hello everyone,
well it looks like some of you didn't really get what my question was or perhaps I was not clear enough.
the question is: why are some compressors rated for 120 &240v? do they come with a 120v or 240v plug ?
I will be buying a scissor lift that is also rated for 120/240. The guy on the phone said that it works perfeclty fine on 120 but they recommend having it on a 240v circuit. Since I'm getting new electricity done in the garage I'd like to put a 240v for the lift. Again most people run these in 120v with no issues
Power is voltage times amperage = watts (a simplification with AC but the math is close.) So, something that can run on either 120v or 240v and provide the same output will use 1/2 the amperage on 240v as it will on 120. Therefor, the wire size required will be smaller for the same load.
Some equipment will be limited by the lower operating voltage. IE, as Norcal mentioned a welder (or my plasma cutter for example) will use a transformer that will automatically switch between the two (an inverter can probably do anything between or anywhere near as well). However, the maximum power of the machine cannot be used unless it is on the higher voltage.
For a lift, this means it may be designed to operate slower.. perhaps not a big deal. But on a plasma cutter, it can mean half the cut capacity is unavailable on the lower voltage.
The plug will be dependent on how you wire things and which you select. You need to know the amperage required at each voltage of this equipment before you make any decisions. If 240v is available, it will be best to install that. If it is a fixed piece of equipment it will be less expensive to hard wire the lift and not use a plug/receptacle whatsoever.
To answer your plug question - much of the larger equipment like welders, lifts and compressors does NOT come with a plug at all... it's up to the user to install it. On my plasma cutter, I installed a twist-lock (not pictured in the table above) for 240v usage as I was using it mostly with my generator, and I also had a pig tail to use it on 120v... most other people would likely be best off with a straight blade plug.