100 amps at 565'

[kaiser715]

My new shop is going to be right at 550' from the main disconnect on the house. I am planning on 100 amp service. (Current shop has 60 amp service, and that has been adequate for the past 15 years...there is only one of me, and I can only do one thing at once).

Figure another 15' or so turning up from the trench and making connections at the house and shop panels, so I figure 565' total distance panel-to-panel. Planning on direct burial aluminum.

Using the southwire voltage drop calculator, I get:

1 conductors per phase utilizing a #350 Aluminum conductor will limit the voltage drop to 3.62% or less when supplying 100.0 amps for 565 feet on a 240 volt system

Biggest single load is welder at 240v/33 amps nameplate. Constant load would be LED high bay lighting, radio, battery chargers. Worse case is 5hp air compressor kicking on while welding. Again, never tripped a breaker on current shop's 60amp feed. I'm thinking 100amps I'd still have enough headroom to run a mini-split in main work area (24x20' -- rest of building is storage) if I ever decided to.

If money was no object, I'd go ahead and run 200 amp service...but I'm maxing out the budget.

Thoughts???

 

[kaiser715]

BTW...to keep voltage drop below 3%, it's 500-500-500-350. Another $600 or so bucks.

 

[Aceman]

Have you contacted your utility company for a quote on a new service?

 

[kaiser715]

Yep. First off, 565' of 500-500-500-350 will cost me right at $3000. Neighbor will trench it and backfill in sand for $1 per foot. I'd "just" have to wrestle the cable in (1000#)

So, call it $3550 to do myself.

Power company will charge $1000 to run cable, set 2nd meter. Meter charge would be $26 per month. That doubled in the last 20 years, so would expect it to double again in the next 20. But, even figuring a straight $26 per month, payback would be 98 months, or just over 8 years. ($3550 - $1000 install fee by pwr co) divided by meter base cost per month.

Only good thing about doing thru the power company...they'd own the line, and repair it if anything ever happened to it. And, I could run 200 amps or more...but don't need it enough to justify the expense.

 

[wyliesdiesels]

For some reason the southwire calculator is always oversizing wire.

with my calcs i got 350McM which will give a 2.89% voltage drop.

So u will need 350-350-350-2/0 (350,000 is approx 4x the size of #1; 2/0 is 4x the size of #6)...

 

[alfredeneuman]

For some reason the southwire calculator is always oversizing wire.

I think that Southwire figures the conductor sizes by the 60 degree column rather than the 75 degree column

 

[davetulk]

If you could swing it I would think the second meter would be a nice option....give you room back in House panel for any future upgrade you may want. Get all the power you would ever need at the shop, interest free payment plan for 8 years Plus the work gets done by them so they are on the hook with depth, inspection, fighting 1000# of cable etc.

 

[Aceman]

At $26/month extra I would choose power company install and power company responsibility for maintaining it versus direct bury any day. I repair LOTS of DB aluminum, the first time you call an electrician out for a locate and repair when your cable faults, is going to blow your payback ratio out of the water.

For some reason the southwire calculator is always oversizing wire.

That's the reason I've never used the Southwire calculator. A company in business to sell wire thats always showing a larger wire needed than necessary, is not a coincidence.

However, I have a Cerrowire app on my Ipod. Their calculated wire sizes for voltage drop always matched my calculations when I did them by hand, so that's the one I use sometimes.

 

[Cmreschke]

The vd calculator is assuming your drawing 100 amps correct?

Have you done an actual load calculation?

 

[kaiser715]

No but I figure worse case:

Lighting LED high bays (divided shop, rare for all to be on same time) 20 amps
Welder @100% -- 33amps
Plasma @100% -- 34amps
Air compressor 5hp -- rated 22amps
Small items -- tool chargers, tractor or rv battery charger, radio (just a hand full of amps?)
Things like hand power tools, drills, etc... (but wouldn't be welding at same time)


Those are the worst. 99.9% of the time, I work alone. Very rarely, I suppose, I could have someone using the plasma while I weld, but I think thats maybe happened once here in the last fifteen years. Something I can easily avoid.

Realistic worst case is welding or cutting at 100%, have all the lights on, and then have air compressor kick on.

 

[Cmreschke]

What items are 120 and what are 240?

