Electrical Service - How Much is Enough?

[Glen Blanchard]

It looks as if my wife and I will be moving into a new house, which would allow me to expand my workshop from its current one-car garage size to an over-sized 2 car garage, and I will be hiring an electrical contractor to bring electrical service to the garage. (We are trying to finalize the purchase of a short sale house that has taken FOREVER, but that's another story!) If we are successful, and it now appears that we will be, I will need to decide if I should get 200 amp service or if a 100 amp will suffice.

Following is a list of the larger stationary tools I either already have or plan on having some day. Of course, not listed, are all the smaller hand held tools and accessories most of us have in our shops. I am not yet aware of the amp requirement for the ductless HVAC I will have installed or that for the overhead lighting.

Any opinions on the size of service I might require for a one man hobby shop? The total here is 158 amps not including the HVAC, the overhead lighting, the air filter, or the portable hand tools.

Thanks.

18" Bandsaw 10a 220v
20" Planer 30a 220v
12" Jointer 18a 220v
Osc Edge Sander 18a 110v
Oneida Cyclone 14.5a 220v
TableSaw 13a 220v
Drill Press 9a 110v
Performax Drum Sander 9a 110v
16" Bandsaw 11.5a 110v
Air Filter ?
Air Compressor 15a 110v
Mitsubishi Split HVAC ?
Lighting ?
Festool Dust Extractor 10a 110v

[Chris Damm]

It depends on how many machines you will be running at a time. My shop has 60 amp service and it the 14 years I have been working in it I have never had a problem. I have 9 8' 2 bulb lights, radio, 3 HP dust collector, 2 HP tablesaw, and a 1500 watt heater running maximum at any one time.

[Eduard Nemirovsky]

I agreed with Chris. Just recently I moved in a new shop and I have 80Amps subpanel. For an one man shop this is more then enough. My maximum load when I run air filtration system, DC 2hp, split AC, lights and one of the big tool are much less then my panel has.

Ed.

[Scott T Smith]

100A should more than cover your needs. The mini-split ac consumes less than 15A (and as I recall less than 10).

Typically in a home shop your "minimum" size would be based upon having your lighting, HVAC, compressor, dust collector, and largest equipment motor running simultaneous, plus a little bit extra.

Personally I like having some good growing room, and would prefer the 100A over a 60 or 80A service.

[Robert Parrish]

It's better to add surplus power now than try to add it later! I have 150 amps now in a 1000 sq ft shop and I'm going to add another 300 next month. I'm glad I put in the 150 when I did as I won't have to worry about adding electric to the new area.

[Aaron Wingert]

The total here is 158 amps not including the HVAC, the overhead lighting, the air filter, or the portable hand tools.


No need to look at it this way Glen. Total amperage of the tools in your shop is generally irrelevant due to the fact that you'll never draw anywhere even close to 158 amps in your shop. Residential electrical systems are designed and installed based on realistic loads that will be drawn, not total capacity of the system itself.

For example, I can legally put 42 circuits in a 200 amp panel. If each of those circuits has 20 amp breakers, that's a total of 840 amps! In a residential application there's just no way each of those circuits will be utilized at its maximum ampacity at the same time, therefore it isn't an issue.

You've got a lot of 220v equipment, which draws less amperage since the load is shared between two phase conductors. That's good from a "total ampacity" standpoint. But it also requires two slots in the panel (A and B phase) for each receptacle you install, and that is the major consideration. Unless you only want to install one or two receptacles, you're going to need a heck of a lot of slots in that panel for all those 220v receptacles. My advice would be to have your electrician set a 100 amp subpanel in your garage, get one big enough that it has plenty of room for breakers, fed off your main panel. You really probably don't need 100 amps in my opinion, but it sure isn't going to hurt.

200 amps would be ridiculous gross overkill.

[Rod Sheridan]

As others have stated, add up your lighting, HVAC, air compressor, cyclone and largest machine, then add a little more.

