230 to garage

[460Rustang]

New member from vintage-mustang.com,....Israel, if anyone hangs out there also.

Existing garage is wired only for 115, recently picked up a 230 compressor and a 230 Lincoln MIG,...now I need some juice.

The existing main svc panel has only the service connections inside leading to the breaker panel inside the house, 200 amp.

I wanna jump from this exterior main svc panel to a closely mounted sub panel, then 125 ft underground to the garage. There's no way to get from the interior breaker panel to the garage. It's a story and a half Acadian with no visible, straight path.

Both the welder and compressor pull 20 amp each. Being a one man hobbist garage, I can't envision needing to run more than 20 amps at a time, there's plenty 115 for all other supply.

But, with that being said, I would like to have two garage outlets, so as not to have to swap back and forth with a single plug.

I've been getting very mixed and conflicting advice on what to run.

I was thinking about 125 ft of # 8 THWN through conduit, from a 30 amp breaker in the sub panel into one garage receptacle then jumping to the next from that one.

Please gimme some input.

Also as a related question, what are some of your tool "must haves", that might make me wanna rethink my 30 amp max requirement?

Currently building a 67 BB Rustang from the ground up, so all tools will be car hobbist related, one at a time having only two hands.

THANKS!!

 

[Charles (in GA)]

Either your meter socket, or the outside disconnect, will need to have two sets of lugs for each wire. One will be the set for the house panel, and the second set will be for the additional disconnect to the shop. You may or may not have this already. If you do not, it is much more difficult to add it, as you could end up changing the outside disconnect to some sort of dual disconnect panel to make it happen.

You will need to run four wires from the house to the shop, two hots, a neutral, and a equipment/earth ground.

As far as current draw goes, expect to use more than you realize. If you decide to buy a blast cabinet to assist in your restoration, you will end up buying a bigger compressor, very possibly a 7.5 hp which draws about 33 amps running. Then you will discover the merits of a plasma cutter to cut out rotted floorboards, etc, and plasma needs compressed air, so that is both devices running at once, plus your lights, the fans or heat, and a few other things you forgot about.

Using copper #8 THHN will get expensive. You can probably get aluminum Mobile Home Feeder, 2-2-2-4 for about the same money, and breaker it at 90 amps (or less due to the long run if you desire). Install a decent sized panel at the shop.

There is another thread going right now covering this same thing.

http://www.garagejournal.com/forum/showthread.php?t=219015

Charles

 

[wyliesdiesels]

Is this garage detached? If so, you will have to abandoned the existing feed to it because u cant have 2 or more separate feeds to a detached structure.

I second the 2-2-2-4 MHF. You will need 2 ground rods and the neutral bar in the subpanel needs to be isolated/insulated from the panel enclosure and the ground bar.

Also, if there will be more than 6 breakers, the subpanel will need a main breaker!

 

[460Rustang]

Either your meter socket, or the outside disconnect, will need to have two sets of lugs for each wire. One will be the set for the house panel, and the second set will be for the additional disconnect to the shop. You may or may not have this already. If you do not, it is much more difficult to add it, as you could end up changing the outside disconnect to some sort of dual disconnect panel to make it happen.

You will need to run four wires from the house to the shop, two hots, a neutral, and a equipment/earth ground.

As far as current draw goes, expect to use more than you realize. If you decide to buy a blast cabinet to assist in your restoration, you will end up buying a bigger compressor, very possibly a 7.5 hp which draws about 33 amps running. Then you will discover the merits of a plasma cutter to cut out rotted floorboards, etc, and plasma needs compressed air, so that is both devices running at once, plus your lights, the fans or heat, and a few other things you forgot about.

Using copper #8 THHN will get expensive. You can probably get aluminum Mobile Home Feeder, 2-2-2-4 for about the same money, and breaker it at 90 amps (or less due to the long run if you desire). Install a decent sized panel at the shop.

There is another thread going right now covering this same thing.

http://www.garagejournal.com/forum/showthread.php?t=219015

Charles

The four runs, like you mention are 2 hots, 1 neutral and 1 ground, can't the ground rod be omitted with the sub panel being close to the main panel, which has one?

I don't want a sub panel in the garage, just two receptacles.

 

[460Rustang]

Is this garage detached? If so, you will have to abandoned the existing feed to it because u cant have 2 or more separate feeds to a detached structure.

I second the 2-2-2-4 MHF. You will need 2 ground rods and the neutral bar in the subpanel needs to be isolated/insulated from the panel enclosure and the ground bar.Also, if there will be more than 6 breakers, the subpanel will need a main breaker!

The garage is attached.

Isn't the neutral BUS isolated by removing a green screw?

