etc) but as you get in to larger wire, after you get to #1 (the smaller the number in that designation series, the larger the wire), you need to go somewhere so the /0 sizes come in to use. Starting at 1/0 and going to 4/0 (smallest to largest). Then you go to kcmil (older style of notation) or mcm (current style of designation) designation. These both refer to thousands of circular mils. Merely a method of measurement. In my line of work 500mcm is a very common size.

here is a chart that defines the actual size of the conductor for a given designation.

http://stevenengineering.com/pdf/34LABEL_WIRE_INFO.PDF
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Old 02-22-2009, 02:15 PM   #8
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Burial wire and a seeming difference of opinion...


Quote:
Originally Posted by SxS View Post
Thank you very much for confirming the above chart and my suspicions.

As stated earlier; I have no idea how the capacitance carrying capabilities of "#2 wire" and "2 ought" compare (or any other size for that matter) and cannot locate a chart beyond the one referenced...which seems to indicate both as entirely different monsters.
As to up/downsizing on the same run (as you mentioned) this was always the mark of a vendor 'getting by' in my former business...somewhat akin to sizing fluid handlers using the motor service factor. If it's code...fine...yet I just don't feel right about it and am glad to hear you express the same (especially when the line 'numbers' don't make sense in terms of the chart or #2 'wire' changing to 1/0 burial and then back to #2 wire).

I guess that I'm back to conduit and 3/0 in a pipe if they don't make it in burial...yet this guy claims that getting 3/0 into my box (basic Homeline model)...is yet another hastle yet!

What is this basic barn feeder line stuff, rocket science?)
actually, there is no requirement in the code (NEC) that requires upsizing the wire for voltage drop. There is a suggestion in the code but no requirement. It is a practical application decision and should be considered and utilized.

there is nothing wrong with changing sizes of wire in the run. You are dealing with the overall resistance of the wire run in determining the voltage drop. Utilizing various sizes in a run is common and acceptable in the trade.

as to no 3/0 direct burial. I would have to look but I see no reason it cannot be found.

and to:

Quote:
What is this basic barn feeder line stuff, rocket science?
at least we remember to convert from metric to standard measurements so we do not run in to Mars. Although it is not rocket science, it is not a simple "look at the chart" like the kids at HD and Slowes like to think it is.

as to the 3/0 not fitting into the panel; I can't tell you offhand if it will or not. If it won;t, you can install a junction box prior to the panel and splice #1 (I believe) (aluminum) or #3 cu (if using copper) to the larger wire and run that in to the panel. Just remember to not use smaller wire than the OCPD demands and if using unlike wire material (copper and aluminum) use the proper splicing devices.
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Old 02-22-2009, 03:07 PM   #9
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Burial wire and a seeming difference of opinion...


Quote:
Originally Posted by nap View Post
"the aught (proper spelling) (as in 1/0, 2/0, etc. ) is merely part of the wire size notation. Wire sizes most people are familiar with use just numbers (#12, #14, etc) but as you get in to larger wire, after you get to #1 (the smaller the number in that designation series, the larger the wire), you need to go somewhere so the /0 sizes come in to use. Starting at 1/0 and going to 4/0 (smallest to largest).."
Thanks; as this jives with my original chart...which doesn't make sense in terms of what I was quoted (agreed?...#2 to 1/0 and back to #2) nor TazinCR's chart above (which I am grateful for also).

Are you guys basically telling me that the only way to do this 'right' (given my load and distances) is to trench out for PVC and run 3/0 in it?
Why in the heck don't they simply sell 3/0 aluminum burial for these longer runs in what would (seemingly) be the least expensive alternative?
And if this is possible...do electricians (using good practice) ever run lesser lines like the #2 wire in the system (my quote above) to get around this 'too big for the box' (supposed) problem inside the structures?

Sorry to ask so many questions; yet I want to do this job right and am frankly flabbergasted that there is lack of consensus on direct burial vs pvc piped systems...let alone what correct size to run in it on your 'average' 100 amp application given this distance.

