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Difference between an isolator switch and a circuit breaker..?

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  1. #1
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    Default Difference between an isolator switch and a circuit breaker..?

    Was wondering if anyone could clarify for my interest the difference between an isolator switch and a circuit breaker.

    Doesn't a circuit breaker switch when turned off act like an isolator switch so in essence why would you bother with an isolator switch?

    Appreciate the explanation.

    Thanks!

  2. #2
    Diamond Member Terrian's Avatar
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    isolator switch cuts power to the circuit breaker so you can safely remove replace circuit breaker.

    should an isolator switch have an isolator switch

  3. #3
    Sparkwah
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    Quote Originally Posted by Terrian View Post

    should an isolator switch have an isolator switch
    Yep it does, a service fuse!

    Isolating switches have a higher KA short circuit breaking rating (6500 compared to 4500 of a normal circuit breaker)
    I am talking about domestic breakers and main isolating switches that I use.
    It's better to be dead and cool than alive and uncool

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    For a non-technical explanation, you can think of a circuit breaker as an 'automatic switch' which turns off (isolates the circuit) at a certain current (amps), where as a switch needs to be manually turned on and off to isolate the circuit.
    Steve.

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    Right but what I'm curious about is why even bother with an isolator over a circuit breaker. I mean as far as I can see the circuit breaker is just an isolator with an added feature that it will turn off if a certain current level is reached. Surely a circuit breaker is preferable over an isolator switch. What am I missing?

    I can understand the isolator switch being used as a control mechanism to isolate many breakers at once *hence the higher KA) in a typical home use but what I'm trying to wrap my head around is why isolators are used near aircons or bathroom fans etc over a typical circuit breaker setup.

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    The Master's Apprentice Bedford's Avatar
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    One reason for having an isolator near an airco, particularly a split with the outside unit, is so any serviceman can isolate within sight whilst working on the unit.

    Whilst he could turn off the main switch, someone could turn it back on when he is working out of view of the main switch.

    My OM is/was a sparkie and always pulled the fuses and took them with him if he was out of sight of the switchboard, you can't do this with hard wired breakers.

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    Quote Originally Posted by Bedford View Post
    One reason for having an isolator near an airco, particularly a split with the outside unit, is so any serviceman can isolate within sight whilst working on the unit.
    Yes I understand the issue of proximity of the "switch" to the appliance as a safety precaution however you can place a circuit breaker in that position just as easily. The thing I'm trying to wrap my head around is why don't people just use circuit breakers in place of isolators in such circumstances. Seems to me you'd get an added level of safety. Is the sole reason that it has the possibility of tripping and if it does you then have to go around the house hunting it down whereas an isolator would in all likelyhood stay "on" so there is only one point you'd need to go to turn the power back on for convenience?

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    GeoffW1
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    Quote Originally Posted by montiee View Post
    Yes I understand the issue of proximity of the "switch" to the appliance as a safety precaution however you can place a circuit breaker in that position just as easily. The thing I'm trying to wrap my head around is why don't people just use circuit breakers in place of isolators in such circumstances. Seems to me you'd get an added level of safety. Is the sole reason that it has the possibility of tripping and if it does you then have to go around the house hunting it down whereas an isolator would in all likelyhood stay "on" so there is only one point you'd need to go to turn the power back on for convenience?
    Well, as mentioned above, an isolation switch can have a higher current interrupt capacity than a CB, but I think the main reason is just cost - cheaper.

    Cheers

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    I just checked the wiring rules and you must have an isolation switch for a motor (which air cons have) to protect against someone getting hurt by the motor starting up.
    A circuit breaker protects the cables going to air con, and it must be fitted at the start of the cable to perform its function, not at the end of the run (which would be adjacent to the air con unit). This is also a requirement of the 'wiring rules'.

  10. #10
    Sparkwah
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    I think we may be getting lost in terminology
    Isolator can mean any kind of switching device that "isolates" a circuit. Your light switch at home is effectively an isolator.
    Circuit breaker means Miniature Circuit Breaker (MCB) in your switchboard
    Main Isolator means main switch, same design as MCB but higher KA rating.
    Air cons have isolators for maintenance requirements.
    Feel free to disagree in condescending manner
    It's better to be dead and cool than alive and uncool

  11. #11
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    There are differences between types of switches.

    An "isolator" may not have "fault make" or "load break" characteristics. It may be generic in the sense that it's "fault make/load break" specs are equal. Many types of switches designated as "isolation switches" have minimal fault/load break characteristics.
    A typical isolation switch is a light switch (provided it is not designed to handle a specific type of load).

    For those who think that a circuit breaker may be treated as an isolation switch, it may but it is not advisealble to use it as an everyday switching device. Most circuit breakers have a noticebly smaller "mechanical life" than a device that is designed to be a "switch". A typical circuit breaker has a mechanical life of between 5000 & 15000 operations (depending upon brand & price). It's electrical life is usually greater than this.
    A switch that is designed to switch a specific type of load (all switches are designed as such) will have a far greater mechanical life than that of a circuit breaker (100 000 operations or more).

    "Fault make" characteristics relate to the amount of "fault current" that a switch can safely handle upon closing. "Load break" characteristics relate to the amount & type of current that a switch can safely handle upon disconnection from the load.

    At the end of the day, your "garden variety" isolator will neither be "fault make/load break". It will have some generic specifications to handle both situations.