I've been trying to supplement by nonexistant knowledge with a little youtube,...LOL

 

[460Rustang]

Don't wanna run aluminum, kinda set on THWN, 167 F / 75 C, breaker will actually handle up to 50 amps, correct,...guess there's no need to limit myself to 30 amp if the same set up with a "hotter' breaker will handle 50 amps?

Is all of the above accurate, where can verify that # 8 will handle the 50 amps @ 125 ft?

 

[wyliesdiesels]

Since the garage is attached, the ground rods and main breaker are not needed. Also, u dont even need a subpanel and can have multiple feeds but a subpanel is still nice to have.

As far as the #8 goes, u can lookup 'NEC 2011 310.16(b)(16)' for ampacity values then u have to calc the voltage drop. #8 at that distance and full load will give u approx a 9.8v drop which is 4% and the NEC recomends 3%. I would bump it up to #6!

 

[460Rustang]

Thanks, is 75 C std for breakers or at least not ususual?

 

[pattenp]

#8 THHN/THWN will handle 50A but you can't just run the 50A circuit to the garage and branch out to a couple of 240v outlets. Depending on where you live building code may not allow multiple outlets that are larger than 120V 20A on one circuit. Usually 240V outlets are wired as a single dedicated outlet. You will need to have a sub-panel in the garage if you want to run 50A to the garage and then have a couple of 240V 20A or 30A outlets. If you run the 50A circuit to the garage without a sub-panel in the garage then any outlets on that circuit will need to be a 50A outlet.

 

[pattenp]

Devices are usually rated at 75 C. And wylie made a good point on the voltage drop.

Thanks, is 75 C std for breakers or at least not ususual?

 

[460Rustang]

#8 THHN/THWN will handle 50A but you can't just run the 50A circuit to the garage and branch out to a couple of 240v outlets. Depending on where you live building code may not allow multiple outlets that are larger than 120V 20A on one circuit. Usually 240V outlets are wired as a single dedicated outlet. You will need to have a sub-panel in the garage if you want to run 50A to the garage and then have a couple of 240V 20A or 30A outlets. If you run the 50A circuit to the garage without a sub-panel in the garage then any outlets on that circuit will need to be a 50A outlet.

Is this beacause multiple outlets may pull more than the 50 amps provided?

Single man, hobbist garage, I really can't see pulling more than 20 amps at a single time, the welder and compressor won't be in use together, with only two hands.

But,....even if they are, pulling 40 from the 50 should be OK, correct?

The only reason why I want two outlets is because the welder and comp will not be placed near each other.

YOU GUYS ARE GREAT!![/B]

 

[460Rustang]

#8 THHN/THWN will handle 50A but you can't just run the 50A circuit to the garage and branch out to a couple of 240v outlets. Depending on where you live building code may not allow multiple outlets that are larger than 120V 20A on one circuit. Usually 240V outlets are wired as a single dedicated outlet. You will need to have a sub-panel in the garage if you want to run 50A to the garage and then have a couple of 240V 20A or 30A outlets. If you run the 50A circuit to the garage without a sub-panel in the garage then any outlets on that circuit will need to be a 50A outlet.

Are machines that only pull 20 amps made with 50 amp plugs, the welder has a plug the comp doesn't.

With no disconect in the garage, don't the welder and comp need to be plugged?

 

[pattenp]

I'm not sure why some places only allow a single 240V outlet on a circuit. Virginia is one of those places.

Welders usually have a 50A plug. Large compressors that don't have plugs are usually hardwired because motor loads will require the plug and outlet to have a HP rating of more than 3HP and you aren't going to find a standard 240V plug that's rated more than 3HP. I'm just saying you can't put a 20A or 30A outlet on a circuit that has over current protection of 50A. The outlets will all need to be 50A outlets, so that means the compressor will have to have a 50A plug on it. Not knowing what the HP rating is of your compressor kinda makes this all a mute point.

 

[460Rustang]

i'm not sure why some places only allow a single 240v outlet on a circuit. Virginia is one of those places.

Welders usually have a 50a plug. Large compressors that don't have plugs are usually hardwired because motor loads will require the plug and outlet to have a hp rating of more than 3hp and you aren't going to find a standard 240v plug that's rated more than 3hp. I'm just saying you can't put a 20a or 30a outlet on a circuit that has over current protection of 50a. The outlets will all need to be 50a outlets, so that means the compressor will have to have a 50a plug on it. not knowing what the hp rating is of your compressor kinda makes this all a mute point.

4.5 hp

 

[pattenp]

Well technically the compressor should be hardwired with a disconnect. Will it work okay on a 50A circuit using a 50A outlet and plug? Yes. But it doesn't meet the letter of the NEC. And on that note what state/country are you in?

Edit: I should ask... is it a 4.5HP label on the Tank or is 4.5HP printed on the motor data plate?

