I'm trying to gain an understanding of all this. So I have a main cable that enters the house and connects to the main circuit breaker box. (See picture below) So here the circuit splits into 2 different parallel circuits. And these 2 circuits arrive at other breaker boxes, and split into more parallel circuits, so overall there are about 20 parallel circuits in different buildings through the property. Lets say I install 10 refrigerators throughout the property, and a number of other appliances that pull alot of amperage. Does this mean that the main cable that enters the house is going to be carrying the combined current of all 10 refrigerators and appliances throughout the property, and lighting, outlets, everything? Id imagine that would add up to some really high amperage.

If that idea is actually how it works, would this mean that the main wire would be the most dangerous for a human to be shocked by?

I don't know who wired this house, but its a mess. Im adding more appliances to the property and am a bit afraid the place is gonna burn down in an electrical fire if I don't change things.

 

The amount of current the conductors is carrying does not affect the degree of shock, it is the voltage level.
The conductors feeding your residence/property are carrying the total load (wattage).
The distribution is at a higher voltage, therefore lower current, until it reaches the property where there is usually a local drop drop down transformer.

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I'm trying to gain an understanding of all this. So I have a main cable that enters the house and connects to the main circuit breaker box. So here the circuit splits into 3 different parallel circuits. And these 3 circuits arrive at other breaker boxes, and split into more parallel circuits, so overall there are about 20 parallel circuits in different buildings through the property. Lets say I install 10 refrigerators throughout the property, and a number of other appliances that pull alot of amperage. Does this mean that the main cable that enters the house is going to be carrying the combined current of all 10 refrigerators and appliances throughout the property, and lighting, outlets, everything? Id imagine that would add up to some really high amperage.

If that idea is actually how it works, would this mean that the main wire would be the most dangerous for a human to be shocked by?

Yes, all of the current has to be supported by that main cable you are talking about, which is why it should be larger than the wire on the final circuits. But that doesn't make it any more dangerous than any other point in the system. If you go out and grab onto the main feed at the first panel or onto the prongs of a lamp plugged into that last circuit (assuming it doesn't have a GFCI on it), you will get about the same level of dead. The only practical difference is that the circuits downstream of a panel at least have smaller (lower current) circuit breakers than the breaker near the stepdown transformer that if feeding your property. But when all it takes is ~50 mA in the wrong place to kill you, knowing that there's a breaker that will open when you get to 15,000 mA is of little comfort.

 

Does this mean that the main cable that enters the house is going to be carrying the combined current of all 10 refrigerators and appliances throughout the property, and lighting, outlets, everything?

Yes. Without getting into the math, and how AC is very different from DC, the basic idea is this: Where else would it come from?

You don't say where you are located, and it makes a big difference in how AC power is distributed outward from the incoming mains point. But if there is only one cable from the power company, then all of the power moves through that cable.

Note that the amount of current *available* is not the same as the amount of current you are drawing at any moment in time. Also, the distribution voltge is relatively constant from 0 A to your maximum amperage draw. Without re-opening the pedantic debate about whether it is the voltage or the current that can kill you, the 240 Vac at an outlet somewhere down the line after an intermediate circuit breaker is just as lethal as the 240 Vac in the breaker box. The breaker is there to prevent a fire, not to save your life. Ground Fault Interrupting (GFI) breakers are a special case, but even those do not cover all possible ways to be electrocuted. They protect against one type of unintended contact with lethal voltage/current, not all of them.

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Consider that probably the electric power utility company is selling you the power, then certainly every bit of that power passes through the electric power meter, and then, usually, into the main power distribution panel.
Usually the wiring into the panel from the pole, (or underground feed) is done in manner proportional to the anticipated maximum load current. Past the main distribution panel portions of the power pass to various points of use, with the individual branch circuits having individual protection arrangements according to their rated capabilities. So having a large number of properly sized branches is by no means a danger.