Everything over 600 VAC is considered High Voltage; where I work but we have alway considered everything over 600 up to 20 KV+ medium. My low voltage "hot gloves" are rated at 1000 volts and I use them when I work 480 hot which is not very often. My high voltage gloves are tested at 10,000 VAC and mostly used at 4160 VAC. Glove testing is every 6 months and air tested before each use.
I test hi-voltage with what we call a "hot-sticK" I also don a 50 cal protective suit. I'll give you a clue. I rather sit in my -20 for an hour than be in this suit for 10 minutes. I'm usually in one each week when entering hot 4160 cubicles when meggering motors. (that's an insulation test for those of you not in this choosen field)
When working with any 480 motor control centers I wear a nomex long shirt. Many in the refinery trades know what these are. My son and I also have coveralls made of this and use them when warming the car especially when using nitro.
My son Patrick is a Troubleman for SCE now nearing 20 years in the business. You earn this position by being an expert lineman. He is a first responder to problems with customers. He works alone and has uses either his insulated bucket truck or by climbing. He is a hot tool expert. I was a lineman for 2 years before going into power plants.
I feel the most dangerous voltage for me is 277 VAC floresant lighting. I just don't like it and it hurts like hell. Just a few miliamps of any voltage can kill.
As a final fun thought. You can let go of alternating current 60 times a second but DC holds you until it's all discharged...........................
................JD
PS: it's 5:45pm Saturday my day off and where am I? At the power plant.