Plan Review Comment - Residential Generator

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Npstewart

Senior Member
We received a plan review comment for a residential generator we recently designed. The comment is as follows:

"Generator load must meet 2008 NEC art. 702.5 (B)(2)b. In case of an ATS the generator the generator must be able to carry the connected load, not a depreciated calculation".

I use the residential optional load calculation. I am more than sure he thinks that this section of the NEC does not allow any diversity to be used when sizing a residential generator.

The load on the house according to the residential load calculation is about 85KW (its a big house). The generator has been sized as a 90KW. The load on the house BEFORE diversity is 177KW. So according to this guy, the only way to put this house on a generator is to have a 177KW generator.

Does he know something that I don't?
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
No, the reviewer does not know something that you do not, I believe the reviewer is mistaken.

702.5(B) says: "The calculations of load on the standby source shall be made in accordance with Article 200 or by another approved method."

You have pointed out that you did the load calculation per Article 220, and have a load of 85kW. 702.5(B)(2)(a) requires the source to be capable of supplying the full 85kW load, which you have done.
 

Npstewart

Senior Member
I would hope that would be the case :)

We have designed hundreds of generators in the past.

This guy is a electrical inspector doing plan review. It seems as though when a inspector does plan review, or a plan reviewer does inspections, it never works out that well USUALLY. Im sure there are many exceptions.

I would be absolutely crazy to change the generator to a 177KW DIESEL generator.

This isn't the first time I have gotten a ridiculous comment from this guy.

The last comment I got from him said that the 2nd panel out of (2) had too much spare capacity (empty poles) and he said that someone could install whatever they wanted in that panel and over-load the service. I guess he expects me to design taking into account that the future electrician may not pull a permit for future electrical work..
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
I would hope that would be the case :)

We have designed hundreds of generators in the past.

This guy is a electrical inspector doing plan review. It seems as though when a inspector does plan review, or a plan reviewer does inspections, it never works out that well USUALLY. Im sure there are many exceptions.

I would be absolutely crazy to change the generator to a 177KW DIESEL generator.

This isn't the first time I have gotten a ridiculous comment from this guy.

The last comment I got from him said that the 2nd panel out of (2) had too much spare capacity (empty poles) and he said that someone could install whatever they wanted in that panel and over-load the service. I guess he expects me to design taking into account that the future electrician may not pull a permit for future electrical work..

I'd stand firm on this. Ask him how he thinks you could possibly need more capacity for the standby source than the normal source. The calculated load is the calculated load.
His comment on too many unused poles is way out there also. I once had an AHJ claiming something similar. He thought if you have more than one service diconnect that the service conductors had to be sized for the sum
of the disconnect ratings, not the calculated load.
:slaphead:
 

John120/240

Senior Member
Location
Olathe, Kansas
Some HI add up all of the values on the breaker handle & then say that the service is too small.

We all know that the number on the breaker handle is the number of operations of that

breaker before replacement is required.
 

Npstewart

Senior Member
I posted this post a while ago in response to a plan review comment I received. I finally got hold of the plan reviewer after weeks and to my surprise he is sticking by his gun that the generator needs to be sized for the CONNECTED load and not the DEMAND load permitted by article 220. He wrote me an email and copied the other building officials. Does anyone know of any of the awesome Mike Holt's sample articles where they go through and size a residential generator (or) is there a sample calculation in the handbook that anyone knows of? My plan is to "Reply to All" with a good resource to put this to bed.

Any help would be greatly appreciated. Thanks Everyone.
 

Shoe

Senior Member
Location
USA
Maybe ask how article 220 evaluates connected load? It's all about demand.

You can always propose to the homeowner a manual transfer switch, taking advantage of 702.5(B)(1)? Although I understand if this is not a viable option.
 

Npstewart

Senior Member
Does anyone know why the section 702.5 (2)(b) uses the word "Connected" load which would indicate this is prior to diversity/demand? There is no technical definition in the NEC 2008 for "Connected" but it is mentioned in the definitions under "Demand".

Thanks
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Does anyone know why the section 702.5 (2)(b) uses the word "Connected" load which would indicate this is prior to diversity/demand? There is no technical definition in the NEC 2008 for "Connected" but it is mentioned in the definitions under "Demand".

