Reliance Controls Ammeter and Wattmeter THP103 AmWatt Appliance Load Tester/Plug, 1-Pack, Blue

Originally bought this to determine what size of generator I would need to purchase to fully power my camper. Very precise. With high energy costs these days this can be used to determine usage from anything in your home to save you money especially during peak hours. You may be surprised how much power things can pull.

Très pratique

Bought this for solar generator and generator usage, to monitor what's being used. Like others have stated, you don't want to overload your generator. It also helps in balancing the load on your generator, so you have more control or watts being used. Less chance of blowing a circuit breaker if your load is balanced. Also, you'll be shocked at how much power appliances, fans, electric teapots, ect ect, use just being plugged in and not being used. I found this information valuable and shocking at the same time. I unplugged alot of things that are not being used. I Hope this helps others.

great tool to have to determine the wattage of certain items. Very easy to use

When sizing for a generator or an inverter you need to know not just the wattage used but the peak or surge watts used. Some items like air conditioners and refrigerators and lots of others will draw a lot of power when they first start up, then quickly settle down and use less while they run. Your power source has to be able to handle the peak usage which can be 2 or 3 or more times the normal running usage. If you want to power several such items, your power source has to be able to handle the peak usage for *all* of them since eventually they all may coincidentally crank up at once.I have a massive, ancient vacuum cleaner that is a great example of this. When I fire it up, the lights in the room dim slightly for a few seconds, then return to normal. That's the surge draw of that old vacuum starting up.Anyway, this little goodie lets you see the watts (or amps) being drawn by an appliance. However, it shows you the watts drawn in real time which doesn't tell you the peak which is what you need to generator/inverter sizing. When you're ready to check out the peak watts of the item you're testing, sit and watch the display carefully and make a note of the highest value shown as the item is starting. Even if the wattage drops substantially after that, the high (peak or surge) wattage is what you need to be able to support. If you just look at the display after the item has passed its startup surge, you're looking at the lower, normal draw. So pay attention and you'll find this to be very handy. It can either tell you that you need to spend more on your power source or replace some particularly power hungry older item (like my vacuum).