 

[American Locomotive]

No but I figure worse case:

Lighting LED high bays (divided shop, rare for all to be on same time) 20 amps
Welder @100% -- 33amps
Plasma @100% -- 34amps
Air compressor 5hp -- rated 22amps
Small items -- tool chargers, tractor or rv battery charger, radio (just a hand full of amps?)
Things like hand power tools, drills, etc... (but wouldn't be welding at same time)


Those are the worst. 99.9% of the time, I work alone. Very rarely, I suppose, I could have someone using the plasma while I weld, but I think thats maybe happened once here in the last fifteen years. Something I can easily avoid.

Realistic worst case is welding or cutting at 100%, have all the lights on, and then have air compressor kick on.

Might want to recheck your calcs, especially with the lighting. 20 amps of LED lights @ 240v is 4.8 KW.

 

[theoldwizard1]

Depending how many hours per year you plan on being in that shop, a good sized generator may be more cost effective.

Lighting LED high bays (divided shop, rare for all to be on same time) 20 amps
Welder @100% -- 33amps
Plasma @100% -- 34amps
Air compressor 5hp -- rated 22amps
Small items -- tool chargers, tractor or rv battery charger, radio (just a hand full of amps?)
Things like hand power tools, drills, etc... (but wouldn't be welding at same time)


Those are the worst. 99.9% of the time, I work alone. Very rarely, I suppose, I could have someone using the plasma while I weld, but I think thats maybe happened once here in the last fifteen years. Something I can easily avoid.

Realistic worst case is welding or cutting at 100%, have all the lights on, and then have air compressor kick on.

Worst case is the plasma cutter because it requires the air compressor.

Solar and some decent batteries would run all you 120V stuff assuming you are NOT out there all day and all night, 7 days a week.

 

[kaiser715]

What items are 120 and what are 240?

240v Lighting LED high bays (divided shop, rare for all to be on same time) 20 amps
240v Welder @100% -- 33amps
Plasma @100% -- 34amps
240v Air compressor 5hp -- rated 22amps
120V Small items -- tool chargers, tractor or rv battery charger, radio (just a hand full of amps?)
120v Things like hand power tools, drills, etc... (but wouldn't be welding at same time)

That was just a guess on light amp draw....was thinking 15 high bay lights at about 120w each, 120v...and rounded way up. See I can go 240 on them too.

I am going to re-consider having poco put a meter at the shop. Future owner (or me...) might really need more juice out there at some point. I'm going to get the guy back out there now that site work is done and road is in, get exact measurements and quote.

That keeps it from passing thru the house panel too, which will save a few dollars and aggravation. Not much, but a few.

 

[Cmreschke]

Considering your actual use, I'd bet you could get away with a 1/0, 2/0 at the very biggest. Your not going to be drawing 100 amps.

 

[forAK]

Hypothetically - If you trench 565' of buried wire and say, you never used the shop for one month. Maybe you went on vacation. How much would your bill increase? I mean, doesn't the wire still consume some electricity even if none is being utilized with a load on it?

 

[kaiser715]

Hypothetically, I've never heard of such a thing. but...on some small scale, I guess it happens. Insignificant compared to any parasitic loads, but.....interesting thought

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[Syberia]

Hypothetically - If you trench 565' of buried wire and say, you never used the shop for one month. Maybe you went on vacation. How much would your bill increase? I mean, doesn't the wire still consume some electricity even if none is being utilized with a load on it?

No, it does not.

 

[rlitman]

No, it does not.

Well, not quite, but close enough for all intents and purposes. A long run of parallel wires has some capacitance. Connected to AC, that capacitor will have current flow that is out of phase with the voltage, so the power loss directly from the current is zero. However, the current will have resistive losses as it flows over a wire. But we're talking about nano-farads, and micro-amps, and those micro-amps are flowing over massive wires, so the voltage losses are infinitesimal, so even over the course of a year I wouldn't expect it to add up to a cent on a bill.

 

[wyliesdiesels]

I think that Southwire figures the conductor sizes by the 60 degree column rather than the 75 degree column

It does for 100a and less, which theyre basing off a misinterpreted code.

At $26/month extra I would choose power company install and power company responsibility for maintaining it versus direct bury any day. I repair LOTS of DB aluminum, the first time you call an electrician out for a locate and repair when your cable faults, is going to blow your payback ratio out of the water.

That's the reason I've never used the Southwire calculator. A company in business to sell wire thats always showing a larger wire needed than necessary, is not a coincidence.

