Joining Two MSBs

Wha....?

One of those rare occasions you get the chance to read pure GIBBERISH!

The purpose of this connection is for redundancy to obtain continuous operation. If one incomer (e.g. MSB-1) is failure the other one will supply power by closing the MSB-2 manually or automatically. There must be interlock between these MSBs to ensure that at a time one of the MSB will be in closed condition.

Are you absolutely sure about that?

The post doesn't make anything clear, if you stick around CR4 you will soon find out how obtuse questions can be.

sure, there is an interlock between them. And I also accept your reason that for redundancy. Thank you so much. now what I want to know is why we have to use 16 cables (16x 400 mmsq XLPE) + (1x250 mmsq) CPC to join these two MSBs.

For the current to pass?

If you do cable sizing means you will get the solution. I am not clear this 16 runs of 400 sq.mm cable is for both MSB or Individual MSB. that 250 sq.mm cable is for neutral. always neutral cable shall be half of the main cable..

If u want more idea give me the details of load, incoming supply, distance and technical data of the cable..

"now what I want to know is why we have to use 16 cables (16x 400 mmsq XLPE) + (1x250 mmsq) CPC to join these two MSBs."

So are you unclear as to why they selected that quantity and size of cables? If so, as compared to what?

You must have conductors that are;

1. rated to carry the current, and
2. easy enough for installers to handle

If for example you wanted to do it with one or even two conductors per phase, have you given thought as to how big that would be and how difficult it would be for an electrician to handle it?

Bus bar would likely be a better choice, but is not always practical, especially in retrofit situations.

With four 400mmsq per phase looks like you have a design problem, distance, volt drop and cost. Needs an engineer to look at a new substation, a higher volts supply.

First you say the two supplies are joined, and power sharing, is this in parallel? Not a trivial matter if it's coming from two separate transformers.

Then there's talk of a changeover with one taking over from the other, i.e. main supply and a standby which comes in on failure of the main supply, with interlocking.

thank you for your sharing. here is the detail of the two MSBs that is going to join with the circuit numbers 1-15 and 2-17. Both MSBs have same rating with 4000AF/2800AT. and MSB1 has separate transformer.

The two incomers are interlocked with the bus-tie breaker, you'll find it's not possible to parallel the two feeders. It's normally two out of three, so one feed can supply both boards or each board runs separately which effectively shares the load.

What are you trying to achieve? If you are overloading on one board you might change the loads around from one MSB to the other.