What size wire??

[aarcuda]

I am in the process of gathering materials for wriing my shop. Its a 30x50x12 and its close to 200' from the house. I have purchased a 125 amp breaker panel for it and have set 20 some odd 20 amp outlets around the shop. I'll have 10 2 bulb (4') fluorescent fixtures and 2 2 bulb (8') flourescents for lighting. I bought a big roll of 12-2 for all the outlets and lighting.

I'll have a grinder, a table saw, an air compressor, a 2 post lift and typical other shop tools but I dont expect too many of them to be on at the same time. I will eventually get some sort of heaters in ther and if its not a woodburning stove, it will probably be electric (maybe a heat pump or strips). I also have a lincoln 225 welder and plan on getting a mig somewhere down the road.

Not having a clue as to power requirements for those items listed above, I cant really tell how much power I'll need and more importantly, since I am ready to buy wire to connect the shop to the house 200' away, I dont know what size wire to buy.

what size wire do I need? I see calculators that say 3/0 is the min and I see other posts that say I could get away with 2/0 or even 1/0.

Can anyone with experience help me out?

 

[anaxagoras]

While I can't tell you the power requirements you'll need I can tell you this from things i have read. I could be wrong, so I encourage the experts out there to correct me where I am wrong.

You never want a breaker to be constantly loaded near 100%, or a piece of wire for that matter. I forget but I think the rule of thumb is something like 75% max? Someone should correct me here.

Also It's better to use heavier gauge wire now, then realize you need heavier gauge wire after all is said and done. If you ever need to expand, it will save you in the long term.

 

[two2fastforu]

My local power company supplied the wire sizes I needed. Also the local Home Depot and Lowes had there printouts showing the wire size to the panel.

 

[Ezzie]

Primary conductors for a 125A sub panel is #3 copper but you might want to use #2 due to the distance. You may not be allowed to use aluminum for a sub panel application (the x/0 sizes mentioned above) but check with your local inspection authority. The #3 or #2 copper is very expensive and may not be available from a Lowes or Home Depot (at least here it isn't). Had to go to an electrical supply store to get it.

 

[OldCarGuy]

I suggest that you get an electrical engineer (the utility company may run the numbers for free) to determine the total load to expect from the devises you named. However you will have to nail down the heating equipment. Heat pumps and strip heaters draw a lot of amperage. And you may need a bigger load center than 125 Amp.

The voltage drop is what you should be concerned about in the 200 feet run you have. And depends on the wire size, length of run, and the amperage draw. Scroll down the page in the following LINK and punch in the type of wire copper or aluminum (I would never use aluminum ), wire size (AWG), voltage (most likely 240 single phase), run of 200 feet, load of circuit in Amps (125 or the number an engineer comes up with). Hit calculate, and read the drop in voltage. I would be concerned about any Voltage drop over 10 Volts. And try to keep it closer to 5 Volts.

 

[aarcuda]

Right now my house is all electric(it has a heat pump and electric stove and electric water heater and electric dryer and it all runs off a 100 amp breaker panel) so Im thinkijng the 100 amp to the shop should be ok IF I get low voltage drop. I used a calculator on http://www.elec-toolbox.com/calculators/voltdrop.htm and http://www.electrician2.com/calculators/wireocpd_ver_1.html and this is where Im getting the 2/0 or 3/0 wire sizes for my distance and theoretical loads (like 50 amps continuous, 80 intermittant)

I tried calling the electric company and they wont advise me . they just want to put a meter in and charge me a monthy fee. I figure, if I buy the wire and do the work myself, I cross over at 5 1/2 years (thats when the eletric co's service fee exceeds the cost of the wire, conduit, panel and trenching)

 

[Stuart in MN]

When you use the www.elec-toolbox.com calculator, I think you're plugging in 120vac when you should be using 240vac instead. That will give you a minimum size of #2 wire.

However, assuming you're putting a 125amp branch circuit breaker in the panel in the house the wire will need to be #1 (further assuming you're talking about THHN 75 degree C in a conduit.)

edited to add: wait a second, I'm confused....you said you currently have a 100 amp panel in the house, but you want to add a 100 amp panel in the shop as well, and then earlier you said you're going to have a 125 amp panel in the shop.