However, I have a Cerrowire app on my Ipod. Their calculated wire sizes for voltage drop always matched my calculations when I did them by hand, so that's the one I use sometimes.

Thats why i steer away from DB anything. Conduit is cheap insurance.

And i was gonna mention that about southwire. Yeah no way its just a coincidence. I wonder if they actually sell more in larger sizes due to their stupid calculator. :dunno

Thx for the tip on the cerrowire calc. Im gonna check it out

The vd calculator is assuming your drawing 100 amps correct?

Have you done an actual load calculation?

Yes but i did my calcs based off of 100a as well and came up with one size smaller.

240v Lighting LED high bays (divided shop, rare for all to be on same time) 20 amps
240v Welder @100% -- 33amps
Plasma @100% -- 34amps
240v Air compressor 5hp -- rated 22amps
120V Small items -- tool chargers, tractor or rv battery charger, radio (just a hand full of amps?)
120v Things like hand power tools, drills, etc... (but wouldn't be welding at same time)

That was just a guess on light amp draw....was thinking 15 high bay lights at about 120w each, 120v...and rounded way up. See I can go 240 on them too.

I am going to re-consider having poco put a meter at the shop. Future owner (or me...) might really need more juice out there at some point. I'm going to get the guy back out there now that site work is done and road is in, get exact measurements and quote.

That keeps it from passing thru the house panel too, which will save a few dollars and aggravation. Not much, but a few.

To bthe code compliant u cannot have 240v lighting on a residential property.

Hypothetically - If you trench 565' of buried wire and say, you never used the shop for one month. Maybe you went on vacation. How much would your bill increase? I mean, doesn't the wire still consume some electricity even if none is being utilized with a load on it?

Not at the magnitude that youre thinking of. Transformers yes, wire no...

 

[forAK]

Not at the magnitude that youre thinking of. Transformers yes, wire no...

Thanks - Learn something new everyday.

 

[American Locomotive]

240v Lighting LED high bays (divided shop, rare for all to be on same time) 20 amps
240v Welder @100% -- 33amps
Plasma @100% -- 34amps
240v Air compressor 5hp -- rated 22amps
120V Small items -- tool chargers, tractor or rv battery charger, radio (just a hand full of amps?)
120v Things like hand power tools, drills, etc... (but wouldn't be welding at same time)

That was just a guess on light amp draw....was thinking 15 high bay lights at about 120w each, 120v...and rounded way up. See I can go 240 on them too.


That keeps it from passing thru the house panel too, which will save a few dollars and aggravation. Not much, but a few.

A few things to consider:

15 x 120 is 1800 watts of lighting - that's just 15 amps at 120v, or ~7.5 amps per leg if you split it up. Remember, the available current is doubled for 120v loads. So if you have a "100 amp service", you can actually have up to 200 amps of 120v devices on it if you balance them properly.

You said it's just you in your shop most of the time. What are the odds your welder, plasma cutter and air compressor are going to be running at full output, at the same time? I mean, what are the odds you even run just the plasma cutter, or welder at 100% output for any significant length of time?

Finally, remember that most breakers are not "instant trip". They're designed to allow for some overload for brief periods of time. A 50 amp breaker will typically allow ~75 amps to pass through it from anywhere between 60 seconds to several minutes. So even if you do push the limits of your service every once in a while, it's unlikely your lights will go out.

 

[AntonLargiader]

The building I'm in (about 6000 SF originally) was lit with two 20A 120V circuits. 12 or 14 twin 8' T12 fixtures per circuit. Retrofitting to T8 makes for pretty decent light and less draw. I didn't notice where you specified the size of the shop, but 20Ax240V is a lot of light.

 

[kaiser715]

Shop is 42x60, 16-6 sidewalls, ceiling 20' at ridge.

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[theoldwizard1]

Out of the box thinking. Purposely UNDER SIZE the wire to achieve about a 15% (32V) drop. At the end install a 208 to 240 transformer.

Of course this is all theory, no practice ...

 

[kaiser715]

...or a 240>600 and a 600>240 transformer. I think the wire will be cheaper!

Thanks for all the help so far! Lots to think about...

