Article 310.15 (B)(3)(7) - Page 3 - Electrician Talk - Professional Electrical Contractors Forum
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Old 01-12-2019, 04:31 PM   #41
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Originally Posted by Wiresmith View Post
did you read my post #27, i think some others posted right after me.
i believe you are allowed to use the 83% allowance even with load shedding so long as your feeder is sized for the entire calculated load of the house.
The feeder doesn't have to be sized to the calculated load of the house.

Show me the code that you think requires that.

This discussion reminds me of the one we had last year in which you pulled stuff out of thin air to support your argument. You are clearly a smart person and understand the written code, but you are being willfully ignorant by continually asserting that your understanding of the intent of the code has any meaning whatsoever.

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i completely see how you come to your interpretation
That's the thing, I am not coming to an interpretation, I am simply reading the code. This is not an instance that requires any interpretation, it is very clear. Load shedding does NOT stop you from using 310.15(B)(7).
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Old 01-12-2019, 04:35 PM   #42
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so say you have a 700KW generator, to be able to see the extreme scenario, say you have a refrigerator and electric heat is all you care to run when the power goes out and those loads are calculated to require 100 amp circuit.

do you believe i could use a 100 amp breaker and use #4 Cu xhhw ?

#4 Cu xhhw 85 amps at 75 c by table 310.15(B)(16)

240.6 ocpd sizes 80, 90, 100
Can you show me the code article that would prohibit it? We've been over this too many times now.
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Old 01-12-2019, 04:37 PM   #43
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If this generator were the sole power source for the house, then the 83% allowance would apply. Since the generator is the sole power source for the house when the ATS is engaged, then logically, the 83% allowance applies. This generator is no different than the utility source, as far as the loads in the house are concerned.
now consider load calculations for the house for the required ampacity.

again, i agree with your interpretation when the typical interpretation of 310.15(B)(7) is used. if you go by how most people on this forum interpret 310.15(B)(7) irrespective of this load shedding issue and transformers, then i agree you are allowed.

now, why shouldn't we then be able to use 83% rule everywhere else?
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Old 01-12-2019, 04:38 PM   #44
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Can you show me the code article that would prohibit it? We've been over this too many times now.
i agree we have been over this too many times, i just wanted to confirm i was understanding the way you were thinking, i was not for sure.

thanks
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Old 01-12-2019, 04:43 PM   #45
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now, why shouldn't we then be able to use 83% rule everywhere else?
We should.

Just like we should be able to use #12 for 25A.

Conductors are limited multiple times. In some instances were are allowed to use them at their full ampacity, or at least an ampacity closer to their full ampacity.

4/0Al CAN handle 200A just fine. Just like #4Cu can handle 100A without issue. That is the only reason why 310.15(B)(7) allows us to use them, because they can handle it. They just took out the extra safety factor that the normal ampacity adds.
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Old 01-12-2019, 04:45 PM   #46
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That's the thing, I am not coming to an interpretation, I am simply reading the code. This is not an instance that requires any interpretation, it is very clear. Load shedding does NOT stop you from using 310.15(B)(7).
i'm just using the word "interpretation". Another way to put it is that if i read that code section and do not consider anything else, i believe it says the same exact thing you are saying. i honestly do, i admit that. like i said, i think this code section is screwed up. i believe it is completely reasonable for a contractor to read that code section and install the way you are describing. i believe there is a solid argument that code interpretation is the way the code is written, i agree.

i will post to your other questions in a minute with my code references.
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Old 01-12-2019, 04:49 PM   #47
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i'm just using the word "interpretation". Another way to put it is that if i read that code section and do not consider anything else, i believe it says the same exact thing you are saying. i honestly do, i admit that.
Ok, gotcha.

I think Dennis disagrees with you and thinks code won't allow it.
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Old 01-12-2019, 05:04 PM   #48
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Ok, gotcha.

I think Dennis disagrees with you and thinks code won't allow it.
i agree that Dennis disagrees with that.

Something else that might throw some confusion into this if you haven't read everything i have wrote is that although i believe what i just wrote, i made sure to choose my words carefully because i believe code as a whole in a way many would see as convoluted does not allow this. i also have to add i believe many people would disagree with me on this without me giving a big long explanation(and most would probably still disagree), that i may work on someday and also submit a code proposal with it. but i understand i am not providing a good clean argument.
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Old 01-12-2019, 05:08 PM   #49
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something to chew on that i ran across while working on putting together my references.

i may have posted this last time.

NFPA70
a98ROC

Quote:
6- 55 - (Article 310, Notes to Ampacity Tables of 0-2000Volts, .
Note 3). Reject

SUBMrITER: Dan Leaf, Palmdale, CA

COMMENT ON PROPOSAL NO: 6-77

RECOMMENDATION: Accept proposal.

SUBSTANTIATION: I agree with the pro[poser'ssubstantiation.