[/b]

4.5 hp

 

[wyliesdiesels]

[/b]

4.5 hp

Since its 4.5hp, I would wire for a 5hp compressor since 4.5hp is not a standard NEC size. Also in the chance that u change to a 5hp compressor, the circuit will be ready for it.

this means for wire: 28a*125%= 35a, so #10 THHN in conduit or #8 NM-b.

#8 or #6 CU THHN wire will be incredibly expensive. I would use aluminum wire. You dont have to be afraid of aluminum wire as the aluminum wire nowadays is a lot better than the stuff from the 60s and 70s that oxidized easily and caught fire!!

 

[Charles (in GA)]

Probably not a true 4.5 hp. The amp draw of a 4.5 hp motor would be somewhere around 25 amps. Most likely this is a 2.5 to 3 hp motor with the typical bogus air compressor hp rating on it.

Virtually all plugs and receptacles rated at 30 amps are, if hp rated at all, are hp rated for no more than 2 hp (thats true, actual hp).

As already noted, if you run a 50 amp circuit, they you must use 50 amp plugs and receptacles. Welders, due to their very limited duty cycles are a special case with NEC and if you have a DEDICATED welder circuit, then you can run a larger then normally allowable breaker on a circuit.

The best thing you can do here is install a small subpanel and then you can split it any way you want later one. Panels are relatively cheap and breakers are cheap too in the big scheme of things. If you are going to go to the trouble of literally wrapping your house outside with conduit and wire to get to the garage, you need to supply more than enough current to work with now and in the future.

You make your panel sound rather in-accessible. You don't have a crawl space or basement? House built on a slab? I take it the panel is on the opposite end from the garage?

Charles

 

[Charles (in GA)]

#8 or #6 CU THHN wire will be incredibly expensive. I would use aluminum wire. You dont have to be afraid of aluminum wire as the aluminum wire nowadays is a lot better than the stuff from the 60s and 70s that oxidized easily and caught fire!!

I agree. The aluminum wire that caused problems was small house wire, 12 and 10 gauge. It was used with standard receptacles and switches that were not designed for it and that is where the problems came in. Larger AL wire used today is different, you use no-corrode paste on connections, and you are using it on breakers and receptacles and connections that specify AL/CU. If it says CU only, you know not to use it.

Charles

 

[460Rustang]

#8 or #6 CU THHN wire will be incredibly expensive. I would use aluminum wire.

I'm seeing # 6 THWN @ .58 ft, I need four runs @ 125 ft, $290
MHF @ $1.82 ft, $228, not a big difference, I see spools are one color, do you just color tape the wires?

The best thing you can do here is install a small subpanel and then you can split it any way you want later one. Panels are relatively cheap and breakers are cheap too in the big scheme of things. If you are going to go to the trouble of literally wrapping your house outside with conduit and wire to get to the garage, you need to supply more than enough current to work with now and in the future.

You make your panel sound rather in-accessible. You don't have a crawl space or basement? House built on a slab? I take it the panel is on the opposite end from the garage?

Charles

Thinking that a sub panel in the garage may be best,.....no basements down here in Mardi Gras Town, slab home, front of the house all the way to the back of the garage, directly behind the house.

 

[pattenp]

Individual wire #6 and smaller need to be the correct color. Hots can be black, Neutral = black with white stripe or all white, ground = green.

 

[pattenp]

The ground wire can be a #10.

I'm seeing # 6 THWN @ .58 ft, I need four runs @ 125 ft, $290
MHF @ $1.82 ft, $228, not a big difference, I see spools are one color, do you just color tape the wires?

Thinking that a sub panel in the garage may be best,.....no basements down here in Mardi Gras Town, slab home, front of the house all the way to the back of the garage, directly behind the house.

 

[460Rustang]

Well technically the compressor should be hardwired with a disconnect. Will it work okay on a 50A circuit using a 50A outlet and plug? Yes. But it doesn't meet the letter of the NEC. And on that note what state/country are you in?

Edit: I should ask... is it a 4.5HP label on the Tank or is 4.5HP printed on the motor data plate?

Nawlins,...

 

[460Rustang]

Is all of the above accurate, where can verify that # 8 will handle the 50 amps @ 125 ft?

Since the garage is attached, the ground rods and main breaker are not needed. Also, u dont even need a subpanel and can have multiple feeds but a subpanel is still nice to have.

As far as the #8 goes, u can lookup 'NEC 2011 310.16(b)(16)' for ampacity values then u have to calc the voltage drop. #8 at that distance and full load will give u approx a 9.8v drop which is 4% and the NEC recomends 3%. I would bump it up to #6!

Does the above mean that # 8, with a 9.8 v drop, available amps will be 50 - 9.8 = 40?

 

[460Rustang]

Not knowing what the HP rating is of your compressor kinda makes this all a mute point.

