Need Wiring Advice - Garage sub panel

Hey everyone!

Well, I finally bought a house. A cool old house with tons of character, but also tons of strange wiring "upgrades" throughout the years.

The house has a 2-car detached garage that I need to get up to speed. The garage currently has a sub-panel that is fed from the main panel. It only has two 15 amp breakers in it so far (one for the door openers and one for the line of receptacles around the walls). The panel itself appears to be plenty to handle the additions I would like to make. But then... I'm FAAAAR from being an expert on household wiring.





One of the mysteries is rather or not the cable running to the sub-panel is substantial enough. It is labled as follows:

E-90490 (UL) 3 CDRS AWG 6 COMPACT AL TYRIPLE ALLOY TYPE SE CABLE STYLE U TYPE XHHW CDRS 600V

I'm guessing that stands for Service Entry cable, is 6 AWG, and is aluminum 3 conductor (2 jacketed and 1 exposed). Is that correct?



So the plan is to add a few recepticles for 220 VAC items. I've always run my welders (Millermatic DVI or Synchrowave 200) and small lathe off of one recepacle (obviously not at the same time), Bridgeport mill is 220 3-phase so it will require phase converter, and then lastly I need to fit an air compressor in the mix (220 single phase).

The questions:

1) Should I wire the compressor directly or use a receptacle? My thought is to wire it directly, since I have no plans of actually moving it once it's set up. Rating will be around 22 AMPS at 240V, single phase.

2) What would be the best way to approach calculating my load for the phase converter for the mill? Can't get to the mill to check load ratings and haven't selected a phase converter yet, but a general approach to the math would be appreciated.

3) I still need to do a load analysis for each of the items and total them up, but since I can't get to a couple of them yet, maybe someone could tell me, just ball park if they think that 6 AWG SEU cable is going to be enough for the power requirements for the garage (assuming mill phase converter and compressor running at the same time).

4) Any concerns about the panel itself or anything else I should be thinking about?

I have to restate, I know very little about household electric, but it seems simple enough and I'm trying to learn more (which is why I'm asking). So bear with me and my lack of knowledge.

Any help would be appreciated!

Thanks guys!
S

1) what size is the "garage breaker" in your main panel?

There are some benefits to a "one man shop" as a homeowner. You only need enough ampacity in your output wires for one of your tools to be running at a time (assuming your concurrent compressor to be on its own circuit.) And your welder is intermittent so you could, if you wanted, run thinner wire.

I'll let an expert chime in with "code issues" regarding hardwiring your compressor or not. Could be a wierd quirk one way or the other.

Also I believe there's a "six breakers and you're off" rule regarding no main disconnect. I see twelve slots, many of which will be populated with double breakers by your plans.

I don't have a copy of the NEC. But if you were in Canada that cable is good for 55amps, which should be enough for your set up.

The main disconnect is in the basement panel, so in Canada at least you have no problem filling that panel.

In stead of a phase converter for your mill, look into a VFD, it'll use less power, and give you a real 3 phase wave, so easier on your equipment.

I'd wire the compressor right to a wall mounted disconnect, and that disconnect to a breaker in your panel.

The value of the garage breaker in the main panel is a great question, and unfortunately I don't know what it is (yet) because the ***** that marked the main panel with a sharpie and it has faded on most breaker locations. So I don't know which breaker it is... YET! Obviously that's easy enough to figure out if I take off the front of the main panel and look for the outgoing 6AWG cable. Either way, I'm sure it will have to get replaced accordingly anyway. Or maybe not! So I can't answer that yet.

What SHOULD the breaker be in the main panel for this sub-panel?

After adding the needed breakers I doubt I will add anything else to the panel. And YES! I was planning on running seperate receptacles for the Mill, welders/lathe, and would be running one for the air compressor if needed. Either way, I was figuring 3 seperate circuits. I COULD run 4, I suppose, and put the welders and lathe on their own.

VFD's are really cool, but also big money. One day it will be considered, but for now I just need to do get it up and running.

Just stumbled on this which appears to be from the 1999 NEC book. Based on this, it seems I'm good to 50 amps for a XHHW SE U type (or USE as it says in the chart). Is that enough?? If the compressor started up while I was welding would it pop the main for the sub-panel?

Is the alternative to pull a 4 gage or larger and change the breaker accordingly?

scootermcrad said:

The value of the garage breaker in the main panel is a great question, and unfortunately I don't know what it is (yet) because the ***** that marked the main panel with a sharpie and it has faded on most breaker locations. So I don't know which breaker it is... YET! Obviously that's easy enough to figure out if I take off the front of the main panel and look for the outgoing 6AWG cable. Either way, I'm sure it will have to get replaced accordingly anyway. Or maybe not! So I can't answer that yet.

