# Circuit breaker for single outlet

I have several 3d printers. One of them keeps tripping the breaker for the room. I'm trying to debug (obviously will not use it regularly until I can determine what is wrong) but in the mean time I need to keep my other printers running.

A power strip's breaker isn't enough for it to trip, so it's drawing less than 15 amps when it spikes. It also draws 50 watts when just running normally. The breaker for the room is 20 amps, but I'm running an AC and various other appliances as well. The combination is what causes it to trip the 20 amp. It's absolutely not the AC causing it to trip. I have eliminated variables and it's one of the 3d printers for absolutely certain.

I'm guessing I need between a 3 and 5 amp resettable breaker, one that works for a single outlet only. 120V.

Where can I buy such a breaker?

Would be even nicer if I could switch between a few different preset values, ie, 3 amp, 4 amp, 5 amp, etc.

My workshop only has one circuit, just how the building is set up. (rather each room has one circuit, I only have access to the room I pay for)

• heaters are regulated slowly so when all are on, these can peak your drain Aug 30 '17 at 22:33
• You have $20\:\textrm{A}$ for the entire room. I think you said that you tested one printer to make sure that it is below $15\:\textrm{A}$. But you admit there are other printers and other devices in the room. The room breaker will trip when the total exceeds its limit. You will have to run fewer devices. You cannot "ADD" a breaker inside the room in order to add to the compliance limit of your room's breaker. That's just silly. I think you want a better service. Find another room with a higher compliance capacity for your equipment.
– jonk
Aug 30 '17 at 22:42
• I think you are misunderstanding. I am running servers and such that total 7 amps or so. All printers total are below 15 amps also, ie, the power strip doesn't trip. But when the printers hit 14 amps, that is more than 20 so the room blows. I want each printer to shut off on its own if it pulls more than 3-5 amps. The 20 amp capacity of the room is not relevant as if any printer pulls more than 3-5, it's faulty. Aug 30 '17 at 22:47

This is complicated since the downstream breaker must be faster then the upstream breakers. It needs to have different time characteristics.

This is called breaker selectivity.

Without replacing upstream breakers, you'd probably need a breaker that is so sensitive that you can't even enable the breaker. The inrush would trip it immediately.

Also, a 20A breaker won't trip immediately at 21A. This will take minutes. See the image in this post.
I think you have a larger overload.

You can buy low current panel mount circuit breakers from Digikey and other electronic suppliers. You could mount one of these breakers and an outlet in a box to produce individual low-current outlets for your printers.

I don't know about the US, but here in the UK I would go to the local hardware store where I could find a consumer unit (I believe the standard term for such an item in the US is a distribution board?) along with a 6A breaker that's designed for lighting a garage, such as this one. Wiring it up is pretty simple, and you can then enjoy protected outlets that won't cause your main circuit breaker to trip. You also get an individual RCD (ground fault breaker) for your circuit too.

If any single device, all by itself when all the other loads are off, is tripping a 20-amp breaker, then it certainly has a serious fault.

Far more likely, it is the sum of all the loads which is tripping the breaker; and no one of the devices is, alone, the culprit; no more than the last straw on top of the pounds of others is really responsible for breaking the camels' back. Devices with motors, such as an AC, are likely to draw a brief but very high load when they start up; laser printers do so too, for their heating element. This momentary draw, added to the normal draws of all the other devices, is exceeding the breaker's rating. (Breakers trip quickly with currents much above their rating, or slowly with currents slightly above their rating; either could be the case.)

Say the AC unit is drawing a steady 12 amps, which is the most it should be drawing if it's got a normal 15-amp plug, and you've got 3 3D printers each drawing 3 amps; well there's 21 amps, which will trip your breaker, not instantly, but soon. But none of the 3D printers is guilty of any excessive draw.

Since you've got a 20-amp circuit and call it AC instead of aircon, I'll guess you're in North America. The device you linked to is for the UK market and very different than anything that would be available (or legal) in the US or Canada. Likewise the small-value breakers at electronics shops are intended for installation within devices, not in line with the AC feed. I don't believe there is any mains breaker less than 15 amps in the US or Canada.

The only long-term solution (unless there is a real fault on one of the devices) is to have additional circuits installed and divide the loads among them. Very likely the AC is the prime candidate for its own circuit. But to figure out what you're dealing with, get a plug-in watt meter. A very common model is called Kill-A-Watt, but others are available too. The feature you're looking for is recording of the momentary maximum current, and a battery-backed memory so you can see the data even if the breaker trips, and I'm not 100% sure the kill-a-watt has that, so find one that does. Run it on each of the devices for a while, at least a full normal operating cycle, then plan your circuits for the worst case of all the machines drawing their maximum all at once, or plan your use of the machines to avoid any chance of exceeding 20 amps at any given moment.