Are you going to have a whole separate electrical service to the shop? The local power company may or may not be willing to do that. Or, are you going to upgrade the service to the house, put in a bigger panel there and then run a branch circuit to the shop?

 

[MXtras]

The use of Aluminum wire in primary service is very, very common.

I do not have my NEC here with me, otherwise I could easily supply you with the answers.

There are a few qualified electricians on this board - I strongly suggest that you wait for them to reply before relying on the idiots at Lowes to sell you what they have on hand.

Scott

 

[Charles (in GA)]

If all you have supplying the house is a 100 amp panel, you either need to 1) put a meter on the shop and run a completely separate service.... or.... 2) upgrade the house, power company feed, meter socket, service entrance cables and your breaker panel to at least 200 amp.

You are suggesting powering a rather large shop with lights, air compressor welder, etc and you really don't have anything to run it with. Sure, you won't be using everything at once, but a welder draws quite a bit, and the lights will be on plus the heat, and the aircompressor might kick on at any time, there is no way you can expect to power a house, and a shop on 100 amps total................... it just isn't going to happen unless you are darn careful about what is on and when, and that isn't worth the hassles and headaches.

You will never regret spending money on a reliable, robust, electrical service that doesn't give you any problems and doesn't require any effort on your part.

Depending on the location of the transformer and whether the Power Company charges differently for a garage meter, and your local inspection and codes, you might consider putting a new 200 amp service on the shop with a 200 amp panel and subfeeding to the house with 100 amps. Any way you do it, what you are wanting to do won't work, at least not very well. Wait till you screw up and have too much stuff on at once and the heat pump kicks in and burns up from low voltage. All that money you saved will be for naught.

Charles

 

[aarcuda]

The service from the Pole to the meter on the house is 200 amp. The breaker panel that feeds the house is 100 amps.

I was told that I could run a SEPARATE panel off the meter at the house with another 100 amp breaker in it that feeds out to the shop. In the shop, I'll have another panel thats rated for 125 to feed the 100 amps around the shop.

#1 wire seems kinda small to run 100 amps 200 feet.

And the point about using 120 or 240 in thew calculators, I wasnt sure about that so I went with 120. Are you sure about this cause #1 wire is a cheaper than 1/0 and if it will take it, I would use it.

 

[Charles (in GA)]

The service from the Pole to the meter on the house is 200 amp. The breaker panel that feeds the house is 100 amps.

I was told that I could run a SEPARATE panel off the meter at the house with another 100 amp breaker in it that feeds out to the shop. In the shop, I'll have another panel thats rated for 125 to feed the 100 amps around the shop.

"I see" says the blind man, that would work. However, make sure the meter socket you have now has two separate lugs. If it has only one set of lugs and your house is connected to them now, you will need a new meter socket with two sets of lugs. 200 amp meter sockets are not commonly found with dual lugs, they are found, but I'll bet yours is not. 400 amp meter sockets are usually dual lug units for doing just this, splitting the service.

#1 wire seems kinda small to run 100 amps 200 feet.

And the point about using 120 or 240 in thew calculators, I wasnt sure about that so I went with 120. Are you sure about this cause #1 wire is a cheaper than 1/0 and if it will take it, I would use it.

To be honest, with all the electricity you are and plan on using, I would run heavy enough cables for 200 amps to the shop, you may want to upgrade the main service to 400 amp someday and up the house and shop to 200 amp panels. Its a little more now, alot more later. Underground direct burial would be 4/0-4/0-4/0-2/0 (you have to carry a ground since the disconnect you place at the meter is your main, and this is technically a sub feed to a subpanel in the garage.)

Charles

 

[hawkeye2]

Check this out
http://www.jhlarson.com/resource.htm

 

[Stuart in MN]

#1 wire seems kinda small to run 100 amps 200 feet.

And the point about using 120 or 240 in thew calculators, I wasnt sure about that so I went with 120. Are you sure about this cause #1 wire is a cheaper than 1/0 and if it will take it, I would use it.

I am assuming you want to run 240 volts out to the shop, since you'll have an air compressor, welder, etc. so yes, use 240 for your calculations.

