distribution board.

[jim23]

got a 3 phase db to do at work and need some advice really as im predominantly electrical maintenance.

the supply cable to the current 2 board is from a busbar chamber. the cable is 4 core swa 70mm.

the circuits i need are( other circuits can be removed as we dont need them)

3 x 30A ring mains
3 x light circuits at 10A each
1 x 30A sub main
1 x motor circuit 10A tp breaker.
1 x clock circuit 3A
5 x circuits supplying 63A switch disconnectors with 3 p+e 63A socket outlets.

firstly can anyone recommend a particular board to use? seen some 250A boards, are these man enough? if not am i better spliiting the load between 2 boards?

also the supply cable doesnt have a point of isolation so im going to fit a switch fused isolator. would there be a problem with me mounting this near the new db ( thus having the protection at the end of the cable and not the start, is this aloud?)

cheers guys.

 

[Spark123]

What size supply is it to the bus bar chamber? 3phase MCB boards normally have a location for an isolator at the bottom, if you are into the realms of a HBC board these generally do not have one. Do we need a point of isolation at the board (for working on the board) or is it viable to use the bus bar isolation?
I find the GEC redspot boards OK, as long as you don't drop the fuse holders and the red spot drops out revealing a live screw!!!

 

[jim23]

hi spark

not viable to use the busbar no. supply to busbar is 400A per phase.

require a means of isolation yeah. thought i could have used the incomer that ive seen on 3 phase db'd but will these be rated enough to take the current and also will i be able to terminate the 70mm's?

 

[jim23]

was definetly looking at mcb's. easy to reset and means i can rcbo the 230 rings too.

just unsure of what rating board i should be looking at in order for it to be able to take the mentioned circuits.

also i would require some protection for the board???

thought best way of doing this was to fit a switch fused disconnector. but unsure what fuses i should be fitting for the board?

 

[Spark123]

What is the Prospective Faulf Current at the busbars? You are going to have to fuse down to 250A using HBCs if you are using a 250A MCB board, more than likely a 250A fused isolator.
Although it is allowed to use underrated MCBs if backed up by supply fuses it is not really advisable.
If your PFC is less than 10KA then both Square D and Merlin Gerin do 10KA breakers (will safely break 10KA but may self-destruct in breaking over 7.5KA). I have used both Square D and Merlin Gerin before in the 100A Busbar versions, they both do 250A versions, single module RCBOs (Square D only do type C for 10KA KQO), don't know for Merlin Gerin.

 

[Lectrician]

You need to protect that 70mm against overcurrent.

A Switch-fuse at the busbar end would be better - 2inch bush/couplers to couple a switch fuse to the busbar, terminate the SWA to the switch-fuse.

I would fit an MEM 200amp board, with a 200amp incomer. The 200amp incomer accepts upto 150mm cables.

What is the actual load like?? Surely you can tell us a little?? What are the TP sockets feeding??

 

[RF Lighting]

Merlin Gerin TP boards will accept a BSEN 60947-2 MCCB main isolator. I have seen these rated at 250A.
The MCCB icommers will happily accept 70mm² cables (with apropriate lugs).
I think you can get the incommers rated at 400A but I can't find a reference on the web to confirm either way. (all the schneider websites seem very hard to use to me)

 

[jim23]

cheers for the help so far guys.

Pfc at busbar is 6.2KA, same at board.

the 3 phase sockets will be mainly used for running welding sets/appliances.

majority of our sets use 2 of the phases only pulling about 45 amps between the 2.

am i right in thinking when we talk about 200 amp boards and incomers that its 200 amp per pole/phase?

sorry bout all the questions guys, ive got all my 2391,2400,2381 etc, but its beeen donkeys since i did any 'proper' installation to be honest so a bit behind with todays gear!.

protecting the swa supply cable was a worry i had because its currently not protected.

do you have a link so i can see these 2 inch bush couplers mentioned anyone?

 

[Lectrician]

It's just a two inch coupler as used on 2 inch galv conduit, and two brass bushes.

6kA PFC - P to N?? Double that for Phase to Phase if you can't measure Phase to Phase.

How many welders are used at once??

Sounds like a 200amp board is fine for the loading. Yes, 200amp per phase.

What is the length of 70mm??

 

[jim23]

thats 6KA phase phase to phase, i doubled it yeah.

probably be only 2 welders used at once on and off, think loading is fine myself personally.

the length of the swa is about 25 metres so not a great distance.

got another question here guys aswell. theres also a high level busbar trunking powering the workshop where the new db is planned.

thing is the busbar is connected to the same main busbar chamber as the db that needs replacing. this busbar trunking is also without an isolator/fused protection.

planning to put one in to aid maintenance. the busbar is a canalis ksa 400ed. im presuming this is 400A PER phase also??????

anybody seen any suitable fused switch disconnectors suitable for this?

just started new job ya see and trying to get the installation up to standard-proving to be a nightmare!!!

 

[RF Lighting]

I would have though 400A per phase.

I seem to thing that SquareD do a 400A TP switch fuse.

If you are doing all this work would it be an idea to ditch the busbar chamber and replace it with a nice shiny new panel board with apropriate protection for those out going circuits?

SquareD (and probably Merlin Gerin) do a 400A panel board.

 

[Lectrician]

By the time you have got a 400 amp sw/fuse (I would go MEM again), and then got a 200 amp one for the DB, a 400 amp 6 way panel board would be cheaper! Better solution all round!


I would also go for an MEM panel board Horses for courses!

 

[jim23]

panel boards a good idea but unrealistic i think because the space is pretty tight and downtimes a big issue.

 

[jim23]

only other possibility could be......

fit a new db off the high level busbar trunking to control the lights and sockets then run the 3 phase 63A sockets direct from the busbar trunking. not sure how diversity works on 3 phase however and think it would probably be overloaded.

loading would be

10x 63A TP switch disconnectors & sockets
1 X 150A submain
3 x 100A TP switch disconnectors supplying lathe's
2 x 20A TP motor circuits
1 x 10A Tp motor
1 x 30A submain
1 x submain feeding 3 x 10A light circuit and 2 30A Ring circuits.
1 x 100A welding applaince.

anybody know if this would pass / fail diversity.

the busbar is TP+N 400A.

 

[SparkyMarky]

I'd probably go for a MEM Glasgow switchfuse. The catalogue is available on-line but is about 10MB so I won't link direct to the pdf file. It's about halfway down this page though: http://www.memonline.com/publications/

As for the DB, normally I'd go with a MEM Memshield 2 board (details on the same link), although of late we've fitted a few Merlin Gerin boards and they seem pretty good. I've had a couple of bad experiences with MEM recently so proceed with a bit of caution if you use them. They don't seem to keep much stock any more so a lot of stuff is manufactured to order and shipped in from Europe (Germany I think). Probably won't be too much of a problem if you stick to their standard kit and you're not in a massive rush.