Posts Tagged ‘GFCI’

Demystifying the mystifying GFCI

2013-07-30 by tester101. 3 comments

A commonly misunderstood electrical device, is the Ground-Fault Circuit Interrupter (GFCI).  Whether posing as a circuit breaker, or a receptacle, the GFCI device is almost always misunderstood. To understand the GFCI, however, you have to know a bit (and I mean a really little bit) about transformers.

This is a transformer.


(Well, a crude representation of one anyway).  It consists of an iron core, and a couple coils of wires.

Transformer Coils

More specifically, it has a primary coil of wire, and a secondary coil of wire.

Transformer Labeled Coils

When you place a voltage on the primary coil, some magnetic magic happens in the core and a voltage is induced on the secondary coil.

Transformer Working

And there you have the most basic crash course, on the most coarse basics of transformers. Which is all you need, to understand how GFCI devices work.

Inside a GFCI device, you’ll find what’s called a Current Transformer (CT).  A crude representation of a CT, looks something like this.


A CT works just like any other transformer. When a voltage is applied to the primary, a voltage is induced on the secondary. The only difference, is that the primary isn’t a coil, exactly.  The primary is instead the ungrounded (hot), and grounded (neutral) conductors of an electrical circuit.


When current is drawn on the circuit, it flows down the ungrounded (hot) cunductor. Out to the consuming device, then returns back to the source on the grounded (neutral) conductor. Similarly, if we draw current from a GFCI device.  It flows down through the ungrounded (hot) conductor, and through the CT core.

CT in GFCI  (Current on hot)

The current then flows back through the CT on the grounded (neutral) conductor, and back to the source.

CT in GFCI  (Current on Both)

According to the right hand rule. If you point the thumb of your right hand  in the direction of current flow, and wrap your fingers around the conductor, your fingers point in the direction of the magnetic field produced by the flowing current.  If this is done with the above diagram, we end up with magnetic field lines like this.

CT in GFCI  (Current on Both with Magnetic feild lines)

Because of the proximity, and opposite-ness of the fields. They cancel each other out, and no voltage is induced on the secondary coil of the CT.

CT in GFCI  (Current on Both with Magnetic feild lines) Even

In the case of a ground-fault, however, not all the current will flow back along the grounded (neutral) conductor. This creates an imbalance in the magnetic fields, which allows magnetic magic to occur in the transformer core, and a voltage is induced on the secondary of the CT.  If the voltage on the CT is large enough, and lasts long enough, the GFCI device will open the circuit.

CT in GFCI  (Current on Both with Magnetic feild lines) Not Even

Next time you come across a GFCI device that continually trips, think about how it works and what it’s looking for.  This might give you a better idea of what to look for, and where to start troubleshooting. And remember to always work safely, and cautiously whenever you’re working with electricity.

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Ground Fault Current Interrupters

2012-03-27 by lqlarry. 2 comments

Ground Fault Circuit Interrupters (GFCI) have been part of the NEC code for over 40 years now and just like your car, things have changed. Over the years the code has changed but also makers of GFCI and Underwriters Laboratories (UL) have made a lot of good changes. Life saving changes that probably nobody except a few electricians have noticed. Today, most people just think of the GFCI in their bathroom or kitchen and will probably never know all the great GFCI that are available.

Today, the sGround Fault Circuit Interruptertandard GFCI that you see in your wall is either 15 or 20 amp and the most noticeable feature you see is a light, usually a little green light. If you don’t see the light or the light has changed colors then your GFCI will not work. What you don’t see is that GFCI are self testing every 15 minutes. A trip can be reset, but a failed GFCI will not reset and you will have to replace the GFCI. Another feature is that the GFCI comes from the factory in the tripped position and if it is mis-wired you will not be able to reset the GFCI until it is corrected.

Tamper Resistant GFCIDid you know there are tamper resistant receptacles and GFCI? Now manufacturers make tamper resistant GFCI for your children’s bathroom. These meet the same stringent requirements of a standard GFCI, but now somebody cannot just stick something conductive into any slot of the GFCI. Now you can sleep better at night knowing your kids are safer. The tamper-resistant receptacles and GFCI have been NEC code since 2008 but not all municipalities are enforcing it yet.

Now you can buy weather resistant GFCI. It will still have to go in a weather resistant cover or even a bubble cover. Weather-resistant GFCI are made to go outside, being able to take extreme temperatures, UV and moisture. The weather resistant GFCI are also made with the tamper resistant feature.