What SHOULD the breaker be in the main panel for this sub-panel?

After adding the needed breakers I doubt I will add anything else to the panel. And YES! I was planning on running seperate receptacles for the Mill, welders/lathe, and would be running one for the air compressor if needed. Either way, I was figuring 3 seperate circuits. I COULD run 4, I suppose, and put the welders and lathe on their own.

VFD's are really cool, but also big money. One day it will be considered, but for now I just need to do get it up and running.

Click to expand...

The cost of a VFD over a phase converter is hardly 20%.
And it is way easier on your equipment.

The cost to add a plug for everything is pretty low, but depends what you think the inconvenience of changing the cords is worth.

Rather then pull the cover off, just turn a breaker or two off, much safer if you do not know what you are doing.

120/240 kills more electricians a year then all other voltages combined. (I would assume residents only ever see 120/240 so would only really be killed by it)

scootermcrad said:

Just stumbled on this which appears to be from the 1999 NEC book. Based on this, it seems I'm good to 50 amps for a XHHW SE U type (or USE as it says in the chart). Is that enough?? If the compressor started up while I was welding would it pop the main for the sub-panel?

Is the alternative to pull a 4 gage or larger and change the breaker accordingly?

http://www.mainelycontrols.com/pics/NEC_table_310-16.png

Click to expand...

Found my coppy of the 2008 NEC, it says 51 amps. Why does the NEC use such odd numbers for allowable ampacity?
I am unsure as to what size breaker that allows you to use in the US.
I would look for a 50 or 60A breaker though.

If the compressor started while you were welding it could very well pop the sub panel breaker. But it could pop a 100a breaker too depending on the brand of panel, your welder, and the inrush of your compressor.

If you are pulling new wire you might as well go #3 copper and go 100amp.

jeff000 said:

The cost of a VFD over a phase converter is hardly 20%.
And it is way easier on your equipment.

Found my coppy of the 2008 NEC, it says 51 amps. Why does the NEC use such odd numbers for allowable ampacity?
I am unsure as to what size breaker that allows you to use in the US.
I would look for a 50 or 60A breaker though.

If the compressor started while you were welding it could very well pop the sub panel breaker. But it could pop a 100a breaker too depending on the brand of panel, your welder, and the inrush of your compressor.

If you are pulling new wire you might as well go #3 copper and go 100amp.

Click to expand...

I was thinking that a VFD was going to run me around $500-$600. Is that wrong? I can put together a phase converter for around $120 that would do the job.

I was afraid you would say that about popping breakers. I really need to be able to weld or machine parts while the compressor is running (or more to the point, starting up). Hmmmph... Pulling a new wire would probably be a heck of an undertaking (and probably big bucks for how long it will have to be). But if that's what I have to do then that's what I have to do. And I agree, larger is better.

scootermcrad said:

I was thinking that a VFD was going to run me around $500-$600. Is that wrong? I can put together a phase converter for around $120 that would do the job.

I was afraid you would say that about popping breakers. I really need to be able to weld or machine parts while the compressor is running (or more to the point, starting up). Hmmmph... Pulling a new wire would probably be a heck of an undertaking (and probably big bucks for how long it will have to be). But if that's what I have to do then that's what I have to do. And I agree, larger is better.

Click to expand...

I don't know how large your mill is. But I was under the impression that a phase converter would be 500, and the VFD would be around 600. But if you are constructing a phase converter then that number is skewed. At even 500 more for the VFD it would seem worth it to me.

It is sometimes easier to run the new cable outside the house and around, rather then follow the existing.

Whether or not it will trip depends on the loads, all of which I am guessing at.

Thanks for the input! Appreciated!

Out of curiosity, about what will 100' of 3 AWG copper 3-conductor (of whatever type and brand appropriate for the application) cost? Didn't really see anything price-wise on the big box store's websites. Is aluminum core cheaper or even suggested for use?

Whatever ends up having to happen, I would like to do most or all of the work myself to save some money. It's something I want to learn anyway, since this won't be my first home electrical project.

This is way out in left field but what if you got a cheapie 120 volt air compressor and plumbed it in to top off your "big one' via a slightly higher shutoff PSI? Then you could count on the "little guy" to come on first and its noise when welding would serve as a caution.

When I'm welding, I'm not doing much else-- can't think of something that would use air.

Breakers have a time delay of a few seconds to accomodate motor inrushes. Since the compressor is only half the load that makes it even better.

Interesting... That is definitely left field. Haha! I usually stand in left field, actually. I think in this case, though, i don't have the extra room in this garage for another compressor and I would rather spend the money on just wiring it up correctly. But, interesting input!

