# 600 Amp Service, 600 Amps Max Breakers?



## 4464528 (Aug 14, 2012)

I am installing a new 200A breaker in an existing 600A service. The service currently has 3 open positions. The other three have 200A breakers. The engineer I am dealing with says that we can't exceed the 600A rating and is asking me to do a detailed eval. of existing current draw to see if we can re-size the existing breakers. I guess my basic question (I think) is - can the rating of the individual breakers in a service exceed the current rating of the service?


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## Awg-Dawg (Jan 23, 2007)

4464528 said:


> I guess my basic question (I think) is - can the rating of the individual breakers in a service exceed the current rating of the service?


 No, you go first.

What do you think?


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## BBQ (Nov 16, 2010)

Yes, the breakers can add up to well above the rating of the main.

BUT .. the load cannot exceed the main rating and as far as the NEC you are required to determine the existing load before adding to it.


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## randas (Dec 14, 2008)

You could put one million 200a breakers in a 600a panel depending on the load.
The EE you are dealing with is a straight up ******.
Ask him if he applys the same logic to all panels? Max ten 20a breakers in a 200a panel I guess??


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## BBQ (Nov 16, 2010)

randas said:


> You could put one million 200a breakers in a 600a panel depending on the load.


I agree




> The EE you are dealing with is a straight up ******.


No, the EE is following what the NEC requires, you cannot (legally) add load without knowing the load you already have.


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## randas (Dec 14, 2008)

BBQ said:


> No, the EE is following what the NEC requires, you cannot (legally) add load without knowing the load you already have.


The way I read the OP is the EE dosent want more than 600a worth of breakers in the 600a panel. He mentioned downsizing the OCP on the existing feeders to 'make room' for the new feeder... thats how I read it.

I agree a load calc is needed, but if the total load comes in under 600a he can add his 200a breaker to the main panel without downsizing the existing feeder OCPs


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## Bbsound (Dec 16, 2011)

Is there a main breaker?


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## BBQ (Nov 16, 2010)

randas said:


> The way I read the OP is the EE dosent want more than 600a worth of breakers in the 600a panel. He mentioned downsizing the OCP on the existing feeders to 'make room' for the new feeder... thats how I read it.
> 
> I agree a load calc is needed, but if the total load comes in under 600a he can add his 200a breaker to the main panel without downsizing the existing feeder OCPs


I give EEs more credit, we are getting this info second hand.

If your name was going on it would you _assume_ you could add up to 200 amps of load on a 600 amp source?


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## Executive (Aug 11, 2012)

BBQ said:


> I agree
> 
> 
> 
> ...


Isn't the load calc already done and the maximum load fixed at 600A when the service is installed? Are you confusing this with the requirement for load calc when multiple service disconnects (up to six) are used on a single service? Once a main breaker is installed, the maximum load is a known commodity.

Chris


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## McClary’s Electrical (Feb 21, 2009)

Executive said:


> Isn't the load calc already done and the maximum load fixed at 600A when the service is installed? Are you confusing this with the requirement for load calc when multiple service disconnects (up to six) are used on a single service? Once a main breaker is installed, the maximum load is a known commodity.
> 
> Chris


The maximum load is 600 amps. What we dont know is the calculated load. What if theres only 100 amps of calculated load on each 200 amp load center? That would leave plenty of room for another 200 amp load center


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## nolabama (Oct 3, 2007)

4464528 said:


> I am installing a new 200A breaker in an existing 600A service. The service currently has 3 open positions. The other three have 200A breakers. The engineer I am dealing with says that we can't exceed the 600A rating and is asking me to do a detailed eval. of existing current draw to see if we can re-size the existing breakers. I guess my basic question (I think) is - can the rating of the individual breakers in a service exceed the current rating of the service?


Why would you want to resize breakers? Agreed no more than six bills worth of load. What is the load of the new 200 amp over current device your installing? What is existing load? 

Not to OP 
Can you determine load on something like this with a meter? You can't can you? You gotta use the NEC don't ya?