 

[braidmeister]

Sounds like an awful lot of work for a measly 100A. My shop was running on 60A 1PH at about 150' from the panel. I needed 3PH for my equipment, so I spec'd out for 200A 3PH on a separate service, 700' from the road. It was only a little more to get 400A 3PH 'while they were at it' - so that's the way I went. $5k to install poles and transformer - electrician took it from there (wiring up shop, barn, lights etc)

It might be worth exploring your options rather than assuming you have to go off the house electric. 100A on a house these days is undersized. 100A on a shop with a real plasma cutter or welder is also undersized (@ 70-80A ea). Something to think about.

 

[brewchief]

To be code compliant u cannot have 240v lighting on a residential property.

Does a detached shop on a residential property count? Does it matter if the shop is served by the same electrical service or a separate one?

I knew that you couldn't use 240v lighting IN a residence but I'm not sure about the details on a detached building.

 

[Bert_]

I calculated you could use a 4/0 with 3.5% drop with a full 100A load.
You could go up one more size to keep it under 3% but 4/0 is probably the best bang for your buck.

I like this Voltage Drop Calculator. It's simple, just tells you voltage drop for a given size and length of wire.

 

[Cmreschke]

Does a detached shop on a residential property count? Does it matter if the shop is served by the same electrical service or a separate one?

I knew that you couldn't use 240v lighting IN a residence but I'm not sure about the details on a detached building.

Looking at the 14 nec I would say 240 volt lighting in a detached building on resi property is acceptable. The voltage limitation is for dwelling units and hotel, motel, apartments (Assuming the habitable rooms for dwelling) not proper terminology on the last bit. But point is compliant.

 

[theoldwizard1]

...or a 240>600 and a 600>240 transformer. I think the wire will be cheaper!

Most readily available wire only has insulation rated for 300V. 600V insulated wire does exist, just be careful what you buy !

 

[wyliesdiesels]

At $26/month extra I would choose power company install and power company responsibility for maintaining it versus direct bury any day. I repair LOTS of DB aluminum, the first time you call an electrician out for a locate and repair when your cable faults, is going to blow your payback ratio out of the water.



That's the reason I've never used the Southwire calculator. A company in business to sell wire thats always showing a larger wire needed than necessary, is not a coincidence.

However, I have a Cerrowire app on my Ipod. Their calculated wire sizes for voltage drop always matched my calculations when I did them by hand, so that's the one I use sometimes.

Whats the name of the app?

I cant find it in the app atore...

Most readily available wire only has insulation rated for 300V. 600V insulated wire does exist, just be careful what you buy !

Not true.

NM-b aka Romex has a 600v rating...

 

[Aceman]

[/b]

Whats the name of the app?

I cant find it in the app atore...

I can't find it either, I've had it for 3 years or so. I don't know if another website may have saved it and kept it available for download??

Just so you know I'm not blowing smoke:

http://ewweb.com/bulletin-board/cerro-wire-offers-iphone-and-ipad-apps-electrical-calculations

 

[wyliesdiesels]

I can't find it either, I've had it for 3 years or so. I don't know if another website may have saved it and kept it available for download??

Just so you know I'm not blowing smoke:

http://ewweb.com/bulletin-board/cerro-wire-offers-iphone-and-ipad-apps-electrical-calculations

Oh i knew you werent blowing smoke.

I already found references to it thru google.

What happens a lot of times is that apps arent updated and they get pulled from the app store...if a device currently has the app, it stays on the device. But if u do a reset, u wont be able to download it again...

 

[Brock Wood]

You are allowing for voltage drop (good) & yes, you are overthinking. When I was a Distribution Engineer for a power company. we diversified the total load. In your case all lighting + plasma + air compressor & any type of heating or cooling would be figured for conductor size & reduced by 10%. You could tell them all day you need more (in your example, it was a 2nd person welding) & they wouldn't do it without passing the extra cost directly to the customer as a 1 time charge due before breaking ground. In absolutely no case did the customer come back & say, "I really did need that size upgrade."
Due to the distance involved in your case, there is an up front charge for such a small load. They figure an amortization rate of about 8 years to finally make a profit for the work of installing your new service. Lines, baring any accidental knicks, will be good for 25+ years. I've done all my electrical expansions on the 1 house meter - $26 per month just to have a 2nd meter really adds up. Just gotta weigh your options......

 

[kaiser715]

Talked to power company last Friday. New rules not reflected in online documentation. Now, a second service at a residence is charged as "small commercial"...right at $35 per month base rate. So, playback will be even quicker putting in my own line.

