Switch board

[edwale]

Hello,
I am in a situation where we are running out of the MCC switchboard spares for future works and so I am planning to rationilise so that I will have all the feeders relocated to a wall mounted switch board to make room available for drives only. The feeders are mainly for 2 air con units and 6 and welding outlets all having the 63A MCCB. The Main Circuit breaker on the MCC Switchboard is a 2000A/50kA Merlin Gerin breaker. My cascade system of the board I am planning to put in is just the wall mounted switch board with 630A/25kA MCCB as the main Circuit breaker.

Is this ok?

Regards

 

[ScottyUK]

How are you proposing to 'extend' the MCC - by direct connection from the main bus to the panelboard incomer?

Draw a single line diagram of what you have, and what you propose to install. Include details such as breaker sizes and breaking capacities, transformer size and impedance, and transformer LV cable lengths if they are more than a few yards. A picture or sketch saves a thousand misinterpretations.

 

[edwale]

Scotty,
Yes it will be direct connection from the the busbar of the upstream through the 630A MCCB as per the sigle line diagram and use the 63A 3pole MCCB for all the aircon and
the welding outlet loads. The switchboard will be wall mounted and is just about 3 meters from the main MCC so I wanted to have the 630A MCCB on the MCC as the only isolator to the new switchboard.

How do we post the attachment?

 

[ScottyUK]

It sounds like it could be viable, but there are certainly a few pitfalls to be wary of. You'll need to be careful you don't exceed the fault rating of the smaller board if the main bus has a high fault level and the new cable is short. The cables will likely need to be sized according to the upstream protection, so they may be impractically large if you have a 2000A main breaker. It might be worth speaking to Schneider to see what they can offer in terms of cable connection to the busbar system.

If you look below the text box where you would write a reply to the thread, there's a smaller box and immediately below that are a couple of hyperlinks to free hosting sites where you can upload scanned sketches, documents or whatever. I tend to use the engineering.com hyperlink out of habit. You can cut & paste the link into the main body of your reply, or enter it in the smaller text box.

 

[edwale]

Hello,
Scotty attached is the link to my porposed sigle line diagram.

Much Appreciated.

Regards

 

[edwale]

Scotty,
Update drawing attached..Typo for the 50kA..

Thanks

 

[collies99]

Please excuse for butting in. If the fault on the 25kA switchboard is greater than the noted rating, you have an issue, unless the 50kA gear has fault capability less than 25kA originally. If downstream fault is greater that 25kA you either have to up-rate or install bus reactor / added reactance to reduce fault to 25kA availability.

Would the 630A MCCB also has 25kA interrupting rating ?

 

[edwale]

Collies,
Are you saying we have two 630A 25kA circuit breakers one on the main MCC and one on the new switch board?

Regards

 

[collies99]

Edwale:
No, that was not the intent. I should have said main CB.

 

[ScottyUK]

Is the 630A MCCB located on the main board or is it the incoming device on the new board? You need to carefully consider the implications of using a cable interconnection between the main bus and the new MCCB, especially if the 2000A breaker is an ACB with a definite time setting or a slow clearance time. As collies99 has rightly pointed out, the main board may be 50kA rated for a reason and it is possible that you could have more than 25kA at the new board.

 

[edwale]

Scotty,
The main CB will be on the main MCC and the cable from there to the new SB. I have looked up the schenider data sheet on the cascade steam the downstream CB suitable for the 50kA fault current fo the main CB is 36kA.