2391-52 help please

[Kaya12]

During Periodic Inspection and Testing, prospective fault current has been tested at the main distribution board (Main DB) using a single-phase test instrument.

The supply and installation form part of a 400 V three-phase TN-C-S system. The value of Zₛ (earth fault loop impedance) for this installation is 0.05 Ω.

Information about the protective devices installed at the remote distribution boards (DBs) is as follows:

Main DB: 3 phases, 10 kA
DB1: 3 phases, 7.5 kA
DB2: 3 phases, 7.5 kA
DB3: 1 phase, 7.5 kA
DB4: 1 phase, 6 kA

At which points in the installation must further testing be carried out?

a) DB1 and DB2
b) DB3 and DB4
c) DB1, DB2 and DB3
d) DB1, DB2 and DB4

 

[westward10]

Do you know the pfc measured at the Main DB?

 

[Kaya12]

No I don’t know tbh can you help with this question please?

 

[westward10]

Do you understand the relationship between the DB KA ratings and the PFC?

 

[Kaya12]

PFC must be less than or equal to the DB’s kA rating.
This ensures the panel can safely withstand a fault.

 

[PS Electrics]

No I don’t know tbh can you help with this question please?

You can work out what the PFC should be when tested single phase given the information.

You can then convert that to 3 Phase PFC.

With that information think about which DB protective devices short circuit breaking capacity might need checking.

 

[westward10]

The key here is calculating your pfc for the three phase and single phase because two boards are single phase and the other two three phase. Then as in #6 which ones then need checking.

 

[Kaya12]

The key here is calculating your pfc for the three phase and single phase because two boards are single phase and the other two three phase. Then as in #6 which ones then need checking.

Further testing should be carried out at DB1, DB2, and DB4 to confirm that the PFC at these points does not exceed the breaking capacities of their respective protective devices is to hid correct ?

 

[Kaya12]

You can work out what the PFC should be when tested single phase given the information.

You can then convert that to 3 Phase PFC.

With that information think about which DB protective devices short circuit breaking capacity might need checking.

the correct answer would include the boards with the lowest breaker ratings, especially single-phase ones, where the PFC formula gives a different result ?

 

[PS Electrics]

the correct answer would include the boards with the lowest breaker ratings, especially single-phase ones, where the PFC formula gives a different result ?

This is a periodic Inspection and test, when you test on a Periodic a test result might give you reasons to perform further tests and this is what the question is probing.

Think about PFC and what it cannot be at points further from the origin?

Given the above info why the single phase ones when we know the maximum single phase PFC at the origin?

Why the 3 phase ones?

 

[westward10]

Have you calculated your single and three phase pfc at the Main DB?