Also, staked out house, looks like it will be about 50-60' closer to the shop.

I am now thinking 100 amps over 4/0

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[wyliesdiesels]

@ full load 4/0 is gonna put u over recommended 3% for feeders.

250McM would be better. Best would be 300McM...

 

[mm08822]

Prior voltage drop calculations in this thread are being calculated using only the dc resistance value (0.061 ohms/1000ft for 350MCM AL, for example) listed for the conductor in Table 9.
Vdrop = 2*100A*0.061ohms/1000ft*565ft = 6.893 volts >>>> 6.893V/240V * 100% = 2.88%.
Another site referenced in an earlier post also erroneously uses only the dc value of resistance.

This is an ac circuit and the inductive reactance in an ac circuit also creates additional voltage drop. Table 9 in NEC also provides the effective impedance(Z) for 3 conductors in various types of conduit at a common power factor of 0.85 for 60Hz operation.
(This site will quickly explain the impedance components: http://ecmweb.com/content/calculating-voltage-drop-power-distribution-systems )

Southwire is calculating the voltage drop of a conductor based upon initial voltage, load amps, Cu/AL, distance, impedance(DC resistance plus AC reactance) and permitted voltage drop (%) based upon user inputs.
In order to stay at or below required % Vd, the impedance(Z) required to meet those requirements is calculated and then the conductor with that impedance value (or next lowest) is able to be looked up and the conductor size is pushed out of the app. It is the impedance of the conductor that determines the minimum conductor size.
The conductor ampacity listed in 310.15 (B)(16) actually has nothing to do with the result.***

For 350 mcm AL…..Vdrop = 2*100A*0.073ohms/1000ft*565ft = 7.3 volts >>>> 7.3V/240V * 100% = 3.44% (This fails the 3% limit.)

For 500 mcm AL…..Vdrop = 2*100A*0.057ohms/1000ft*565ft = 5.7 volts >>>> 5.7V/240V * 100% = 2.68% (This passes the 3% limit.)
Southwire app reports back needing 500 MCM AL.

***There is a note in the Southwire app and online calculator that the 60C table is used for conductor sizes in branch circuits. Since 334.80 specifies that NMB, etc….can’t exceed the 60C ampacities, Southwire references the 60C ampacities assuming we are using NMB. NMB is available in #14 - #2 Cu. From #1 and larger, they jump to 75C ampacity references.
They have added confusion and created skepticism by forgetting that branch circuits and feeders can be run with 75C rated insulation in this range without a good explanation of referencing 60C vs 75C ampacities.

It doesn’t matter. Follow the example below:

Situation: 240 vac supply, single phase, conduit, 3% max drop desired, 25amp load, Cu, 250ft distance
From Southwire online calc:
“1 conductors per phase utilizing a #6 Copper conductor will limit the voltage drop to 2.31% or less when supplying 25.0 amps for 250 feet on a 240 volt system.
For Engineering Information Only:
55.0 Amps Rated ampacity of selected conductor
0.4662 Ohms Resistance (Ohms per 1000 feet)
0.051 Ohms Reactance (Ohms per 1000 feet)
7.199 volts maximum allowable voltage drop at 3%
5.523 actual voltage drop loss at 2.31% for the circuit
0.9 Power Factor”

A quick calc by hand:
Vdrop(#6 wire) = 2*25A*0.45ohms/1000ft*250ft = 5.63 volts >>>> 5.63V/240V * 100% = 2.34%

Since we are concerned about eliminating voltage drop, #6 Cu wire must be installed and in order to get ~3% or less Vd, it must have ocp at 30A to maintain this criteria. It doesn’t matter if nmb(55a) or thhn(65a) is used - #6 Cu is #6 Cu.

Where conductor insulation rating and ampacity would matter is in derating for number of conductors in conduit and temperature correction for elevated temps. Elevated temps would increase the dc component of the reactance and effect the Vd. Southwire app makes no adjustment for these two situations.

 

[padroo]

I lost one leg of my under ground service to my back garage due to a lightning strike. If I do it again I would use conduit unless the electric company was responsible for the service.

 

[Aceman]

I lost one leg of my under ground service to my back garage due to a lightning strike. If I do it again I would use conduit unless the electric company was responsible for the service.

Some people have to learn about direct bury wire the hard way....