The general rule of thumb is to use #3 copper wire for a 100 amp circuit, #1 for 125 amps, #3/0 for 200 amps, and either two sets of #3/0 or one set of 500MCM for 400 amps. (some people may say you can use #4 for 100 amps, #2 for 125 amps, and 2/0 for 200 amps, but that applies only to the service entrance wires from the utility to the house.) For a 400 amp circuit, I would guess most electricians would rather run two sets of #3/0, since working with 500MCM is like wrestling with an elephant trunk.

Depending on the length, the wire size needs to be increased to limit voltage drop - another rule of thumb is 100 feet is about as far as you want to go with a 120 volt circuit, and 200 feet for a 240 volt circuit before you need to upsize the wire. However, since there are so many handy calculators out there it's just as well to figure out the actual requirements.

 

[Bib Overalls]

I am in Jonesboro. The co-op here provides free meter bases. But I opted to buy my own. The one I got has a belt in pannel that takes four standard sized circuit breakers, two on each leg plus lug to connect to the service panel. We run 100 amps 220 to the shop and 30 amps 110 to the pool pump. I have one space left for yard lights or whatever. Cost less than $200 and it was a real headach saver.

 

[Powerband]

I suggest that you get an electrical engineer ...


The voltage drop is what you should be concerned about in the 200 feet run you have. And depends on the wire size, length of run, and the amperage draw. ...
. Hit calculate, and read the drop in voltage. I would be concerned about any Voltage drop over 10 Volts. And try to keep it closer to 5 Volts.

Hey OldCarGuy: Thanks that calculator link is great. I don't get the one spec:

"Enter 1-way circuit
length in feet (the calculation is for the round trip distance"

Does that mean the wire length is twice the distance from the breaker??

Thanks

Powerband

Garage has a 50A breaker on a feed from the house @ 50' away. a 30A breaker feeds the Continuous duty 3HP Wayne air compressor at the "end of the line".

I estimate @ 60' from the breaker on #10 wire. The lights show the compresion stroke of the compressor.

 

[Stuart in MN]

"Enter 1-way circuit
length in feet (the calculation is for the round trip distance"
Does that mean the wire length is twice the distance from the breaker??

When calculating voltage drop you need to take into account the entire length of the circuit, out and back. However, most if not all those online calculators build that into their calculations, so you only have to enter the distance from point A to point B instead of the round trip.

 

[W-Cummins]

When calculating voltage drop you need to take into account the entire length of the circuit, out and back. However, most if not all those online calculators build that into their calculations, so you only have to enter the distance from point A to point B instead of the round trip.

Only if you have a grounded conductor and are coming back.

William....

 

[aarcuda]

btw, when tapping off the meter like I planned, is it typical to run 3 wires, 2 hots on 1/0 and then a #6 neutral and just drive a grounding rod into the ground by the shop?

 

[groove grabber]

I'm sitting in the exact same situation as you are, 200 amp to house, running 190 ft to barn off a 100amp breaker in house to a 100 amp panel in shop. Also have lift, welder and everything else you mentioned. I am using #2 Alum triplex. Voltage drop calculates well within range. With the price of copper, every expert I've talked to said it was perfectly fine to run #2 alum triplex. I bought mine at lowes for 1.16 ft. Anyone see any other problems with this, I'd like to know now before it goes underground?

 

[aarcuda]

I actually looked at my breaker panel for the house and its is a 150 amp panel (not 100 amp as I originally believed).

I think I am going to go with #1 copper (I can get it for $1.57 per foot at the local supply house) and # 6 for the ground. I will also get a new meter base with double lugs and put the wire in sched 40 pvc in a trench.

The only question now is what size is the neutral wire? would that be #1 as well?

 

[53sled]

I feel so lucky. I bought a house with 220v/200a to the shop, then it runs to 100a for the house. meter is on the shop. I just wish the shop was BIGGER!

 

[OldCarGuy]

The neutral should be sized as the other two hot conductors you're using,, #1..

 

[woodturner9]

I think I am going to go with #1 copper (I can get it for $1.57 per foot at the local supply house) and # 6 for the ground. I will also get a new meter base with double lugs and put the wire in sched 40 pvc in a trench.

The only question now is what size is the neutral wire? would that be #1 as well?

The neutral and the ground should be the same size as the "hot" conductors.

