Figuring Out Woodshop Power Requirements

Amps, volts, watts, horsepower, and all that jazz: here's an instructive thread on how to figure out if a building's power supply will support your plans for shop equipment. July 9, 2007

I'm looking to move to a 4000 sqft shop with a better layout and office. However, it has 200amp 3ph service. I'm getting a CNC router that takes 63amps and likewise for the vacuum hold-down. Will I have enough power? Naturally, the salesman tells me no problem.

Forum Responses
(CNC Forum)
From contributor R:
You have enough power to run the router and a 7.5hp DC and not much else.

From contributor B:
It depends upon how many machines will be running at once. If' you operate a one man shop, you'll probably be fine. If you have one guy running the CNC under full load all day long while someone else is running other 5hp to 10hp machinery, you're going to see a lot of dimming lights.

I have a 200a service into my 3 man operation. Our CNC typically cuts 1" hardwoods at about 150 ipm with a 10hp spindle. As such, we never press the limits of the spindle and rarely draw 10hp worth of current. However, if the CNC is running and we start up the wide belt, we definitely get some incandescent light dimming taking place.

From the original questioner:
Thanks. We too are a three man shop. Are you also using a vacuum hold-down? We'll be processing panels the majority of the time. I don't anticipate running all day and probably on separate schedule from other operations. We really like the location and layout of this space. However, sounds like we may want to keep looking for a space with more power. It would be a bad thing to find out my new equipment trips out in the middle of production because someone turned on a light. By the way, we purchased a MultiCam with a 7.5HP spindle and a 20HP vacuum.

From contributor D:
You do not have enough power, unless the CNC is all that will be on. Vacuum pumps run at full load all of the time. Salesmen know absolutely nothing about the power requirements of the machines they sell, let alone the rest of the shop.

From contributor A:
I would check for the conductor size to the 200amp panel. We had 400amps and would blow it when we started wide belt with the CNC, dust collection, planer, and vacuum pump already running. The conductor from the transformer was big enough to go to an 800amp service. We bought a used panel and meter base from a salvage yard for about $600.00 and had it installed by a local electrician for $800.00. The price of new meter and panel was over $3000, so do some research for electrical salvage in your area.

From contributor J:
What is the voltage of this 200 amps? 440 Volts, 200 Amps = 220 Volts, 400 Amps... 208 Volts, 200 Amps = 220 Volts, 180 Amps...

You could try to negotiate more power into your lease/purchase offer. If you add more power to the building, bring in 440 to 480 volt power. Motors like this better than 208/220 volts, plus the cost of the wire, breakers and disconnects are lower.

From contributor N:
If you are planning on any growth ever, I would get more power - at least 400 amps at 440. You'd be better off to have it and not use it than to not have it and need it. We are now over a year waiting to get our power increased. Have two machines in the warehouse that haven't been installed for lack of power.

From contributor Z:
There is a very simple formula that I use to determine how many amps are required to run a shop. The formula is based on full load amps which does not really mean that you will ever draw the full load, but it is a good guideline. Another thing to consider are your local electrical codes which often require that the breakers in your panel be sized at 125% of the full load amp rating on any particular connection. The formula is as follows.

Take the total HP and multiply by .745 and then multiply by 1000 and then divide by your line voltage. This will give you the total number of amps required.

Here is an example. Your total combined HP for your shop equipment is 65 and your shop voltage is 220.

65 x .745=48.525(Total Kw)
48.525 x 1000=48,425(total watts)
48,425/220v=220.11 Amps(watts/volt=Amps)

You should also calculate your lighting and other loads which most likely will be represented in watts. You can simply add this total to the total above before you divide by the volts. Remember the simple rule that Watts/Volts=Amps.

And by the way, I am a machinery salesman that knows nothing about voltage requirements for machines or the rest of the shop. LOL.

From contributor J:
I forgot to mention that I too am a machinery salesman that knows nothing about power in the shop...

From the original questioner:
Thanks. This is great information that truly benefits me and I hope others. Can you tell me the difference between breakers and disconnects? Additionally, would you know why my little 7.5 HP MultiCam spindle would require 60 amps? I'm confirming this with MultiCam, but really appreciate information for you. Using the total HP formula, I am nowhere near the 65 amp example. My biggest machine is that 20 HP regenerative vacuum. The rest of my equipment is small machinery. So there is a chance I could still be okay with this location.

From contributor J:
The differences are:
* Breaker - acts like a fuse, opens the circuit when it detects amperage in excess of its rating. Also is a switch that can be used to depower the circuit.
* Disconnect - Manually operated switch used to disconnect power to machinery.

