Check Dave's Blogs on cheap multimeter's... He has a lot to say re: safety of some of the cheap Chinese units- food for thought. I have five m-m's, only one of which I trust with high power. I have previously checked line-voltage (in Aus. it's 240V, with less current potential, but same power overall) with cheap m-m's with no ill effects. BUT be ABSOLUTELY CERTAIN you have the m-m set correctly- i.e AC Volts in the right range setting, depending on the m-m. Different m-m's have different range maximums. The safest way is to start at the highest setting (750 volt?)- or whatever your m-m has, then work down to increase resolution, stopping before you go too far! Also, you should ensure the red lead goes to the active terminal for maximum safety. BOTTOM LINE... DON'T do it until an electrician has shown you how to do it and keep safe, AND checked your m-m! Frayed lead's, poor quality leads (my oldest m-m leads have smooth handles with no way to stop your fingers sliding down onto the probe tips), or a dodgy m-m are just a few of the potential hazards. View ep's. 6.1&2, 10.1&2, 66, 91 and esp. 94-and some tutorials, not mentioned here, but, again GET PROFESSIONAL ADVICE FIRST!