db changes

[steveB1]

hey guys,

Seems like there's some knowledgeable sparks on here so wondered if i could pick some brains about how others would go about doing this particular job ive got.

the job is changing 2 db's. ive changed plenty of CU's and db's before but this is bigger than my usual. and yes im a proper sparks ( apprentice trained with 2360,2381,2391 ect....)

the current setup is.......

a 4 core swa 120mm (wired from a bussbar chamber protected by 800A fuses in each phase). think the rating of this was 267A per phase conductor, and yes i can see the danger in this.

this goes to a tripe pole isolator (fused with 100A fuses) which feeds 2 db's.

circuits in db 1 are 3 x 30A ring mains, 1 30A submain, 5A timer buzzer, 4 x 63A three phase socket outlets incorpaating switch disconnectors. and 1 roller door supply currently on a 10A tp breaker.

circuits in db2 are 6 x 63A sockets and switch disconnectors and 3 lighting cicuits for high bay lights 400w lights.

the boards are 12 way each. rest of ways not mentioned are spare.

anyone got any input on this?

obviously im going to try fitting an isolator after the bussbar chamber to protect the supply cable for the boards. then planned to split the cable to feed 2 seperate local isolators next to the boards, one for each.

am a bit unsure if this is the best way of doing thing?

also has anyone any input into the ratings of isolators and boards i should be using taking into the cable thats there? or anything else they think may be important to consider.

appreciatte any views.

great site by the way.

 

[Pensdown]

Wow, thats' a big DIY project, have you got a drawing of existing and proposed?

 

[plugwash]

the first question to ask is how much current is really being drawn through the boards.

you can get MCB boards with 100A TP and TP+N switched incomers easilly so i don't see any need for a seperate isolator next to them assuming that is that 100A per phase per boards is sufficant. Some brands also i belive offer 125A switched incomers.

iirc short runs from bussbar chambers to fused isolators are i belive given some exceptions in the protection rules but such unprotected runs should still be kept short and be mechanically protected.

 

[steveB1]

No drawing of current set up no, its like most other things-they dont exist!

the cable run from chamber to isolator and boards is about 25 metres.
im aware that some cables are eligible for exception in terms of rules for protection but ive never really understood how that works and how cables qualifyanybody want to enlighten me?

and seen as its one cable feeding the boards how would others split the cable to feed the 2 boards?

 

[RF Lighting]

the cable run from chamber to isolator and boards is about 25 metres.
im aware that some cables are eligible for exception in terms of rules for protection but ive never really understood how that works and how cables qualifyanybody want to enlighten me?

This will need a switch fuse at the busbar end to protect the cable.

and seen as its one cable feeding the boards how would others split the cable to feed the 2 boards?

1. use the cable to feed a panel board and take one cable to each dist board.

2. Feed the first DB with the cable, and make the second dist board a sub mains

3. If both boards are next to each other then just fit one big board. No need to split the cable then.


BTW Square D dist boards will accept upto a 250A TP MCCB incommer. (I think Merlin Gerin do too)

 

[Spark123]

For Square D you have to specify your current rating when you buy the board, the KQ+ range come in 125A or 250A flavours.