[/b]

4.5 hp

I should ask... is it a 4.5HP label on the Tank or is 4.5HP printed on the motor data plate?

You're probably right, it's a Kobalt, not a Quincy, you got me thinking now,..I'll haveta check.

 

[460Rustang]

As far as the #8 goes, u can lookup 'NEC 2011 310.16(b)(16)' for ampacity values then u have to calc the voltage drop. #8 at that distance and full load will give u approx a 9.8v drop which is 4% and the NEC recomends 3%. I would bump it up to #6!

Does the above mean that # 8, with a 9.8 v drop, available amps will be 50 - 9.8 = 40?

What would the drop be with #6?

You guys are awesome here, knowledgeable and FAST,..THANKS!

 

[wyliesdiesels]

Does the above mean that # 8, with a 9.8 v drop, available amps will be 50 - 9.8 = 40?

No. Youre talking apples and oranges. Voltage drop means just that! If the drop would be 9.8v, that means at the end of the wire under full load of 50a, the voltage would be 240v-9.8= ~230.2v

What would the drop be with #6?

You guys are awesome here, knowledgeable and FAST,..THANKS!

The following is the formula so u can figure it out for yourself:

vd= k*2*I*L/cmils= voltage drop

k= resistance of wire; 12.9 for CU and 21.2 for AL
I= amps
L= one way length of circuit

cmils can be referenced here:

http://www.engineeringtoolbox.com/awg-wire-gauge-circular-mils-d_819.html

so #6 CU @50a would have approx ~6.14v drop

Keep in mind that #6 THHN wire is rated for 65a. If sing NM-b(romex) then youre limited to 50a!

 

[460Rustang]

Gotcha, volts vs amps,.....is there an amp loss with 125 ft ?

That formula is way over my head,...

Keep in mind that #6 THHN wire is rated for 65a. If sing NM-b(romex) then youre limited to 50a!

Why bring the above statement up, am I missing something?

 

[Charles (in GA)]

Nawlins

Accents and slang don't always come to me on the internet. Even after seeing you were in "Mardi Gras Town" it still didn't dawn on me what "Nawlins" is. Finally Googled it and Urban dictionary says....... N'awlins
The first sign that you are a tourist is if you pronounce New Orleans as N'awlins. Locals actually pronounce the city name as New Awlins. People from other cities hear N'awlins because of the way locals drag out and connect their words. Most locals actually hate hearing people say N'awlins or New Or-Leans.

Hi, I from Jaw-ja.......... jawja
Redneck slang for 'Georgia', without negative connotation like 'Bama'
You jawja boys are some of the nicest, most respectful southern fellers I's ever met.

Charles

 

[pattenp]

There is no amp drop. Amps is the current you pull through the wire. Volts is the pressure pushing the current through the wire. Think of it like water going through a pipe. The longer the pipe the water pressure is going to drop more from one end to the other. You can get the same amount of water through the pipe but it will have a slower flow rate(volume over time). So the longer the wire the more the voltage/pressure drops at the end. You can still pull through the required amps but the flow rate drops(watts over time). This is why using a larger pipe/wire helps prevent the pressure/voltage drop.

Gotcha, volts vs amps,.....is there an amp loss with 125 ft ?

That formula is way over my head,...

Keep in mind that #6 THHN wire is rated for 65a. If sing NM-b(romex) then youre limited to 50a!

Why bring the above statement up, am I missing something?

 

[wyliesdiesels]

Gotcha, volts vs amps,.....is there an amp loss with 125 ft ?

That formula is way over my head,...

Keep in mind that #6 THHN wire is rated for 65a. If sing NM-b(romex) then youre limited to 50a!

Why bring the above statement up, am I missing something?

Theres no such thing as amp loss. Its voltage loss. remember the term- 'it takes volts to push amps'....

The formula is not hard at all!

I said that statement because u were talking about a 50a feed with THHN wire. THHN has a higher ampacity than NM-b wire, aka Romex!! So #6 THHN- 65a and #6 Romex- 50a!!

 

[2ManyProjects]

New member from vintage-mustang.com,....Israel, if anyone hangs out there also.

Existing garage is wired only for 115, recently picked up a 230 compressor and a 230 Lincoln MIG,...now I need some juice.

The existing main svc panel has only the service connections inside leading to the breaker panel inside the house, 200 amp.

I wanna jump from this exterior main svc panel to a closely mounted sub panel, then 125 ft underground to the garage. There's no way to get from the interior breaker panel to the garage.

Are you ABSOLUTELY CERTAIN of that? Your later mention that this is an attached garage would imply that there MUST be some way to route that cable inside, presuming that you have at least a crawl space, if not a real basement. And as Charles pointed out, feeding multiple "main" service panels from your meter pan may turn out to be much more "involved" and expensive than you might think.

It's a story and a half Acadian with no visible, straight path.

