Adding a Sub-panel to the shop

[Spunjin]

Hey Everybody.

I just added 3 8' T5 light fixtures in my garage, an upgrade from a single CFL. Next I have to add a sub-panel for the additional outlets I need to add to run my equipment.

I am planning in running just 50A to the sub-panel with a couple 20A circuits and a couple 15A tandem circuits in the box.

Should I run more power to the sub-panel or is 50A fine? I don't have any 220 equipment at the moment and I just run a 2HP dust collector while running the TS, Planer, or Router. So the absolute max of 35A would be pulling at one time.

Thanks for the help in advance.

Regards,

-Sean

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[Vic]

I got by with a 60 amp sub panel in my first garage shop.

[Eric.]

I have a 50A sub-panel for my shop. I had enough room on it to run (3) 220 circuits, (3) 110 circuits, and another circuit or two was left over to use in the basement (where the panel resides). As was mentioned above, you'll probably never exceed a 50A panel's capacity. I run a 2hp DC, plus a 2 or 3hp TS, planer, jointer, BS, etc, plus a 220 space heater at times, plus all the lights in the shop, and I've never tripped the panel's breaker. I'm probably approaching capacity with all those things going at once, but it's enough. Still, it might be wise to take hhh's advice and just go with 60 or 100 if you're starting from scratch...because why not.

[Spunjin]

Thanks everybody. I just may go with the 100A circuit then. I would like to have some larger machines in the future so the extra capacity for more outlets would be good.

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[Joraft]

... Point is, if you think you are going to get a 220 tool or two in the future, go at least 60. Why have to re-do it in a couple of years....

Don't forget that 220v motors draw about half the amperage of 110v motors. If you're replacing 110v machines with 220v your amperage requirements will actually go down.

[mds2]

I would do 100a if it were me. I'm actually heavily considering it.

[tim0625]

Thanks everybody. I just may go with the 100A circuit then. I would like to have some larger machines in the future so the extra capacity for more outlets would be good.

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Good move....you'll always do more in the future than you envision now and as it was said, why have to redo it? I set mine up as a 100A and then got the itch for a wire welder. It's ok because I have more than enough power.

[BenMinshall]

Whenever you're sizing a panel, you should always work in watts (or kilowatts) instead of amps. This is how you can account for 120V and 240V loads in the same calculation. When figuring tools marked in HP, you can count roughly 800 watts per horsepower; it doesn't matter whether the tool is wired for 120V or 240V. When counting up loads other than tools (lighting, heaters, etc), simply add up the wattage of the bulbs or the value supplied by the manufacturer.

You only need to sum the loads which you expect to be on at the same time. In a one man shop that basically means you only need to size the panel for the largest tool plus the dust collector and lighting. Example:

2HP dust collector (1600W) + 3HP table saw (2400W) + 400W fluorescent lights = 4400W simultaneous shop load

To figure the minimum size of the panel you need: 4400W / 240V = 18.33 A

This example shop would just fit with a 20A panel. It is generally advised to bump up at least 20-25% or to the next standard size so this shop would be just fine with a 30A panel.

Unless you're using some pretty intense tools it is extremely unlikely you need a panel larger than 50A in a non-commercial shop. The price of the panel itself isn't that much greater to go to something like 100A, but the cost of wire can be pretty significant.

[Spunjin]

Thanks, Ben. I ended up going with a 50A circuit.

My next question is: can I run a 30A breaker in the sub panel with 10G wire for my 2 hp jointer? I ran all the electric myself and had the inspector check it out. Now I need the 220v service for the jointer. Am I good with what I have now?

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[SteveM]

I don't see why not, just make sure you use a 30A outlet such as the NEMA 6-30R.

[calblacksmith]

A disconnect switch at the outlet may be something to think of also, they are nice for making sure the power is off to the machine while leaving everything connected. YMMV

[BenMinshall]

A 30A circuit is far too big for a 2HP motor.  The 2HP jointer draws about 6.5 amps (1600W / 240V) which means it should have a 15A breaker on the circuit.  NEC requires that breakers for motor circuits be no larger than 200% the actual draw of the motor (in some rare cases 250%).  Because there are no 10A breakers, you go up to the next available size of 15A. This size circuit can be run with wire as small as #14.  There is no problem with using #10 other than it is unecessary expense.

 

 

can I run a 30A breaker in the sub panel with 10G wire for my 2 hp jointer?

[wdwerker]

==> NEC requires that breakers for motor circuits be no larger than 200% the actual draw of the motor (in some rare cases 250%).

 

isn't that limited to dedicated circuits?

Aren't most 220 /240 circuts dedicated? I can understand the distinction with a string of 120v outlets. Just asking ,all my knowledge is 70's & 80's vintage.

