The Laws of Circuit - you can learn and practice by just reading

copyright. Charles Kim 2006

 

KCL and Zero Cash Flow

 

KCL (Kirchhoff's Current Law) is a portrait of middle class America that spends all they earn. Well, in 2006, the saving rate in America is in the negative zone. This means in average each household spends more than it earns, with borrowed money. Cash flow is a way to measure between income and expense. If income is bigger than expense, we have positive cash flow, and out of this positive, we can save or invest. If income is the same as expense, cash flow is zero, zero cash flow.

 

This zero cash flow situation is not recommendable in real life, no saving and no investment and no retirement at sight, the nature however seems to love this "zero" thing. This "zero" thing is usually expressed as "conservation" law or theory. Like energy conservation which basically says energy produced in a closed system must be the same as the energy consumed. KCL is also part of the big conservation law. It dictates that there should not any cash (current) left in a household (node) in the society (circuit). If a household has one income source (a current flowing into the node) that income must be distributed to all expenses (the currents flowing out of the node). If there are multiple income sources (salary, rental income, dividend income from equity, etc), they all must be spent to expenses. As Americans under Conservation Rule live in zero cash flow, all circuit lawyers exercising KCL must apply that all the currents flowing into a node should be distributed to all the currents flowing out of the node. In a simple formula: The sum of all the currents into a node is the same as the sum of all the currents out of the node.

 

Often novice circuit lawyers assume, when applying KCL, that there is one current into a node and there is one current out of the node, even when the node has 3 branches! Each branch connected to a node has its own right of current path, either into or out of the node. Point here is to consider all the branches connected to a node in KCL application.

One good thing for circuit lawyers in KCL case is that, unless current flow direction is not given in the circuit, they have full freedom to choose the direction of the current flow: out of or into the node. What a wonderful situation they are in! In real world I cannot claim my lunch money expense at the Five Guys as my income.

 

My advice: When you do not practice the circuit law, practice positive cash flow. And save and invest. I know a guy who just gradated and got Bachelor's degree in electrical engineering (which means he practiced the circuit law like you do now), practiced positive cash flow and saved and invested as he entered the college.And he's already a millionaire with his name in the deeds of two 4-unit apartments. Of course he's not in rural America. He's in the nation's capital. If you do not know what "deed" means, don't worry. Practice positive cash flow for a few years, then you will not only see but also get one.

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