Not another Voltage Drop question

[KP2]

Hello folks, just looking to get some verification on voltage drop.

When I calculate the voltage drop of the Feeder going to an apartment in a multifamily building I am using 2% as my permitted voltage drop, along with the connected load, not the demand load.

As I see it, using 2% and the connected load, I should capture the worst case scenario.

I'm sure the demand load would give a more practical result, but I can't seem to find any information as to which load should be used.

Also, I would like to confirm the fact that I use the voltage drop permitted for feeders which is 2%; as others I've seen use 3% on these runs.

Thanks
Kevin

 

[charlie b]

There is no code requirement here. An Informational Note following 210.19(A) - and in other places as well - says that if you limit the VD along the branch circuit to 3% and the VD along both the feeder and the branch circuit to 5%, then you will have reason to expect satisfactory performance. That means the feeder can be 2% or more, so long as the total is no higher than 5%.

I would use the demand load for the calculation. But you are right in saying that using the connected load will give you a more conservative result.

 

[don_resqcapt19]

If your loads were calculated per Article 220, there is no question I would use those load calcs...that number will likely be twice the actual load.

 

[KP2]

Thanks for the feedback, I will use the demand load moving forward; however I am still plagued with using 2% in place of the 3%.

Believe it or not, this swings my adjustments by about 30'; which in turn would force me to install 250kcmil SER to 8 units, but at 3% I'll only need to run 250's 2 units.

I know that Voltage Drop in an informational note, but project documents call for the EC to confirm all voltage drop based on installed runs.

I feel safe using the 3% and the demand Load knowing that the overall is permitted to be 5%, and the longest circuit in one of these apartments is under 150' with the majority being 40' - 50'.

Thanks again for the support.
Kevin

 

[tw1156]

There is no code requirement here. An Informational Note following 210.19(A) - and in other places as well - says that if you limit the VD along the branch circuit to 3% and the VD along both the feeder and the branch circuit to 5%, then you will have reason to expect satisfactory performance. That means the feeder can be 2% or more, so long as the total is no higher than 5%.

I would use the demand load for the calculation. But you are right in saying that using the connected load will give you a more conservative result.

The only code requirement I can think of would be if your building is required to comply with ASHRAE 90.1. Even then, it doesn't tell you to use demand or connected load, so it is left up to the designer.

ASHRAE 90.1 (2016) - 8.4 Mandatory Provisions
8.4.1 Voltage Drop
The feeder conductors and branch circuit conductors combined shall be sized for a maximum of 5% voltage drop total.

 

[romex jockey]

The only code requirement I can think of would be if your building is required to comply with ASHRAE 90.1. Even then, it doesn't tell you to use demand or connected load, so it is left up to the designer.

ASHRAE 90.1 (2016) - 8.4 Mandatory Provisions
8.4.1 Voltage Drop
The feeder conductors and branch circuit conductors combined shall be sized for a maximum of 5% voltage drop total.

ASHARAE , a century old ,in 132 countries, and i never heard of them, guess i live a sheltered life....

that said , there's always a focus on serv end & feeders, but go place a VD meter on the far end of a larger structure's branch circuits

~RJ~

 

[tw1156]

ASHARAE , a century old ,in 132 countries, and i never heard of them, guess i live a sheltered life....

that said , there's always a focus on serv end & feeders, but go place a VD meter on the far end of a larger structure's branch circuits

~RJ~

I would say a sheltered life is ok after you start delving into ASHRAE so don't feel like you're missing out.

There are two competing main Energy Conservation Codes that compete with each other; ASHRAE and IECC. ASHRAE, for electrical purposes, tends to be more involved and can really bog down a design. Examples of ASHRAE differing from IECC are calculating the voltage drop to the final circuit and it requiring plug load control. Plug load control is as it sounds, it uses an occupancy sensor to turn off a receptacle.