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## McClary’s Electrical (Feb 21, 2009)

nolabama said:


> Why would you want to resize breakers? Agreed no more than six bills worth of load. What is the load of the new 200 amp over current device your installing? What is existing load?
> 
> Not to OP
> Can you determine load on something like this with a meter? You can't can you? You gotta use the NEC don't ya?


 

I completely understand what you're saying, but the code does allow this exemption from load calcs.:


*220.87 Determining Existing Loads.​*​​​​The calculation of a
feeder or service load for existing installations shall be
permitted to use actual maximum demand to determine the
existing load under all of the following conditions:
(1) The maximum demand data is available for a 1-year
period.​
_Exception: If the maximum demand data for a 1-year period
is not available, the calculated load shall be permitted
to be based on the maximum demand (measure of average
power demand over a 15-minute period) continuously recorded
over a minimum 30-day period using a recording
ammeter or power meter connected to the highest loaded
phase of the feeder or service, based on the initial loading
at the start of the recording. The recording shall reflect the
maximum demand of the feeder or service by being taken
when the building or space is occupied and shall include by
measurement or calculation the larger of the heating or
cooling equipment load, and other loads that may be periodic​in nature due to seasonal or similar conditions.
_


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## Executive (Aug 11, 2012)

220.87 is an optional calculation. It can be used in lieu of the standard calculations for a premises system. Once a main breaker is installed, you can add as much load as you want after it. Is this the best installation? Absolutely not, but 90.1(B) says it can be done. 

Look at it a different way. A single phase 40 position 120/240 panel can hold 40 20 amp breakers. That's 800 amps of potential but the load is never going to exceed 200 amps. Same situation with the OP. 

If I missed the article that says a recalculation is necessary before adding load to an existing premises on the load side of a main breaker, please educate me. I will thank you, and buy you a beer if you are ever in my area. Nobody is perfect and we're all here to learn so I hope I learn something.

Chris


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## cory3408 (Aug 12, 2012)

The EE has a rational concern but he is confusing 2 different concepts.

The 600a main breaker protects the busswork and wire from the 600a breaker to the line side of the individual feeder breakers (200a in your case)

200a feed breakers SC/GF/ OC protection for everything load side of the feeder

Others on the thread are correct that the main must be sized accordingly via the methods discussed in the thread, but simply lowering the feeder breaker ratings does not reduce the circuit demand so derating does not accomplish anything in terms of the panel main breaker rating


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## don_resqcapt19 (Jul 18, 2010)

cory3408 said:


> The EE has a rational concern but he is confusing 2 different concepts.
> 
> The 600a main breaker protects the busswork and wire from the 600a breaker to the line side of the individual feeder breakers (200a in your case)
> 
> ...


I don't see anything that tells me this service has a main breaker. It appears to be a service that has 2 to 6 means of disconnect and 3 of those six are in use now. The OP is adding the 4th service disconnect.


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## Executive (Aug 11, 2012)

don_resqcapt19 said:


> I don't see anything that tells me this service has a main breaker. It appears to be a service that has 2 to 6 means of disconnect and 3 of those six are in use now. The OP is adding the 4th service disconnect.


Now that I read it again, you have a point. Absolutely if there is no main breaker, calculations are required. This looks like 230.80 would be in effect. The combined rating of all disconnects _could_ still be greater than the 600 amp service size, though.

Chris


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## don_resqcapt19 (Jul 18, 2010)

Executive said:


> Now that I read it again, you have a point. Absolutely if there is no main breaker, calculations are required.


Even if there is a main, the addition of additional load requires a load calc.


> This looks like 230.80 would be in effect. The combined rating of all disconnects _could_ still be greater than the 600 amp service size, though.
> 
> Chris


Yes, when you have multiple service disconnects, the total of the OCPDs can be greater than the ampacity of the service conductors and panel bus as long as the calculated load is less than either of those two things.