[Rugby2]

Don't forget that 220v motors draw about half the amperage of 110v motors. If you're replacing 110v machines with 220v your amperage requirements will actually go down.

[Rugby2]

Hoarfrost is correct. Changing from a 110 volt machine to a 220 volt machine will lower the amp draw by half, IF the new machine is the same HP of the original. If you are upgrading from a 1.5 HP machine to a 3HP machine, the amp draw will be roughly the same.

[Rugby2]

Aren't most 220 /240 circuts dedicated? I can understand the distinction with a string of 120v outlets. Just asking ,all my knowledge is 70's & 80's vintage.

[Rugby2]

The NEC is actually a subset of the National fire code, and is intended specify how power wiring should be designed and installed in order to prevent electrical fires. The purpose of breakers is to prevent the electrical system from overloading the wiring and other devices to prevent fires. The the wiring system is the determining factor for the breaker size. The wire size is determined by the distance of the run, and te load size. You can pick up a wiring guide at a local hardware store to help get te sizing correct.

[carlj]

I just built a 18X20 shed in my back yard and added a 100 AMP Sub-Panel to it.

 

I recommend going 100 amp as you will have lots of room to add circuts and even your 220 lines in the future.

 

The 100A panel can be had for $52 - $80 depending on the size and breakers included, at either of your local big box stores.

They come with the 100 AMP Main Breaker and 6 -15 or 20 Amp breakers in the box.

I spent 80 on mine at lowes. Its mfd'd by square D and the breakers are about $3.50 ea.

 

I fed the panel from my home 200 Amp panel, putting a 100 Amp breaker in there to power it. I hired an elictrician to run the cable from the home panel to the shed sub-panel, and I wired the shop from there.

 

I did the trenching to save on electricians labor and bought the plastic conduit, but they connected the ends to the shed and house and drove 2 grounding rods into the ground.

 

I mounted the 100A sub- panel inside the shed and they connected the end of the conduit to it and hooked in the wire to/from the house. They supplied the 80' of #2 aluminum wire, 4 cables, 2 hot, a neutral and a ground, I went with #2 aluminium as copper is way more expensive.

 

Cost wise, the electrician charged me $725, and it included 2 guys for 6 hours, the #2 wire, and all the misc rods and connections needed to go from the house to the shed, about an 80 foot run with 40' underground.

 

100 Amp service panel was $80, plus I got 16 extra breakers at 3-6 each was about 140 total.

I ran 14 circuits, each outlet on its own 20 amp circuit, plus 4- 220V outlets for my new SawStop. I have 3 - 220 V outlets on 1 circuit and 1-220 V outlet on the other. 3 outlets in the rear of the shed and one in the front so I can roll the saw around.

 

Copper wire is expensive, I have about $300 into that. All #12/3 w/ground. Plus about about another $100 for all the outlets, switches and covers.

 

So all in I have about $1,200 -$1,300 into the electrical, plus I will get a ductless mini-split for about another $1500, for lighting I bought 3- 6-bulb t8 shop lights off craigs list for $120 and put a chandellar in front of the entry door for about $60.

So. whole shed wired, lighted and HVAC's for about $3,000 all in. Plus $89 for the electrical permit. I just passed my final inspection and am powered up.

Get an electrical permit, you don't want your home insurance company denying a claim for un-permitted electrical should anything ever happen to the shop.

 

I put the pricing in to give you a realistic idea of how much you can expect to spend. I am VERY tight with a dollar, so, what I quote is very rock bottom pricing and sweat equity. I almost had a heart attack when I priced the electrical out. I originally guesstimated a few hundred bucks.

 

If you go less that 100 amps on the sub-panel, you might save $20 on the panel itself and $30 on the feeding power lines, (30 cents a foot on thinner wire, (#4 or #6). but you'll be under-powered for future growth. Then if you get biger machines, youll have to hire the electricians again and buy the wire and panel again in the bigger size.

 

So, don't skimp up front. Do as much as you can yourself, it's very easy to do.

YouTube had lots of video's on how to install a sub-panel and wire outlets, as well as buying an electrical wiring book for $20. If your not comfortable doing part of the work, hire an electrician to do that piece.

 

Best wishes!

 

Oh, to comment on your 2hp dust and another tool.

Your dust collector will draw about 20 amps when running, plus your jointer 15-20 amps when running, your lights are pull about 3-5 amps plus your radio, TV, and whatever, your at almost 50 AMPS minimum just at the start.

Add a mini fridge or fan and you'll be tripping that 50 amp main every time you go to use a big tool.

 

Also, going from 110 to 220 techiically does cut amp draw in half (per circuit), BUT not your total amperage use on the machine. 

