Circuit amperage

I’ve been preparing my shop for the Shapeoko Pro, and hopefully my final parts arrive this week so I can get up and running. I assumed this section of my shop where the machine will run was mostly on 15 amp breakers, but noticed that this particular rear section is on a 20amp breaker. Is this acceptable or should I be swapping that 20 amp out for a 15 amp?

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I’m not an electrician - but there is no difference between a 15A and a 20 A circuit as far as the electricity goes. The difference tells you that the wires in the wall fo a 20A circuit are thicker and can handle a greater load than a 15A and that the breaker in the box (that protects against the load overloading the wires, making them hot and potentially starting a fire) will allow 20A to flow before it breaks the circuit.

Devices draw the amperage that they draw…it isn’t impacted by the rating on the line. It’s not like there is more electricity coming to a 20a box than a 15a box. It’s more about what the line can safely tolerate.

So you should be perfectly fine plugging a device rated to run on a 15A circuit into a 20A circuit. It also means you can handle more amperage on that line for things other than the shapekoko (like your dust collection, laser, etc.)


As @GJM notes it will be fine — if you have the choice, say there are two circuits, one 15 amp, the other 20, then it’s best to put the machine and computer on the 15, and the spindle/vacuum on the 20, since the latter should have the heavier draw.

In my shop, the shapeoko, laser, light, router, mini vac with carbon filter (used only with the laser), laser warning light (an LED) all sit on the same 20A circuit. My larger “shop vac” (Oneida Dust Cobra) sits on a different circuit, that is also 20A - but it would run just fine on a 15A circuit as well.

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I’m working on a subpanel setup so this is likely a temporary situation anyway…most of the wire in the shop is 14/3 so better rated for the 15 amp for sure. Thanks for the input!

@KingTut Just as an FYI: If you look at a receptacle built for a 20A circuit (in America), you’ll see that it’s just like a 15A receptacle, except that it has an extra tab hole for the plug, perpendicular to the left tab. Devices that will ONLY run on a 20A circuit (because they draw more than 15 amps) will have a plug that has that tab. This way, you cannot plug a 20A rated device into a 15A circuit. But going the other way around is allowed…you’ll see that 20A receptacles have provision to receive a 15A plug (the two straight lines) making it OK to plug a device rated under 15A to be plugged into a 20A circuit.


If you run a 20A circuit, you will need to use 12 gauge wire (or thicker). The dangerous part is running 14 gauge wire into a 20A breaker - because the breaker will not trip until 20A are exceeded - and the thickness of the wire can only safely handle 15A.

This is against code in the US…so don’t do it.


If you have a 20 Amp 120 Volt Duplex recepticle

The one on the left, then you are fine to run your Shapeoko. The 20A 120V circuit will safely run anything with a 15 Amp Plug. And as stated above it should be on 12 gauge wire. 15A 120VAC are wired with 14 gauge. It is important that you power off that outlet, and verify it is off, and pull the plug out and verify you have 12 gauge wire. If it is 14 gauge wire then you need to replace the receptacle with a 15 Amp duplex.

The reason this is important is for safety. 15 Amp circuits run safely on 14 gauge wire and 20 Amp circuits run safely on 12 gauge. When you have a 20 amp outlet but only 14 gauge wire attached to it is the heat generated by 20 amps max load could melt your insulation and start a fire from exposed wires.

Depending on when your home was built but the electrical code require that garages and shops use GFCI and any areas that can be wet. You can either have the whole circuit protected with a GFCI breaker or the first outlet in a branch circuit have a GFCI outlet and would protect that circuit and all outlets down stream. GFCI (Ground Fault Circuit Interrupter) protects you in the event of any shorting of neutral or hot which could result in a shock. To identify how many outlets are on a branch circuit plug up a light, fan or other appliance that you can visually tell it is on. Then shut down your breaker and see if the small appliances go off. You can have 8-13 outlets on a single branch circuit so assume there will be multiple outlets on a single branch circuit.

So make sure your 20 amp circuit is got the proper wire and how many other outlets are on that branch circuit. Make sure it is protected by GFCI of the appropriate amperage 15 or 20.

Wire thickness 12 and 14 Gauge

12 Gauge Wire 0.1040 in 2.052 mm
14 Gauge Wire 0.0800 in 1.626 mm

If you do not feel comfortable with this checking then get an electrician to do it.


Just one correction on this…
If you find that your 20A circuit has 14 gauge wire, CHANGE THE BREAKER TO A 15A. The receptacle really doesn’t matter. The only reason to change the receptacle at that point, is to dissuade someone from thinking that a device that requires a 20A circuit can be supported on the line - and if they did plug it in it would pop the circuit breaker (which is now 15A). So the receptacle is really just to help you avoid popping the circuit breakers (and relying on them).

People get confused about this all the time…the breaker is a safety measure that trips when the draw in amperage on the line exceeds the rating of the breaker. It doesn’t modify the power going through the lines - the same amount of power goes to your devices regardless of the amperage of the breaker (at a given voltage). Your device is the thing that determines the amperage draw. Your device is going to draw a certain number of Amps regardless of the circuit it’s on. The wire on the run acts like a resistor, and will heat up as electricity goes through it. The thicker the wire, the less it will heat…so thin wires heat faster. The wires are rated as to how hot they can get before insulation start to disintegrate (and they get hot enough to start a fire).

So…the whole 15A vs. 20A breaker thing is to protect the wires. The weakest link in the line is going to be the lowest amperage rating of wire (or receptacle, if you’re chaining through the receptacles) on the run. You HAVE to choose the breaker based on the lowest amp rating on the line - or you run the risk that the line will take a higher load than the wire can handle, the breaker will not trip (because it is a higher rating than the weak link), and the weak link can heat and potentially, over time, burn.

But there is no hazzard in plugging a 20A device into a 15A circuit - it will just trip the circuit breaker


Good point Gary. I assumed that if the wire were 14 gauge the breaker would be 15 Amp. If a real electrician originally installed the circuit it would be a 15 AMP breaker, 14 Gauge Wire and a 15 AMP outlet. Many times home owners have a 20 AMP plug and simply change the outlet. Most appliances that have a 20 AMP plug dont really pull the full 20 AMPs and you may be able to get away using a 20 AMP plug on a 15 AMP circuit.

The point of our advise is to inspect the outlet and fix if necessary. Hopefully it is a 12 gauge wire and 20 amp breaker. Just make sure it is.


I measured the total draw of my setup using an generic $35 killawatt (similar to this). Shapeoko XL with Carbide 3D router, dust collection, laptop, small air compressor, led lights, fans, and a UPS, all going to the same socket. With everything running I see a rather consistent 11 volt amps, with a peak right at 13.


… and, what is that telling you?

I have swapped out the 20amp breaker for a 15…easiest solution! 14 ga wire and a 15 amp outlet…now the breaker matches. I appreciate everyone’s input!

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I have almost the same one inline to my shapeoko. But presently, the only things plugged into it are a 27" samsung monitor, shapeoko power supply and an HP computer. Draw is 478mA consistently. Does not matter if the machine is working or idle.

no point, just sharing

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I assumed that was telling me not to worry about tripping a 15amp breaker.

Can’t your router draw more than 7 Amps when cutting?

I have a project planned for this weekend, I will monitor the amps and report back. However what I remember from the last time I did this is that the routers usage was small as compared to the vacuum.

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That’s consistent with the way most/all seem to use their Shapeokos (even those with “2200 Watt - 3 HP” spindles).