I have a 35 ampere feeder for my shop,

Cyclone 8.5A

Saw/shaper 16A

Since my shop is in the basement, lighting is fed from the main panel, compressor is in the garage so it's fed from the main panel.

The tendancy is to go overboard on shop power, if you're like me you'll only run one machine plus the cyclone at a time.

Plan for one machine that's larger than what you have, plan for the HVAC, compressor, cyclone, lighting, and add a little.

Don't go crazy................Regards, Rod.

[Dave Beauchesne]

Gentlemen:

I have to chime in here.

As an HVAC guy ( I understand electricity for the most part ) and the worst thing you can do is under power a shop.

While you can say '' I will only be running XXXX , YYYY and maybe ZZZZ at the same time, and they only consume a total of 23 amps, a 50 amp service should suffice, right? Remember, this is a new installation that is subject to being inspected, and must be in compliance with all local codes etc., not a cobbled together shop.

It is a total of the loads to some degree; however, another ( MAIN ) consideration is space in the panel! A 200 amp panel is usually relatively inexpensive to install ( the electrical contractor has to be in the loop as well as the distance to the main ) . You have at least 20 spaces spoken for in your initial assessment, and the electrical Inspector will add up the TOTAL load as well as spaces in the panel required when assessing the situation. The arguement of, '' I will only be using 23 amps at one time '' does not wash.

As for the HVAC unit - it really depends on the tonnage required - it WILL be a 220v circuit, and it may easily be a 20 or 30 amp breaker required.

My opinion would be to price both 100 and 200 amps, see what the difference is, and decide from there. Remeber, to upgrade later will be a whole lot more hurt than shelling out a couple hundred bucks now.

Remember as well - allow a method to add wiring later - i.e.; don't finish around the panel with drywall all nice and neat. Have a removeable panel so you can get into the panel later, better yet, pull a few extra PVC drops into the panels so wire can be fished in later if need be.

JMHO

Dave Beauchesne

[Ray Bell]

"200 amps would be ridiculous gross overkill".

While this may be true, why not? I just recently went through this. My detached shop/garage was fed from the house through a 30 A sub panel. I was continuously tripping breakers, and whether it was or was not a safety problem, it just always bothered me that the house and garage were connected this way. The connecting wires were under ground, and under about 20' of concrete patio ran through ridiculously small conduit. Too small to pull larger wires through. So for peace of mind I decided the garage had to be on it's own service. The city ran new wires, and installed a meter on the garage and a licensed electrician installed a 200A breaker panel, and did some extensive inside wiring for me. I now have plenty of dedicated 220V circuits and a "ridiculously grossly overkill" worth of extra breaker room in the new panel, but so what. If I do ever need them they are there. Also the 200A service just wasn't that much more expensive than the 100.

[Tom Godley]

If you add up the maximum load you will be using at any give time I think you will be surprised at how little it is.

But, you get into a cost factor with labor being the major cost and in my case the ridicules permitting costs. A 60 amp panel will likely be more power than you will ever need but the relative cost of bumping up to a 100 amp panel is small because it is a very common size. It also allows you many more spaces than the smaller amp panels to provide individual breakers for various machines - if that is the way you want to go. My electrician thought I was crazy to want the 100amp panel - I felt the extra spaces were worth the cost.

In my case I did not have to run the line all that far and by purchasing copper I was able to get in place with out any problem. Getting an aluminum feeder for a 200amp panel would have been impossible and overkill. And downrating the 100amp panel to 60amp service was a very small savings.

My last work area had a 40amp panel -- and I never had any problem other than I had no extra spaces.

[John Grabowski]

I would like to chime in on a few things....I dont know if you can run a wire from your main to a sub at 200 amps?? I think you have to run a separate meter which means separate bill with sep taxes and fees every month.

