Understanding three-phase EVSE Power Management

[JMFSE]

Hi all,

Question about a EVSE power management algorithm i'm observing for a three-phase panel.

Lets say a 600A rated panel has an EVSE Power Management policy to limit a group of chargers to 300A based on available capacity of the panel.
The way the software works is it takes the total specified power ceiling (300Amps) and divides that amongst the three phases so that the group of chargers on each phase will be limited to 100A (for load balancing purposes). I'm trying to understand if this makes sense versus having each phase support the full 300A.

The reason I'm asking is because based off my understanding, when filing out a panel schedule and balancing loads, the VA of each phase can total to the same VA rating of the entire panel and not just 1/3rd of it. For example, balancing a 300A 208V would allow each individual phase to have 108kVA (300x208x1.732) connected load.
Is this correct or is it proper to assume that each phase would only be able to handle 1/3rd of that number? If the latter, would the main breaker of the panel be at risk of tripping if a single phase was overloaded beyond 33%?

 

[jaggedben]

...For example, balancing a 300A 208V would allow each individual phase to have 108kVA (300x208x1.732) connected load.

Incorrect. 108kVa is the total connect load, not per individual phase.

Is this correct or is it proper to assume that each phase would only be able to handle 1/3rd of that number?

1/3rd
The line current on each phase would be 173A.

If the latter, would the main breaker of the panel be at risk of tripping if a single phase was overloaded beyond 33%?

What's the rating of the main breaker? Does the question assume that there is other load? More info needed to clarify your question.

 

[jaggedben]

If the goal is to limit the max Ev charging line current on any one conductor to 300A, then a single phase could have up to 300A or 62.4KVA, *but only when the other phases are consuming nothing at that moment*.

 

[winnie]

1) When a 3 phase circuit is described as being X amps, that means X amps on each 'hot' wire of the circuit at the same time.

This number might be a breaker trip rating or something related to potential current flow. For example a 3 pole 100A breaker will carry 100A on each pole (adjusted by trip curve). The 100A is not a total for all 3 poles.

2) The 'power ceiling' you describe is not fully specified. I could imagine the control system limiting the chargers to any of a) maximum 300*208*1.732 VA in any combination (in the maximum unbalanced condition this would put > 300A on 2 legs) b) maximum of 300A drawn on any supply leg (which could be a limit of 300*208 VA in the worst case unbalanced condition), c) maximum of 164*208 VA on any of the 3 branches, or d) 0.8 times any of the above.

Jonathan

 

[brycenesbitt]

Not germane to the EVLMS load management question, but perhaps to your project.
J3400 retains the same 277 volt specification as the NACS/Tesla connector for use
with wye/star three phase.
....
Are you intending to charge slower at 208V on J1772? Or use an extra transformer?
Or take a walk on the wild side and stuff 277V into a J3400 EVSE?