I have a circuit in one room in my house that I use for a home office. The only things plugged in are my laptop, monitor, desk lamp, and a laser printer. When the laser printer is in use, my desk lamp gets dimmer and flickers (led bulbs). Does this sound like a bad circuit breaker? Wondering what things I should check first. I my plans for this room are to eventually add a small window ac unit and a desktop computer. Before I increase the load on the circuit I’d like to get this figured out.

***Update. I measured voltage to be 124v with the printer on standby and while printing the voltage goes down to 120v. Is that too much drop? It’s a smaller desktop laser printer. Not like a giant office printer. It seems like I shouldn’t be seeing my lamp flickering.

 

How old is your house? Do you think you have knob and tube or aluminum wiring? I doubt you have a bad circuit breaker but you might have a weak connection somewhere on the circuit.

 

It's common for laser printers to cause that problem. It's the heater cranking up to melt the toner into the paper. You could check outlet connections to make sure you don't have back stabbed connections.

 

A 4-volt voltage drop is nothing. Typically 120 volts +/- 10% is acceptable. I bet when everybody is home with the A/C running and running the electric over you will also find the voltage has dropped.

 

Hello, thanks for sharing your concern. From the looks of it, it seems that your printer may be drawing overcurrent which means using more current than it should or even simply it may just require a lot of current to operate. Most common residential circuit breakers for indoor living space such as bedrooms, bathrooms, living rooms, etc. are rated at 15-20 amps which is needed to power receptacles (outlets) and lighting. In your case, the circuit breaker doesn't look to be the problem as they rarely go bad and instead would cause it to trip below it's rating, cutting off power to the circuit. Calculating the amperage of each individual device connected to the circuit is the best way to determine if you are near the current rating of the breaker. Keep in mind that loads/devices draw more current during initial start up. One other possibility can be that your main electrical panel may be powering large loads all at once such as large appliances, small appliances, iron, heaters, etc. Which requires a large supply of current flow, so the lights dimming during printer operation is normal. One test you can do is find a small piece of appliance or something with a similar current rating as the air conditioner you want to purchase and plug it into your receptacle (outlet) while operating all your devices in your office. If the breaker trips, then you maxed out your circuit. If all your devices remain on and function properly then you may install the air conditioner. I hope this helps, and please ask questions if you are unsure before attempting any electrical work. Best of luck!

 

As pattenp said, this is common with laser printers. I've seen it suggested to keep laser printers on a separate circuit from computer equipment for this reason.

But why can't the circuit handle the current draw? It's not a large enough draw to trip the branch circuit breaker or the main breaker, so neither of these overcurrent protection devices is limiting current. So why should lights get dimmer?

 

Try putting maximum load on the ciruit with a high constant current devices, like heaters or hair dryers, to draw 15A or whatever is the max and see if the circuit would sustain the load for long. If light only dims but doesn't flicker, then you have high resistance wiring. If the light flickers, you have a bad connection. If this starts a fire in the wall, that narrows down the location of the bad connection.

 

Overcurrent devices don't limit current. They completely interrupt it if exceeded.
Length and size of wire as well as load is what determines voltage drop.

The lights will dim more on a #14 line as opposed to a #12 line based on current carrying capacity.