Contactor Interlocked Auto change over Vs Motorized MCCB Change Over 2

[NickParker]

The distribution board gets power from two UPS and I'm planning to install a Auto change over system. (Break before make)

Since the loads are critical (but can accept a short time interruption), which is beneficial? Contactor Interlocked Auto change over (or) Motorized MCCB Change Over

 

[RRaghunath]

Contactor based changeover ill be faster than the MCCB one.
The choice depends on how long the load can withstand power interruption!
If it is just a few milliseconds, you may need a static switch even.

 

[che12345]

Dear Mr. NickParker (Electrical)(OP)22 Dec 21 08:49
"...The distribution board gets power from two UPS and I'm planning to install a Auto change over system. (Break before make). Since the loads are critical (but can accept a short time interruption), which is beneficial? Contactor Interlocked Auto change over (or) Motorized MCCB Change Over".
1. Both mechanically interlocked [contactor] or [motorized MCCB] are acceptable; if the transfer speed is within the acceptable short time interruption.
2. Contactor is lower cost and lower short-circuit (kA) capacity. Attention: may need to add fuses, which is a serious security setback!
3. Motorized MCCB is higher in cost but with much higher short-circuit (kA) capacity. Attention: no additional fuses are required.
4. For higher security, motorized MCCB is a better choice, if security supersedes the cost. See 2. above.
Che Kuan Yau (Singapore)

 

[NickParker]

Is there any issue with applying a Motorised swich disconnector as a Incomer instead of MCCB for the auto change over scheme?

 

[che12345]

Dear Mr. NickParker (Electrical)(OP)24 Jan 22 11:08
"...Is there any issue with applying a Motorised swich disconnector as a Incomer instead of MCCB for the auto change over scheme? ..."
1. The two incoming conductors are protected by the respective MCCBs in DB "A" and "B" . The issue is on the [device selection for the auto changeover scheme]. There is no protection function. Therefore, [ Motorised switch disconnector] instead of [ MCCB ] may be acceptable.
2. Attention:
a) the Motorised switch disconnector usually of lower short-circuit kA rating shall be coordinated with the up-stream MCCB in the DB.
b) the out-goings conductors to the final loads shall be individually protected by MCCB/MCB of appropriate current ratings.
Che Kuan Yau (Singapore)







mcb