I have a 100 amp panel in a 1200 sq foot shop with 14 foot ceilings with LOTS of receptacles. LOTS of 220's and LOTS of lights. DC, 8in Jointer, 15 in 3 hp planer, 18 inch Bandsaw, did I mention LOTS of lights. I work alone for the most part but I did have my friends come over and work in the shop all together and I was able to run planer, DC, table saw, sander and all lights at the same time with no problem. Thats at 100 amp sub panel.

BEst of luck...It is fun having ample power and receptacles where its needed...Much better than extension cords stretched everywhere.

John G

[Foras Noir]

If it is permittable by your situation, get 400 A. You can easily do either a metered main or a simple sub panel and split all the non-shop motor loads (HVAC and don't forget dehumidification - helps keep that EMC where you want it).

All that assumes you can't get 3 phase 120/208 V or any form of 480 V. If you can, you can safely drop the mains to 200 A.

On my present shops I changed service 4 times. Total cost in excess of $20K. My fault. Stupid thoughts about saving some money. With a 400 A 3 phase 120/208 V Wye, I am in good shape for motors as large as 15 HP (planar and wide belt). Even then, it took some engineering to do the load balancing (that cost $500).

What I am trying to say is get the biggest main you can and set it up as a metered main to keep your build costs lower.

This site is great: http://www.allaboutcircuits.com/

You can download the individual chapters. The one you need is: http://www.allaboutcircuits.com/pdf/AC.pdf


Have fun.

[Don Jarvie]

Easiest way is to ask the electrician when he comes over to see what he thinks. Since he will know the local codes, etc he'll be able to help you.

My 2 cents is use a full panel instead of a sub-panel. More slots for breakers, etc.

[Jim O'Dell]

The biggest thing I've seen in this is how many circuits/breakers are you going to use? I went to a 200 amp service to get the number of slots I needed. I would be fine with 100 amps, but I couldn't find a box with enough slots. I wanted a separate circuit for each of 8 220 runs, and 5 110 runs. And the 220 circuits take 2 slots each if you use full size breakers. I might have been able to get a 100 amp main breaker for this box, but since I had the power, (separate service from the pole) I went ahead and got the 200. I have a few slots available if I need to add anything. Unfortunately, no floor space to put it!! :rolleyes: Jim.

[Foras Noir]

I don't respond to posts on posts. But, I can't let this one go.

If you ask a residential electrician what to do, make sure they know they will not get paid if you need to upgrade your service when the in-rush current from your HVAC trips your mains anytime your shop is in use. Seriously, non-shop motor loads will totally wipe out all your shop calculations.

The problem with shops is not FLA (fully loaded amp draw) which is what people on this board talk about day in and day out. It does not matter in shop builds. The problem is in-rush current from low speed (say 1,700 to 3,500 RPM), high torque shop motors. I junked a 7.5 HP 3 phase 208 V air compressor because it pulled 150 A in-rush for 7 seconds every time it kicked. We changed the motor out to a single phase 208 V 5 HP motor frame equivalent and it drew 173 A for 9 seconds. That is not at all uncommon in home shop tools. Anything, I mean anything at all, which is single phase and over 2 HP will have insane in-rush. Please read the reference material I posted.

Electricians without actual industrial motor control experience will not know how to even measure in-rush. Make them show you their test gear. Make them do a 48 hour logging run. If their approach is to read the motor plate (which is how residential electricians are trained), you will be back on this board asking how to upgrade the service.

Residential electricians are not qualified for this job. They know nothing about low speed, high torque motors on shop tools. Your power company (if they work like the three I know well) will do the logging and help project your in-rush. They can size the service based on vastly greater experience. They also get no "bonus" income by coming back to upgrade your service.

One last time, get the largest service you can. Make sure it is a metered main with at least two feeder breakers (one for shop loads, one for the rest). Everything else will get safer and less expensive.

Your local "time and materials" electrician is the last guy I would ask about this problem. This entire line of argument is valid for all residential contractors. They know nothing about shop infrastructure. I speak from experience.

Ok - I will go back to my Grey Goose and FOX news channel. I think Beck is on.

