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Electrical riddle no.5 – DC Control systems and polarity

Usually the circuit is supplied by positive and negative polarity of one battery. In almost electrical circuit diagram sheets we can see a positive line of DC polarity in top of sheet and negative line in bottom of sheet that is purposed to supply electrical equipment of circuit.

How can you explain that polarity arrangement? Why the negative polarity is usually located in bottom and positive polarity in top of sheets?
Is it habit activity in drawing circuits or not? If all used electrical equipments, for example auxiliary relays, open and close coil of power circuit breakers and so on could be activated by inverse polarity, would we change that mentioned norm, and use negative in top of sheets and positive polarity in bottom, without any circuit configuration changing?



Author : Hamid
 
#1
Mon, October 1, 2007 - 16:24
Generally electrical equipment that used in auxiliary control systems shown in bottom of pages. Therefore equipment (relay etc.) that usually installed in field area is directly connected to one of two polarity continuously, and other polarity connected to the other terminal of equipment via auxiliary contact of controller devices that shown on top of pages transitionally.

Continuous connection must be negative, to prevent corrosion of equipment due to electrolytic action, because they usually installed in outdoor and corrosive area.

Of course this recommendation related to battery system grounding way.For more information you can refer to Grounding Riddle No.20 . 
Author : Hamid - From: Iran
 
#2
Tue, October 9, 2007 - 09:06
The CONVENTIONS used by Fore-Runners are accepted by all the communities in the world, although these are improved for easy-understanding & beauty of the game; not as rivalry.

Our Fore-fathers in the early days named the days of the week as: Sunday, Monday & all should not criticised now but accepted as STANDARDS as those are universally accepted.

You know the USA still has not adopted Meteric-system [ISO> in its industry although it is adopted by rest of the world.

And here we like to change the way all Electrical / Electronic Drawing System for no reason of improvement but just to make ourselves introduced.

We should know that "Drawings conventions & Drawings" have International Language. You can generally work on any drawing having totally different language markings / notings, but cannot on a drawing having drawn on different convetions or standards.

Now come your question:

************ Quote **************
"If all used electrical equipments, for example auxiliary relays, open and close coil of power circuit breakers and so on could be activated by inverse polarity, would we change that mentioned norm, and use negative in top of sheets and positive polarity in bottom, without any circuit configuration changing?"
************ Quote Ends **************

Not only (+) polarity is kept normally on top of drawings, but for AC Supply Live is also,
due to the reason that universally [except some very old designs pre-standardisation era>
(+) end & Live are SWITCHED or controlled and the other-ends are not switched.

Haajee, Pakistan.
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Author : Haajee
 
#3
Tue, October 9, 2007 - 14:40

I've never thought of this concept. I remember early on in the automobile when they were first adding electrical devices to them, a few had positive grounds. Probably didn't take long for them to find the corrosive action, becaue of this configuration and negative ground became the standard world wide.
Without this information you have posted, I would never have really know why. Thanks for sharing this. Sometimes we do things because its the way we have always done it. Now we can all know why.

Jim

 
Author : JimmyDee
 
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