Phase Indication Lamps on Incoming Lines

[NickParker]

1. Can Miniature Circuit Breaker(MCB) be directly connected to the bus in the Low Voltage switch gear as per the IEC standard?
2. For Phase Indications of Incoming lines, (on the line side of the Incoming circuit breakers), should small control step down transformer be provided even if it has 3 phase 4 wire for low voltage. Why can't it be directly connected to the pilot lamps? for example, I have 3 phase 380 Volts with 4 wires which means I also have 220 V in it, So why can't I put the pilot lamps directly to the Incoming lines with fuse/MCB protection?

 

[ScottyUK]

Most MCB's have a limited breaking capability of 6kA or 10kA. If the prospective fault level is less than this value then it would be technically acceptable. Most bus taps on British gear are via a bar-mounted backup fuselink with an accessible fuselink or MCB located within the metering chamber. The backup fuselink won't ever operate except under fault conditions on the cable between the bus tap and the metering chamber.

You could directly connect the lamps, via suitable fuselinks. I wouldn't personally go for this and would rather see a control transformer down to 110V or 24V, but it's common in bottom-end equipment where shaving every penny out of the design is the primary goal of the designer.