Adding Circuits to a main panel

[engineerithink]

Hi,

I am working on a project to add a 480V delta feeder panel to an existing 480V delta main panel at an industrial type warehouse. The main panel (mlo) is being fed by three single phase 167KVA transfomers which means that they are rated to supply 602 amps total. I know the current setup is to code because if I sum up all the breakers on the main panel and multiply them by 80% I come up with a number less than 602 amps (because they should be sized at 125% of their load). My problem is that if I add a 125 amp breaker to the panel I now exceed the 602 amps. Since there are no load calculations for the facility I have no idea what to do. Any suggestions? Is there a rule of thumb I can use so that I can avoid having to perform load monitoring?

 

[steelerfan28655]

Is the load on the panel individually metered by the power company? If so, you can look at the kW demand readings to get an idea of the peak power in the panel.
This does not, however, solve the problem of NEC compliance. But it can be useful information when adding additional load to a service.

Happiness is a way of travel, not a destination.

 

[wareagle]

The number and size of the breakers in panel has nothing to do with the load on the panel. You need to do a load calculation to determine exactly what the load is. Its possible that you could have 600 amps of load connected but only 300 amps are on at any one time. Your adding a 125amp breaker does not necessarily mean you would over load the panel.

 

[engineerithink]

Wareagle

The problem is the original engineer didn't show any load calculations. The main 480V delta panel feeds other 480V delta panels which feed motors and 208Y/120 lighting panels. The lighting panels don't even have ckts schedules. Like you said, it might be that only 300 amps is being drawn at one time, but i have nothing to work with. NEC 220.87 indicates a method used for determining existing loads, but I would have to purchase a load monitoring device to follow it.

 

[waross]

Talk to the AHJ. I have never had any trouble obtaining 2 years of back power invoices from an industrial customer. What better load monitoring can you have than monthly peaks taken by calibrated and sealed meters.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

You can also rent meters or hire a testing agency to apply meters for a month. Done all the time.