Polarity Reversed in High Rise, What / How to check?

[LRicci]

We live in a 23 story building in Milwaukee Wisconsin (US) Our utility company didn't realize we are a residential building when they disconnected our power to replace a transformer early last Sunday. When they realized they'd trapped residents in a building with no elevators, water, air conditioning, etc. they quickly backed out and turned the power back on, BUT reversed the polarity. We all ran appliances, computers, televisions, etc. for a day or so before the problem was discovered. They took the system down, reversed the polarity back to regular, and brought the building back up. We have some high voltage pumps that are fried.
I don't think we suffered from a power surge.
Now, we are faced with figuring out what we need to check for damage, and how. If an item works, does that mean it is undamaged? If not, how can we figure out whether we have a problem that simply hasn't shown up yet, but will? What type of engineer would be qualified to advise us?

 

[Mark R]

There is no 'polarity' in an AC power system.

It's possible that there was a phase order issue - but this only applies to 3-phase supplies. In a 3-phase system the voltage will rise and fall in order. (e.g. A, then B, then C). If any 2 of the phase wires are swapped around, then the effect will be to reverse the phase order to A,C,B.

Reversed phase rotation will only affect 3-phase motors, which will rotate in the opposite direction. So reversed phases, could very easily burn out heavy-duty pumps by making them run in reverse.

Reversed phase order won't affect single phase equipment or 3 phase electronic equipment (including motors connected to electronic controllers - e.g. variable speed controllers used in elevators).

Single phase and split-phase equipment (such as you would have in your apartment) should not be affected at all.

 

[Paperdoc]

Mark R is quite right, and it's a good bet a whole high-rise building DOES have a 3-phase supply. In that situation it is quite conceivable that the utility company reversed two phase leads in their haste, BUT it would NOT affect individual apartments that are supplied only from two phases.

I'll disagree slightly here on the opening phrase: "There is no 'polarity' in an AC power system." The output of transformer secondary windings in an AC power system do not have "polarity" in the sense that a DC system does. However, in North America virtually all domestic power distribution systems artificially establish a reference point by connecting one secondary winding junction to true earth Ground. This is duplicated in the building or private home - the same line is Grounded there again. Thus within the dwelling one side of the AC power lines is always at earth Ground potential (or very close to it), and it is called the Neutral Line, almost always on the white-colored wires. Then the other lines (two in a household system) at a breaker box are Hot lines whose voltages swing to both the positive and negative sides of that Neutral reference line. So, referenced to "safe" true Ground, one outlet slot (the narrower one) is Neutral and VERY close to zero volts at all times, although NOT guaranteed to be at true Ground potential, and the other (wider) slot is Hot.

 

[Rubycon]

Right - it's called reversed wiring in AC systems.

Happens too often when a distribution transformer is changed out and someone doesn't mark the wires.

PITA when all your motors are running backwards! With compressors and recirculating pumps that can be a major PITA if single phase/reversed phase protection is not employed.

 

[futuristicmonkey]

Mark R is quite right, and it's a good bet a whole high-rise building DOES have a 3-phase supply. In that situation it is quite conceivable that the utility company reversed two phase leads in their haste, BUT it would NOT affect individual apartments that are supplied only from two phases.

I'll disagree slightly here on the opening phrase: "There is no 'polarity' in an AC power system." The output of transformer secondary windings in an AC power system do not have "polarity" in the sense that a DC system does. However, in North America virtually all domestic power distribution systems artificially establish a reference point by connecting one secondary winding junction to true earth Ground. This is duplicated in the building or private home - the same line is Grounded there again. Thus within the dwelling one side of the AC power lines is always at earth Ground potential (or very close to it), and it is called the Neutral Line, almost always on the white-colored wires. Then the other lines (two in a household system) at a breaker box are Hot lines whose voltages swing to both the positive and negative sides of that Neutral reference line. So, referenced to "safe" true Ground, one outlet slot (the narrower one) is Neutral and VERY close to zero volts at all times, although NOT guaranteed to be at true Ground potential, and the other (wider) slot is Hot.

The wider one is the neutral.

 

[Rubycon]

The wider one is the neutral.

Yes it is. Of course this can be confusing as some install the outlets with the ground up instead of down. Supposedly it's safer in case something falls along the wall into a partially plugged in outlet. It will touch the ground first instead of bridging the neutral and hot prongs.

 

[Paperdoc]

"The wider one is the neutral."

Of course you're right, and I'm sorry I wrote it wrong. I sometimes think of it this way: In some appliances and other devices the Neutral wire in the cord is actually connected to the device's chassis (very poor design), so having the Neutral blade of its plug wider ensures you cannot connect the Neutral to the Hot side of the outlet.