paralleling fuse boards

[sparks will fly]

First time post although avid reader. And first post is a question, sorry!
What are people's thoughts about paralleling fuse boards. Been asked to install a new board by linking off the existing boards supply as the current board is full. They are lug and bolt terminals so can easily double the cables up and the existing cable and supply breaker from the LV panel is big enough to protect both boards. Apart from the obvious problem of both boards going down should a fault occur on the cable, which the client understands, is there any reason why this can't be done.
*Puts tin hat on.

 

[Engineer54]

You will need a means of SINGLE point switching!! E.g.... A switch to isolate both DB's from the supply!!

 

[shanky887614]

You will need a means of SINGLE point switching!! E.g.... A switch to isolate both DB's from the supply!!

Chop cable and insert another sub board inbetween.

Would be a temp solution though

 

[kingeri]

I would normally take supply tails into isolator, then from isolator to Henley block, then from Henley block to the two DBs.

 

[i=p/u]

Il say nothing wrong if can take booth cables... But I'd come from underside.. So when isolate one the both isolated . Or as above use iscos..

 

[VoltzElectrical]

If supply cable is big enough to handle the additional load then surely there is no difference between what you suggest and a bigger board?

 

[Sintra]

You could make yourself a spare way in existing board by extending a circuit into the new board. Then use the newly created spare way to supply the new board.

 

[guest119]

Take a circuit from old db, assumed 3phase, to new db to clear a space for a new breaker.
Fit 63a tp breaker in old db to feed new adj. db.
Then old db isolator kills both as E54.
All depending on loads of course.
Maybe move the circuits around to feed the lighter loads from the new db?

Boydy

 

[Sintra]

That's what I said

 

[VoltzElectrical]

if you have a full board, and want more circuits, then either fit a bigger board or split the tails.

As long as there is sufficient upstream protection, then there shouldn't be a problem.

If upstream protection is a problem, and only IF, then this is when you need to add another (board off a board) if you see what I mean!

If the upstream fuse will cope with the extra demand, then there is no need to add more protection, just treat it as a bigger board and do as I said.

Basically, you are only increasing the capacity of a small board (within the capacity of the supply cable).

 

[Knobhead]

As E54 pointed out, you need a common point of isolation. I don’t like the method but done correctly, there should be no problem.

A single isolator cabinet mounted midway under the two boards serves the purpose.

This is all dependant on the possible load increase and diversity.

 

[sparks will fly]

Thanks for your replies

Its a 630a 3 phase supply using 300mm singles. The existing board is full as I say but pulling around 80-90a per phase. The board has a 400a disconnector built in. The new board will be the same as the existing. Client not really keen to remove cables and split in an isolator or sub panel as this will cost a lot more and increase down time.

Can someone point me towards the single point of isolation
regulation please as I'd like to look at that in more detail. I've seen reg 537.1.3 which says each installation needs provision for disconnection for supply.
So if that applied then maybe the 630a MCCB could be classed as isolation for both. Obviously suitably labelled.

 

[scammell man]

Thanks for your replies



Can someone point me towards the single point of isolation
regulation please as I'd like to look at that in more detail. I've seen reg 537.1.3 which says each installation needs provision for disconnection for supply.
So if that applied then maybe the 630a MCCB could be classed as isolation for both. Obviously suitably labelled.

I was thinking the same. Common points of isolation are very rare in large installations, unless fire service has requested a building isolation point. It is quite possible to have multiple supplies onto a bus bar that goes out to multiple distribution boards. If you have a single incommer from the DNO this would normally be your common point of isolation. What is upstream of these 300mmcables?
As an observation most domestic installations with a PV system do not have a common point of isolation.

 

[Dcf]

Could you not get an extension board to sit on top of the existing one ?
most of the ones I've come across do a link kit of some sort