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I live in a recently renovated Brooklyn (NY) building where the service entrance for the main panel comes into the basement and then is fed up to my floor via a backfed panel (100 amp service and 60 amp breaker to apartment). In the basement the neutral and ground are bonded together, but there are only three conductors (hot1, hot2, and neutral) going up to the apartment.

It seems like the interweb is pretty insistent that 4 conductors be run to a subpanel.

The people I know tell me this is allowed in my area, except as a layperson, was just wondering if this is true or not and what the justification is. Does the drywall/copper pipe in the building distribute whatever current that doesn't return via the neutral?

There is a small water supply line to a water cooler on the first floor that someone told me shocked them one time when turning on the valve, which I have not been able to reproduce. With my layperson multimeter, I did notice a few volts on the water supply pipe, but do not know if this is the correct way to determine fault current.

Can anyone help me clarify the situation?

Thanks!!

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    Are the wires going to the apartment in metal conduit?
    – JACK
    Commented Feb 11, 2022 at 14:21
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    Yes, so the metal cladding serves as ground?? Commented Feb 11, 2022 at 14:29
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    Correct. But likely not cladding (that's armored cable, which is sometimes a valid ground but not necessarily) but rather conduit. Commented Feb 11, 2022 at 14:35
  • I see, it looks like armored cable was installed, maybe for ease of installation not having to bend conduit or whatever.... Thank you very much! Commented Feb 11, 2022 at 14:39
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    Pictures of (a) your panel and (b) the armored cable/conduit/whatever would help. There are different types and the experts (not me) can often tell right away what you've got. Commented Feb 11, 2022 at 14:43

1 Answer 1

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Code doesn't require 4 conductors anywhere.

It requires discrete neutral and ground.

Neutral's job is to handle all return current. The neutral must serve only the hot wire(s) in its own circuit, otherwise it would be at risk of overloading. (And neutrals don't have circuit breakers, so we would never know.)

Ground's job is to be a "catch-all" for any fault current. The idea is that ground returns the fault current, which flows enough current to trip the breaker. Meanwhile it also suppresses lightning and static electricity (ESD).

But nothing says ground must be a wire. It absolutely can be the metal pipe itself. Provided the pipe is UL-listed as a NEC Chapter 3 wiring method that permits its use as ground (e.g. EMT, IMC, RMC, etc.)

My "go-to" wiring method is THHN individual wires in EMT metal conduit. I own 10 colors of wire (to distinguish circuits) and none of them are green. I just don't have call for ground wires. It's an excellent system; I use it even when I don't have to. It's "aiming higher than the minimum".

2-of-3-phases is common in apartments and NYC

When I read the title I thought ground wasn't a player and you were asking about 3-phase power. Your power source is 3-phase, not the "2-phase that's really just 1 phase with a center tap" most Americans get. New York just set that as a weird little provincial standard.

However most apartments in NYC get "2 of 3 phases", which is a little weird. It's hot-hot-neutral-ground like the rest of the country, but the phases are "at an angle" to each other. So the phase-phase voltage is weird. It's 208V instead of 240V.

Bad appliances and wiring can be found anywhere, though.

Fair chance the runs from panel to outlet are also metal conduit, which means the safety grounding should be dead-nuts perfect. However if they were able to get the wiring approved without grounding, e.g. using cables in the walls, that could be a problem.

GFCI to the rescue

Ground is meant to give "shocking" faults a speedy path back to the panel, so it results in immediate breaker trip. However ground can't be everywhere.

Technology has given us a better way to detect escaping current, called the Ground Fault Circuit Interruptor or GFCI. (also called the Residual Current Device across the pond). It compares current on the hot wire(s) and current on the neutral wire. They should be exactly equal. If they're not, current is leaking out a third path (e.g. shocking someone). So GFCI is a "silver bullet" to such safety problems in older wiring.

GFCIs exist as outlets and also as circuit breakers (and a few other formats). They are also able to protect downline wiring, so they can catch faults in the wires themselves.

Installation of GFCI is probably a good idea anywhere someone reports a shock. Any shock that doesn't kill you could have if the path to ground had been better.

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