I would venture to say the majority of dwelling unitswith a

minimum 100-ampere service seldom approach the computed

load current much less the service conductor ampacity.

PANEL ACTION: Reject.

PANEL STATEMENT: The data developed for Note 3 was from

actual utility company data for 120/240V 33wire dwellingunitS. It

established that the conductors specified could be usedon a

calculated dwelling unit of the load shown. It does not

reestablish conductor ampacity
. Byeliminating the 120/240V

requirement,the proposal adds additional heating to the $-wire

circuit becausethe common conductor now carries

approximatelythe same current as the other phases. In a

240Vapplication the third conductor carries only the

imbalance. Thesame issue is true for the expansion of the Note

to three-phaseapplications. The fact that an additional current

carryingconductor will be in the conduit or cable is not

contemplated bythe values or loading permitted presently by the

Note.

NUMBER OF PANEL MEMBERS ELIGIBLE TO VOTE:

11

VOTE ON PANEL

ACTION:

AFFIRMATIVE: 11




sidebar; i like digging into stuff like this with you guys, it also helps me become more familiar with the code and learn new things, but damn this takes up a lot of time and often seems like a waste, especially when things get disrespectful.

and thank you for the compliment, although we argue a lot i appreciate your input on ET, even what i disagree with.
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Old 01-12-2019, 06:02 PM   #50
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The feeder doesn't have to be sized to the calculated load of the house.

Show me the code that you think requires that.
this is the big one to me

Quote:
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. Conductors shall be sized to carry not less than the larger of 215.2(A)(1)(a) or (b). (a) Where a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum feeder conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

Exception No. 1: If the assembly, including the overcurrent devices protecting the feeder(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the feeder conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

Exception No. 2: Where a portion of a feeder is connected at both its supply and load ends to separately installed pressure connections as covered in 110.14(C)(2), it shall be permitted to have an allowable ampacity not less than the sum of the continuous load plus the noncontinuous load. No portion of a feeder installed under the provisions of this exception shall extend into an enclosure containing either the feeder supply or the feeder load terminations, as covered in 110.14(C)(1).

Exception No. 3: Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100 percent of the continuous and noncontinuous load. (b) The minimum feeder conductor size shall have an allowable ampacity not less than the maximum load to be served after the application of any adjustment or correction factors.
i think i remember your argument from last time that 310.15(B)(7) changes the ampacity of the conductors, and i believe it is reasonable to come to that conclusion the way the code section is written and where it is. And that it appears to me to be the way many people teach that section.(i refer you to my previous post #49 cmp comment about the study where they came up with the wire sizes)

but, i give you something to think about if you want it.
one way i could see this section being putting in this area of the code originally.
so looking at it from the angle of not using overcurrent protection for service conductors (i posted code reference earlier where we don't have to protect these at all with ocpd), i believe it makes sense for the cmp to come up with a wire size for a service size (i refer you to my previous post #49 cmp comment about the study where they came up with the wire sizes).



we are obviously looking at two different angles as well, i'm looking at what i know of as the code as a whole and you are looking at that section, which i believe you should be able to do but i believe the code is not perfect and in some areas poorly written or maintained. this is why i try to find the intent, not that it changes the text, it doesn't, but just for my understanding.


i have to get off here for now, if you respond don't take my silence as me not coming back to this, if you want to continue. and if i missed some of your other comments i will try to respond to them later. i am curious of your thoughts on what i am posting if you want to give them.

thanks

and Dennis if you are still reading, like last time i would appreciate your thoughts as well if you want to give them.
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Old 01-12-2019, 06:03 PM   #51
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Old 01-12-2019, 06:17 PM   #52
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this is the big one to me
I can't get into hardcore code right now, but I feel confident that the feeder coming from a generator does not have to be sized to the calculated load of the house. You can run a feeder from the generator sized to the generator's output or OCPD. In the situation of the generator being an automatic standby system, the generator itself has to be sized to the load that it is connected to, not the calculated load of the entire house.
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Old 01-12-2019, 06:22 PM   #53
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I can't get into hardcore code right now, but I feel confident that the feeder coming from a generator does not have to be sized to the calculated load of the house. You can run a feeder from the generator sized to the generator's output or OCPD. In the situation of the generator being an automatic standby system, the generator itself has to be sized to the load that it is connected to, not the calculated load of the entire house.
That makes sense. It may be a house panel, subpanel or generator /emergency panel. Load calc will be different for each depending on the connected loads.
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Old 01-12-2019, 06:26 PM   #54
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I can't get into hardcore code right now, but I feel confident that the feeder coming from a generator does not have to be sized to the calculated load of the house; You can run a feeder from the generator sized to the generator's output or OCPD. In the situation of the generator being an automatic standby system, the generator itself has to be sized to the load that it is connected to, not the calculated load of the entire house.
i agree, it does not have to be sized for the house.

it has to be sized for its load, if you down size to 83% in the scenarios i listed where the load was the ocpd rating, i say you're not complying with 215.2.
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Old 01-12-2019, 06:33 PM   #55
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i agree, it does not have to be sized for the house.

it has to be sized for its load,
I disagree. That would mean that a manual transfer switch for a typical interlocked portable generator connection (30A) connected to a typical house with a 200A service would require a huge feeder sized to the calculated load of the entire house to connect the 30A inlet to the 30A backfed breaker.

