Yeah, I've always been trained to start with all the breakers off, then flip them starting at the
power source moving toward the lamp/
fixture/device. Obviously it isn't
practical to do this all the time, but at the very least, it's good practice when you're turning on a new
system or new gear you just connected for the first time. In the same vein, it's good practice to
meter your
power as much as possible, especially whenever you're in a new facility or using newly received gear. While meters are expensive, they're an investment that will last a long time and it will most certainly save you on many occasions, such as this one. Shy of that, the PD should be clearly marked with exactly what's on the other end of the
receptacle, although I'd still highly recommend double checking this with a
meter whenever possible. It's not unheard of for a shop or a manufacturer to accidentally configure a rack or PD wrong, and instead of the 120V you were expecting, you have 3Ø 208V on your hands.
In the areas I work, it's an unofficial standard that 208V
power always runs through L6-20 connectors, and 120V is always 2P&G (or L5-20 in rare circumstances/L5-15 for
dimmer doubling). This does a pretty good job of eliminating problems at the
connector, but since
Socapex is used to carry both 120V and 208V
power, this is the
point where things can get messed up. A PE I worked for had us
cover both connectors of any
socapex cable that would be used with 208V
power with orange
e-tape - and on the female end, the orange
e-tape would
cover the connection between the
soca and breakout, so it was impossible to remove the breakout without taking off the tape. I've since adopted this
system myself, and it works pretty well as long as everyone knows the
system. However, it's still always best to take the extra 30 seconds and
meter your
power if you have any doubts at all.
I hate to say it, but you really lucked out here - had you plugged certain moving lights or other devices into the 208V
power, the damages could have been disastrous, dangerous, and extremely costly. Electricity is extremely dangerous, and you need to carefully think about what you're doing EVERY time you
plug something in. More than just ruining a few hundred thousand dollars of gear, not paying attention when making connections can be very dangerous. Even something as simple as plugging a microwave into a spare
outlet could theoretically bring down an entire
system. Use this as a learning experience, and always be sure to double check your
power source before you
plug anything in.