"Mexico has a national electric code similar to the NEC: I've seen a document from the NFPA (I think) where it was considered possible to create a common Canadian-US-Mexican code out of the present codes. Therefore, it can't be very different."
I have heard this to be true, but if it is, enforcement is very spotty, to say the least. The cities usually have 120/208 3phase distribution, and individual houses and small businesses usually have 120V 30A service. Exposed knife switches are still frequently seen, fused neutrals remain very common, conduits are usually discontinuous and grounds frequently nonexistent. I've seen open meter sockets with jumpers in them, disconnects with doors open and aluminum foil jammed into the fuseholders.
The most common wiring method is something that looks like zip cord. It is white and has two 12 AWG solid conductors. "Conduits" are sometimes made by coating a piece of water hose with lard and embedding it in concrete. Once the concrete hardens, the greased hose is pulled out and reused. Receptacles are NEMA 5-15 and 1-15, but some houses and most public markets have no receptacles. You will see two wires, spliced with or without tape, wrapped through the holes in the exposed blades of a 1-15 plug.
The maquiladoras (Free-trade zone factories)appear to be wired to North American code standards, as far as I could tell from the window of a passing bus. I have heard that IBEW electricians wishing to work in Mexican industrial plants may apply at the El Paso local.
I have also heard that in some locations, the nominal voltage is 127V.
