adjustable trip

[lmchenry]

Can an adjustable trip breaker be dialed down to fix a problem of undersizing the service conductors? For example, a 2500 amp main adjustable with 4 parallel 750s giving 1900 amp is dialed down to 75%. Does this violate 230.42 B?

 

[don_resqcapt19]

Can an adjustable trip breaker be dialed down to fix a problem of undersizing the service conductors? For example, a 2500 amp main adjustable with 4 parallel 750s giving 1900 amp is dialed down to 75%. Does this violate 230.42 B?

It might not violate the rule in 230.42(B). See 240.6(C).

 

[lmchenry]

Does anyone consider the rating of the disconnecting means still 2500 after the breaker is dialed down? Also, a similar example would be 4000 amp rated switch gear and disconnect with 3500 amp fuses. How do you size the service conductors?

 

[brian john]

Per the overcurrent device be it fuses, or the rating plug, or setting of the device. Breakers come in frame sizes if you have a 400 amp Frame CB with a 300 amp rating plug are you going to run 500 kcmil or 300 kcmil? 300 kcmil I would think

 

[ron]

Since you cannot buy a 3500A rated switch, you would need to provide a 4000A switch and 3500A fuses for a 3500A service. The wires would be sized for 3500A ampacity minimum.