220.85 two dwelling units

[Tyler Cavanaugh]

Could someone please send me an example question of how to actually apply this to a caculations? I recently just took my 01 master exam and there was two questions that pertained to this. Not quite sure how to actually apply this. Please help and thank you!

 

[charlie b]

I can't invent an example for you, but here is the concept:

You have one feeder that powers two dwelling units. I suppose that could mean that the feeder lands on some manner of junction box and separate conductors go to each unit. You wish to calculate the load on that feeder, so that you can determine its conductor size. Do two calculations. First, calculate the total load of the two units using the "standard method." Secondly, calculate the total load that would result from a (fictitious) set of three units that are identical to the two you have, but this time use the "optional method." Size the feeder based on the smaller result of these two calculations.

 

[Tyler Cavanaugh]

I can't invent an example for you, but here is the concept:

You have one feeder that powers two dwelling units. I suppose that could mean that the feeder lands on some manner of junction box and separate conductors go to each unit. You wish to calculate the load on that feeder, so that you can determine its conductor size. Do two calculations. First, calculate the total load of the two units using the "standard method." Secondly, calculate the total load that would result from a (fictitious) set of three units that are identical to the two you have, but this time use the "optional method." Size the feeder based on the smaller result of these two calculations.

Thank you that makes sense. So if the question asks to calculate the feeder load for a duplex using the optional method, would I calculate the load from a (fictitious) set of three identical units?

 

[charlie b]

If that is the way the question is worded, I would say no. The article under discussion is written in a "permissive" sense. You are permitted to calculate the load two ways and select the one with the lower result. But this question is straight forward: calculate the load of a duplex. So you use the optional method to calculate two units.

This is the type of question that would originate from a deviously demented mind, especially if the question mentions 220.85. The question's author could be leading you down one path while calling the other path the "right answer." I know of no protection against such evil.