The best path may well be anything but straight, and not immediately obvious. But I'd wager it's there, if you look closely enough. I'd start by tracing the existing circuits which feed the garage.

Both the welder and compressor pull 20 amp each.

Per later comments, it appears that you underestimated these figures. That's notable for a couple of reasons -- particularly to show that you cannot really count on what your FUTURE needs might be.

Being a one man hobbist garage, I can't envision needing to run more than 20 amps at a time,

But I can imagine it, very easily. More on that shortly.

there's plenty 115 for all other supply.

Define "plenty" in this context. How many outlets, served by how many circuits/breakers, of what capacity? And what about lighting?

Also as a related question, what are some of your tool "must haves", that might make me wanna rethink my 30 amp max requirement?

Currently building a 67 BB Rustang from the ground up, so all tools will be car hobbist related, one at a time having only two hands.

Two Words: Plasma cutter.

http://www.lincolnelectric.com/en-us/Equipment/Pages/product.aspx?product=K2807-2
http://www.lincolnelectric.com/assets/global/Products/K2807-2/e11200.pdf
http://www.lincolnelectric.com/assets/servicenavigator-public/lincoln3/im10020.pdf

If you're doing much in the way of metal fabrication, you're going to want one, sooner or later. Even a relatively modest one can not only overwhelm a 30A circuit by itself; but more importantly, it will also require a decent-size compressor to be running concurrently.

I don't want a sub panel in the garage, just two receptacles.

I would suggest that you re-think this. Installing a sub-panel now would make any future additions/expansions/upgrades MUCH easier (and cheaper). At worst, the cost is not all that much more than running a couple of independent circuits; and if you wind up needing more than "a couple" circuits (which it sounds like you very well might), it could even be LESS expensive to do the sub-panel.

The garage is attached.

So no need for separate ground rods. You WILL need four conductors, all the way back to the main service panel.

Isn't the neutral BUS isolated by removing a green screw?

Usually, yes.

I've been trying to supplement by nonexistant knowledge with a little youtube,...LOL[/B]

That could be dangerous. Any idiot can post to YouTube, and MANY idiots do.

Don't wanna run aluminum, kinda set on THWN, 167 F / 75 C, breaker will actually handle up to 50 amps, correct,...guess there's no need to limit myself to 30 amp if the same set up with a "hotter' breaker will handle 50 amps?

Personally, and given the usage you've described, I near-certainly would NOT stop at 50 Amps. You could use up that much (and more) in a heartbeat with a modest plasma cutter and a sufficiently robust compressor to feed it running concurrently.

That said...

Is all of the above accurate, where can verify that # 8 will handle the 50 amps @ 125 ft?

Follow the math:

CM = K x I x L / E

where:
	CM = Minimum required cross-sectional area of the wire, in Circular Mils
	K = Resistivity Constant -- 10.75 or 12.9 for copper, depending on the specific alloy (and who you believe); use the latter figure to be conservative
	I = Maximum Load current for the circuit
	L = Total ROUND TRIP distance of the wire run
	E = Maximum permissible Voltage Drop (generally accepted to be 3%)

CM = 12.9 x 50 x 250 / 7.2
CM = 161,250 / 7.2
CM = 22,395.83

So, to properly support 50 Amps @ 240V over a (one-way) run length of 125 feet, we need copper wires which are AT LEAST 22,395.83 CM. Referring to either:

http://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes
or
http://www.engineeringtoolbox.com/awg-wire-gauge-circular-mils-d_819.html

we find that AWG 8 provides only about 16,500 CM; hence, it is inadequate. You would need to step up to at least AWG 6, which will provide approximately 26,300 CM.

If you want to consider using Aluminum (which would probably be much less expensive), re-run those same calculations using 21.2 as your value for "K".

Does the above mean that # 8, with a 9.8 v drop, available amps will be 50 - 9.8 = 40?

No. It doesn't work that way.

What would the drop be with #6?

Well under your 3% target, so no need to worry about it beyond that.

No. Youre talking apples and oranges. Voltage drop means just that! If the drop would be 9.8v, that means at the end of the wire under full load of 50a, the voltage would be 240v-9.8= ~230.2v

Gotcha, volts vs amps,.....is there an amp loss with 125 ft ?

Again, no.

The Voltage Drop is determined (in part) BY the current flow, which is whatever it is, as determined by the load device. You can always draw still more current out of a given circuit, if the resistance of the load device is low enough. Many devices (such as motors) will draw progressively more current as the supply voltage is reduced; they will also start to heat up and run poorly in the process. (That's called "overloading the circuit", BTW; and you most definitely do NOT want to do that!) Hence the importance of ensuring that the load device is ALWAYS supplied with adequate voltage.

That formula is way over my head,...