The breaker can act like a switch/disconnect, but it should not be used as a disconnect for safety reasons. Use disconnects at each machine so you can safely perform maintenance and/or quickly disconnect power in case of emergency. One breaker can support several disconnects.

One other thing to consider is a manual transfer switch for non-coincidental loads. These are inexpensive switches that prevent certain machines from operating when others are operating and can sometimes help you when you are limited on power.

Regarding the total load of the MultiCAM, there are more power users on a CNC router than just the spindle. The drive motors (2 for X, 1 for Y and 1 for Z), tool changers, drill block, inverters, etc., all consume power. 60 amps at 220 volts is quite reasonable for a small CNC.

Remember that when planning electrical requirements, most codes require that you size the electrical system as if everything was operating at the same time (this includes shop and office lights, coffee pots, etc.).

I'd recommend that you create a list of all of your machines and their electrical (and air and dust collection) requirements and have a qualified electrician evaluate it, within the applicable code. Codes vary from city to city.

From the original questioner:
My first order of business Monday morning is to do just that. If some are interested I'll post my findings. It might make a good case study.

From contributor T:
I am not sure if this will compare to your situation, but here is what our situation is. We have a 2400 sqft shop with a 208v 200amp panel. We have a 15hp dust collector, Biesse 5x12 flat table router (12hp spindle) with 2 Busch 10hp oil flood vacuum pumps, 37x75 Timesaver, Holz-Her edgebander, 10hp rotary screw compressor, spray booth with 1,000,000 btu air makeup unit, 5hp 3ph 10" table saw, etc.

I was convinced that we would need to bring in 400 amps to even run the Biesse and the dust at the same time. The cost to do that was quite high. Our electrician convinced us to try running the equipment with the current panel before we upgraded to 400amps. Well to my surprise, we can run every piece of equipment simultaneously. We have turned on the dust while the CNC was in motion and the vac pumps were on with no problems. The dust pulls quite a bit of power when it is first turned on (the wires rattle in the conduit for the first second or two), so it surprised me that we have had no problems.

The main difference between your shop and our shop is size. We really don't have any room for expansion right now, so probably would never need any more power than we have now. With 4000 sqft, you are probably going to need more power later.

From the original questioner:
Wow, I'm surprised you can fit all of that in there. That is very encouraging. I will be meeting with a contractor to dive into the details of this suite today. I want to determine the cost to upgrade the power and also rewire to our liking.

Your shop pretty much mimics our plans for the next 6 months. We have all the standard equipment and obviously have the CNC underway and will have booth shortly. Waiting on the edgebander for the big show in Vegas to test drive them all. But I digress.

My power usage on my CNC is 20 amps less than expected. Based on very rough estimates from the contractor taking consideration of the HVAC, lighting, coffee maker, blah, blah, blah... We are looking at around 180A on a 208/220 3 ph.

If the price is right to increase the power, we might try as is and be ready to have them increase the power if needed.

From contributor P:
We have a 200 amp 230v single phase service with a 20hp phase converter that runs: 10hp compressor, 7.5hp dust collector, 11hp vacuum pump, CNC router with 5.5hp spindle, 7.5hp table saw, 9hp router, 5hp router, 15hp wide belt, Olimpic K208E edgebander (whatever that draws), and miscellaneous (feeder, another shaper, line drill, etc.). We used to run all this on a 100 amp breaker to the 3 phase panel, just upgraded to 200 amp because when the wide belt, dust collector and edgebander were all running and the compressor kicked in, it would trip the 100 amp breaker. We just installed the CNC router and have had no problem running it, the vacuum pump, blower, compressor and table saw at the same time. The 9hp router is 440v so I wired in a transformer in reverse. A technician from the transformer company told me that there was no way it could work. Reality often pays no attention to theory.

From the original questioner:
Just got back from meeting with the contractor onsite. Turns out we have 200 AMP at 480 Volts. We should be fine with our power usage based on a 600 sqft office, 1 AC unit, 2 swamp coolers. Our usage on the router and vac is around 120 amps at 220 volts. I'm going to check if we can run most of our equipment on 480. Thanks to everyone for making this thread so worthwhile.

From contributor J:
That's great news! Most routers have an auto-transformer so they can be wired on site for most voltages. You will most likely have to specify the voltage for the vacuum pump.
If you need 120 amps at 220V, you will draw only 60 amps at 480 volts.