DB Extension.

[Derlyn]

Came across the following yesterday.

18 way surface DB became too small when 2 air cons were added to the installation, so another 8 way DB was installed next to it to house the 2 air con mcb's
and labelled " Main DB Extension" and containing only 2 single pole mcb's. ( No main breaker etc. )

The question is,........ Can this added small DB be seen as part of the main db or must it be seen as a seperate DB with it's own double pole main breaker etc.

When doing a COC, do I include 2 test reports or 1 ?

[GCE]

I would say it is a sub DB and needs a main isolator and labeled as Sub DB 1 - 2nd test report would be needed then

[Derlyn]

Thanks GCE. I actually thought it was quite a novel way of increasing the size of the db. I have quoted on doing exactly as you suggested. Thank you.

[Tradie]

You have to look at the big picture. I see this kind of challenge all the time, but just in a large scale, where multiple compartments are attached to each. For example a 1000 or 15000 amp main switch in one compartment, with a bussbar at the bottom which runs the entire width of the whole DB or in some cases would be refered to as a control centre. Each section of the DB/control centre might have a circuit breaker, the design, bussbar sizing and the circuit breaker are carefully selected to reduce the fault level and protect the busbars/cabling.

Because there is no picture, I would need to assume a few things.

The person who attached the smaller DB to the larger DB, would have drilled a hole between the DB's and installed a cable large enough to link directed to the bussbar, in that case it is just an extension of the main DB. If the smaller DB is within arms reach of the main switch and addtional circuit breakers are added to the small DB, it wouldnt be a problem. I would just fit a main DB lable on both the large rand samller DB.

If the small DB was added and only a 4 mm sq cable was used to link the 2 x 20 amp mcbs for the AC units, then I would suggest a double pole 30 amp circuit breaker is installed in the smaller DB, labelled local main.

Lastly, You could install a 6 mm wire, to allow for futhure expantion, fit a 40 amp mcb in the larger DB, a main switch in the smaller DB. YOu could then label thelarger DB - Main DB and the smaller one Sub DB 1.

This is good expample of why we have a basic guidlines (the sans regs) and why it is so imprtant for electricans to spent time in training centres, and on site with mentors.