With all due respect, if that is really the case, you probably ought not attempt ANY of this stuff yourself. The formula in question, no matter how presented ("wyliesdiesels" and I used slightly different forms of the same basic equation, as we were solving for different variables) is relatively simple algebra -- barely (if any) above simple elementary-school arithmetic.

Keep in mind that #6 THHN wire is rated for 65a. If sing NM-b(romex) then youre limited to 50a!

Why bring the above statement up, am I missing something?

He's talking about the temperature-limited ratings for different types of wiring. Per code, the "ampacity" of Type NM-B (a.k.a. "Romex") must be derated using a lower ambient temperature target than some other types of wiring.

 

[460Rustang]

You, my new friend are awesome, lemme look all of these comments over and get back with you,...in a word, THANKS!

This forum is truely awesome!

Are you ABSOLUTELY CERTAIN of that? Your later mention that this is an attached garage would imply that there MUST be some way to route that cable inside, presuming that you have at least a crawl space, if not a real basement. And as Charles pointed out, feeding multiple "main" service panels from your meter pan may turn out to be much more "involved" and expensive than you might think.



The best path may well be anything but straight, and not immediately obvious. But I'd wager it's there, if you look closely enough. I'd start by tracing the existing circuits which feed the garage.



Per later comments, it appears that you underestimated these figures. That's notable for a couple of reasons -- particularly to show that you cannot really count on what your FUTURE needs might be.



But I can imagine it, very easily. More on that shortly.



Define "plenty" in this context. How many outlets, served by how many circuits/breakers, of what capacity? And what about lighting?



Two Words: Plasma cutter.

http://www.lincolnelectric.com/en-us/Equipment/Pages/product.aspx?product=K2807-2
http://www.lincolnelectric.com/assets/global/Products/K2807-2/e11200.pdf
http://www.lincolnelectric.com/assets/servicenavigator-public/lincoln3/im10020.pdf

If you're doing much in the way of metal fabrication, you're going to want one, sooner or later. Even a relatively modest one can not only overwhelm a 30A circuit by itself; but more importantly, it will also require a decent-size compressor to be running concurrently.



I would suggest that you re-think this. Installing a sub-panel now would make any future additions/expansions/upgrades MUCH easier (and cheaper). At worst, the cost is not all that much more than running a couple of independent circuits; and if you wind up needing more than "a couple" circuits (which it sounds like you very well might), it could even be LESS expensive to do the sub-panel.



So no need for separate ground rods. You WILL need four conductors, all the way back to the main service panel.



Usually, yes.



That could be dangerous. Any idiot can post to YouTube, and MANY idiots do.



Personally, and given the usage you've described, I near-certainly would NOT stop at 50 Amps. You could use up that much (and more) in a heartbeat with a modest plasma cutter and a sufficiently robust compressor to feed it running concurrently.

That said...



Follow the math:

CM = K x I x L / E

where:
	CM = Minimum required cross-sectional area of the wire, in Circular Mils
	K = Resistivity Constant -- 10.75 or 12.9 for copper, depending on the specific alloy (and who you believe); use the latter figure to be conservative
	I = Maximum Load current for the circuit
	L = Total ROUND TRIP distance of the wire run
	E = Maximum permissible Voltage Drop (generally accepted to be 3%)

CM = 12.9 x 50 x 250 / 7.2
CM = 161,250 / 7.2
CM = 22,395.83

So, to properly support 50 Amps @ 240V over a (one-way) run length of 125 feet, we need copper wires which are AT LEAST 22,395.83 CM. Referring to either:

http://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes
or
http://www.engineeringtoolbox.com/awg-wire-gauge-circular-mils-d_819.html

we find that AWG 8 provides only about 16,500 CM; hence, it is inadequate. You would need to step up to at least AWG 6, which will provide approximately 26,300 CM.

If you want to consider using Aluminum (which would probably be much less expensive), re-run those same calculations using 21.2 as your value for "K".



No. It doesn't work that way.



Well under your 3% target, so no need to worry about it beyond that.




Again, no.

The Voltage Drop is determined (in part) BY the current flow, which is whatever it is, as determined by the load device. You can always draw still more current out of a given circuit, if the resistance of the load device is low enough. Many devices (such as motors) will draw progressively more current as the supply voltage is reduced; they will also start to heat up and run poorly in the process. (That's called "overloading the circuit", BTW; and you most definitely do NOT want to do that!) Hence the importance of ensuring that the load device is ALWAYS supplied with adequate voltage.



With all due respect, if that is really the case, you probably ought not attempt ANY of this stuff yourself. The formula in question, no matter how presented ("wyliesdiesels" and I used slightly different forms of the same basic equation, as we were solving for different variables) is relatively simple algebra -- barely (if any) above simple elementary-school arithmetic.



