Would anyone mind trying to help me understand this question please

[Rather be Fishing]

I initially went for answer b) because in GN3 page 68 (2.6.17) I read

"At every relevant point of the installation"

but then I read

The inspector must have knowledge of the design in this report as, for example, if the switchgear at the origin of an installation is suitably rated for prospective fault current and switch gear of similar short circuit rating is used downstream of that point, then no further checks are necessary.

which made me change my mind and go with answer d)

seeing as the correct answer is a) I'm clearly not getting it and wondered if anyone would mind trying to educate me please?

 

[Lister1987]

I initially went for answer b) because in GN3 page 68 (2.6.17) I read

"At every relevant point of the installation"

but then I read

The inspector must have knowledge of the design in this report as, for example, if the switchgear at the origin of an installation is suitably rated for prospective fault current and switch gear of similar short circuit rating is used downstream of that point, then no further checks are necessary.

which made me change my mind and go with answer d)

seeing as the correct answer is a) I'm clearly not getting it and wondered if anyone would mind trying to educate me please?

DB3 operating at 400v, DB2 operating at 230v. I=V/R. Higher voltage results in higher fault current.

 

[Rather be Fishing]

DB3 operating at 400v, DB2 operating at 230v. I=V/R. Higher voltage results in higher fault current.

Thanks for trying to help @Lister1987 but I'm not sure if that answers it for me mate.

The questions says

At the origin of DB1, the maximum Ipf was recorded as 8kA

where else must the test be undertaken within the installation.

the options it gives me are

a) DB3 only
b) DB2 and DB3
c) DB2 only
d) Nowhere else

The answer is a) DB3 only

But why is that. Does anyone know

 

[Lister1987]

Thanks for trying to help @Lister1987 but I'm not sure if that answers it for me mate.

The questions says

At the origin of DB1, the maximum Ipf was recorded as 8kA

where else must the test be undertaken within the installation.

the options it gives me are

a) DB3 only
b) DB2 and DB3
c) DB2 only
d) Nowhere else

The answer is a) DB3 only

But why is that. Does anyone know

Due to it being at a different operational voltage, the others are at 230v, so testing then would give identical results to DB1

 

[Rather be Fishing]

Due to it being at a different operational voltage, the others are at 230v, so testing then would give identical results to DB1

But DB1 is 400v 3 phase DB2 is 230v single these and DB3 is 400v three phase

 

[Lister1987]

But DB1 is 400v 3 phase DB2 is 230v single these and DB3 is 400v three phase

DB1 has 10kA switchgear, DB3 has 6kA switchgear. You want to test at the lowest rate switchgear to ensure that you measured Ipf (8kA) wil be within its operational limits. Also DB3 (400v) has the higher voltage than DB2 (230v).

In this scenario DB3 would require higher kA rated switchgear to handle the measured Ipf.

 

[Rather be Fishing]

DB1 has 10kA switchgear, DB3 has 6kA switchgear. You want to test at the lowest rate switchgear to ensure that you measured Ipf (8kA) wil be within its operational limits. Also DB3 (400v) has the higher voltage than DB2 (230v).

In this scenario DB3 would require higher kA rated switchgear to handle the measured Ipf.

Thank you kindly @Lister1987 appreciate you input mate. Nice one