200 amp panel amperage flow

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Gremaley

DIY
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I am trying to understand the amperage flow in my 200 amp main panel.

In theory, (example only), let's say you had a 200 main panel installed with (7) single pole 20 amp breakers on each hot leg.
So (14) single pole breakers total ...
For the sake of this example let's further assume you had just one outlet wired to each breaker and those outlets all had a hair dryer pulling were plugged in and running (pulling 15 amps each ... If my math is correct, that is 105 amps through each each hot leg. My understanding is that this would NOT trip the main breaker because the panel can only see 105 amps total since each hot leg is out of phase with the other hot leg.
So 105 amps total flow, alternating between the 2 legs (60 times a second) - not 210 amps total.
Do I understand that correctly?

The thing I can't quite get is that you are effectively pulling 210 amps (if all 14 hair dryers are running) yet the panel is only seeing 105 amps.

Solution
Yes, and you should have what is known as a split phase supply.
therefore because of some wizardry of sine waves and phase shifting, the Neutral current can not become more than the current flow in either of the 2 live wires, it is in fact roughly the difference between the 2.
eg. if you have 150A on L1 and 100A on L2 the N current will be 50A
NOT the total of the 2 lives that would be 250A

James

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you are close in your understanding.
imagine only every 2nd single pole breaker was switched on
15A x 7 devices =105A on L1
turn the other breakers on and you also have
15A x 7 devices =105A on L2

James

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good video to explain the basics

OP
G

Gremaley

DIY
you are close in your understanding.
imagine only every 2nd single pole breaker was switched on
15A x 7 devices =105A on L1
turn the other breakers on and you also have
15A x 7 devices =105A on L2

Thanks James, so the reason the 200 amp main doesn't trip is because both L1 and L2 can safely have up to 200 amps flowing on each bus bar? It seems like that is the case, we have a very old building that still has an old style disconnect with (2) 200 amp fuses that protect L1 and L2 before they enter the main panel.

James

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Yes, and you should have what is known as a split phase supply.
therefore because of some wizardry of sine waves and phase shifting, the Neutral current can not become more than the current flow in either of the 2 live wires, it is in fact roughly the difference between the 2.
eg. if you have 150A on L1 and 100A on L2 the N current will be 50A
NOT the total of the 2 lives that would be 250A

Last edited:
OP
G

Gremaley

DIY
Bingo! The marble just dropped! Thank you for that explanation!
Between the video and that last nugget I have it now.

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