He's talking about the temperature-limited ratings for different types of wiring. Per code, the "ampacity" of Type NM-B (a.k.a. "Romex") must be derated using a lower ambient temperature target than some other types of wiring.

 

[460Rustang]

Edit: I should ask... is it a 4.5HP label on the Tank or is 4.5HP printed on the motor data plate?

Probably not a true 4.5 hp. The amp draw of a 4.5 hp motor would be somewhere around 25 amps. Most likely this is a 2.5 to 3 hp motor with the typical bogus air compressor hp rating on it.

Tank HP is stickered 4.5, while the tag,....not suprisingly is rated, "SPL". I hadda do a little research to find out what that means. Literature states this 4.5 to be, "Running HP"; whats that mean?

Amp pull on this "SPL" compressor is actually 22, what HP do you think that really is?

The Lincoln 180 welder is literature listed as pulling 17.5 - 18.5 amps.

 

[460Rustang]

2manyprojects,...many good points brought up,..thanks to you and everyone else.


OK, so hear me out, due to the many great points brought up,...I've rethought my thinking.

Sub panel mounted within one ft of main panel
125 ft of #6 THWN run through 1" conduit
tied into a interior garage sub panel, no copper grounding rod since it's an attached garage
dedicated lines to outlets as needed


Do I need #6 THWN ground wire, or can I go smaller?

#6 THWN @ 167 F / 75 C is good for 65 amps, so we'll have 65 amp when needed, but for now 30 amp breakers for the welder @ 20 and the compressor @ 22, correct?

What do I do about the 20 amp welder, the existing plug looks like a 50, why?

What about the 22 amp compressor, what amp plug do I attach here, 30?


For the record, as suggested, I'll NOT be doing any tie-in to the main panel, just the grunt work, then have someone come by, look it all over and hook up the first sub panel to the main breaker.

 

[Charles (in GA)]

Ground wire can be #10 when used with #10/#8/#6 sized wire.

Charles

 

[460Rustang]

Ground wire can be #10 when used with #10/#8/#6 sized wire.

Charles

Thanks for the input, hows everything else sound?

Dusty was a handsome looking feline, I'm a huge cat fan,.....

 

[2ManyProjects]

2manyprojects,...many good points brought up,..thanks to you and everyone else.


OK, so hear me out, due to the many great points brought up,...I've rethought my thinking.

Sub panel mounted within one ft of main panel
125 ft of #6 THWN run through 1" conduit
tied into a interior garage sub panel, no copper grounding rod since it's an attached garage
dedicated lines to outlets as needed

I'm not sure I'm following you here. Are you suggesting installing TWO sub-panels? If so, why? Unless I'm grossly misunderstanding things, there's no need for a sub-panel adjacent to the main panel. You only need an adjacent pair of breaker slots in the main panel in which to install a dual-pole breaker of adequate capacity to support your garage-mounted sub-panel. And even if you don't currently have sufficient "spare" slots for this, you can near-certainly free up at least one or two by disconnecting the individual branch circuits which currently run to the garage, as they will be fed off the sub-panel once it is installed. If things are really tight, you might have to "rearrange" things a bit inside the main panel to get your two open breaker slots next to each other; but I can't imagine this would be impossible.

As for the type & size of the wiring between the main panel and the sub-panel... I would be inclined to go with a single multi-conductor cable (such as Type SER, perhaps), rather than fuss with individual pulls through conduit (let alone getting the conduit into place first, which I can envision being a real bear).

In addition, as previously discussed, AWG 6 will not support more than about 55-60 amps at that distance, before voltage drop becomes an issue; and even that presumes copper conductors (aluminum would have to be considerably fatter). If you're going to go to the trouble of making this upgrade, you really should upgrade enough to carry you as far into the reasonably foreseeable future as possible. For example, either AWG 4 Copper or AWG 2 Aluminum will support at least 90A, which will give you a LOT more "wiggle room" for future tool additions/upgrades. Notably, the former is about six times as expensive as the latter:

4361SERCX500 4/3 SER Copper 500' -- $10.76 per FT
https://www.platt.com/platt-electri...ultiple/4361SERCX500/product.aspx?zpid=230217

23SERGX1000 SER Service Entrance Cable, 3/2, Aluminum, 1000' -- $1.76 per FT
https://www.platt.com/platt-electri.../Multiple/23SERGX1000/product.aspx?zpid=62444

Do I need #6 THWN ground wire, or can I go smaller?

#6 THWN @ 167 F / 75 C is good for 65 amps,

In terms of raw ampacity, yes. But that isn't the only consideration.

so we'll have 65 amp when needed, but for now 30 amp breakers for the welder @ 20 and the compressor @ 22, correct?

