1. Introduction and Disclaimer For a trouble-free operation of a system containing inverter/chargers and batteries, it is essential that the wiring in the system is done correctly. Many system problems are due to bad wiring. A system might underperform due to sub-standard wiring on both the DC or the AC side. In this document we aim to explain about wiring, the importance of getting it right and assist the installer in making the correct choices. We would like to acknowledge that electrical wiring regulations are different based on where you are in the world. Local electrical regulations can differ from the wiring advice given in this document. It is your responsibility to always seek professional advice and instruction form local authorities and/or licensed electricians prior to commencing any electrical work. The sole purpose of this document is to aid in the understanding of basic principles behind certain electrical concepts. This document is intended as a guide only. 2. Theory To be able to understand the underlying factors are that determine wiring thickness and fuse ratings. You do need to know some basic electrical theory. You might already know this and can perhaps skip this chapter, but we highly recommend that you at least have a read. 2.1 Ohm’s Law This basic electrical law allows you to be able to calculate the current that runs through a cable or a fuse at different voltages.
Electricity is movement of electrons. When you pass electricity through a material it meets a certain resistance. When the resistance is low the elections move easily, and the current is high. When the resistance is high the electrons move slow or do not move at all and the current is low. The resistance determines how much current runs through a material at a given voltage. This can be represented in a formula. The formula is called Ohm’s Law:
Current (A) = Voltage (V) / Resistance (Ω) I = V/R
2.2 Power
Ohms law can be used to derive other formulas. All possible formulas are listed in the image on the right. Please note that there are two symbols in use in the world that represent Voltage. These are U or V.
Some of these formulas are very useful when calculating current in cables.
One often used formula is this formula.
I = P/V
It calculates the current through a cable when the voltage and the load is known:
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