[Ray Bell]

Foras,

I agree with every thing you say including the Grey Goose, but I cannot go with you to Fox News, and Glen Beck. After all the NFL drafts are going on, and Seattle really needs a quarterback....oops Colt McCoy just went to Cleveland. One pick ahead of Seattle....

[Scott Dallesasse]

[QUOTE=Foras Noir;1406953]I don't respond to posts on posts. But, I can't let this one go.

If you ask a residential electrician what to do, make sure they know they will not get paid if you need to upgrade your service when the in-rush current from your HVAC trips your mains anytime your shop is in use. Seriously, non-shop motor loads will totally wipe out all your shop calculations.

The problem with shops is not FLA (fully loaded amp draw) which is what people on this board talk about day in and day out. It does not matter in shop builds. The problem is in-rush current from low speed (say 1,700 to 3,500 RPM), high torque shop motors. I junked a 7.5 HP 3 phase 208 V air compressor because it pulled 150 A in-rush for 7 seconds every time it kicked. We changed the motor out to a single phase 208 V 5 HP motor frame equivalent and it drew 173 A for 9 seconds. That is not at all uncommon in home shop tools. Anything, I mean anything at all, which is single phase and over 2 HP will have insane in-rush. Please read the reference material I posted.

I'd like to know how you get a 3 phase service for a residential occupancy. Most utilities will not provide this to a residence, even for multi-family properties.

If you want to make sure the service is sized properly, ask to see their load calculations. There are specific places in the code that requires this for the proper OCPD (fuses or breakers) to be sized. This is what is really going to cause the service to need to be increased or not. Just getting the largest one can be just as costly as having to upgrade in the future. Accuracy is a MUST when properly sizing a service, and should not be taken lightly.

[Tom Veatch]

...
You've got a lot of 220v equipment, ... That's good from a "total ampacity" standpoint. But it also requires two slots in the panel (A and B phase) for each receptacle you install, and that is the major consideration. Unless you only want to install one or two receptacles, you're going to need a heck of a lot of slots in that panel for all those 220v receptacles. ...

Difference in local codes?

My shop has several 240v branch circuits, each of which has multiple 240v receptacles and only one breaker for each circuit, certainly not one breaker for "each receptacle". Even has some 4-wire dual voltage circuits with dual voltage NEMA 5/6 - 20 receptacles. All permitted and approved by the electrical inspectors.

Do local codes up in KC prohibit 240v branch circuits with more than one receptacle?

[John Davidson]

I don't respond to posts on posts. But, I can't let this one go.

If you ask a residential electrician what to do, make sure they know they will not get paid if you need to upgrade your service when the in-rush current from your HVAC trips your mains anytime your shop is in use. Seriously, non-shop motor loads will totally wipe out all your shop calculations.

I have worked in industry for 20 plus years as a Electronics/Electrical technician. It would be crazy for any one to apply the same standard to the home/hobby shop. Industrial equipment can and will have all loads on and at full load and in many cases overloaded during some conditions. This will never happen in a home shop unless it is really be used as a bussness and with several employees were the equipment can be all running at once.

The problem with shops is not FLA (fully loaded amp draw) which is what people on this board talk about day in and day out. It does not matter in shop builds. The problem is in-rush current from low speed (say 1,700 to 3,500 RPM), high torque shop motors. I junked a 7.5 HP 3 phase 208 V air compressor because it pulled 150 A in-rush for 7 seconds every time it kicked. We changed the motor out to a single phase 208 V 5 HP motor frame equivalent and it drew 173 A for 9 seconds. That is not at all uncommon in home shop tools. Anything, I mean anything at all, which is single phase and over 2 HP will have insane in-rush. Please read the reference material I posted.Small AC induction motors pull around 7 time FLA at start up. However, this inrush should be over in a secound or two. If your compressor was pulling this inrush for 9 plus secound you sould look at the machnical load and make sure you motor is not under sized or that there is not a problem with the compressor itself. You also refer to 1700 to 3500 rpm motors as being slow speed motors. I would challenge you to find a AC industrial motor that runs faster than 3560rpms when connected directly to the line. To run a motor faster than 3560 requires a drive system of some type. Also Breaker are made to handle inrush current on these small AC induction motors. Breakers are designed to trip uquickly under a short circuit or ground fault but are much slower under an overload condition.