Nope, a #10 is fine and code compliantly installed millions of times.


Quote:
if you down size to 83% in the scenarios i listed where the load was the ocpd rating, i say your not complying with that. unless the round up clause 240.4 gets you there(without the 83% rule actually being used).
I don't know what you are saying here.
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Old 01-12-2019, 06:36 PM   #56
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I disagree. That would mean that a manual transfer switch for a typical interlocked portable generator connection (30A) connected to a typical house with a 200A service would require a huge feeder sized to the calculated load of the entire house to connect the 30A inlet to the 30A backfed breaker.

Nope, a #10 is fine and code compliantly installed millions of times.
i completely agree with you on this, there is some miscommunication between us, i will read back through to see how you think i think that.

Quote:
I don't know what you are saying here.
i'll try to state it better
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Old 01-12-2019, 06:39 PM   #57
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i completely agree with you on this, there is some miscommunication between us, i will read back through to see how you think i think that.
What is the miscommunication?

You say that it has to be sized to the load, I say that it doesn't. And I gave an example that you agreed with

I'm done, goodbye!
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Old 01-12-2019, 06:53 PM   #58
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i agree, it does not have to be sized for the house.

it has to be sized for its load
I disagree. That would mean that a manual transfer switch for a typical interlocked portable generator connection (30A) connected to a typical house with a 200A service would require a huge feeder sized to the calculated load of the entire house to connect the 30A inlet to the 30A backfed breaker.

Nope, a #10 is fine and code compliantly installed millions of times.
by load i mean the load the generator is actually going to run, i don't mean the entire house load

Quote:
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Quote:
Originally Posted by Wiresmith View Post
it has to be sized for its load, if you down size to 83% in the scenarios i listed where the load was the ocpd rating, i say you're not complying with 215.2.
I don't know what you are saying here.

just fyi, i edited my post and you got the older version, i'm horrible about doing that, i apologize but you are much quicker than others i talk to, the edited version may make more sense. in the original i posted 240.4 and was wrong.

earlier i asked this


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so say you have a 700KW generator, to be able to see the extreme scenario, say you have a refrigerator and electric heat is all you care to run when the power goes out and those loads are calculated to require 100 amp circuit.

do you believe i could use a 100 amp breaker and use #4 Cu xhhw ?

#4 Cu xhhw 85 amps at 75 c by table 310.15(B)(16)

240.6 ocpd sizes 80, 90, 100
the calculated load is 100 amp
ocpd 100 amp

if i use 83% rule i can use #4


i believe that violates 215.2
and i refer you back to my posts #49 and #50 where the cmp stated B(7) doesn't change ampacity



i'm not sure what your response will be to this but if it is "of course, in that situation you can't use #4"

the problem i have with that rebuttal is that it undermines the idea that 310.15(B)(7) changes the ampacity,

i don't believe that would be your response, but i see at least someone saying that, so i thought i should add that
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Old 01-12-2019, 07:03 PM   #59
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by load i mean the load the generator is actually going to run, i don't mean the entire house load




just fyi, i edited my post and you got the older version, i'm horrible about doing that, i apologize but you are much quicker than others i talk to, the edited version may make more sense. in the original i posted 240.4 and was wrong.

earlier i asked this




the calculated load is 100 amp
ocpd 100 amp

if i use 83% rule i can use #4


i believe that violates 215.2
and i refer you back to my posts #49 and #50 where the cmp stated B(7) doesn't change ampacity



i'm not sure what your response will be to this but if it is "of course, in that situation you can't use #4"

the problem i have with that rebuttal is that it undermines the idea that 310.15(B)(7) changes the ampacity,

i don't believe that would be your response, but i see at least someone saying that, so i thought i should add that
I believe you're confusing "entire load" with "calculated load".
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Old 01-12-2019, 07:04 PM   #60
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by load i mean the load the generator is actually going to run, i don't mean the entire house load
There is nothing restricting the load on a manual transfer switch connected generator. I routinely connect small portable generators to entire houses with an interlock. The full load of the house is on the generator.

So the load that the generator is actually going to run is whatever the homeowners choose. And that is perfectly code compliant.

As for the rest of your post, I really donít know where youíre going with that. I donít understand what you are saying.

Code is really stupid. Very rarely is the code written to properly cover the intent. There is no continuity. I believe a typical 11th grade high school class could write the code clearer.
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