Mccb used as main switch isolator

[Ian1981]

A question regarding the use of a mccb as a 3 phase main isolation switch to a DB.
Is it a necessity?
Current set up is I have a 3 phase 70mm supply feeding a DB.
The origin of this supply is unknown, hence I’m getting northern power out to investigate as the main cut out earthing arrangement and metering is unknown
As I do not know the primary OCPD protecting the 70mm swa and lets assume for the minute that they are adequately protected via bs 1361 or bs 88 fuses, is the mccb totally necessary protecting the DB final circuits?
The existing one is broken and does not isolate the DB.
Spoken to Hager and the range is now obsolete and can’t be retro fitted.
It’s a 250 amp mccb with its In set to 200 amp minimum setting so it’s rated to high for the 70mm swa anyway.
Comments welcome:mtongue:

 

[buzzlightyear]

Could you not ask the DNO to stick in a 3 phase isolator for you before changing it .with out them coming back and forth .

 

[buzzlightyear]

Try flie bay lots on their.

 

[Ian1981]

The current mccb is too large for the 70mm swa anyway, the Ir setting is set at its 0.8 minimum setting giving it an In of 200 amps which I have the 70 mm swa at a ccc of 128 amps reference method D and a correction factor of 0.9 which I already have applied to raise the ambient temperature to 30 degrees inline with section 433 where overload protection is required.
The whole job and trying to salvage circuits for the refurbishment is a pile of s#ite and it’s only 12 years old.
The ventilation system has been installed with soil stack pipe with no back draft excluders for the inline fan venting individual rooms

 

[Ian1981]

It maybe that the 70 mm swa is the DNO’s cable and the mccb is the device used for protection of the swa against over current
God knows what has happened to the metering tho

 

[Nigel]

Is there a way currently of isolating the whole installation?

 

[Ian1981]

Is there a way currently of isolating the whole installation?

No
It’s a big issue In itself
As it’s stands all I’m doing at the moment is carrying out an eicr however we will be doing the alterations to the electrical installation during the refurbishment works so it will need addressing

 

[westward10]

Have you had a walk around for any remote brick buildings where the intake could be maybe hidden in bushes.

 

[Ian1981]

Have you had a walk around for any remote brick buildings where the intake could be maybe hidden in bushes.

I’ve found the supply.
The DNO have been out and their LV supply goes to a meter room housed in another building about 200 meters away from the building im working in.
The 70mm is connected to an old handle bar isolator (looks ancient and if isolated may not reconnect)from which an swa from the DNO’s metering cut out feeds.
Worryingly tho I’ve a 25mm cpc entering the building but it’s a 16mm that connects to the remote isolator at the supply end.
The maintenance guy who looks after the building where the metering is kept informed me that originally the sub mains that was installed back in 2006 was too small so the contractor had to upgrade the cable, all sounds a bit comical.
I need the DNO to tell me the earthing arrangement as I need to assess the possibility that the 16mm/25mm is inadequate for the protective bonding requirements to the building.
There’s no pme label at their end so I’m hopeful that it’s TN-S as the possibility of making the building TT is a no go really.
The LV cable looks like PILC but I’d need to confirm