There are code exceptions that allow reducing the size of the ground in some cases. However, I do not recommend it. The purpose of the ground is to carry ALL the current in case of a fault - that's why it is sometimes referred to as the "safety ground".

You also mentioned using a 125A panel fed from a 100A breaker. Your inspector may approve this, but it's not really "right". Why not use the correct size breaker - either use a bigger breaker or a smaller panel?

Remember, too, that you need to remove the bonding strap for the branch panel - the neutral reference is the house panel or meter socket (usually the meter socket, depends on the municipality), NOT the branch panel ground.

 

[Charles (in GA)]

I would think that NEC 215.2(A)(1) would cover this. Minimum Rating and Size, Feeders not more than 600 volts. "ungrounded conductor shall not be smaller than that required by 250.122..." However, common sense tells me to run a full size neutral, you cannot go wrong, and you will never overload it, even if you put EVERY 120V breaker on the same side of the buss! (Yes, as stupid as it sounds, I've heard of it being done.)

Charles

 

[markb1]

NEC Article 90
90.1 Purpose.
(C) Intention. This Code is not intended as a design specification or an instruction manual for untrained persons.

220.61 Feeder or Service Neutral Load.

You need to do load calcs to reduce the neutral. Otherwise do as Charles said and run full size neutral.

Let the flaming begin.
Mark

 

[Aceman]

The neutral and the ground should be the same size as the "hot" conductors.

There are code exceptions that allow reducing the size of the ground in some cases. However, I do not recommend it. The purpose of the ground is to carry ALL the current in case of a fault - that's why it is sometimes referred to as the "safety ground".

What?

The ground only needs to match the "hot" conductor size up to a 30 amp circuit. After that, it's smaller. This is not an exception, it is common practice and very much allowed by code.

You also mentioned using a 125A panel fed from a 100A breaker. Your inspector may approve this, but it's not really "right". Why not use the correct size breaker - either use a bigger breaker or a smaller panel?

There is absolutely nothing wrong with this. The inspector WILL approve it.

 

[markb1]

Table 250.122 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment.

Example:
100 amp overcurrent Device in Circuit Ahead of Equipment.
#8 copper or #6 Al. equipment grd. conductor.

Common terminology:

Neutral conductor= grounded conductor
Ground conductor= equipment ground
Grounding Electrode Conductor:
The conductor used to connect the system grounded conductor(neutral) or equipment to a grounding electrode (grd. rod, uffer grd.) or to a point on the grounding electrode system.

 

[woodturner9]

What?

The ground only needs to match the "hot" conductor size up to a 30 amp circuit. After that, it's smaller. This is not an exception, it is common practice and very much allowed by code.

Common practice does not necessarily equal good practice. NEC sets MINIMUM standards. Like a house built to BOCA, a house wired to NEC is likely to leave one dissatisfied. NEC's focus is safety, not performance. So, for example, wire sizes specified to NEC are too small to prevent light dimming when used for power tools.

It is "legal" to use a ground smaller than the conductor size. It's also unsafe. In the event of a ground fault, the ground wire will carry ALL the current. A ground wire smaller than the conductor size is called a "fuse". In that event, the individual will likely not survive the experience.


The ground only needs to match the "hot" conductor size up to a 30 amp circuit. After that, it's smaller. This is not an exception, it is common practice and very much allowed by code.

You also mentioned using a 125A panel fed from a 100A breaker. Your inspector may approve this, but it's not really "right". Why not use the correct size breaker - either use a bigger breaker or a smaller panel?

There is absolutely nothing wrong with this. The inspector WILL approve it.

NEC is a basic standard - municipalities can and do impose more stringent standards than NEC. So one can't be certain a local electrical code or inspector will allow this.

As I said, though, it's more an issue of it not being "right". There are some potential safety issues, but they are relatively unlikely to occur, so the primary benefit of sizing the breaker correctly for the branch panel is so that home inspectors and others subsequently inspecting the work don't think the person who wired it is an idiot.

 

[Aceman]

Common practice does not necessarily equal good practice. NEC sets MINIMUM standards. Like a house built to BOCA, a house wired to NEC is likely to leave one dissatisfied. NEC's focus is safety, not performance. So, for example, wire sizes specified to NEC are too small to prevent light dimming when used for power tools.

