Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

This question already has an answer here:

I have been told that a GFCI receptacle is a "circuit breaker" in the sense that it will trip under overload. Everything I know, have been told, and have read from experts to manufacturers says this is not the case.

So the question stands: Is a GFCI receptacle device a circuit breaker?

share|improve this question

marked as duplicate by Speedy Petey, BMitch Jan 23 at 15:27

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

    
Incidentally I have tested this. The GFCI outlets available for me to buy cannot function as circuit breakers as they will not trip on overload. – Joshua Jan 22 at 23:09
    
@Johnny, yes it is. I forgot all about that. – Speedy Petey Jan 23 at 12:14

No.

Each type of device serves a distinctly separate protective purpose.

Breaker

A circuit breaker detects overcurrent faults, it does not detect ground faults. A circuit breaker will stop your house catching fire when the wiring in the walls overheats from prolonged overcurrent, it wont stop you and your family being killed by electrocution.

A typical UK breaker protecting a 6A circuit might only trip out when the current reaches 30A. There are several ratings in the UK:

  • Type B trips between 3 and 5 time full load current;
  • Type C trips between 5 and 10 times full load current; and
  • Type D trips between 10 and 20 times full load current.

The reason for this is that some appliances have a high inrush current and you don't want lots of nuisance trips.

It is probably worth noting that breakers don't trip at a specific current, it depends on how long that current is sustained. A small overcurrent will take a long tome to heat wall wiring to dangerous levels, the breakers typically take that into account.

GFCI

A GFCI detects ground faults, it does not detect overcurrent faults. This is mostly designed to prevent electrocution. It won't stop your house catching fire.

The assumption here is if the current supplied on hot is more than is returning through neutral, the difference might be flowing to earth through someone's body.

A class-A GFCI may trip out for a very low imbalance in current between hot and neutral, perhaps only 5 mA (i.e. five thousandths of an amp).

The UK equivalent, an RCD, might trip at 30 mA - there are many types designed for various purposes - which is why it is sometimes best to employ a professional electrician to select and install these.

AFCI

An Arc Fault Circuit Interrupter (AFCI) is designed to detect arcing. This is where a poor connection, for example in a plug or outlet, causes sparking as the electric current crosses a small air gap. These are the types of faults that can cause fires even though the current being drawn may be well below what will trip the breaker.

Combination devices

UK

In the UK you can use an RCBO that combines RCD (GFCI) and MCB (circuit breaker) functions in a single device in the "consumer unit" (main distribution panel).

A typical UK installation would have two RCDs in the main distribution panel. You can buy plug-in RCD devices. You can buy sockets with built in RCD protection - mainly for outdoor use where an electric mower might cut it's own lead.

US

The US have similar combination devices. They can combine breaker and GFCI or all three functions.

From what I've read, historically, there seems to have been a practice in the US of putting breakers in the panel and GFCI in the outlets. One GFCI in a circuit can be used to protect ordinary outlets downstream of it. Nowadays people tend to use GFCI, AFCI and combination protective devices more.

Regulations

Nowadays you generally need all types of protection.

Usually, existing installations don't need to be brought up to date unless you are making significant changes like adding new circuits.

Obviously, regulations vary from place to place. You need to check what applies in your location.

share|improve this answer
    
+1 Yes, there are circuit breakers that are also GFCI. And there are breakers that include AFCI. And there are now circuit breakers that combine both AFCI and GFCI with overload protection. – bib Jan 22 at 12:37
    
The above comment describes the situation in the US. I do not know what is available elsewhere. – bib Jan 22 at 14:40
    
@bib: thanks, I have amended the answer to include some of your information as best I can. – RedGrittyBrick Jan 22 at 15:59
    
Your comment about usual practice is right, but more and more people are using GFCI, AFCI, and combo breakers as the prices come down and they get more reliable. They used to be finicky, and they still cost a good bit more than standard breakers (but a standard breaker and several GFCIs adds up). – bib Jan 22 at 16:05
    
@bib: thanks, updated. – RedGrittyBrick Jan 22 at 16:18

I don't think the argument was that a GFCI was designed to be a circuit breaker, but that something in their construction caused them to trip due to an overload.

I can say with 100% certainty that GFCI devices are not designed, nor intended to take the place of circuit breakers. However, without actually seeing the internal circuitry, or the design specifications. I can't say with 100% certainty that a GFCI could not respond to an overload.

There's also the fact that older GFCI devices were flawed, and often tripped due to other factors (nuisance tripping). So one might not understand why the device tripped, and incorrectly assume that it was due to an overload.

In the end, a GFCI device is designed to protect against ground-faults. It is not designed, intended, or advertised to provide overcurrent or overload protection.

share|improve this answer
    
The argument was that a gfi receptacle was also a circuit breaker that tripped under an overload. Its just unfortunate to be called names and told we as PROFESSIONALS don't know what we are doing by someone who thinks they know better than all the professionals on this site. – Speedy Petey Jan 22 at 14:26
1  
@SpeedyPetey I agree, and hopefully that problem has been sorted out. The rest of the community respects the professionals among us, and appreciates them taking time to share their knowledge and experience. – Tester101 Jan 22 at 14:31
1  
I for one enjoy reading what the professionals here have to say - both when knowing exactly what part of the NEC to quote and sharing real life experiences and good ideas (e.g. X is not required by code, but do it anyway). – Snowman Jan 22 at 15:38

In the vernacular: no, a GFCI device is not a circuit breaker unless it says it's a combination GFCI/breaker.

Technically speaking: a GFCI contains circuit breaker switching guts, but replaces the normal thermal-magnetic trip with a differential trip, or adds the differential trip in the case of a combo device.

Large circuit breakers (industrial/commercial switchgear type) or utility protective relays are designed so that the trip sensors and logic are separate from the disconnecting (tripping) means -- this allows them to be configured for complex protective functions, including:

  • Instantaneous short-circuit
  • Inverse-time overload
  • Overvoltage or undervoltage
  • Derangement of a source
  • Differential (ground fault)
  • Phase out (i.e. when one phase of a 3 phase source fails)
  • Various other quirky things...
  • And combinations of the above
share|improve this answer

Not the answer you're looking for? Browse other questions tagged or ask your own question.