Query; I have a panel board(mccbs) containing 100amp mccbs...

[mrloy99]

Hello engineers.
I have a query. I have a panel board(mccbs) containing 100amp mccbs supplying various "life safety DBs" lifts, water mist pumps etc.The panel board has an MCCB of 250 AMP as the main switch. It is supplied from an ATS in 120mm sq.4 core with 70mm earth.A run of 20m.The ATS is supplied via 1x4core 150mm sq plus separate earth,120mm so. a run of 180m and the second is 1x4core 150mm sq. plus separate earth 120mm...a run of 210m.They are to be supplied from 2 separate switch rooms. One of them is from an ACB 1600amp set at 1024amp and the second is ACB 1000amp set at 640amp.I can understand that the 250amp mccb on the panel board will mean that it will not be possible to draw more than that ampage so what about fault protection. Is it adequate?

 

[westward10]

Are you asking whether the installed cables can carry the anticipated fault current or whether the circuit will disconnect as required under fault conditions. Is this an existing installation or are you installing it.

 

[shaun1]

Assuming the maximum load on the pannel board is under 250A? So why are the two supplies to the ATS so much larger? And why are they different?

(I don't have any real experience of distribution curcuits on this level, just interested...)

 

[mrloy99]

Are you asking whether the installed cables can carry the anticipated fault current or whether the circuit will disconnect as required under fault conditions. Is this an existing installation or are you installing it.

I'm just the tester on the job. I still have't seen the switch rooms. I'm guessing that these are existing breakers at their lowest settings.. I'm just used to seeing a breaker at the origin that would protect the cable. I'm asking will they disconnect under fault conditions. I'm not sure the declared settings on the attached protection study by the designer are correct.