I'm trying to understand all the differences between newer and older receptacles.

Newer ones tend to be polarized and many receptacles and wires come with grounding conductors. How do these technologies affect the performance of breakers as a safety feature in circuits?

I read someplace that grounding increases the speed at which a breaker trips when there is a problem like a short circuit. I'm not sure that makes sense to me. If there's a short circuit and no ground, the conductor would heat up/increase in amperage, tripping a breaker. If there's a short circuit and ground, most excess amperage would safely find its way out of the circuit through ground, reducing the chance that stray amperage would cause damage someplace, but not necessarily 'tripping a breaker faster'.

I'm still learning about the benefits of polarizing receptacles so I can't comment much on how I'd expect those to affect breakers tripping.

  • This is an excellent question and the answers would be useful to any home DIY electrician. Unfortunately the Home Improvement SE format is not conducive to broad tutorial questions like this. I wish there were some adjacent site or blog where a general tutorial text would be appropriate, but I guess the closest thing would be Wikipedia. – A. I. Breveleri Jan 12 '18 at 17:51
  • It is a broad question for sure, but it's more specific than the Wikipedia page on grounding or polarization I'd think, probably highlighting a small part of both. Understandable though if this gets closed for being too broad. – cr0 Jan 12 '18 at 18:15

When you talk about the safety function of "breakers", one generally expects to be talking about overcurrent protection. There is also ground-fault (residual current) protection in GFCI/RCD+overcurrent combo breakers, and there is arc-fault protection in AFCI+overcurrent combo breakers.

There are several kinds of safety at work here.


Is generally about life safety. The general idea is that of the two conductors, hot and neutral, one of them is fairly near earth potential because neutral is pegged to earth in the main service. You are unlikely to be shocked if you get between neutral and earth, as there'll only be a volt or two of difference there.

Therefore on a polarized machine, the "hot" part of the machine is made innermost - the least likely for you to come in contact with.

This will not make overcurrent protection more likely to trip. If a faulty polarized machine came in contact with a well-grounded feature like a water pipe, the part coming into contact is more likely to be at neutral potential, which will not make overcurrent protection trip.

It may make GFCI protection trip, and the arcing could cause AFCI to trip.


This is about both life safety and fire prevention.

The idea of grounding is that if the machine has an internal problem, and "hot" goes somewhere it should not be going, the first place it will go is the grounded surfaces/chassis/etc. This impacts life safety because the "hot" goes to ground instead of via a human to another ground. Electricity takes all paths in proportion to their conductivity (1/resistance), and the ground provides a very, very good path which should carry virtually all of the current.

So yes, ground gives a very good path for a faulting device to trip the overcurrent device. You were told correctly.

It impacts fire protection because if it flows enough current to start a fire, the current will be efficiently carried back to the main panel and through the neutral-ground bonding back to source (neutral), allowing high currents to flow, which the breaker will detect and overcurrent trip. In other words, the goal is to turn a ground fault into a bolted ground fault and assure a trip. Without this grounding, a much lesser amount of current could flow, not assuring a trip.

A GFCI breaker will trip on even a very small leakage current. Again, ground helps even a small current find its way back, to assure that the GFCI will trip. By giving current a path to arc against, this also helps an AFCI trip.

  • Thanks for the thorough answer! Your last point about grounding a circuit facilitating an AFCI's ability to keep the circuit safe reminds me of another question I've had, which is about how combos of AFCI & GFCI protection on breakers and outlets affect the overall circuit safety & performance. I posted that separately here: diy.stackexchange.com/questions/131367/… – cr0 Jan 21 '18 at 6:07

Having, or not having, a grounding pin, or a polarized Neutral blade, has ZERO relevant effect on the speed or efficacy of a circuit protective device. So whomever told you that was just wrong. Grounding pins are there to add a level of safety to the device you MIGHT plug into a receptacle, because there is now way to PREDICT what someone might plug into it. All devices that can be plugged in must provide some minimum level of safety from electrocution by those using them, either by providing an easier and SAFER path to ground than the user, OR by being constructed as "double insulated". When you see a device with only 2 prongs (made sometime after around 1970), it is "double insulated", meaning there are no parts inside that can come in contact with the user's skin during normal operation (i.e. you did not disassemble it). Since implementation of double insulated construction, plugs in the US have been required to be "polarized", where the Neutral pin is taller than the "hot" pin, because part of the design relies upon the fact that here, Neutral is bonded to Ground at the service entrance, so making the pins a different size means that you can't plug it in "backward" and put the Hot conductor on something inside that was not supposed to have it.

When you see a device that has that extra ground pin, that means it is NOT built as double insulated. So there are potentially conductive parts on the outside, i.e. metallic cases, that a user can come in contact with and if anything were to happen inside where a conductive element shorted to that case, the path to ground would go through that ground pin, because it would present LESS resistance to the flow of electricity than the human skin.

Yes, technically a breaker would, I suppose, trip faster in that case, but that's kind of irrelevant. If YOU were to ever become the conductive path, any breaker could allow enough current to flow to kill you long before it trips (non-GFCI).

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