10KA or 6KA breakers?

[yellowvanman]

I know the difference between the 2 sorts but I'm thinking do I need to fit 10KA breakers in this scenario, when I've got 6KA MCBs in the van!

3 phase DB, Isc 4.9KA (phase to earth), all circuits from this DB are single phase. Will never be 3 phase in future (HMO).

Worst case short circuit (phase to phase) would be 9.8KA, but that could only happen in the DB itself, which is protected by the 100A 1361 DNO fuse.

 

[loplug]

can you be sure that there isnt 2 phases in the same switch or containment any where in the install i would fit 10ka on that information to be on the safe side

 

[yellowvanman]

can you be sure that there isnt 2 phases in the same switch or containment any where in the install i would fit 10ka on that information to be on the safe side

I'm sure

 

[MDJ]

I know the difference between the 2 sorts but I'm thinking do I need to fit 10KA breakers in this scenario, when I've got 6KA MCBs in the van!

3 phase DB, Isc 4.9KA (phase to earth), all circuits from this DB are single phase. Will never be 3 phase in future (HMO).

Worst case short circuit (phase to phase) would be 9.8KA, but that could only happen in the DB itself, which is protected by the 100A 1361 DNO fuse.

All about design of the circuits fella.

 

[Sintra]

6KA is fine in this scenario.

 

[Chr!s]

I know the difference between the 2 sorts but I'm thinking do I need to fit 10KA breakers in this scenario, when I've got 6KA MCBs in the van!

3 phase DB, Isc 4.9KA (phase to earth), all circuits from this DB are single phase. Will never be 3 phase in future (HMO).

Worst case short circuit (phase to phase) would be 9.8KA, but that could only happen in the DB itself, which is protected by the 100A 1361 DNO fuse.

6kA will be okay going of thebinfo provided

 

[Darkwood]

IF you have a upstream protective device that meets requirements then any device downstream does not even have to meet the S/C current rating because if the downstream device is destroyed and maintains a fault then the upstream device will still operate safely.... Note im not saying this is good design in any way but if you find you have a DB full of none compliant devices you can fit a upstream device with a higher Ka rating to give the installation a pass.

 

[yellowvanman]

All about design of the circuits fella.

Don't understand what your saying, sorry!

 

[MDJ]

Don't understand what your saying, sorry!

Eh? If you are going to connect a large motor to a circuit using a B type mcb would silly yes? one socket for a kettle then a b fine?

 

[Engineer54]

IF you have a upstream protective device that meets requirements then any device downstream does not even have to meet the S/C current rating because if the downstream device is destroyed and maintains a fault then the upstream device will still operate safely.... Note im not saying this is good design in any way but if you find you have a DB full of none compliant devices you can fit a upstream device with a higher Ka rating to give the installation a pass.

Maybe, but i'm a great believer in providing the correct rated OCPD's. I've only seen the result of using grossly under rated Breakers once, (and there was other issues) but that breaker was missing almost half of it's casing and bit's of it's internals and busbar all over the DB, with quite a few damaged adjacent breakers to boot!! lol!!!! The upstream protection did trip, but not fast enough to prevent some expensive damage to the DB...

As an example, i always make sure that small power final DB's in our project S/S rooms are provided with MCB's rated at 25KA...

 

[Chr!s]

Maybe, but i'm a great believer in providing the correct rated OCPD's. I've only seen the result of using grossly under rated Breakers once, (and there was other issues) but that breaker was missing almost half of it's casing and bit's of it's internals and busbar all over the DB, with quite a few damaged adjacent breakers to boot!! lol!!!! The upstream protection did trip, but not fast enough to prevent some expensive damage to the DB...

As an example, i always make sure that small power final DB's in our project S/S rooms are provided with MCB's rated at 25KA...

Its not technically correct either, theirs a little bit more to cascading than what has been mentioned.

 

[Engineer54]

Its not technically correct either, theirs a little bit more to cascading than what has been mentioned.

Oh that's for Sure!! ...lol!!

 

[Darkwood]

Agree designed correctly all sub boards tend to have larger supply cables etc to allow for cascading for discrimination a positive consequence of this is your up front devices by design tend to have a high Ka tolerence anyway..... i did put a note in my last post about the comment i made wasnt good design but i was just reflecting on requirements .... if the downstream device is destroyed because it has a limited Ka rating the upstream device will still cover the fault and operate thus the supply is diconnected as required... yes the downstream device requires replacement but this is down to installation design which could be better and not the fact that its not in compliance.

 

[Engineer54]

Agree designed correctly all sub boards tend to have larger supply cables etc to allow for cascading for discrimination a positive consequence of this is your up front devices by design tend to have a high Ka tolerence anyway..... i did put a note in my last post about the comment i made wasnt good design but i was just reflecting on requirements .... if the downstream device is destroyed because it has a limited Ka rating the upstream device will still cover the fault and operate thus the supply is diconnected as required... yes the downstream device requires replacement but this is down to installation design which could be better and not the fact that its not in compliance.

Both go hand in hand as far as i'm concerned, and will certainly save any severe and costly damage occurring at the downstream position.

 

[Darkwood]

Agree fully E54 my comments were for pre-existing installs and how to get around the issue without massive costs... new installs etc should not be seeing these set-ups and i wouldn't condone implementing what i said in a new install.