Electricians -- what does this picture mean?

The black circles are connector areas on my system where power wires are connected to. The wires are connected in a way that the "H","N","NO",and "C" are attached to them. What do those letters mean?

What sort of insects can destroy your house by eating wood?

fix for wobbly ceiling fan?

My home shakes daily, to the similarities of an earthquake tremor, due to explosions from a nearby quarry.?

What would make water discolored (like weak tea) coming out of the pipes?

Does homeowners insurance cover replacing broken sewer line?

how do you treat a wood deck that is begining to dryrot?

Any opinions on Carolina Carports Incorporated in Mount Airy, NC?

where can i get a draught excluder for my letterbox in my door?

Glad Wrap+ Microwave= Bad or gd?toxic?