Required Load Calculations for addition to existing Switchgear

[mull982]

I'm currently involved in a project where we are feeding a new 480V panel from existing 480V switchgear in an industrial setting. The new 480V panel will serve new 480V loads as well as feed a transformer that feeds a 120/208V panel that will serve new and existing loads.

For this particular instance are we required to show existing load calculations at the 480V Switchgear where we will be feeding the new loads from? Do we need to show these load calculations on the One-Line or Riser diagram where I typically see them shown? Or in this instance is it sufficient enough to show only the new loading that will be added?

If load cannot be calculated then can the switchgear be monitored for a period to determine existing loading?

 

[mull982]

I was able to find the "Electrical Plan Review Guidelines" for commercial buildings in the county but nothing related to industrial.

On the commercial requirements there is nothing that specifically references load calculations per NEC Art 220. It references service entrance conductor sizing and installation as it relates to Art 230 but noting specific about calculations. I have seen plan review requirements for commercial buildings in other counties/cities that do reference specific load cals per 220.

I also found the plan review guidelines for residential buildings in the county and it does specifically reference load calculations per 220. I find it strange that the essential guidelines would specifically reference this while the commercial does not.

Although there is nothing specifically related to industrial installations one would think that the commercial requirements could be adopted as a conservative measure. Based on what I see and mentioned above it would not be specifically required to show load calcs for the specific installation I referenced in my original post.

The panel schedules for the two now added panels do show the connected kVA, demand kVA, and total design kVA for each of the existing and new loads that are being added.

Just curious to hear some thoughts and experiences from others related to this type of installation.

 

[Fitzdrew516]

I'm currently involved in a project where we are feeding a new 480V panel from existing 480V switchgear in an industrial setting. The new 480V panel will serve new 480V loads as well as feed a transformer that feeds a 120/208V panel that will serve new and existing loads.

For this particular instance are we required to show existing load calculations at the 480V Switchgear where we will be feeding the new loads from? Do we need to show these load calculations on the One-Line or Riser diagram where I typically see them shown? Or in this instance is it sufficient enough to show only the new loading that will be added?

If load cannot be calculated then can the switchgear be monitored for a period to determine existing loading?

Unless you have as-builts then you won't be able to do an accurate load calculation; you will have to do an existing load calc based on 220.87. I usually figure the existing load based on peak demand from utility bills, multiply that by 1.25, then add the calculated loads of the new equipment to that. I usually just make a small excel load summary to show that the service is not overloaded.

- Drew

 

[mull982]

Unless you have as-builts then you won't be able to do an accurate load calculation; you will have to do an existing load calc based on 220.87. I usually figure the existing load based on peak demand from utility bills, multiply that by 1.25, then add the calculated loads of the new equipment to that. I usually just make a small excel load summary to show that the service is not overloaded.

- Drew

In this particular case it is not a service (sorry should have clarified that) but rather at existing 480V switchgear located downstream of a 4.16kV distribution system in a plant.

Do load calculations really only apply for service calculations?

 

[jumper]

In this particular case it is not a service (sorry should have clarified that) but rather at existing 480V switchgear located downstream of a 4.16kV distribution system in a plant.

Do load calculations really only apply for service calculations?

No, the calculations in part III of article 220 apply to feeders and service conductors.