Like posted above, the NEC is not a design tool. It's the electricians responsiblity to size for voltage drop.

It is "legal" to use a ground smaller than the conductor size. It's also unsafe. In the event of a ground fault, the ground wire will carry ALL the current. A ground wire smaller than the conductor size is called a "fuse". In that event, the individual will likely not survive the experience.

Are you saying every circuit, no matter the size or length should have a full size ground? Or just the circuits that are oversized to account for voltage drop?

NEC is a basic standard - municipalities can and do impose more stringent standards than NEC. So one can't be certain a local electrical code or inspector will allow this.

As I said, though, it's more an issue of it not being "right". There are some potential safety issues, but they are relatively unlikely to occur, so the primary benefit of sizing the breaker correctly for the branch panel is so that home inspectors and others subsequently inspecting the work don't think the person who wired it is an idiot.

What is the problem running a smaller circuit with a correctly sized breaker to an oversized panel? Someone might purchase the larger panel for more breaker spaces but not necessarily need the increased ampacity. Larger panels being more common are often times cheaper than the smaller panels as well.

 

[woodturner9]

Are you saying every circuit, no matter the size or length should have a full size ground? Or just the circuits that are oversized to account for voltage drop?

Essentially, yes.

What is the problem running a smaller circuit with a correctly sized breaker to an oversized panel?

With two breakers in series, with the larger breaker "downstream", in the event of a moderat fault neither breaker may open. It's not common, but it is a known failure mode.

There is also the issue of identifying the service disconnect - there are really two. A better arrangement, IMHO, would be to use the breaker in the main box as the disconnect and use a branch panel (i.e. one without a main breaker) at the garage instead of a service panel (one with a main breaker).

 

[Aceman]

Essentially, yes.

We'll have to agree to disagree then as Table 250.122 allows it. It's definitely not cost effective nor practical in my opinion to go above and beyond this requirement.

There is also the issue of identifying the service disconnect - there are really two. A better arrangement, IMHO, would be to use the breaker in the main box as the disconnect and use a branch panel (i.e. one without a main breaker) at the garage instead of a service panel (one with a main breaker).

There is only one service disconnect, it is the main breaker for the house. This is a feeder to a garage, not a service. Since detached garages require a disconnect, the simplest way to meet this requirement is to install a main breaker panel.225.31

 

[woodturner9]

We'll have to agree to disagree then as Table 250.122 allows it.

I agree that NEC allows it, but my point is that (IMHO) it's not good practice, and also that some municipalities impose more stringent requirements. Thus it may comply with NEC but be prohibited by local code in some areas.

There is only one service disconnect, it is the main breaker for the house. This is a feeder to a garage, not a service. Since detached garages require a disconnect, the simplest way to meet this requirement is to install a main breaker panel.225.31

The meter socket is (usually) the service disconnect for the house. In this case, it would also be the service disconnect for the garage.

Every branch panel requires a disconnect, usually the breaker in the main panel feeding it.

I wasn't thinking of the requirement for a detached building to have a local disconnect - I agree with you on that requirement. Typically it is provided through a disconnect switch, though a breaker is OK if it is the same size as the feeding breaker.

I did find a web page with some decent information specifically on the requirements for outbuildings:
http://www.iaei.org/subscriber/magazine/04_a/04_a_johnston.htm

 

[aarcuda]

There is also the issue of identifying the service disconnect - there are really two. A better arrangement, IMHO, would be to use the breaker in the main box as the disconnect and use a branch panel (i.e. one without a main breaker) at the garage instead of a service panel (one with a main breaker).

the panel that I have for the shop (the 125 amp panel) does not have a main breaker in it. The box that I will mount at the house has a single 100 amp breaker in it.

 

[woodturner9]

the panel that I have for the shop (the 125 amp panel) does not have a main breaker in it. The box that I will mount at the house has a single 100 amp breaker in it.

That's fine, but as Aceman noted, you would need a local disconnect at the shop to meet NEC.

 

[tokyo]

i don't know about you guys..but my head is spinning...

tok

 

[Bevis]

i don't know about you guys..but my head is spinning...

tok

don't feel bad..,

 

[Jaytree]

Reading through all of this,
I was beginning to think it was just me!