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Old 10-08-2009, 08:28 AM   #16
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Subpanels Nightmare in Baltimore


Great information -- but would be wonderful if someone elaborates on the subject of "load leveling" when you have a larger breaker box. For example, you can have breakers addiing up to 120A on a 100A box, but it is very unlikely that they will be ALL used together. In contrast, a small panel, which has 2 breakers, may experience full load when both happen to be turned on at the same time.

Is there advantage or disadvantage to hooking up all sub-panels to one main panel, or feeding from one another? Also, would wiring be different based on the configuration?Thank you.

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Old 10-08-2009, 09:01 AM   #17
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Subpanels Nightmare in Baltimore


Usually all subs run from the main panel
If you daisy chain one sub off another sub then the power draw keeps adding
So that 1st sub's main breaker may kick off if too much draw
All depends upon the subs & power draw

200a main, 100a sub, then you run a 30a sub for some small kitchen outlets
Unlikely you will overload that 100a sub

Now instead put a 50a sub for a hot tub off that 100a sub
You have now used possibly 50% of the 100a subs power when the hot tub is running


Load levelling
Example your main breaker & service is a 100a
240v loads will pull power from both hots - possibly equally
Now you add some 120v loads but they are only pulling from one hot
That 100a breaker protects each hot to 100a
If either side exceeds 100a then the main breaker kicks off

Usually panels are setup so that as you fill the panel the buss alternates
So installing breakers is automatically pulling from alternating hots
But say you just happen to install the heavy pull 120v items on every other breaker as you go down
Then the heavier loads would be pulling from the same hot feed
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Old 10-08-2009, 09:34 AM   #18
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Subpanels Nightmare in Baltimore


Sometimes you cannot do load leveling just by looking in the panel.

You need to go through the house and make a note of where the bigger appliances (including hair dryers and large audio systems) are plugged in at the present time or where you plan to plug in new large appliances soon. Then make a list of the affected circuits and the approximate wattages.

Then re-arrange the breakers in the panel as needed.

Don't bother listing the 240 volt appliances; they load both sides of the line equally.

For 120/240 volt (3 wire) subpanels, also spot check the present and projected future loads on their branch circuits (subcircuits if you insist) on each side of the line.

If you have two 120 volt (2 wire) subpanels, you can make an educated guess and put their main panel breakers on opposite sides of the line.
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Last edited by AllanJ; 10-08-2009 at 09:46 AM.
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Old 10-08-2009, 06:31 PM   #19
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Subpanels Nightmare in Baltimore


Allan J (Poster #18)
...Or with an "Amprobe" (again using Trademark for product/class identification), inductive ammeter!. Attach to each feeder, successively (and successfully) at nearly full load. Then, according to listed draw of appliances, rearrange breakers in panel to +- balance load! Eliminate Confusion through Education!!! (No matter what)Don't Drink and Drive, Ever!!!

Last edited by spark plug; 10-08-2009 at 06:32 PM. Reason: Missing letter;
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Old 10-08-2009, 09:51 PM   #20
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Amprobe, Klenex, Post-it, whatever... :-)

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