It seems to me that you may be conflating the sub-panel feeder with the individual branch circuits which will subsequently be fed from that sub-panel. They are two completely separate and distinct things. Once you have a properly fed sub-panel installed in the garage, you can then do whatever you need in the way of additional branch circuits, ALL of which would originate in that sub-panel. So, if you think 30A is adequate for your welder and/or your compressor, then you would presumably install individual 30A branch circuits from the sub-panel for these devices. Assuming these runs are short enough that voltage drop is not an issue, AWG 10 would be adequate for 30 Amps.

What do I do about the 20 amp welder, the existing plug looks like a 50, why?

Welders are something of a special case. Because of their typically low "duty cycle", you can "get away with" lighter wiring than would otherwise be needed based on the raw amperage draw. Whether or not this is a good idea is another matter, which will in part depend on the specific individual application. Others here with more direct experience with welders can probably give you more specific guidance. As for the plug supplied by the welder manufacturer, my take is that's at least partially a matter of what they think their customers will want.

What about the 22 amp compressor, what amp plug do I attach here, 30?

Unless that compressor is on wheels, I'd hard-wire it, with a disconnect within reach of the compressor, probably using a short length of Type BX armored cable between the disconnect box and the compresor itself. If you MUST use a plug/receptacle combination, NEMA 6-30 types would be adequate for 30A.

For the record, as suggested, I'll NOT be doing any tie-in to the main panel, just the grunt work, then have someone come by, look it all over and hook up the first sub panel to the main breaker.

All well and good. But I think your "plan" still needs some refinement.

 

[wyliesdiesels]

.....He's talking about the temperature-limited ratings for different types of wiring. Per code, the "ampacity" of Type NM-B (a.k.a. "Romex") must be derated using a lower ambient temperature target than some other types of wiring.

Slightly off. The temperatures(60* c, 75* c, 90* c) listed in T310.15(b)(16) are not ambient temperature ratings. They are the temperature ratings of the insulation of the wire AND the temperature ratings of the termination points such as breaker lugs!! However, the ampacities in this chart are BASED on an ambient temperature of 86* f (30* C). Ambient temperatures are factored at different temperature levels and need to be considered when sizing breakers. Refer to T310.15(b)(2)(a) for the different ambient temperature ranges and the percentage to use for factoring the corrected ampacity. NM-b HAS to be rated at 60* C because of the paper in the cable.

And I guess thats one way u could look at NM-b wire ratings(being derated) since the conductors are actually 90* C rated.

.....Unless that compressor is on wheels, I'd hard-wire it, with a disconnect within reach of the compressor, probably using a short length of Type BX armored cable between the disconnect box and the compresor itself. If you MUST use a plug/receptacle combination, NEMA 6-30 types would be adequate for 30A......

Since his compressor is rated @ 22a, this would mean his compressor is over 3hp. Standard NEMA plugs, such as the 6-30R(rated 2HP) u suggested, are not rated for more than 3hp (http://frentzandsons.com/Hardware References/plugandreceptacleconfiguratio.htm),

so the compressor would HAVE to be hardwired! Unless the OP doesnt mind spending big $$$ for a pin and sleeve high horsepower rated receptacle and plug:

http://www.entherm.com/Meltric 2009-db.pdf

 

[460Rustang]

It took the better part of the afternoon, up and down the stairs many times, a few small sheetrock drill holes for location references and one big 1" drill hole where I came out close, but not dead on. Long story short, I was able to stay within the house for the wiring, at least for getting a line from the panel up to where the breezeway routes towards the garage. This was the scariest part that had me worried, the final leg shouldn't be a problem.

Thanks for the reassuring words that there is usually always a way to fish wires through studs, had to think really outta the box here, but was able to get her done.

THANKS!


OK, so now were looking at about 75 ft of 6 / 3 Romex, no conduit, thanks again, from the main panel to a sub panel. There was a point referenced that more than a 3 hp motor had to be hard wired, so we'll hard wire the compressor and stay with the plug for the welder.

Hard wiring the comp will require a disconnect at the panel vs a plug, correct?

Looks like NM is rated @ 55 amps, 60 C / 140 F, correct?

 

[jsherid1]

On Aluminum wire keep in mind that your loads may be heavy and will be periodic vs. continuous so there will be thermal expansion and contraction that is greater than with Copper even with the modern alloys. That means you may have to check and adjust your terminations on both ends on a regular basis and you should also use fixtures (like your outlets) that are designed for Aluminum. Please note that I'm not an electrician or electrical engineer but we have been working with a large company who builds a lot of large facilities and have investigated this in detail with their engineers--the conclusion was to use Aluminum for feeder lines only as they see continuous loads. That said, a lot of large projects use all Aluminum wire these days (Southwire has a gallery of projects on their web page). Bottom line, I'd probably use Copper for this application myself for peace of mind.

Whatever path you choose spend some time on manufacturer websites as they are often a wealth of information on applications, installation and maintenance.