200 amp single phase service, per line or combined?

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Old 11-29-16, 08:43 AM
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200 amp single phase service, per line or combined?

Hello All,
I have a question in regards to residential single phase service and would appreciate some clarification. I've done quite a bit of electrical through the years but never really considered the following because there has never been a question of capacity or maybe I'm just slipping due to age.


Please clarify that 200 amp service is per line. So in essence you have 400amps total (200amp x 2 lines).

I want to install a 100 amp sub-panel off a main 200 amp service panel. Sub-panel "A" will consist of a few 20amp single pole breakers and one 60 amp double pole breaker that will feed a second sub-panel "B", which will have a few 20amp single pole breakers as well.

As long as neither of the lines/legs exceed 100 amps then I should have no issue with sub-panel "A" correct?

In theory.....

*I could run 60 amps on each leg of subpanel "B" (3 20amp breakers line A, 3 20amp breakers line B)

and 40 amps on each leg of subpanel "A" (2 20amp breakers line A, 2 20amp breakers line B).


I would never run full capacity (80% rule) of course. I'm just trying to better understand something I never truly had to consider, because in this instance I have electrical limitations.


Thanks,
Ralph
 
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Old 11-29-16, 09:41 AM
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Please clarify that 200 amp service is per line. So in essence you have 400amps total (200amp x 2 lines).
No. You have 200 amps at 240 volts.
However you can derive 400 amps at 120 volts using each of the 240 legs with the neutral.
As long as neither of the lines/legs exceed 100 amps then I should have no issue with sub-panel "A" correct?
You seem to misunderstand how a panel is wired. It doesn't use one line It uses two hots, the two legs of 240 volts to your house, and one neutral from which 120 volts is derived in conjunction with one of the 240 volt hot legs.

Actual load is used to determine panel capacity not the total of the breakers because they are unlikely to ever be fully loaded and it is even less likely they will all be fully loaded at the same time.

Take a look at the subpanel diagrams to get a better idea. http://www.doityourself.com/forum/el...-diagrams.html
 

Last edited by ray2047; 11-29-16 at 12:50 PM. Reason: Add information and clarify.
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Old 11-29-16, 11:09 AM
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It's both. Each line supplies 200A at 120V, or together 200A at 240V.
 
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Old 11-29-16, 11:23 AM
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A perfectly balanced panel could supply 400 amps at 120 or 200 amps at 240.
 
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Old 11-29-16, 12:10 PM
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Y'all wrong. 48 kiloWatts. You can make many combinations of Amps/Volts with transformers at the house, but 240V/200A service will limit you to 48kVA.
 
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Old 11-29-16, 07:17 PM
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You can make many combinations of Amps/Volts with transformers at the house, but 240V/200A service will limit you to 48kVA.
I doubt that as well as the transformer that is feeding the service is likely only 15kVA transformer.
 
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Old 12-09-16, 08:58 PM
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quote by pcboss...."A perfectly balanced panel could supply 400 amps at 120 or 200 amps at 240."
Thanks, that is the answer I was looking for and what I assumed.



To reply to a few other questions/statements.

1) Yes, there are two "hot" legs to a single phase panel. Each leg has 120volts, combined they equal 240volts. A 3 phase panel will have three "hot" legs but the combined reading will vary according to the service you have.

2) Yes, you would never typically have a panel loaded up or maxed out due to a heavy load on every circuit. Consequently, the total number of 20amp breakers in a normal home panel could well exceed on paper what the panel is actually rated for.

However, this is not a typical case and why I made the inquiry. Most of the circuits on the panels will be loaded up as they are powering a very large Christmas lights display. I am highly accustomed to checking and balancing loads but I've never been in a situation where it's possible to max out a panel (80%). I just wanted to verify my understanding of what a full load is.

The panels will have around 150amps per leg (120volt circuits) so 300amps total on a 200amp panel. This was throwing me because I've never had to consider such a load on a panel.

God Bless,
Ralph
 
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Old 12-09-16, 11:11 PM
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The panels will have around 150amps per leg (120volt circuits) ... on a 200amp panel.
That's perfectly fine.

so 300amps total on a 200amp panel.
Despite we are already clear that you are referring to 150Amps on each leg, stating 300Amps total is just NOT quite practical nor acceptable to be expressed that way when talking about the total electrical load being used..., just state 150Amps per leg (at 120Volts) on a 200Amps service, THAT'S IT. In this case the total amount of 300Amps total load between both legs is NOT necessary to be stated, do not sum 150 + 150 = 300 total, because doing so will cause confusion and lead to undesirable misunderstood electrical concepts.


This was throwing me because I've never had to consider such a load on a panel.
Don't worry you can keep adding loads and max up the panel, because if you ever use more than the maximum rating of the 200Amps breaker, the breaker will trip and you will know you are exceeding the maximum rating by either way having more than 200Amps per phase (at 120Volts), or having more than 200Amps at 240Volts. Same applies for branches circuits if you exceed the rating of the single pole breakers protecting those circuits the breaker will trip and you will know you are overloading the circuit. If that happens you just have to reduce the load to the level where the breaker doesn't trip. But, indeed, you can have up to 200Amps per phase at 120Volts and everything should keep working perfectly. IF everything in the circuit is wired correctly, (correct size/rating of the conductors and breakers) then only thing can happen by overloading the circuit is that you will trip (using more amps than the rating of the breaker) or don't trip the breaker (using less amps than the rating of the breaker). Nothing more is suppose to happen.

HOWEVER, IF the load trips the breaker what you CAN'T NEVER do is to change the breaker to higher rating without upgrading the conductors in order to match or allow for higher ampacity than the rating of the new breaker.



May YAHVEH the Almighty Elohim of Israel Bless you.

Jos.
 
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