2 Questions about NEC 220.82

[Tainted]

Question1:

220.82 says that the following conditions need to be met so that I can use the optional method for dwelling unit:

"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."

Most people's interpretation to this is that the voltage and ampacity of feeders conditions must be met to use optional method. However my interpretation is that only 1 of these conditions must be met because they don't use the word "and" they only use the word "or". See above text in red. Please clarify.


Question2:

Suppose I use optional method for a single dwelling unit and my demand load came out to be 100.6 amperes. Could I use a 100A breaker or will that not be code compliant and I would need the next size up? I mean it's only 0.6 Amperes over...

 

[suemarkp]

Using commas where a grammar expert knows the meaning isn't required, but it would be helpful. I think your are reading one of two ways:

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.

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.

I think the 2nd interpretation is correct. You must meet the single set and voltage requirement, and a connected load of 100A or greater.

Technically, I would think a 100.6A calculation would require a 110A breaker and wire rated for 101A. But there is usually enough fuzziness in the calculation that you could find a way to get rid of one amp. Just the square footage can be different depending on who is measuring and how (interior square footage, exterior without siding, exterior with siding). There are also things that people seem to never count (garage door openers) or can't agree if it is fastened in place or not (is the sump pump with a rigid water pipe exhaust with a quick disconnect fitting fastened in place or not)?

 

[Tainted]

Using commas where a grammar expert knows the meaning isn't required, but it would be helpful. I think your are reading one of two ways:

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.

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.

I think the 2nd interpretation is correct. You must meet the single set and voltage requirement, and a connected load of 100A or greater.

Technically, I would think a 100.6A calculation would require a 110A breaker and wire rated for 101A. But there is usually enough fuzziness in the calculation that you could find a way to get rid of one amp. Just the square footage can be different depending on who is measuring and how (interior square footage, exterior without siding, exterior with siding). There are also things that people seem to never count (garage door openers) or can't agree if it is fastened in place or not (is the sump pump with a rigid water pipe exhaust with a quick disconnect fitting fastened in place or not)?

My brain just sees “or” and thinks only either of the conditions must be met because there’s no “and” in it… the first example you wrote is close to how I’m reading it.

And it would suck that I would need a 110A breaker because it’s an existing apartment and they’re just adding 2 loads and it would be ideal to not change the feeder and breaker over just 0.6amps…

 

[Electromatic]

The "or" is just describing how the dwelling unit is being served. A stand-alone building would probably have "service" conductors serving it. A unit in an apartment complex would probably have "feeder" conductors serving it. The 100A or greater ampacity would need to be met regardless.

 

[Tainted]

The "or" is just describing how the dwelling unit is being served. A stand-alone building would probably have "service" conductors serving it. A unit in an apartment complex would probably have "feeder" conductors serving it. The 100A or greater ampacity would need to be met regardless.

Can we use feeder as said in 310.15? Or does it have to be 100A feeder

 

[Electromatic]

310.15 tells you how to pick the type and size of conductor for the load you've calculated.
If this were a feeder for equipment or a subpanel, for example, it could be whatever size meets your calculated load. If this is serving an entire dwelling unit, 230.23 says the conductors shall not be smaller than #8Cu or #6Al. Additionally if this is serving an entire dwelling unit, the IRC (International Residential Code) says the ampacity of the conductors shall not be less than 100A.

 

[wwhitney]

1) The meaning is the following, where the []s show the scope of the or:

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.

2) There's a rule saying that you can round 0.4A down, but 0.5 A and above must be rounded up. So you round to 101A, and a 100A breaker is too small. You need the next size up breaker, and conductors with a (rounded) ampacity of 101A.

Or you need to pore over your calculation and find a place to reduce the total load by 0.2A.

Cheers, Wayne

 

[Tainted]

Thank you, t

1) The meaning is the following, where the []s show the scope of the or:

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.

2) There's a rule saying that you can round 0.4A down, but 0.5 A and above must be rounded up. So you round to 101A, and a 100A breaker is too small. You need the next size up breaker, and conductors with a (rounded) ampacity of 101A.

Or you need to pore over your calculation and find a place to reduce the total load by 0.2A.

Cheers, Wayne

Thanks you, the brackets helped me better see the meaning behind it. It would suck to have to upgrade the whole service over 1A though lol