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Discussion Starter #1 (Edited)
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
 

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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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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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Discussion Starter #4
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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Discussion Starter #5 (Edited)
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? :no:
 

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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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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?) :no:
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:

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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Discussion Starter #9
"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?) :huh:
 

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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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=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.


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

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

..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?

I've gone from #2 wire all the way...to #2 and 1/0...what the heck? (are they even close on this sizing?) :huh:
close, sure but depending on material and what load to use for calcs, what is right?
 

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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.

Jamie
 

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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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Discussion Starter #16 (Edited)
SxS Quote:
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?
nap;234756 Quote:
"...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..."

The reason I ask is that the two largest electrical suppliers in town don't even carry it and only stock 2/0 or 4/0. Again, 4/0 seems to be overkill with the "#2 wire" quoted seemingly not even close...and "1/0" seemingly not even in the ballpark (especially when combined).

It seems that many electricians (who don't want to mess with pipe) are stretching 2/0 for all its worth at 100 amps (or more when significant distances are involved) then simply switching to 4/0 for 200 amp service for a lack of available product or the desire to perform proper calculations. 250 feet has got to be a fairly common run for outbuildings (with a 2% voltage drop) and it sounds as if I have run into the common 'get by' mentality that was so difficult to get around in the fluid transfer business.

SxS 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?
nap:
"..see my previous post.."

Apprecated and noted (I apoligize for not catching this earlier)...yet the reason I asked goes back to the MSU ag chart once again. #2 wire doesn't even make the chart for carrying a 100 amp load with a 2% drop. I have to standardize using 'something' and nobody has yet disputed this info as proper engineering at 80% load or not.

I appreciate your recommendation of 1/0 into the box...yet need to talk intelligently to my bidder in regards to why #2 (wire) coming off of 1/0 (which the chart says is also undersized for the distance) is unacceptable.

SxS 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.
nap:
personal preference

I'm being told that installing pvc pipe is approaching twice the costof the entire job; which (to me, granted) had darn well better be twice as good for a 46 year old man who won't give a rip what happens to any of this when they bury me right beside it. :) It's almost as if 3/0 burial is made scarce for a reason...sell bigger jobs with more materials or more expensive wire...as in 4/0 (trench me a hole and lay the darn wire in it for gosh sakes...I'll size the wire accordingly if I need to upgrade).

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

I thought thatthis was answered in the original chart:

"...There are a number of variables that need to be considered when determining the minimum size of wires to supply power to a farm building. As a result, the selection process can get so complex that it just simply gets ignored. The following three tables make the process easy. The tables assume the single-phase load on the wires is 80% of the rating of the main circuit breaker in the service panel, and that the voltage drop will be limited to 2%. The electrical code recommends 2% to 3% maximum..."


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?) :huh:
nap:
"...close, sure but depending on material and what load to use for calcs, what is right?.."

Does the original chart referenced (in aluminum) under the referenced load and voltage drop even come close?
Again, thank you very much for your time and expert opinion. I just can't see going from 3/0 (in the table) down to #2 wire and some 1/0 thrown in "only because 'I' want it" with all that you and everybody else has alluded to.
 

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Discussion Starter #17
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.

Jamie
I just had to standardize at some number for quoting purposes and the length of run involved. I don't mind paying for the wire up front for future considerations...and especially if I'm receiving quotes for near double the price if PVC is laid (which almost prevents me from ever upgrading in dollars spent vs value gained anyways). I mentioned what was being run out there (probably mistakenly) to eliminate the sense that I was running all that a 100 amp box could handle. Bottom line...my bids have been all over the map and not even close to being performed in the same manner....which I should have prepared for before the first guy showed up (I even know better; as the fluid business was something of a goat rodeo most every where one went also..and that was in industry! :no: ).
 

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Discussion Starter #18 (Edited)
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.
I'm from the same area and this is why I finally bit the bullet and made the switch. You also have to maintain the pole; which becomes a hastle with falling limbs on the overhead wire (vs burial to the house). I also needed backup power from the house that I was not receiving for our gate and security related items.

Thank you, wirenut and Jamie also.
 

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The reason I ask is that the two largest electrical suppliers in town don't even carry it and only stock 2/0 or 4/0. Again, 4/0 seems to be overkill with the "#2 wire" quoted seemingly not even close...and "1/0" seemingly not even in the ballpark (especially when combined).
if you can't get it easily, it will most likely end up costing more than the next size up. You might even have to buy entire reels so especially in that case, upsizing would be the most cost efficient. It never hurts to go big. It can hurt to go smaller.



Apprecated and noted (I apoligize for not catching this earlier)...yet the reason I asked goes back to the MSU ag chart once again. #2 wire doesn't even make the chart for carrying a 100 amp load with a 2% drop. I have to standardize using 'something' and nobody has yet disputed this info as proper engineering at 80% load or not.
Any wire in the run can not be smaller than required by amp rating even without considering voltage drop. So, the short section of the smaller wire will not increase resistance enough to offset the larger wire used for the voltage drop. Depending on what type of wire is used, #1 or 1/0 (aluminum) should be fine for the short reduced section.

