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What determines size of main breaker?

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What determines size of main breaker? Big Giant Head 05-07-2007
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Posted by Big Giant Head on May 7, 2007, 12:29 pm
On branch circuits the size of the wire and type of circuit determines the
breaker size but what determines the size of the main or combination of
mains? Can it be as large as the panel is rated for or must it match the
size of the utility's drop?

We have an old panel with two mains, one is a double 50A feeding the rest
of the panel. The other is a double 30A feeding the dryer outlet directly.
The town now mandates 100A and I think homes get inspected when sold.
Rather than replace the whole panel I could replace main #1 with a double
70A (if available) OR maybe better would be to replace main #2 with a
double 50A (or higher) and have it feed a small subpanel in which I would
put a double 30A for the dryer and maybe throw in a few others as well.
That's within the rating of the main panel but not sure about the utility
drop.

Posted by hallerb@aol.com on May 7, 2007, 12:33 pm
On May 7, 12:29=EF=BF=BDpm, Big Giant Head
> On branch circuits the size of the wire and type of circuit determines the
> breaker size but what determines the size of the main or combination of
> mains? =A0Can it be as large as the panel is rated for or must it match t=
he
> size of the utility's drop?
>
> We have an old panel with two mains, one is a double 50A feeding the rest
> of the panel. =A0The other is a double 30A feeding the dryer outlet direc=
tly. =A0
> The town now mandates 100A and I think homes get inspected when sold. =A0
> Rather than replace the whole panel I could replace main #1 with a double
> 70A (if available) OR maybe better would be to replace main #2 with a
> double 50A (or higher) and have it feed a small subpanel in which I would
> put a double 30A for the dryer and maybe throw in a few others as well. =
=A0
> That's within the rating of the main panel but not sure about the utility
> drop.

Main breaker must match main service drop and meter can and panel.

With such low ratings how is the physical condition of your drop?

I have a friend epoxying his drop to keep the outer jacket together


Posted by hallerb@aol.com on May 7, 2007, 12:34 pm


go with 200 amps its well worth just a few bucks extra


Posted by John Gilmer on May 8, 2007, 11:39 am

>
>
> go with 200 amps its well worth just a few bucks extra
>

As another poster noted, the main panel breaker is sized to the drop from
the power company. IF the drop supports 200 amps then, yes, you might as
well spring for the larger panel. You never know when circumstances might
cause your unit to draw over 100 amps.



Posted by Eigenvector on May 8, 2007, 4:09 pm

>
>>
>>
>> go with 200 amps its well worth just a few bucks extra
>>
>
> As another poster noted, the main panel breaker is sized to the drop from
> the power company. IF the drop supports 200 amps then, yes, you might as
> well spring for the larger panel. You never know when circumstances
> might
> cause your unit to draw over 100 amps.
>
>
How would you know if the drop was sized for 200A?


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