How many amps used to estimate the voltage drop for residential application?

[zemingduan]

They can do that somewhat reliably for a stead load, but changes in load will throw it off. If you have "down days" with little or no load the voltage can possibly be higher then desired during those periods. Times with even more load than designed for will result in lower voltage.

roughly every 100 ft will require a wire size upgrade. for long runs, the utility may change the taps for you but with limits. they can usually go 2 up or 2 down at 2.5% per step. however, they are usually compensating for primary drop, not secondary drop. with a dedicated transformer, they may consider changing the tap but should look at voltage regulation and voltage at minimum load.

utilities usually compensate for secondary drop with bigger wire or sometimes a bigger transformer and may expect you to do the same. the bigger transformer will help secondary regulation but they probably will ask you to pay for the upsizing.

Thanks for bringing this up! I agree if adjusting the secondary taps setting shall be based on the minimum load.

If adjusting utility transformer 2 up at 2.5% per step which is 208*1.05 = 218V, will the higher voltage at "down days" cause problem? I think almost all 2 pole home appliances are rated at 208V -230V and the voltage fluctuation is also not a problem for the 200V motors some times? Will 120V*1.05 = 126V be a problem for 120V appliances?

 

[jaggedben]

My major concern is the performance wise. For example, if you obtain a voltage less than 190V at the A/C condensers on the roof, I think that is not good for the compressor long term.

No it's probably not good, but if that's what's worrying you then use the full compressor load, plus some reasonable amount for the rest of the load.

Is this data for single dwelling unit or a multifamily dwelling apartment?

Thank you!

Single dwellings. But I doubt multi-family would be a whole lot different. Commercial would be different.

 

[kwired]

Thanks for bringing this up! I agree if adjusting the secondary taps setting shall be based on the minimum load.

If adjusting utility transformer 2 up at 2.5% per step which is 208*1.05 = 218V, will the higher voltage at "down days" cause problem? I think almost all 2 pole home appliances are rated at 208V -230V and the voltage fluctuation is also not a problem for the 200V motors some times? Will 120V*1.05 = 126V be a problem for 120V appliances?

Is really no different than using a buck-boost to compensate for voltage drop. Is sort of a no-no unless it is for a fixed load that pretty much never varies.

 

[ron]

I check the energy code. Philadelphia adopt the IECC 2018. The voltage drop requirements are only found in the commercial provisions. (https://up.codes/viewer/philadelphia/iecc-2018/chapter/CE_4/ce-commercial-energy-efficiency#C405.9)



This means it only apply to commercial building. And it doesn't require the voltage drop calculations or specify the calculation based on NEC calculated code. I think inspector will measure the voltage on site to check if it is code compliant.

The residential provisions of IECC 2018 regarding the electrical power and lighting system is very short. It only has below requirements. (https://up.codes/viewer/philadelphia/iecc-2018/chapter/RE_4/re-residential-energy-efficiency#R404)

Since "commercial" is not a occupancy type found in the Building Code, it would take a little research to determine if the IECC commercial section would apply to the service for an apartment building, which would seem pretty commercial to me (without looking at definitions) and as you mentioned, not likely for the feeder to an apartment. IECC C405.9 is very vague in that it doesn't dictate what load to use in the calculation, and at some point, when plan reviewers get their act together, they will be dinging you before construction if there isn't some indication of compliance during that process.
I use NEC Article 220 loads, because anything else is a SWAG and not documented by a consensus standard or guideline.

 

[zemingduan]

Since "commercial" is not a occupancy type found in the Building Code, it would take a little research to determine if the IECC commercial section would apply to the service for an apartment building, which would seem pretty commercial to me (without looking at definitions) and as you mentioned, not likely for the feeder to an apartment. IECC C405.9 is very vague in that it doesn't dictate what load to use in the calculation, and at some point, when plan reviewers get their act together, they will be dinging you before construction if there isn't some indication of compliance during that process.
I use NEC Article 220 loads, because anything else is a SWAG and not documented by a consensus standard or guideline.

Very appreciate that you bring this up. I double check the definitions in IECC 2018. You are right that some apartment buildings are "commercial building" defined in IECC 2018. And unfortunately, my project is actually classified as commercial building per the definitions. The definitions are below (https://up.codes/viewer/philadelphia/iecc-2018/chapter/CE_2/ce-definitions#C202):

RESIDENTIAL BUILDING. For this code, includes detached one- and two-family dwellings and multiple single-family dwellings (townhouses) and Group R-2, R-3 and R-4 buildings three stories or less in height above grade plane.

COMMERCIAL BUILDING. For this code, all buildings that are not included in the definition of "Residential building.