Thanks

I think you meant 702.4(B)(2)(b)? It seems to me that 702.4(B) is pretty clear on capacity and to use Art. 220 to determine same. 702.4(B)(2)(b) is just to make sure that if you are using a load management (shedding) scheme (because the stanby system is not sized for the entire CALCULATED load, that the system has capacity to carry the non-shedded load. IMO if the plan reviewer is using this to require capacity for "connected" load he is taking it out of context and is completely wrong. In fact, if you are sizing the system to carry the entire load and not using load management, then 702.4(B)(2)(b) does not even apply and is moot.
 

Npstewart

Senior Member
We have a meeting with this guy on Monday at the building department. This is so ridiculous. I have gotten about 5 opinions on this plus everyone in this forum. Now I have to drive 45 minutes away to try and explain the code to this guy and after all that he might still think he is right.


He is now saying that we should put these load shedding DEVICES on individual circuits such as the oven and dryer. Absolutely ridiculous.
 

Smart $

Esteemed Member
Location
Ohio
Does anyone know why the section 702.5 (2)(b) uses the word "Connected" load which would indicate this is prior to diversity/demand? There is no technical definition in the NEC 2008 for "Connected" but it is mentioned in the definitions under "Demand".

Thanks
Because that's the wording used in the original proposal. Additionally, in my opinion, it is used in the generic sense to differentiate between connected and not connected to the standby system... rather than connected vs. calculated demand.

FWIW, here's the "report on proposal" ...

ARTICLE 702 — OPTIONAL STANDBY SYSTEMS
____________________________________________________________
13-168 Log #2741 NEC-P13

Final Action: Accept in Principle
(702.5)
____________________________________________________________
TCC Action: It was the action of the Technical Correlating Committee that
further consideration be given to the comment expressed in the voting and
“with a or b” should be revised to read “with (a) or (b)”.
The Technical Correlating Committee directs that the Action on this
Proposal be rewritten to comply with 4.1.1 of the NEC Style Manual.
These actions will be considered by the Panel as a Public Comment.
Submitter: Jim Pauley, Square D Company
Recommendation: Revise NEC 702.5 as shown below.
702.5 Capacity and Rating.
(A) Available Short Circuit Current. Optional standby system equipment
shall be suitable for the maximum available fault short-circuit current at its
terminals.
(B) System Capacity. The calculations of load on the standby source shall be
made in accordance with Article 220 of by another method that is acceptable to
the authority having jurisdiction.
(1) Manual Transfer Equipment. Where manual transfer equipment is
used
an optional standby system shall have adequate capacity and rating for the
supply of all equipment intended to be operated at one time. The user of the
optional standby system shall be permitted to select the load connected to the
system.
(2) Automatic Transfer Equipment. Where automatic transfer equipment is
used, an optional standby system comply with a or b.
(a) Full Load. The standby source shall be capable of supplying the full load
that is transferred by the automatic transfer equipment.
(b) Load Management. Where a system is employed that will automatically
manage the connected load, the standby source shall have a capacity sufficient
to supply the maximum load that will be connected by the load management
system.
Substantiation: Due to the recent natural disasters the increase in generator
installations has grown significantly. At a number of IAEI meetings in 2005,
the question has been asked about what to do for the size of an optional
standby source that uses automatic transfer. It appears that automatic transfer
equipment is being installed with generators that have a capacity that is much
smaller than the total load (typically an entire panelboard) being transferred.
There has been significant disagreement about how the NEC treats these
automatic transfer situations.
The objective of this proposal is to try and address a number of concerns that
have been raised by both inspectors and installers. Of primary concern has
been that in an automatic transfer application, the user may not be available to
“select the loads” that will be supplied. This defeats the intent of the automatic
transfer and renders the system somewhat useless.
The proposal does the following:
1. Rearranges the existing 702.5 text to split up the paragraph and provide
headings that will make it easier for the code user.
2. Create an “Available Short Circuit Current” heading and moves the
sentence about adequate ratings for fault current to this new heading. In
addition, the term “fault current” is replaced with “short circuit current” to
make it consistent with the rest of the code.
3. System capacity is now split into Manual Transfer and Automatic Transfer
applications. In addition text has been added to indicate how the load is to
be calculated. For instance if you are including the branch circuits in a home
that supply part of the general lighting load, how do you do that calculation.
The most logical approach is to use Article 220 and the new language makes
that clear. However, it is recognized that a number of jurisdictions are allow
recorded load measurements and similar information to be used to provide the
capacity. The new text would allow other methods that are acceptable to the
AHJ.
4. For manual transfer, the existing language is used to simply require that the
supply be adequate to supply the equipment intended to be connected at one
time. It also retains the existing permission for the user to be able to select the
loads that will be connected.
5. For automatic transfer, new language is provided to address the concerns
raised in the field about the user not be available to select the supplied loads.
In the automatic situation, there are a couple of options. Item “a” provides
and option where you size the standby supply to pick up the entire load that
is being transferred. The typical application in this case is where a small
generator is connected to a new subpanel with a set number of critical loads.
Under normal power the subpanel is supplied by the normal source. When the
power fails, the subpanel is transferred to the generator source.
Item “b” is intended to allow a system where some of the load in a larger panel
may be shed in order to reduce the loading to an adequate level to be supplied
by the standby source. We allow this in larger applications of 700 and 701, so it
makes sense here.
Article 702 has become very popular because of the number of outages that
have occurred in the country. This proposal updates the requirements to
installations that have become more common.
Panel Meeting Action: Accept in Principle
Accept the proposal as submitted except revise (B) as proposed to read as
follows:
(B) System Capacity. The calculations of load on the standby source shall be
made in accordance with Article 220 or by another approved method.
Panel Statement: The editorial revision conforms to NEC Manual of Style
and corrects a typographical error.
Number Eligible to Vote: 14
Ballot Results: Affirmative: 13
Ballot Not Returned: 1 Gustafson, R.
Comment on Affirmative:
SWAYNE, R.: In Section 702.5(B)(2), editorially add the word “shall” after
“system” to complete the sentence structure.
 