 

On a 110 circuit you have a hot (black) and a neutral (white) (ignore the ground for now), So if you have a 20 amp dust collector that draws 20 amps, 20 amps of current will be running through that 1 hot wire (black).

 

If you have that same machine powered with 220V, the power cable has 2- hot lines (red and black) and a neutral (white). each hot line will be 110 volts at 10 amps each. So the total amperage flowing is the same, but there are more feeding wires on the 220 requiring less current in each.

 

But, to get 220V to your shop, you need to feed it with 2 - 110V branch feeder cables.

 

Here is the math.

 

110V x 20 amps = 2200 watts

220V x 10 amps = 2200 watts

 

So the total power draw is the same.

 

your power company charges you by the watt - they always getchya'..

KWH= Kilowatt hours = 1,000 watts per hour

 

20 amp machine running for 1 hour at 10 cent per KWH = $0.22 or 22 cents per hour.

20 X 110 / 1000 X .10 = $0.22

 

Hope that makes sense.

[carlj]

YES- actually 2 ground rods installed at the shed. Code called for that.

 

I'm really happy I had the electricians feed the shed, there are lots of small items I would have missed (code requirements) and working with the fat #2 cables required specialized crimping tools that I did not own. Plus - they had to crawl in my attic to snake the feeder cables to the house panel while it was about 90 outside in the shade.

 

I'm big on safety, and doing things right; up-front is the best place to start.

I actually over wired the shed, but my time didn't cost me any extra $$. And I know it's done right.

 

The building inspector complimented me on pulling the permits and the quality of the work on the whole structure.

I'll post photos on the WW shop photos section when its done. Paint and trim to go.

 I enjoyed looking at everyone's shops and getting some ideas from there before building mine.

[BenMinshall]

Oh, to comment on your 2hp dust and another tool.

Your dust collector will draw about 20 amps when running, plus your jointer 15-20 amps when running, your lights are pull about 3-5 amps plus your radio, TV, and whatever, your at almost 50 AMPS minimum just at the start.

Add a mini fridge or fan and you'll be tripping that 50 amp main every time you go to use a big tool.

That isn't exactly right -- you can't directly add up amperage from 120V loads and 240V loads. You have to convert to power (watts) to get an aggregate draw on the service or do a circuit-by-circuit analysis for the panel box. Remember the service to the building is a split phase 240V/120V at 50A so it is actually capable of powering 100A of 120V loads or 50A of 240V loads or some combination of the two.

 

Also, going from 110 to 220 techiically does cut amp draw in half (per circuit), BUT not your total amperage use on the machine.

I think you meant to say power. A motor that can be wired for either 120V or 240V will draw half the amperage at 240V. The power (watts, horsepower) will be the same at either voltage. This is one of the advantages of wiring motors for higher voltage. You get the same power, but when the amps are lower the motor will run cooler thus extending the life of bearings and lubricants.

 

On a 110 circuit you have a hot (black) and a neutral (white) (ignore the ground for now), So if you have a 20 amp dust collector that draws 20 amps, 20 amps of current will be running through that 1 hot wire (black).

In a 120V circuit, the same current flows in the hot and neutral wire. Both the white and black will carry 20A in this case.

 

If you have that same machine powered with 220V, the power cable has 2- hot lines (red and black) and a neutral (white). each hot line will be 110 volts at 10 amps each. So the total amperage flowing is the same, but there are more feeding wires on the 220 requiring less current in each.

In this case both the red and black wires each will carry 10A, and the white neutral will not be used. A 240V motor does not use the white neutral wire.

 

But, to get 220V to your shop, you need to feed it with 2 - 110V branch feeder cables.

That is one way to think of it, but to be clear the two 120V components are not independent. It is actually a 240V service which is split in two halves.

BTW, I'm not trying to pick on you Carl. It's a complicated topic and I'm attempting to clarify the concepts to avoid confusion. I'm glad your shop came out so well. I look forward to the day when I can build my own shop space rather than squeezing into the garage.

[BenMinshall]

Branches up to and including 20a (110 or 220) don't have to be dedicated --- covered under NEC 210.

Exactly right.

He would not have passed me if the DC was on a shared circuit.

It's a reasonable interpretation for him to decide the DC is a "continuous load" per NEC definition and require the separate circuit. One could do some code gymnastics to decide otherwise but I think he made the right call.

Everything 3-phase had to be dedicated.

Some local jurisdictions would consider any building with three phase service to be commercial, so you might have gotten a bit closer look from the inspector than a typical residential shop might. In fact a lot of power companies will not even install a three phase service to a property unless it is zoned commercial land.

[carlj]

If you want to get really techincal, I can copy and paste electrical theroy all day long. I forgot way more than I know now.

