Determining the Amperage of All Circuit Breakers


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Old 02-19-20, 07:20 PM
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Determining the Amperage of All Circuit Breakers

Okay. Let me start by stating that I really am not looking for someone to go postal on me if I am completely off base on some point or they feel I am asking a stupid question. I'm just trying to understand a relatively complex interaction of components and electrical functionality.

That said, I understand the idea that a my panel is supplied with 200 amps and the capacity of the circuit breakers in the box theoretically doesn't matter, they could all be 50 amp breakers with a single light bulb attached to each breaker and everything will run without an issue. If you summed up all the breakers it would far exceed the 200 amp circuit, but because the power draw of all the bulbs actually is only a tiny fraction of the 200 amps everything will chug along happily. Now don't get too worked up, I do understand that it would be a very wrong setup, I'm just exaggerating in order to make a point... hopefully a correct one.

What really matters is (A) matching the breaker appropriately to what will be on the circuit and (B) ensuring that the actual summed amps being used by the items on the circuits don't exceed the 200 amp supply. And yes, I know there is a buffer and you don't actually want to try and use up to the 200 amps... just trying to keep it simple so I can explain and get a simple, understandable answer.

So, with the caveats listed I hope you agree with my assertions. If so (or even if not), help me with this question. There are codes and best practices. With those in mind, should I be concerned about how many amps the breakers themselves sum up to compared to the capacity of the main circuit? IF all the breakers are sized appropriately for their circuits but they collectively ALLOW the possibility of drawing lots of simultaneous power that exceeds the supplied power it will result in the primary breaker being tripped and shutting off power to the entire house.

So, I guess my question surrounds established guidelines that would reduce the likelihood of such a condition happening.

I know there are lots of unknowns based on what is being used in the house. If it really doesn't matter about the breakers and you will recommend a use analysis on all connected devices, I can accept that.

I hope I was coherent in my post without ruffling too many feathers!
 
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Old 02-19-20, 07:25 PM
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Adding up the breaker ratings is not a useful calculations.

Suggestions and sometimes rules are made for what and how many receptacles you can put on a branch circuit.

Some circuits must be dedicated to certain usages, for example the laundry area needs a 20 amp circuit for a washing machine but not shared with any other room.

The main breaker will (should be sized so as to) keep the total load from overloading the meter or the service conductors or the feed cable entering the panel. Staying within the amperage limit of each branch circuit and of the main breaker is done using manual discipline.

General purpose 120 volt circuits, for lights and small appliances and most electronics, are always 15 or 20 amp. A typical arrangement, not a rule of thumb, is to have a separate branch circuit for each room, not counting the dedicated circuits hinted at earlier. Large appliances usually require their own branch circuits and their instructions state what the amperage rating needs to be.

For a use analysis, a sample set of rules and formulas is the "load analysis" at the back of the National Ellectric Code book. For planning the wiring for a basement you are finishing or an addition to your home there are easier to understand books on installing and repairing wiring; Home Depot has had a few displayed in their electrical equipment section. I think the title of one is "Wiring Simplified".
 

Last edited by AllanJ; 02-19-20 at 07:50 PM.
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Old 02-19-20, 08:02 PM
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So, with the caveats listed I hope you agree with my assertions. If so (or even if not), help me with this question. There are codes and best practices. With those in mind, should I be concerned about how many amps the breakers themselves sum up to compared to the capacity of the main circuit?
No. Because a breaker does not use power. It all depends on what is connected. Many of your breaker are probably using 0 amps.

So, I guess my question surrounds established guidelines that would reduce the likelihood of such a condition happening.
The established guideline would be called a demand load calculation. The NEC code has rules for how to calculate the potential max load and establish what size service should be installed.
 
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Old 02-20-20, 08:40 AM
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I had run across the NEC load analysis sheet and saved it for using later. Thanks for your responses.
 
 

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