You may also have problems even if you determine you have copper wiring. Consider that you may have undersized wiring, overloaded circuits, a general state of bad or corroded connections in the devices (receptacles, etc.), or even an undersized electrical service. A good electrician will be able to determine the source of the problem. Keyword here is good.
A few things you can do:
- Stick a voltmeter in the outlet where the hairdryer is plugged in, note the voltage difference while starting and running the hairdryer. More than 5 volts drop is abnormal and you are in risk of starting a fire.
- Turn on all the lights and turn the hairdryer on an off a couple of times to see which lights dim; this will indicate how much of your wiring is on this circuit.
- If just the bathroom dims, you may have a single weak or undersized circuit (should be 20 amps at the breaker panel #12 AWG wire).
- If the whole house dims, you probably need an electrical service upgrade. You can double check this by turning on the stove, oven, dryer, all the lights, plug in the iron and hairdryer, toaster, microwave... JUST KIDDING. You DON'T want to do that prior to having an electrician inspect your wiring.
- If a large number of lights dim, but not all, this outlet may be on a overloaded or overconnected circuit. You may need to get an electrician to run some dedicated 20 amp circuits for: bathroom, laundry room, kitchen, etc. where you use high power appliances.