Back up for a Friday...

scootermcrad said:

Interesting... That is definitely left field. Haha! I usually stand in left field, actually. I think in this case, though, i don't have the extra room in this garage for another compressor and I would rather spend the money on just wiring it up correctly. But, interesting input!

Back up for a Friday...

Click to expand...

Or wire the welder and compressor from a transfer switch, so only what you have the switch turned to will work.

100' of 3 conductor #3 copper will be around $900 I think.
Don't go to HD for it though, go to an electrical wholesaler and put it as a cash sale under the largest electrical company in town that you can think of, as they get the best price generally. And should be 20-30% cheaper then HD.
Although a roll of 14/2 is cheapest at lowes (around here anyways).

I really need to have the ability to run the compressor while other things are going. Good example why is if I ever finally get around to getting a plasma cutter, they both need to run at the same time. That's just one reason, though.

Looked over the welder manuals this morning. They ask for a 30 AMP time delay or a 35 AMP standard breaker. So, if I had essentially a 30 AMP breaker for the compressor and a 35 AMP breaker for the welders, that would probably represent the largest amperage pull at one time. That does put me over the 6 AWG mark that is currently installed. But if I pulled a new copper 4 AWG, 3-conductor cable I shold be okay, I think. 70 AMP breaker in the main panel for the garage? Thougts?

What about a ground? Would I be better off dropping an earth ground from the sub-panel in the garage to a new stake?

Next year I'm planning on pouring a slab for the new shop. Ultimately, the equipment in this garage will all move over to the new shop and won't need much more of a load. Maybe I'm better off just dealing with not running the compressor at the same time as the welder or mill and just deal with the basics. Then pull a monster cable over to the new shop with more than enough power. Probably doesn't make sense to pull the same cable to two shops if I'm only going to use one of them with all that load, later.

scootermcrad said:

I really need to have the ability to run the compressor while other things are going. Good example why is if I ever finally get around to getting a plasma cutter, they both need to run at the same time. That's just one reason, though.

Looked over the welder manuals this morning. They ask for a 30 AMP time delay or a 35 AMP standard breaker. So, if I had essentially a 30 AMP breaker for the compressor and a 35 AMP breaker for the welders, that would probably represent the largest amperage pull at one time. That does put me over the 6 AWG mark that is currently installed. But if I pulled a new copper 4 AWG, 3-conductor cable I shold be okay, I think. 70 AMP breaker in the main panel for the garage? Thougts?

What about a ground? Would I be better off dropping an earth ground from the sub-panel in the garage to a new stake?

Next year I'm planning on pouring a slab for the new shop. Ultimately, the equipment in this garage will all move over to the new shop and won't need much more of a load. Maybe I'm better off just dealing with not running the compressor at the same time as the welder or mill and just deal with the basics. Then pull a monster cable over to the new shop with more than enough power. Probably doesn't make sense to pull the same cable to two shops if I'm only going to use one of them with all that load, later.

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If it says it only needs a 30A for the welder and a 30A for the compressor, you should be find as long as you are not loading it up with a huge lighting load, odds are the welder will only draw 15 amps, and the compressor, thats a big compressor for at home, damn.
What brand is the panel in the house? Probably a Siemens too, they are not bad for holding an extra few amps for a short time.

How many HP motor does the compressor have? Probably a 7.5 or so?

I'd say you'll be find now that I know more. Although a plasma cutter can draw a lot depending on what you get. But worry about that when you get it I think, especially if you plan to move shop, given a little time having to pick upgrade the garage or do the last push for the shop it might give you a little more reason to push.

jeff000 said:

If it says it only needs a 30A for the welder and a 30A for the compressor, you should be find as long as you are not loading it up with a huge lighting load, odds are the welder will only draw 15 amps, and the compressor, thats a big compressor for at home, damn.
What brand is the panel in the house? Probably a Siemens too, they are not bad for holding an extra few amps for a short time.

How many HP motor does the compressor have? Probably a 7.5 or so?

I'd say you'll be find now that I know more. Although a plasma cutter can draw a lot depending on what you get. But worry about that when you get it I think, especially if you plan to move shop, given a little time having to pick upgrade the garage or do the last push for the shop it might give you a little more reason to push.

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Just took a look at the manual for the compressor. "23 Amps "full load" at 230V. Single phase." Recommended breaker is actually a 40 AMP!! Geesh...

Lights are simply a couple of fluorescents.

I would pull 100 AMP service if you are re-doing it. When you start adding more lights and plugs and such, it's better to do once and done... You can keep that same panel, just re-pull the wire and replace the breaker in your main panel.

What is the HP on your air compressor? Is it a "real" 5HP? Then yeah a 40 AMP would be correct.