I appreciate your recommendation of 1/0 into the box...yet need to talk intelligently to my bidder in regards to why #2 (wire) coming off of 1/0 (which the chart says is also undersized for the distance) is unacceptable.
corrrect. 1/0 is too small to account for voltage drop, at least at the ampacity I was speaking of. It may be adequate for a much lesser amp rating. #2 is also too small since is not rated for the 100 amps of the breaker. You need to use wire no smaller than what it requires to meet or exceed the breaker (OCPD) size for ampacity.



I'm being told that installing pvc pipe is approaching twice the costof the entire job; which (to me, granted) had darn well better be twice as good for a 46 year old man who won't give a rip what happens to any of this when they bury me right beside it. :) It's almost as if 3/0 burial is made scarce for a reason...sell bigger jobs with more materials or more expensive wire...as in 4/0 (trench me a hole and lay the darn wire in it for gosh sakes...I'll size the wire accordingly if I need to upgrade).
I am surprised to see this cost difference. Not sure why. Obviously there is some cost increase from the pipe. I would have to check to see the difference in wire prices from THWN to a direct burial rated wire.

I thought thatthis was answered in the original chart:

"...There are a number of variables that need to be considered when determining the minimum size of wires to supply power to a farm building. As a result, the selection process can get so complex that it just simply gets ignored. The following three tables make the process easy. The tables assume the single-phase load on the wires is 80% of the rating of the main circuit breaker in the service panel, and that the voltage drop will be limited to 2%. The electrical code recommends 2% to 3% maximum..."
sounds good but some were suggesting running smaller due to the total calculated load. Actually, it's not that complex but trying to determine what numbers to use for ampacity (of the load) is somewhat arbitrary if you are not intending to feed the panel for full capacity. and yes, code recommends no more than a 3% voltage drop.




Does the original chart referenced (in aluminum) under the referenced load and voltage drop even come close?
Again, thank you very much for your time and expert opinion. I just can't see going from 3/0 (in the table) down to #2 wire and some 1/0 thrown in "only because 'I' want it" with all that you and everybody else has alluded to.
let's make this simple.

100 amp panel. figure at 80% load like the suggestion above BUT that is only for the voltage drop calc. The wire still have to be rated to carry at least what the OCPD allows (100 amp). Choice of aluminum or copper. Wire also has a temperature rating that affects the ampacity of the wire. two wires the same size yet different insulations can be rated for different ampacities. Generally, in a feeder such as this, you will be dealing with the 75º rated wire. NM (romex) has a 60º rating and does not allow as much ampacity for a given size of wire but you will not be dealing with NM. THere are a few other wires rated at 60º but most are 75º or higher. You generally can't use the higher rating (90º is the next step up) as it gets in to other items (breakers and such) that also have a temp rating, so lets stop with the 75º and work with that.

100 rated aluminum wire (no VD consideration)

#1


when considering the VD (<3% @ 80 amps @ 300 ft (don't forget to include any up or down length as well. It all counts))

3/0


So, you need to use wire no smaller than #1 but considering voltage drop you need to use 3/0 to offset the VD. If you cannot fit the 3/0 in the panel or especially the lugs of the breaker (the breakers are rated for wire size, it should be right on the lug), you can set a junction box shortly before the panel and change the wire size from 3/0 to #1. That short piece of #1 will not cause a problem. It is still rated for the minimum of the breaker rating and the added resistance for a very short piece will not be great enough to cause a problem with VD.

due to the unavailability of the 3/0, you may want to upsize to 4/0 due to the cost factors.

wasn't that simple?
 

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"...So, you need to use wire no smaller than #1 but considering voltage drop you need to use 3/0 to offset the VD. If you cannot fit the 3/0 in the panel or especially the lugs of the breaker (the breakers are rated for wire size, it should be right on the lug), you can set a junction box shortly before the panel and change the wire size from 3/0 to #1. That short piece of #1 will not cause a problem. It is still rated for the minimum of the breaker rating and the added resistance for a very short piece will not be great enough to cause a problem with VD.

due to the unavailability of the 3/0, you may want to upsize to 4/0 due to the cost factors.

wasn't that simple?.."
(lol)...:wink:... very simple and what do you know...exactly in line with what the state of Michigan puts out for farmers in that simple little chart referenced earlier.
Thank you very much for taking the time to help me out here and effectively moving this project forward. I knew better than to have somebody else write/bid the spec. here and although I am back at square one...I feel confident of the information that you have shared and (more importantly) the source from which it originates.

Very much appreciated from your fellow southwest Michigander. :thumbsup:
 
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