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Dad, What's a Circuit?

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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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  • 0
    If you have two haystacks  in separate fields and we use the telehandler to move the bales so you merge them into a new pile  in another place, is it too great a mental leap to see that we still have one haystack, just a rather larger one ?

    In that case  1+ 1 = 1 is not a problem, just the '1' symbols refer to different things, as this is not simple arithmetic..


    Also something similar happens here.

    If one electron leaves the MCB, another one will arrive at the neutral bar,  and some charge has completed  ' a circuit'.


    Now that may be much like a runner going round a track in the simplest case, or perhaps more like a mini-bus load of  scouts going round  a motorway services, in both cases, in the end they all return to their point of arrival.. usually, some having expended more  than others,and some having longer routes ..


    Much the same could be said at the substation -  for every amp (1.6E 19 electrons per second) that leaves down the red phase of the transformer the same number will return to the other end of the winding via one of many routes. 

    This current too has completed ' a circuit' of the wiring but not all of it has taken the same route.

    Mike.
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  • 0
    If you have two haystacks  in separate fields and we use the telehandler to move the bales so you merge them into a new pile  in another place, is it too great a mental leap to see that we still have one haystack, just a rather larger one ?

    In that case  1+ 1 = 1 is not a problem, just the '1' symbols refer to different things, as this is not simple arithmetic..


    Also something similar happens here.

    If one electron leaves the MCB, another one will arrive at the neutral bar,  and some charge has completed  ' a circuit'.


    Now that may be much like a runner going round a track in the simplest case, or perhaps more like a mini-bus load of  scouts going round  a motorway services, in both cases, in the end they all return to their point of arrival.. usually, some having expended more  than others,and some having longer routes ..


    Much the same could be said at the substation -  for every amp (1.6E 19 electrons per second) that leaves down the red phase of the transformer the same number will return to the other end of the winding via one of many routes. 

    This current too has completed ' a circuit' of the wiring but not all of it has taken the same route.

    Mike.
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