Cable Sizing Calculation for Star Delta Starter

[SSKLC]

Hi,
I am trying to size cables from Star Delta Starter to Motor

During Star connection,
Load Current in Cable from SWGR – Motor Term. U1, V1, W1 = 1/3 (33%) of actual FLC
Load Current in Cable from SWGR – Motor Term. U2, V2, W2 = 1/3 (33%) of actual FLC
Starting Current in Cable from SWGR – Motor Term. U1, V1, W1 = 1/3 (33%) of actual Starting Current
Starting Current in Cable from SWGR – Motor Term. U2, V2, W2 = 1/3 (33%) of actual Starting Current

During Delta Connection,
Load Current in Cable from SWGR – Motor Term. U1, V1, W1 = 1/√3 (58%) of FLC
Load Current in Cable from SWGR – Motor Term. U2, V2, W2 = = 1/√3 (58%) of FLC
(Note that reclosing current transient during star to delta transition is ignored as present only for very small duration)

For Star Connection,
Running VD = √3 x (33% of FLC) x (2xL) x (RcosØ + XsinØ) / (No.of runs X V)
Starting VD = √3 x (33% X starting current Mulitplier x FLC) x (2xL) x (RcosØ + XsinØ) / (No.of runs X V)

For Delta Connection,
Running VD = √3 x (58% of FLC) x (2xL) x (RcosØ + XsinØ) / (No.of runs X V)

Based on above, worst case cable size to be selected for cables between Star Delta Starter to Motor.
Please advise if I am missing anything.

 

[LionelHutz]

The CEC is apparently NOT in harmonization with that of the NEC !?

You're interpreting the code wrong. The cited line says to use 58% of the FLA to size the conductors, which does not negate any other rule that also apply when sizing conductors for motors.

 

[waross]

The two codes are very close but not identical.
The interpretation varies also.
Instance.
Both codes have basically the same rule dating back probably over 75 years from a time when open knife switches were in common use.
The rule also applies to knife switch type disconnect switches.
The rule prohibits mounting switches in such an orientation that gravity will tend to close them.
The NEC interprets this rule to include circuit breakers, the CEC does not apply the rule to circuit breakers.
So, under the NEC a residential breaker panel may not be mounted horizontally as that would put half of the breakers in the orientation where gravity would tend to close them.
The similar rule in the CEC is not applied to circuit breakers and in Canada, residential breaker panels are seen mounted horizontally most often in re-wires where it may be difficult to find a suitable space to mount a new panel vertically in an old structure.
I'll buy the first round of coffee Mr Che.
Thank you for the clarification Lionel.
Your information is as I expected, however given the close but not exact harmonization of the NEC and the CEC, and the occasional differences in interpretation of the same rule, I chose not to comment on the NEC rule.
You are welcome to join us for coffee.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[SSKLC]

Thank you Waross and Che...

My confusion is clear...that additional √3 factor not to be applied for calculating voltage drop, as current is calculated considering 58% of nameplate rating.

Other than that I agree that conductor needs to be derated based on grouping of cables, however, conductor current ampacity check is separate check than Voltage drop calculation and in my understanding needs to be performed even before calculating voltage drop.

Thank you for your valuable feedback.