Today’s confusion over terminology comes from the domain of power; specifically UPS devices.
“I’ve been looking at putting some of my gear on a UPS and in the process of trying to figure out how large a unit to buy I’ve come up against things like ‘load factor’ and volt amps that are confusing. I figured I could just calculate the approximate current draw of my gear and just go with that. What is all this other stuff?”
Commonly available information tells us that wattage is the product of voltage and current. Given our voltage at a standard electrical outlet is a pretty consistent 120 volts, this would mean that if you know the wattage consumed by a given device you can figure out its current draw (Current = wattage/120), or if you know its current draw you can figure out its wattage consumption (Wattage = current x 120).
This actually works for DC circuits or purely resistive circuits. In the case of actual real world loads there is some amount of inductive reactance. This “load factor” means you don’t always get the actual amount of watts (which do the real work) from your voltage and current. Therefore actual usable watts is always some amount lower than VA.
A typical example of this is:
120 volts x 10 amps = 1200 VA x .70 load factor (somewhat typical) = 840 watts (actual usable power).
The math can also be reversed:
1200 watts (actual power needed) / .70 (load factor) = 1714.3 VA, which means:1714.3 VA / 120 volts = 14.3 amps of current are actually required to operate the device.
So if your equipment says it requires 1200 watts, it may actually need 1714 VA. At a fixed voltage of 120v, then that means you actually need 14.3 amps to supply the required power. This is all based on a load factor of .70. Load factors are a moving target though. Quite often they are as low as .90; it just depends on the specific equipment in question.
On the other hand, wattage and current ratings on equipment are often very liberal. The device will typically use much less power than its rating. In the practice of figuring out electrical loads this tends to negate the problem of load factor somewhat. That’s why many people say you can ignore the load factor and just calculate power using only voltage, current, and wattage.