FacelesFaceless High Current GFCIs GFCI are also made. This is just GFCI made with only the test and reset buttons, no receptacle built in, like it’s name implies.

Another faceless GFCI is the high current GFCI which can handle up to 80 amps at 240 volts. These feature a current sense transformer called a donut which is powered by 120 volts. If you need a GFCI for your spa or equipment and cannot find a breaker, then these will come in handy. The high current GFCI should only be installed by a licensed electrician.

Do you need a night light or a guide light? GFCI are made with a receptacle and a light. A photo sensor turns the light on and off. How about a pilot light with your GFCI? The light comes on when there is a load on the GFCI. Comes in handy in basements with sump pumps. All the lights are LED for low power consumption and long life.  Do you need a switch and the only room is a GFCI? Replace the GFCI with a combination switch and GFCI. The switch is independent of the GFCI and can turn on that vent or light. These combination devices can also be purchased with the tamper-resistant feature and no safety feature has been removed.

There are other GFCI made like extension cords with GFCI, or GFCI that can be wired in as the plug of an extension cord.  Panel mount GFCI are available for sump pumps, generators or temporary power.

Assorted GFCI

Night Light GFCI, Pilot Light GFCI, another Night Light, Switch Combo, and Cord GFCI

While this might not have been the most exciting read you’ve had today, I hope that this might help on your next DIY Home Improvement Project.

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Arc Fault Breakers

2012-03-06 by lqlarry. 3 comments

Arc Fault Circuit Interrupter Breaker

Before we get into Arc Fault Circuit Interrupters (AFCI), let’s look at their uncle, the Ground Fault Circuit Interrupter (GFCI). GFCIs first appeared in the NEC code in 1971, and then only for swimming pools (not spas) and exterior outlets. Today, bathrooms, kitchens, wet bars, garages, rooftops, spas and any place that water can be a problem must be protected by a GFCI according to code. Without getting into what a GFCI does, it basically can save your life. This has been proved over and over, and unfortunately also proved when GFCIs have been removed, tampered with, or failed.

Let’s start off with some questions:

What is an Arc Fault? An arc fault is when current goes through your wires and somehow takes an unintended course that produces a spark, or arc.

Why don’t my regular breakers protect me from arcs? Your breakers protect you, but what an AFCI does, that a regular breaker can’t, is detect a very low level arc. If not detected, that low level arc could quickly become a life threatening event – in your house!

Why do I need AFCIs and GFCIs? A GFCI protects you and others from fatal electric shocks when a ground fault happens, like if you try to make toast while taking a bath and drop the toaster. That would be a ground fault due to water. As explained above, an AFCI protects you and your valuables from a potential fire caused by a low level arc.

What causes arc faults? Worn or damaged wire; damaged plugs or receptacles; loose electrical connections; screws, nails or staples driven into wires; furniture pinching lamp or appliance cords; broken wire; frayed wires; and even wire chewed on by your pets. Probably anything your kids do when you’re not around. The NEC uses the term combination to describe fault protection. This covers both parallel arcs (two wires arcing together) and series arcs (arc caused by one wire arcing between two damaged areas)

Can I buy AFCI receptacles? Not at this time. Breakers will protect everything downstream from the breaker, but an AFCI receptacle would not protect the wire between the receptacle and the breaker.

Cause and Effects of Arc Faults

Cause and Effects of Arc Faults

Whether you need AFCIs or not depends on your local codes. Not all local codes have accepted AFCIs as code, and some might accept them but not otherwise be up to the current national code. The current NEC Code, 210.12 says All 120-volt, single phase, 15- and 20-ampere branch circuits supplying outlets installed in dwelling unit family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sun-rooms, recreation rooms, closets, hallways, or similar rooms or areas shall be protected by a listed arc-fault circuit interrupter, combination-type, installed to provide protection of the branch circuit.”  Even if your local code does not call for it, you still can install AFCIs in your home. Of course, if local code requires AFCIs then they will have to be installed on new homes and remodels.

AFCIs keep improving, just like GFCIs. With these improvements, specifications change and an older AFCI might not pass on a new job, depending on when the permits were issued.  Just because a breaker says AFCI on it, that does not mean it will pass inspection. Your electrician will know which ones to use and your local code office will also have that information.


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