“Safe” is not the same as “it works”!


During a home inspection, I will see situations that I will call out as “not safe” or a life-safety issue.  More often than not, these un-safe issues surround the electrical installations.
The most common of these issues are caused by inexperienced people working on the electrical systems.  Generally DIYer’s who change a receptacle, or add a new one.
Without realising they create a safety hazard that is not safe or detectable without proper testing until it’s too late.

The most common of these electrical issues in houses with modern wiring is a reverse polarity connection.  This is where the “hot” and the “neutral” wires in a fitting are reversed.  Let me take you on a journey of discovery and show why these situations are not safe.  I will explain why, when they are found by a qualified Inspector, an electrician is recommend to inspect and fix, rather than leave it to the home owner.

A background to residential electricity.

Very simply put, there are two types of electric current in a wired system, Direct Current or DC, which is produced by a Battery or Dynamo, and Alternating Current or AC which you get from an Alternator.

Most modern house wiring is supplied by Alternating Current (AC) electricity.  Unlike Direct Current (DC) where one end of the circuit is positive and the other is negative AC current is driven by alternating voltages.

If you could see electricity, an AC electric flow would look like a sine-wave in the picture below.  In this diagram the top is positive, and the bottom is negative, and this effect is created by an Alternator, which generates electricity by spinning magnets inside a coil.  As the magnets approach the coils the electromagnetic force increases the voltage in the coil and as the magnets move away from the coils the electromagnetic force decreases hence the up and down movement of the voltage, which when spread over time creates the sine-wave you see in many pictures.

Safe electrical wiring: Positive-Negative sine-wave
If you imagine this electrical wave to be inside a wire, then it makes the notion of Alternating current easier to understand.  This sine wave, in North America bounces up and down 60 times a second.  This is known as the frequency, and it is measured in Hertz after some German dude called Heinrich Rudolf Hertz, anyway I digress.

In a wire, instead of the electricity going up and down, it does what all electricity does, it flows from where the voltage is high to where it is lower.  It a bit like water in a pipe, it always flows from high-pressure to low pressure.

So looking at the sine-wave again, we can envisage the electricity flow as in the diagram below.

Safe electrical installations - Alternating current
The current in a closed circuit travels first one way, and then another along the wires, and it does this switch 50 times every second.
So in an A/C circuit there is no concept of positive and negative poles like you’d find in a batter or a D/C circuit.

So why does it matter which way wires are connected in residential properties?

Because of this to-and-for flow of electricity, most loads will operate when wired backward (or connected to reversed-polarity receptacles).  The untrained or unskilled believe that the polarity of the wires in a circuit has no significance. Many such installers will use the “it works” as an indication of the fact that they have completed their work.

This couldn’t be farther from the truth.  When a circuit is closed (on), current does flow both ways through both conductors of the circuit.  In this circumstance both wires will be dangerous to touch.

However, when the circuit is open (off), in North American residential installations, the white (‘neutral’, grounded) wire should be connected to earth at the panel.  This will produce a zero voltage delta to almost anything else in the building.   When a properly installed AC circuit is switched off the white wire should be safe to touch.  This doesn’t mean you should go around touching them to test this.  The results of such stupidity can sometimes be, for want of a better word, shocking.

In the same type of installation, the black (‘hot’, ungrounded) wire is connected via a breaker to a big transformer on a utility pole outside, and its voltage cycles between zero and 120 volts, 60 times a second, as explained above, and will shock you at all times unless the breaker is switched off.

If the polarity of the wiring is reversed, then all bets are off.  If the polarity is reversed only at the receptacle, then anything plugged into the receptacle will have electricity common out of the “Neutral” side of the outlet.

Potential Killers in the home

Reverse-polarity receptacles and indeed anything without the proper polarity 2 pin plugs inserted the wrong way round into properly wired receptacles makes everyday things potential killers.

Safe design of an Edison Screw Fitting Bulb

Take for example an Edison Screw Fitting (ESF) Lamp.  This is designed in such a way that the button on the end of the bulb is supposed to connect to the “hot” side of the circuit.  The large screw on the outside is supposed to be grounded through the Neutral.   Unscrewing an ESF bulb from it’s socket disconnects the button first, and immediately turns off the light as it breaks (opens) the circuit.

This is still the case even when the lamp has reverse polarity. The difference is that in a properly wired connection, it is difficult for you to touch the hot part of the lamp holder.  It is buried deep inside the socket of the lamp holder.

When the lamp holder has a reverse-polarity circuity running through it, the screw fitting of the lamp holder becomes the “hot” side of the circuit.  Unscrewing the bulb exposes this dangerous side of the circuit and exposes you to shock.

Touching the screw part of the bulb or lamp holder will close the circuit using you as part of it and, at best, the next thing you know is you are waking up in hospital.

Lamp-holder not safe with reverse polarity

While a reverse-polarity lamp-holder gives an easy to explain example to why polarity matters in AC wiring,  polarity matters for other AC appliances, as well.

All electric devices sold for use in the North America must be tested and listed for specific uses by an underwriting agency, in Canada it’s the ESA or CSA.

This testing verifies the safety of devices when connected to a properly polarized circuit and used as directed.  It does not confirm safety when the product is energised with reversed polarity.

Many appliances,  washing machines, tumble dryers, dishwashers, blenders, mixers etc.,  have metallic casings.  These are protected, following National Electrical Codes by main disconnect (cut-off) switches (which are not conductive of electricity), and internal fuses on the hot side of the circuit if a fault occurs.
If the appliance is plugged into a reverse-polarity outlet, the fuses and cut-off switches become useless, as the electricity is traveling the wrong way around the circuit and fuses and cut-off are on the side of the circuit which is the way out.

If a fault occurs inside the appliance it may stop, as the fuse will blow or the safety cut off may operate, but the circuits inside the appliance will still be energized.  The act of touching the appliance may be all that is needed to complete an electrical circuit using you as part of it, once again, someone will end up dialing 911.

Recognise what you home inspector is telling you.

Next time you see an inspection report, were the only thing wrong is a reverse-polarity receptacle, and a recommendation to call an electrician in to fix it, don’t discount it as fear mongering.  Good, well qualified home Inspectors not out to write reports to make themselves look good, nor do we do it to look good on TV.

We don’t write things up that don’t need attention, and when it comes to safety issues, we would like to have you round in the future for repeat business.   If you see a safety issue in a report,  ensure it is fixed before you buy the home, and get it re-inspected, or get it fixed yourself immediately after the purchase.

Remember that reverse polarity in an AC circuit matters even if it seems as though it doesn’t.  If you don’t it may be the worst house buying decision you make.

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