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Dad, What's a Circuit?

Zoomup
Well son that a long story.


In my dictionary a circuit is: roughly a circular route, a track for motor racing in the U.K., a regular journey around a district by a judge to hear cases, a system of conductors and components forming a complete electrical path. It comes from the Latin word "circuitus." (No doubt related to the Latin word "circulus," which means circle.


I can see why ebee's friend considers two lighting circuits connected to just one M.C.B.to be two circuits connected together. Two individual circuits connected in parallel in fact.


When we are taught about electrical circuits at school we are told that the circuit starts at the source, which could be a battery terminal , continues to a load, which could be a light bulb, through the load, and then returns back the the battery's second terminal. Or the same arrangement could be made using a transformer's secondary winding.


But B.S. 7671 defines a circuit as: "An assembly of electrical equipment supplied from the same origin and protected by the same overcurrent protective device(s)."


So, a 1.0 mm2 T&E cable supplying lighting connected to a 6 Amp M.C.B. is a circuit. In B.S. 7671 land if a second 1.0 mm2  T&E lighting cable is added to the same M.C.B. there is still only one circuit even though one lighting circuit may supply upstairs in a house, and the other downstairs. Or perhaps originally the two originated from two separate M.C.B.s.


So in B.S. 7671 land, 1 circuit plus 1 circuit = 1 circuit. How could it be any different?


I personally, still though, prefer to call that situation two circuits connected in parallel.


Z.

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    davezawadi (David Stone):

    No Zoomup, unfortunately not. The video is subtly incorrect because at GCSE the definitions may be considered slightly "wooly". He means that the circuit (from a single power source) has two paths in parallel, with different resistances, so that the current splits between them as per Ohms law. You know that the next stage is to apply Kirchoffs law, which applies to a single circuit, and describes in more detail how to calculate the current in branched circuits which may be much more complex. There are then more steps, the superposition theorem, Thevenin's theorem, and Nortons theorem, which allow the analysis of more complex networks, all of which should be familiar to Electricians (but very rarely even remembered as names). Power electrics are extremely simple versions of much more complex circuits, which may have multiple sources of power (the Grid), many more component parts (motors and transformers), and components with more unusual properties (PFC capacitors) which equally respond to analysis with these "Electrical Network" theorems. Apart from the BS7671 definition (deliberately very simple) the entire country is really one huge Electric Circuit, because everything is connected together. An electron (consider this as the carrier of the power) can take any route through any of the country, its route does not define the path, the potentials along the route do. Perhaps, with a bit of luck, you can see why we use the BS7671 definition? Anything else is actually meaningless because we work only on a tiny part of one huge circuit!


    Don't you try to confuse me with all of the old dead geezers' complications Dave, I'm a very simple person. Muddying the water will not convince me or other sensible souls.


    Here is an example of a circuit. One circuit. The vehicles go around and around.

    https://www.racingcircuits.info/europe/united-kingdom/brands-hatch.html#.YL-i_KqSnIU


    Z.


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  • 0
    davezawadi (David Stone):

    No Zoomup, unfortunately not. The video is subtly incorrect because at GCSE the definitions may be considered slightly "wooly". He means that the circuit (from a single power source) has two paths in parallel, with different resistances, so that the current splits between them as per Ohms law. You know that the next stage is to apply Kirchoffs law, which applies to a single circuit, and describes in more detail how to calculate the current in branched circuits which may be much more complex. There are then more steps, the superposition theorem, Thevenin's theorem, and Nortons theorem, which allow the analysis of more complex networks, all of which should be familiar to Electricians (but very rarely even remembered as names). Power electrics are extremely simple versions of much more complex circuits, which may have multiple sources of power (the Grid), many more component parts (motors and transformers), and components with more unusual properties (PFC capacitors) which equally respond to analysis with these "Electrical Network" theorems. Apart from the BS7671 definition (deliberately very simple) the entire country is really one huge Electric Circuit, because everything is connected together. An electron (consider this as the carrier of the power) can take any route through any of the country, its route does not define the path, the potentials along the route do. Perhaps, with a bit of luck, you can see why we use the BS7671 definition? Anything else is actually meaningless because we work only on a tiny part of one huge circuit!


    Don't you try to confuse me with all of the old dead geezers' complications Dave, I'm a very simple person. Muddying the water will not convince me or other sensible souls.


    Here is an example of a circuit. One circuit. The vehicles go around and around.

    https://www.racingcircuits.info/europe/united-kingdom/brands-hatch.html#.YL-i_KqSnIU


    Z.


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