panelboard phase load balancing

[bluepalm]

hello. would just like to know the maximum % difference allowed of loads between phases on a panelboard. for example in a 3 phase panel, in phase a, the total connected load is 100 amps, phase b 150 amps, phase c 200 amps.
thanks.

 

[iwire]

Your power company greeenbook may have that information the NEC does not put any numbers to balancing.

 

[mivey]

No real numbers for our regulated POCO:

"When designing a wiring system, the Customer should balance the load connected across each phase of the system as nearly as practical."

[edit: In addition to the GPC bluebook, the service rules really narrow it down: "the load of any three-phase service shall be reasonably balanced between phases by the customer"]

 

[mivey]

I peeked at IPL's greenbook and they are more specific:

"Load shall be balanced as nearly equal as possible on all 3 phases. The difference in amperes between any two phases at the customer's peak load shall not be greater than 10%."

 

[billsnuff]

Fwiw

Fwiw

just finished with a 3 ph panel that had 2 leg at 75 or more and 1 leg at 40. finished at 67.5, 67.3 and 63.3. that allowed us to change primary feed to 480/208 xfmr from FRN 100A to FRS-R 45A, greatly reducing incident energy.

 

[charlie]

I peeked at IPL's greenbook . . .

Nosy

 

[beanland]

Changes with Time

Changes with Time

A thing to remember is that load changes with time. Even if you get perfect balance at one time, it will go out of balance as equipment is turned off, people come and go, and operations change.

The biggest downfall that I have observed from load unbalance is poor voltage (high or low) due to the added voltage drop/rise on the neutral due to the unbalanced current flow.