 

The split is not done inside the house, its done on the power company side of the equaison. You still need the 2 legs coming from the pole into the house to the main panel, then he needs to run the 2 hot legs to the sub-panel into the new shop.

3 phase has 3 hot legs, usually not seen in residential.

 

Some older homes (and Eileen) only have one hot leg   coming into the house main from the pole, and you won't get 220 in a system like that. The whole service would have to be upgraded.

 

Also, Whether the neutral is used or not depends on the machine being used. My SawStop only uses the 2 hot legs (and the ground), the neutral is not used, however my arc welders use the neutral. If he runs the wire to the outlet, he can cap the neutral at the outlet and only use whats required to power the tool. This way, the wiring is behind the wall, and should things change in the future, its just a matter of changing the plug outlet and connecting the wire. New wire won't need to be re-run.

 

Don't get too caught up with the NEC. Local municipalities all have their own codes for every trade.

The thing that matters the most is what the local inspector wants done on the job. If they want a seperate circut, they get a seperate circuit. They are the lords of their domain.

 

You can argue NEC all day long, but you won't get your inspection passed unless they are happy.

Try arguing logic with your wife and see what happens...

[tim0625]

I'm a little late coming to this party and I jump in and immediately see that Eileen has only one hot leg and I'm thinking "oh my....poor Eileen....there must have been an accident"....I'm still lost and don't really want to understand because you guys are talking way above my pay grade....I hope at Eileen is adjusting.

[carlj]

Yeah, TripleH, you hit it right on the head.

 

I used to build sub-divisions a few years back and I've been down that road before with city engineers and inspectors. Fight them, any you'll cost yourself a lot of time and money. Then have to do it their way anyhow..

 

I always get input in the planning and permitting stage from the city engineers and inspectors to get their input into the plans. this way, construction would go a bit smoother. Pre-construction meetings, etc.

I knew an "eccentric" city engineer (CE) who liked to be involved in a lot of the construction work. I always said yes- no problem. If He wanted the road to meander when we had an approved set of plans with our roads straight, I had the plans re-engineered e with a curved road. It cost a few dollars, but well worth the hassle of not complying.

As a result, he would help us out whenever he could, approving "field engineering" from just  a phone call.

 

I knew a contractor who went over the city engineers head , to the city manager to complain about about a small change the CE wanted.

The CM told the contractor that they hired the CE to make those decisions, and to go back to see him. (He backed his guy) Well, in the future, the CE would not meet with the contractor to discuss anything. And the CE always watched all stages of construction, and if he saw that contractor doing something he didn't want done, he kept silent.

Until it came time to inspect the finished work.

 

The CE made that complainng contractor rip out 7 miles of curb because he did not approve of the way it drained. Talk about not winning the battle and losing the war.. And that was just the start.

 

I'm happy to learn from others..

 

Wow, kind of way off topic, but stuff you don't really think of until you try to go up against the bureaucracy..

 

But still kind of related. Back to NEC. The National codes are the starting point for regulations and are expanded upon by the local municipalities to fit the local building climate. The regs won't be softer than the national codes, but will add stricter issues to deal with. Miami Dade County in FL is the pioneer of strict building codes, and their codes are being mirrored nationwide by a lot of aggressive municipalities.

 

If your doing some work that you will be permitting, its real simple to call your local building department to get their advice before you do any work.

But, if you arn't permitting your work, DON'T alert them to what you are doing. Use common sense.

[Eric.]

 

If you go less that 100 amps on the sub-panel, you might save $20 on the panel itself and $30 on the feeding power lines, (30 cents a foot on thinner wire, (#4 or #6). but you'll be under-powered for future growth. Then if you get biger machines, youll have to hire the electricians again and buy the wire and panel again in the bigger size.

 

 

Oh, to comment on your 2hp dust and another tool.

Your dust collector will draw about 20 amps when running, plus your jointer 15-20 amps when running, your lights are pull about 3-5 amps plus your radio, TV, and whatever, your at almost 50 AMPS minimum just at the start.

Add a mini fridge or fan and you'll be tripping that 50 amp main every time you go to use a big tool.

 

 

 

While I agree with the first part, since IMO bigger is always better, I can tell you from personal experience the second part is not correct.  I have a 50A sub-panel for my shop, and I've never tripped the breaker, running a 2HP DC along with a 3HP planer or jointer or TS, plus a 220V space heater, plus another 110V space heater, plus all the lights, radio, batteries charging, etc.  Never tripped the breaker.  That's not to say I'm not getting close...I probably am, which is why I think it's good advice to just go with the 100A sub-panel...I'm a big fan of overkill...but 50A is good enough for a one-man hobby shop.