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Npstewart

Senior Member
Thank You "Smart" for that technical commentary.

I submitted a technical code inquiry to NFPA today on this issue. Has anyone ever done this before? What should I expect for a time line?
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Thank You "Smart" for that technical commentary.

I submitted a technical code inquiry to NFPA today on this issue. Has anyone ever done this before? What should I expect for a time line?
If it's only a request for information, not too long; however, it will only be an "opinion" of an NFPA staffer. If you made a request for a "Formal Interpretation," don't hold your breath - and you will still most likely only get an "opinion" of an NFPA staffer.
 

Npstewart

Senior Member
I had the meeting yesterday with the plans examiner.

The argument is with 702.5(B)(3)a: "The standby source shall be capable of supplying the full load that is transferred by the automatic transfer equipment".

The argument comes in where it says "FULL LOAD". I am saying that FULL LOAD is determined using article 220 of the NEC for dwelling units. He is saying that FULL LOAD is calculated by adding all the loads together in the entire house without diversity from 220.
 

Smart $

Esteemed Member
Location
Ohio
I had the meeting yesterday with the plans examiner.

The argument is with 702.5(B)(3)a: "The standby source shall be capable of supplying the full load that is transferred by the automatic transfer equipment".

The argument comes in where it says "FULL LOAD". I am saying that FULL LOAD is determined using article 220 of the NEC for dwelling units. He is saying that FULL LOAD is calculated by adding all the loads together in the entire house without diversity from 220.
What is the actual service rating?

Provided it is not [substantially] greater than your calculated load, ask him if normal service is capable of supplying the same full load. In this case it is an apples-to-apples comparison.
 

Npstewart

Senior Member
I made that exact point. This is a 400A service. Without the demand factors allowed by article 220, the service would be required to be 800A.


I also made the point that if the generator has a "load" of 800A, then the disconnect for it has to be 800A, which means the conductors and transfer switch has to be rated for 800A, then I would assume the panel would have to be 800A too because somewhere the load is a load of 800A. Where would someone put a 800A panel in their house...
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
I know you probably don't want to do this for "obvious reasons" but you may have to go over his head.
Meaning drag the state into it.
He doesn't seem to be willing to back down and you can't go back to your customer
to tell them they have to spend a substantial amount more because of him.
They may even think you screwed up and now want them to pay for it by blaming the plans reviewer
 

Npstewart

Senior Member
I sort of went over his head already by speaking with the head building official but the problem is that the building official's background is more in structural/architectural.

Also, like I said yesterday, I sent in for a clarification to NFPA but then I got an email that said I was required to be a member of NFPA for an interpretation unless I was a building official/AHJ. I have a login cause im a free member but we dont pay the $125.00/year so now I don't think I will get any interpretation.
 
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