Electricians without actual industrial motor control experience will not know how to even measure in-rush. Make them show you their test gear. Make them do a 48 hour logging run. If their approach is to read the motor plate (which is how residential electricians are trained), you will be back on this board asking how to upgrade the service.

Residential electricians are not qualified for this job. They know nothing about low speed, high torque motors on shop tools. Your power company (if they work like the three I know well) will do the logging and help project your in-rush. They can size the service based on vastly greater experience. They also get no "bonus" income by coming back to upgrade your service.Remember the average house is full of AC induction motors, the frig, the freezer, air handlers, AC compressor units. Do you really think thay don't know what thier doing?

One last time, get the largest service you can. Make sure it is a metered main with at least two feeder breakers (one for shop loads, one for the rest). Everything else will get safer and less expensive.

Your local "time and materials" electrician is the last guy I would ask about this problem. This entire line of argument is valid for all residential contractors. They know nothing about shop infrastructure. I speak from experience. I have about the same equipment in my shop but I have a 2 tom HP with 10kw heat strips for back up. I have a 100 amp service fed from its own meter base. I did the calculations myself as well as the installtion and I have never tripped a breaker. People just don't realize that 100amps is a lot of power for one person to be pulling from the line in a home shop.
Ok - I will go back to my Grey Goose and FOX news channel. I think Beck is on.


Foras Noir
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[Tom Godley]

I guess I read the original post incorrectly -- I thought you were running a sub-panel from the house.

If you are running new service with a new meter just for the shop - I bet you will find the the cost difference between the 100amp and the 200amp service is very small -- making the 200 the way to go.

[Glen Blanchard]

I guess I read the original post incorrectly -- I thought you were running a sub-panel from the house.

If you are running new service with a new meeter just for the shop - I bet you will find the the cost difference between the 100amp and the 200amp service is very small -- making the 200 the way to go.

Actually Tom, we don't know yet. It appears as if we will move into this house in mid-May. It is a pre-owned home, so the current homeowner occupies the house now. As a result, we have not been able to get an electrical contractor to go to the house and determine if the house's service will support a 100 amp sub-panel to the garage. Hope to find out soon.

[Kevin Rector]

This probably doesn't in any way answer your question, but I am in the process of building a shop. I have 200 amp service at my house and I will be running 2 gauge wire out to the house where I'll be installing a full 100 amp subpanel.

In my estimation, for almost any residential hobby shop 100 amps should be substantially more than plenty of juice.

[Curt Harms]

I would look at the maximum number of machines running at one time + lights + any HVAC type loading. I may have 4 240 volt 15 amp machines but I can only use one at a time, plus dust collection. If there are 2 or more people working at the same time, that changes the calculation. It's certainly cheaper to go big enough the first time than having to redo it later, but no need to go nuts.

[Joel Earl]

I run 2 220a tools at a time - like the 2hp DC with the big saw. Lights, music, flip on other 110a's sometimes too. I feed the shop with a 30a sub - thats it. No flicker ever either. If I am running the heat, lights, music, and such in the winter and then kick on the saw and DC at the same instant I have seen a nano second flicker in lighting. But I have on 20 - 8' flourescents too, so at start-up all that stuff must be right there on the edge. Solution is simple - fire up one or other, then the second tool 5 seconds later.

Never happens unless all the heats on - not even with the AC running so I suspect the hog is the heating.

I would maybe have gone to 50a looking back as I might add some extra Boys Toys in future. If I don't I don't - not a big deal when I know manner in how to flip on things.

I didn't say that I have in the main house only 100A service either. 3200sf and 100a and never had a problem. They say balanced load is HUGE. I think that is the real answer