When can I not use the optional method?

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Tainted

Tainted

Senior Member
Location
New York
Occupation
Engineer (PE)
I know the minimum is 100A but when are we not allowed to use the optional method for calculating the apartment load?

220.82(A) says:

This section applies to a dwelling
unit having the total connected load served by a single
120/240-volt or 208Y/120-volt set of 3-wire service or feeder
conductors with an ampacity of 100 or greater.

Can we use this method if we have a combined apartment with 2 panels metered separately? The combined apartment has no wall separating each other. The code in 220.82(A) refers to a single 120/240 or 120/208V feeder but there's 2 feeders in the combined apartment so it's not a single.. Could I do the optional method on each of the panel separately?
 
Tainted said:
Can we use this method if we have a combined apartment with 2 panels metered separately? The combined apartment has no wall separating each other.
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I would say that if the units were combined only by taking out a wall, and there are still two kitchens, etc., you could continue to treat them as 2 units and use 220.82. Otherwise, if you need to treat it as a single unit, obviously no, 220.82 does not apply, as there is no single feeder or service supplying the total connected load of the dwelling unit.

Cheers, Wayne
 
wwhitney said:
I would say that if the units were combined only by taking out a wall, and there are still two kitchens, etc., you could continue to treat them as 2 units and use 220.82. Otherwise, if you need to treat it as a single unit, obviously no, 220.82 does not apply, as there is no single feeder or service supplying the total connected load of the dwelling unit.

Cheers, Wayne
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There is only 1 kitchen. My boss argues that by law they are considered 2 seperate units even though there is no wall and 1 kitchen, this means you can use 220.82 on each of the panels separately
 
If there's only one kitchen, there's only one dwelling unit as far as the NEC is concerned, so no to your boss. Per Article 100:

Dwelling Unit. A single unit, providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation.

Cheers, Wayne
 
To add to this I believe there would need to be a firewall between the building in order to consider it a separate unit but as Wayne stated it definitely is not considered 2 dwellings based on definition
 
Dennis Alwon said:
To add to this I believe there would need to be a firewall between the building in order to consider it a separate unit but as Wayne stated it definitely is not considered 2 dwellings based on definition
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Ok, that’s actually what I initially thought and I wanted to confirm with you guys. There will be no way convincing my boss and he’ll get really angry if I do my load letter the correct way…
 
Tainted said:
He thinks his way is the right way. If I question it and tell him it’s not, he’ll get really angry with me
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A skill that I have worked on all my career as an engineer is the ability to switch positions quickly and without rancor when faced with the evidence that proves me wrong. It is self-defeating to invest emotional currency in debates over matters of fact. It either is or it isn't; it is better to be correct than to be "right". If your boss habitually assumes incorrect positions from which he cannot gracefully back down, it may be time to find another boss.

That said, it is important that whenever you show him why his position is incorrect you do not couch it in terms of winning an argument.
 
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