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## Executive (Aug 11, 2012)

don_resqcapt19 said:


> Even if there is a main, the addition of additional load requires a load calc.


Help me out, I can't find the article that requires this.

Chris


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## Pete m. (Nov 19, 2011)

*215.5 Diagrams of Feeders.* If required by the authority
having jurisdiction, a diagram showing feeder details shall
be provided prior to the installation of the feeders. Such a
diagram shall show the area in square feet of the building
or other structure supplied by each feeder, the total calculated load before applying demand factors, the demand factors used, the calculated load after applying demand factors, and the size and type of conductors to be used.

Pete


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## BBQ (Nov 16, 2010)

Executive said:


> Help me out, I can't find the article that requires this.
> 
> Chris



You did not think you could just add load without concern for the existing load did you?

Branch circuits



> 210.11 Branch Circuits Required. Branch circuits for
> lighting and for appliances, including motor-operated appliances,
> shall be provided to supply the loads calculated in
> accordance with 220.10..........




Feeders



> 215.2 Minimum Rating and Size.
> (A) Feeders Not More Than 600 Volts.
> (1) General. Feeder conductors shall have an ampacity not
> less than required to supply the load as calculated in Parts
> III, IV, and V of Article 220..........



Services



> 230.42 Minimum Size and Rating.
> (A) General. The ampacity of the service-entrance conductors
> before the application of any adjustment or correction
> factors shall not be less than either 230.42(A)(1) or
> ...


So while I do agree with you that specifically 220.87 is optional way to determine the existing load, the act of determining the existing load is not optional.

Now I do live in the real world and few of us do load calculations when adding a 20 amp circuit to a 600 amp service but if I was adding potentially 200 amps to a 600 amp service you can bet I would be concerned with the existing load.


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## Executive (Aug 11, 2012)

BBQ said:


> You did not think you could just add load without concern for the existing load did you?
> 
> Branch circuits
> 
> ...


You're mixing up a few articles that do not apply directly to the original question. 

210.11 just says that branch circuits must be provided to serve the calculated loads from 220.10 -- this article does not help our discussion.

215.2 states that feeders must be sized according to the load that they supply. Again this does not help our discussion because we are talking about the service and if it is adequately sized for the loads served.

230.42 is applicable in that it requires service entrance conductors to have an ampacity sufficient to comply with 230.42 (A) (1) or (2). Adding significant load could have an impact on compliance with this calculation.

Of course I consider the available current when adding load. That's just being thorough and providing your customer with a good job. We still don't know if the OP refers to a main breaker or a set of (up to six) main disconnects. In my area I have never had an AHJ ask for a load calculation when adding to an existing service with a main, though it is within his jurisdiction to do so according to 215.5.

Adding the 200A feeder as suggested in the OP depends on a couple of things. If this new 200A is one of the six permitted disconnects, I agree 100% that a calculation must be done and it must be determined if the existing 600A service is sufficient. If there is a 600A main, it must be determined if factors such as non-coincident loads or load diversity will allow the added load to operate without issue at the main. 

I like your comment about "living in the real world" as it reminded me of my old code instructor who used to say that all the time. I agree that few electricians, myself included, bother to do a calculation when a small addition is made, but where do we begin to be concerned about this? When a main is present and load is added at least we know that the service entrance conductors are protected since the main will open at or near the conductors' capacity. Maybe we lean on this safety factor too much when adding to an existing installation in the interest of getting the job done and keeping our customers happy. I'd love to sell a service upgrade to every commercial customer whenever they add 20 or 30 percent more load to their service but it's just not going to happen...

By the way, I'm thrilled to have found this site. Very nice to have an educated and respectful discussion with other professionals.

Chris


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## 123electric (Jun 3, 2012)

Always remember 240.4 (B) (C)


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## McClary’s Electrical (Feb 21, 2009)

Executive said:


> educated and respectful discussion with other professionals.
> 
> Chris


 
What site have you been reading?


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## 4464528 (Aug 14, 2012)

No main breaker


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