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Voltage Drop, Wire Size and Conduit !

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Joe

06-15-2001 08:18:21




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I am about to run power to my workshop from my house main panel (200 amp service). I already have some conduit run in the direction of the workshop(25 feet of 1.25 rigid PVC)under a concrete pad.I plan to extend the conduit underground to the workshop (approx 150 feet from main panel to distribution panel in the shop). The largest load will be a Linde 295 arc welder. My question is two-fold,What is the largest feed that I can run in the 1.25 PVC to my sub panel and will that size of feed effect the performance of the welder due to excessive voltage drop? I realize there may be regional differences in the electrical codes but I am just trying to figure out if I should be continuing to run the rest of the 1.25 inch conduit or to take another approach. Running a seperate service is not one of my options at this point. Any advice would be appreciated.

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bill b va

06-19-2001 19:50:14




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 Re: Voltage Drop, Wire Size and Conduit ! in reply to Joe, 06-15-2001 08:18:21  
i am working on almost an identical project..... ..... ..... ..... ....
i am not a electrician but the formula is Ed = K x I x L x 2 /CSA . K = resistance in ohms per circular-mil foot at approximately 75 degrees C .... for copper approximately 12 ohms ..... .. CSA = cross-sectional area in circular mils . for # 6 wire = 26,240 , for # 4 wire = 41,270 , for # 3 wire = 52,620 .



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BlueLite

06-19-2001 14:48:47




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 Re: Voltage Drop, Wire Size and Conduit ! in reply to Joe, 06-15-2001 08:18:21  
I have a similar setup, the panel, PVC etc.
My line is 100 feet of #8 3wire stove, shop to main 200A. I have a lincoln 225. I have never had it higher than 150A welding, so can't say for higher than that. One things sure, I have a 40A breaker at the
main for the shop and at that setting I have never
had the breaker trip, and that's with 4 100watt
lites on. But if you want to get technical, figure 10%
loss for every 100 feet. It's been a while since
college, but that could be for single strand which
you won't be using I'm sure. So it's probably
less loss for multi strand due to the higher
total cross sectional area. So if I had your situation I'd go for a #6 to make up for the added length and welder capacity
and up the breaker to 60A. On a note about setup. Make sure you break
at the source panel not the shop, this will give
you protection for underground shorts. Of course you can add a breaker at the shop too. Plug up
both ends of the pvc with stainless steel wool or copper scrub pad to keep the mice from eating the insulation in the pipe and to keep them from using your pvc as a convenient "chunnel" to your house.

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Jerry A

06-16-2001 06:04:45




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 Re: Voltage Drop, Wire Size and Conduit ! in reply to Joe, 06-15-2001 08:18:21  
Try>Link

Check you local library for books on electricity; they might have some other useful info, such as a fairly recent copy of the National Electric Code.

Good Luck.



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GPWT

06-15-2001 10:15:42




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 Re: Voltage Drop, Wire Size and Conduit ! in reply to Joe, 06-15-2001 08:18:21  
You should size the wire to the rating of the main breaker in the shop panel. For example; If your loads total 60A but the breaker is 100A, then the wire needs to be capable of handling 100A. Also, the breaker supplying the feed needs to be no larger than the wire capacity.
The wire size is determined by two things, 1: The safe current carrying capacity, and 2: the allowable voltage drop. The distance doesn't impact the first, but it does impact the second. You need to look at both.
I recommend using type USE2/RHH/RHW2 wire for this, your 1 1/4" conduit should hold 2 #2's for the hot leads and 1 #4 for the neutral. In aluminum, this is safe for 100A but you still need to figure voltage drop.

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Dennis/Ohio

06-16-2001 19:41:16




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 Re: Re: Voltage Drop, Wire Size and Conduit ! in reply to GPWT, 06-15-2001 10:15:42  
I would guess you are an electrician, I am not. The wire you suggest is underground service entrance and is direct burial? No need for conduit? Has a very tough water proof jacket? Would cool better in the dirt than in conduit? Must have sealer at connections for aluminum conductor? It is commonly used and is the least expensive way to get the job done? Thanks in advance, Dennis..... .



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GPWT

06-18-2001 09:59:25




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 Re: Re: Re: Voltage Drop, Wire Size and Conduit ! in reply to Dennis/Ohio, 06-16-2001 19:41:16  
The USE2/RHH/RHW2 wire is rated for direct durial and exposure to the elements. It would cool a little better direct buried but not enough to change the current capacity. It probably is the most cost- effective way to do the job especially if distance is long and the trench has a lot of curves. Just make sure that you bury 24" and there are no sharp objects in contact with the wire. Hadle carefully so no nicks in the insulation. Your local supply house probably stocks #2,#2,#4 combos (and others) and calls it "URD". If you use aluminum, be sure to use the anti-oxidant on all connections. You want to make sure the wire is direct burial type, don't use THHN, THWN, etc for this. I am currently redoing my electrical service using this type.
I am not an electrician but know enough about it to do the job SAFELY, since electricity is not an area to work in if you have doubts.

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GPWT

06-18-2001 10:04:29




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 Re: Re: Re: Re: Voltage Drop, Wire Size and Conduit ! in reply to GPWT, 06-18-2001 09:59:25  
I made a misleading statement- When I ended the paragraph with "this type" I meant that I am using direct burial, not THHN/THWN.



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Joe

06-15-2001 21:33:29




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 Re: Re: Voltage Drop, Wire Size and Conduit ! in reply to GPWT, 06-15-2001 10:15:42  
What is the best method to determine the voltage drop? I will be running copper wire ( probably #2 or #3)depending on what the code book allows for 1.25 conduit. Do I need to find the resistance for the wire and calculate the voltage drop based on the maximum current for the combined loads or is there a fancy chart for determining voltage drop given the distance ,wire size and load.



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Ray,IN

06-15-2001 22:17:28




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 Re: Re: Re: Voltage Drop, Wire Size and Conduit ! in reply to Joe, 06-15-2001 21:33:29  
I'm not a electrician! That said, visit a wholesale electrical supply store and get a pocket size notebook they pass out. It will have a chart you need that gives voltage drop for wire size per xx feet and required wire size for length of run. The chart works great for the profesionals-should work for us too. I've seen union electricians use them every day.



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Dean

06-15-2001 09:51:33




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 Re: Voltage Drop, Wire Size and Conduit ! in reply to Joe, 06-15-2001 08:18:21  
The manual you got with the welder, or the plate on the welder, will tell you exactly the size of the breaker you need for it. Don't guess.

When you add all the other shop loads and the welder you'll likely re-think a separate service.



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Old Sparky

06-16-2001 17:03:13




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 Re: Re: Voltage Drop, Wire Size and Conduit ! in reply to Dean, 06-15-2001 09:51:33  
Any conductors in the buried conduit must have the letter "W" in their insulation type identification,THW for example. It is possible to get conductors with 100 ampere rating into this conduit. If you are welding and it is one-man shop, few other loads would be at the same time. The conduit must be buried 2' deep (Article 300-5 table) .



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