I've gone from #2 wire all the way...to #2 and 1/0...what the heck? (are they even close on this sizing?)
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Old 02-22-2009, 03:26 PM   #10
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Burial wire and a seeming difference of opinion...


Your wire needs to be sized according to the OCPD that's feeding it. Some are giving you wire size based on the load you have and some are giving you wire size based on the whole 100 amps. Yes, the distance and load are the big factors.

I'd be willing to bet you can get 3 aught in direct burial.
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Old 02-22-2009, 03:28 PM   #11
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Burial wire and a seeming difference of opinion...


Quote:
=SxS;234738]
Why in the heck don't they simply sell 3/0 aluminum burial for these longer runs in what would (seemingly) be the least expensive alternative?
i'm pretty sure they do. i would need to look for it but i can just about guarantee there is 3/0 direct burial wire.


Quote:
And if this is possible...do electricians (using good practice) ever run lesser lines like the #2 wire in the system (my quote above) to get around this 'too big for the box' (supposed) problem inside the structures?
see my previous post

Quote:
Sorry to ask so many questions; yet I want to do this job right and am frankly flabbergasted that there is lack of consensus on direct burial vs pvc piped systems.
personal preference

Quote:
..let alone what correct size to run in it on your 'average' 100 amp application given this distance.
calculations give us the answer. the problem comes with what to use for the calcs. max possible load? current calculated load?

Quote:
I've gone from #2 wire all the way...to #2 and 1/0...what the heck? (are they even close on this sizing?)
close, sure but depending on material and what load to use for calcs, what is right?
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Old 02-22-2009, 03:30 PM   #12
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Burial wire and a seeming difference of opinion...


Quote:
Originally Posted by SxS View Post
A contractor bids my near 300 feet run from the house to an existing 100 amp panel in #2 aluminum wire (burial grade for 190 feet of it). I look up a chart (below) that claims 2/0 (cable?) is good for 250 feet only with a 2% voltage drop. I suggest 3/0 as an upgrade; even though I am only running but a 5 HP 220 volt compressor; 4 flourescents; a few plugs and maybe 5 or 6 500 watt security halogens.

He comes back with around $300 more for 1/0 (or one 'awt') between the garages (190 feet; direct burial also) and the same #2 wire runing from the junctions to the boxes inside.

I am obviously completely ignorant on wire vs cable using the table below; as it seems to indicate 3/0 AWG for a 100 amp service...period.

Is there that many proper ways to run a simple aluminum feeder line this distance on relatively light service...or am I at some crazy length (250-300 feet) that begs this much conflicting info?

One guy would only run the entire thing in pvc pipe...period...(well over a grand more) and claimed that copper and aluminum were within $150 of each other at this point in time. I respect everybody's opinion; yet I received 3 very different ways to do the same job and for some reason don't like the idea of stepping up or down in wire size (?) or type (?) from my background in sizing fluid systems.

Thanks for any help in advance.

See aluminum wire chart: (sorry, I couldn't copy the table properly)
http://www.egr.msu.edu/age/aenewsletter/1_nov_dec_03/surbrook11_03.htm

Maybe I am missing something, but why do you need this level of service at the detached building? Why not run larger conduit now (conduit is pretty darn cheap) and run whatever amp service you actually need now, then with the conduit, you can easily upgrade it later.
??

Maybe I didn't understand why you need the large service It sounds like you could run everything off of a 30a feed.

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Old 02-22-2009, 03:50 PM   #13
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Burial wire and a seeming difference of opinion...


Have you checked with the POCO about just getting a separate meter?
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Old 02-22-2009, 03:57 PM   #14
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Burial wire and a seeming difference of opinion...


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Have you checked with the POCO about just getting a separate meter?
in my area, that means you pay commercial rates for the second meter plus there are costs simply for the meter to be there, regardless whether you use any power or not.
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Old 02-22-2009, 03:59 PM   #15
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Burial wire and a seeming difference of opinion...


We have a minimum, i think it's $25 and the cost to install is usually cost of materials. Very reasonable.

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