Burial Wire And A Seeming Difference Of Opinion... - Electrical - Page 2 - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 02-23-2009, 10:16 AM   #16
SxS
Newbie
 
Join Date: Feb 2009
Posts: 15
Rewards Points: 10
Default

Burial wire and a seeming difference of opinion...


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?)
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.

Advertisement


Last edited by SxS; 02-23-2009 at 07:28 PM. Reason: correction
SxS is offline   Reply With Quote
Old 02-23-2009, 10:32 AM   #17
SxS
Newbie
 
Join Date: Feb 2009
Posts: 15
Rewards Points: 10
Default

Burial wire and a seeming difference of opinion...


Quote:
Originally Posted by jamiedolan View Post
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! ).
SxS is offline   Reply With Quote
Old 02-23-2009, 10:38 AM   #18
SxS
Newbie
 
Join Date: Feb 2009
Posts: 15
Rewards Points: 10
Default

Burial wire and a seeming difference of opinion...


Quote:
Originally Posted by nap View Post
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.

Last edited by SxS; 02-23-2009 at 10:40 AM.
SxS is offline   Reply With Quote
Old 02-23-2009, 10:04 PM   #19
nap
You talking to me?
 
nap's Avatar
 
Join Date: Dec 2007
Location: sw mi
Posts: 5,407
Rewards Points: 2,000
Default

Burial wire and a seeming difference of opinion...


Quote:
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.



Quote:
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.

Quote:
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.



Quote:
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.

Quote:
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.




Quote:
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 75 rated wire. NM (romex) has a 60 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 60 but most are 75 or higher. You generally can't use the higher rating (90 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 75 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?
nap is offline   Reply With Quote
Old 02-24-2009, 10:16 AM   #20
SxS
Newbie
 
Join Date: Feb 2009
Posts: 15
Rewards Points: 10
Default

Burial wire and a seeming difference of opinion...


Quote:
Originally Posted by nap View Post
"...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)...... 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.

Advertisement

SxS is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
When wire needs to be outdoor / direct burial rated jamiedolan Electrical 23 02-25-2009 12:46 PM
hooking up dryer....bronx ny code SURFBUG Appliances 6 10-14-2008 10:41 PM
Installing Fluorescents in Garage rzrbkpk Electrical 26 04-08-2008 10:00 PM
Electrical Sub Panel #4 burial wire w/60 breaker FrankA Electrical 4 12-31-2007 08:19 PM




Top of Page | View New Posts