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    Quote Originally Posted by Lovey View Post
    I just checked the wiring rules and you must have an isolation switch for a motor (which air cons have) to protect against someone getting hurt by the motor starting up.
    A circuit breaker protects the cables going to air con, and it must be fitted at the start of the cable to perform its function, not at the end of the run (which would be adjacent to the air con unit). This is also a requirement of the 'wiring rules'.

    I know what the rules say. Trouble is the rules don't go into the reasoning behind them. I'm trying to go a little deeper and understand why a breaker isn't used over an isolator. Like I said before a circuit breaker isolates the appliance from the voltage/current else any fault on the line would cause a fire if the isolation didn't occur under fault conditions. I'm just curious as to why isolators are used instead of circuit breakers since by it's definition a circuit breaker is just an isolator that triggers upon a certain current limitation being met.

    Perhaps one of the reasons is as Elkangorito mentioned..The amount of times it can be triggered before it dies and since the circuit is already protected by a breaker anyway why trade off mechanical switching life for an already protected circuit.

    Quote Originally Posted by elkangorito View Post
    For those who think that a circuit breaker may be treated as an isolation switch, it may but it is not advisealble to use it as an everyday switching device. Most circuit breakers have a noticebly smaller "mechanical life" than a device that is designed to be a "switch". A typical circuit breaker has a mechanical life of between 5000 & 15000 operations (depending upon brand & price). It's electrical life is usually greater than this.

  13. #13
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    Isnt it a case that when an isolator switch is needed the standard is just allowing you to use the most relaible and cheapest switch that will do the job ?. If you have circuit breaker with correct rating and you really want to use that in place of an isolator switch it seems that you can. From my exerience it quite common in industry to use a circuit breaker as an isolation point ( providing it can be safely locked out).

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    I forgot to add that the term "isolator" represents the function of a switch mechanism. In this case, the "isolator" may not need to "withstand" any fault currents. Usually, this isolation switch is used in conjunction with a device that will limit/cut any fault/overload currents in the circuit. This isolator is not generally used as a normal switching device for the load.

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    Quote Originally Posted by NigeC View Post
    Yep it does, a service fuse!
    should a service fuse have an isolator switch

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    Quote Originally Posted by Terrian View Post
    should a service fuse have an isolator switch
    Not necessarily.

    Almost all service fuses are the "plug in" type. As such, all that needs to be done is to ensure that no current is being drawn. This can be achieved by switching off your main isolator (main switch) in your meter panel. After the the switch is off, the service fuses can be safely withdrawn & replaced.

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    Quote Originally Posted by elkangorito View Post
    After the the switch is off, the service fuses can be safely withdrawn & replaced.
    Never done. Just attach them to a paint roller extension, line them up and ram it in.

  18. #18
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    Isolator also known by us as a disconnector. Just to add, the isolator as a "safety"
    device must comply to certain standards, such as the isolating gap between the
    contacts. Which does not apply to circuit breakers. That's why according to set standards you use circuit breakers for certain points of an installation and isolators in others.
    Hope this might clarify.
    South Africa.

  19. #19
    Apprentice (new member) mekon's Avatar
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    Hey,

    A "circuit breaker" is the "switch" that turns the power on and off to a circuit and is located in your electrical switchboard.

    An "isolator switch" is a switch that turns on and off a "hard wired" appliance. In your house this typically refers to electric ovens and A/C. Hard wired meaning it cannot be unplugged, the cable is "terminated" directly into the appliance.

    This "isolator switch" is used to quickly and easily turn off an appliance should there be a problem. It should be located nearby the appliance and should be located so it may be reached safely - e.g. if the stove is on fire, you don't want to reach through flames to turn off the stove isolator. It should be located to the side.

    In recent years the Australian Standards have changed to require "isolator switches" for these hard wired appliances. Thats why you don't see them in older homes.

    So thats the difference between a circuit breaker and an isolator switch.

    Hope I've been of assistance, and use an electrician for your electrical work.

  20. #20
    Sparkwah
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    A main switch (isolator) will not operate automatically whereas a circuit breaker will depending on the current rating.
    Apparently a main switch can handle a 6KA short circuit. I doubt it though
    It's better to be dead and cool than alive and uncool

  21. #21
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    AS3000:2007 (+A1) defines the uses of "isolation devices" in 2.3.2.2 Devices for isolation.

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    This will throw a spanner in the works, ELCB or OLCB ?

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    Quote Originally Posted by Kunngee View Post
    This will throw a spanner in the works, ELCB or OLCB ?
    Well thats just random I love it!

    Here I was just beleving it was There as a lock out device and so a sparky could terminate and test an instalation then bugger off and let the next trade be it fridgie or plumber with a b class do there thing without worring about being liable for what they do because his coc would specify that they had only wired as far as the isolator.
    Just me I guess it's my demarkation point.

  24. #24
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    Default Isolator v mcb

    Quote Originally Posted by montiee View Post
    Was wondering if anyone could clarify for my interest the difference between an isolator switch and a circuit breaker.

    Doesn't a circuit breaker switch when turned off act like an isolator switch so in essence why would you bother with an isolator switch?

    Appreciate the explanation.

    Thanks!
    Hi just to inform you,an isolator is a different type of protection device not made to isolate a circuit automatically but manually instead.for your own safety and that of a maintanance issue.a circuit breaker breaks the live feed only whereas an isolator switch breaks both live and neutral supplies instantly.

  25. #25
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    Nah, depends on the isolator. A single pole isolator would break only the active. Same goes for breakers - 1 or 2 (or 3 or 4) pole.

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  27. #27
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    A wild guess I know , but I reckon the OP probably got their answer by the time of the last post in 2010 - gotta watch those thread dates . . .
    Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.


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