Plug vs hard-wire is just personal preference. If you hard wire it you will obviously need a properly sized disconnect at the device location. Me personally, it depends on how many things are going in a particular area... It looks kind of cluttered if you try to cram a bunch of disconnect boxes in a corner, while it looks okay if you have a couple plugs of different styles. Also if you have multiple devices that uses the same power (i.e. a 220v 20AMP is common) then it's easier to just unplug and plug in each device. If they are hard-wired you would need a dedicated run for each.

My air compressor is connected via a plug (30A). I don't have anything else that uses that plug style, but it's nice because I can unplug my compressor and move it away from the corner to clean & service it. If I had it hardwired it would take a little more effort but not impossible.

A bridgeport knee mill will typically have a 1.5 or 2HP motor MAX. But those are 3-phase motors. I don't know the loss or dynamics of using a phase converter, I wouldn't assume anything larger than 30 AMPs would be necessary for it.

After all this thinking, I think this is what I'm going do (or not do)...

Since I know I'm going to be building a new shop that I will be pulling some heavy wire for, and my current garage will simply become a place to park cars (MAYBE put a lift in), I think I will try to make do with what I have and just limit my parallel usage.

I like the idea of not hard wiring the compressor in so I can move it to clean. I'm going to read up on phase converters, and I'm going to guess it's probably correct that it won't exceed 30 or 35 AMPS. So I might be able to get away with one receptacle for my lathe, mill/ph-converter, welders, and then one receptacle for the compressor. So two seperate circuits; 30 amp and 40 amp. And then I'll just have to turn off the compressor when welding and what not.

Pulling a bunch of new heavy cable (probably 150' worth = $$) for the garage that won't always be used for this purpose would probably be silly.

New shop/garage will get 100+ amp service, and appropriately sized cabling. I'll have to do a careful load anaylsis on the main panel at that point, as well as have the main box and service feed inspected. But then that's a whole nother topic for later...

I do not know where the real shop is going to be and if it makes any sense anyway but you could also feed your sub panel in the new shop from the sub panel in the existing garage if properly sized.

scootermcrad said:

Just took a look at the manual for the compressor. "23 Amps "full load" at 230V. Single phase." Recommended breaker is actually a 40 AMP!! Geesh...

Lights are simply a couple of fluorescents.

Click to expand...

That's a big compressor.
You may still get away with it. But maybe put an on/off switch in line with the plug you will be using for the compressor, so you can click it off easy when welding.

acer66 said:

I do not know where the real shop is going to be and if it makes any sense anyway but you could also feed your sub panel in the new shop from the sub panel in the existing garage if properly sized.

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This is a good idea, if the garage is on the way to the new shop, or not far off line.

jeff000 said:

That's a big compressor.
You may still get away with it. But maybe put an on/off switch in line with the plug you will be using for the compressor, so you can click it off easy when welding.

Click to expand...

Yeah, sort of big, pump and motor wise, but still only a 60 gallon. Would rather have the 80 gallon, but that one has a 7.5 hp motor and is REALLY pulling some juice. I don't want to buy a compressor twice. I really just want to carry this one over to the new shop when it's ready.

Suggestions on a switch I can wire in that would handle these sort of loads?

acer66 said:

I do not know where the real shop is going to be and if it makes any sense anyway but you could also feed your sub panel in the new shop from the sub panel in the existing garage if properly sized.

Click to expand...

Hmmmm.... That is a very interesting thought, actually. It's not directly in-line to the shop, but it might be an option. I'll have to sit down and do some planning before I can decide rather or not it makes sense to do that. My first thought is that it would probably be about the same distance from main panel to the new shop as it would be to the current sub-panel, but about half that distance from the sub-panel to the new shop. But it might not be. Plus, I'm not sure I LOVE the way the cable was run through the house. It was pulled through the crawl space, up through the first floor into the secondfloor, then through the roof that covers our breezeway, and down into the garage wall. Not bad, per say, just not ideal. Was probably just a quick easy solution, vs. the ideal more labor intensive way of doing it.

scootermcrad said:

Suggestions on a switch I can wire in that would handle these sort of loads?

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Yeah, it's called a disconnect box... lol...

If your compressor has a magnetic starter, you can wire a small switch up in-line with the coil. That's what I did on one so it had an on/off on the side of the starter box.

EOC_Jason said:

Yeah, it's called a disconnect box... lol...

If your compressor has a magnetic starter, you can wire a small switch up in-line with the coil. That's what I did on one so it had an on/off on the side of the starter box.

Click to expand...

Haha! Figures! Perfect. Sounds like the way to go! Thanks!

Here's a non-fuseable disconnect/safety switch. Any reason this wouldn't work? Good to 60 amps.