Commercial sub mains exceed max zs of mccbs

[jackhammerJIM]

So you have 0.40 at the 80A switch-fuse which supplies a switch panel at which Zs is 0.57 thus, the Zs for the 125A device at this panel will be excessive due to the 0.57?

0.57 zs is on the outgoing sub mains from the 400 amp panel . sub mains are protected by 125 amp mccbs

 

[westward10]

You need to be clear in your Report as we have been confused.

 

[jackhammerJIM]

You need to be clear in your Report as we have been confused.

Read the first post again it is not that confusing .

The report will state that the 125a sub mains from the 400 amp panel board exceed maximum permissible zs values but the disconnection time will be met by the 80 amp switch fuse at source

 

[westward10]

It isn't confusing to you because you can visualise it but to someone reading you first post it is not clear.

 

[westward10]

Read the first post again it is not that confusing .

The report will state that the 125a sub mains from the 400 amp panel board exceed maximum permissible zs values but the disconnection time will be met by the 80 amp switch fuse at source

This statement to me gives the impression is all okay and maybe it is as fault protection is provided but the issue of selectivity is not clearly addressed. There is no selectivity between x and the supply protective device y whereby fault protection is provided by y. Or something along those lines.

 

[davesparks]

Are the 125A mccbs set at full or have they been adjusted down to a more sensible level?

 

[jackhammerJIM]

Are the 125A mccbs set at full or have they been adjusted down to a more sensible level?

Hi Dave this type is not adjustable

 

[jackhammerJIM]

This statement to me gives the impression is all okay and maybe it is as fault protection is provided but the issue of selectivity is not clearly addressed. There is no selectivity between x and the supply protective device y whereby fault protection is provided by y. Or something along those lines.

I have commented on the poor discrimination between devices and made them aware of the inconvenience a fault may cause .

cheers lads thanks for your input ....

 

[westward10]

Selectivity these days

 

[jackhammerJIM]

Selectivity these days

person receiving the report won't under stand either term

 

[arashabb]

Hi Guys,
in an installation with one main Distribution board and several submain-DBs, do when you measure Zdb on a submain-DB incomer? and do we need to verify the Zdb value with the up stream protection device?( for example, a 125A, MCCB on the MDB outgoing). If yes, how can I get the max Zs values for MCCBs ?

 

[westward10]

Hi Guys,
in an installation with one main Distribution board and several submain-DBs, do when you measure Zdb on a submain-DB incomer? and do we need to verify the Zdb value with the up stream protection device?( for example, a 125A, MCCB on the MDB outgoing). If yes, how can I get the max Zs values for MCCBs ?

Hello Arashabb this is an old thread so you need to create a new one.