Main Supply Conductor question

[JIM4179]

Was asked a question today and want to confirm my findings after reading the regs

we have a 1000A main supply (1000A ACB ) and from this we have 2 sets of supply conductors, 1 goes to a 600A Panel Board the other to a 400A Panel board with the tails being contained in a metal trunking, we plan to install a C/O Panel prior to the outgoing ways, the question I was asked was do the tails conform to the Regs, I believe that the overcurrent protection is provided by the Panel Board main switches with the fault protection coming from the 1000A ACB and also cosidering that they are installed in Metal trunking with no danger of Electric shock.

I believe that best procedure would be to split the supply near the origin with 2 MCCBs but we do not have the space.

The conductors are correctly sized.

Can anybody help

 

[somersetsparks]

As long as the cables are correctly sized for as you say they are I can see no problem with this setup, It would be more useful to be able to isolate each panelboard supply cable individually but Its not a regulation as far as I know.

 

[JIM4179]

Thanks for the reply
I looked at the regs and like you say I could see nothing wrong, although not ideal

 

[guest119]

What is a C/O panel?

 

[ian.settle1]

What is a C/O panel?

Change over panel

 

[guest119]

Yes Ian but what I really meant was where, in this install description.
Not a lot of info but it reads like a 1000a acb feeding 2 supplies to 2 boards with tails that will need to be 1000a rated and connected to the dbs???

Boydy

 

[Engineer54]

Was asked a question today and want to confirm my findings after reading the regs

we have a 1000A main supply (1000A ACB ) and from this we have 2 sets of supply conductors, 1 goes to a 600A Panel Board the other to a 400A Panel board with the tails being contained in a metal trunking, we plan to install a C/O Panel prior to the outgoing ways, the question I was asked was do the tails conform to the Regs, I believe that the overcurrent protection is provided by the Panel Board main switches with the fault protection coming from the 1000A ACB and also cosidering that they are installed in Metal trunking with no danger of Electric shock.

I believe that best procedure would be to split the supply near the origin with 2 MCCBs but we do not have the space.

The conductors are correctly sized.

Can anybody help

Got any photo's of this set-up?? To be honest from your description here, it sounds like a right royal lash-up!! I'm assuming that this 1000A ACB is fed from an on-site TX, and as such should be located in a Main Switchboard, that also houses the two outgoing MCCB's that feeds the two panel boards.
So i'm not getting this '' tails in trunking'' that your talking about??

 

[Knobhead]

Like E54 you’re description of the “tails” gets me worried. This set up would seem to be downright dangerous.
Some photographs are needed.

 

[Hants-Spark]

Like Eng54 and Tony have stated, this set up doesn't sound correct to me. As previously stated by others I would expect the 1000A supply to be fed from the local TX, which in turn via bus bar sections within the panel feed 2 600/400 ACB/VCB's. These then supply panel boards in a suitable sized SWA, I'm not sure I like the sound of tails within trunking.
How are you planning on installing the C/O panel, will this be to allow either 600/400A supply take all the load in a reduced capacity?

 

[Darkwood]

Like Eng54, Tony, Hants-spark ........ you get the drift

 

[JIM4179]

Thanks for the input guys, sorry I have no photos from the site report I was given it was described:
1000A DNO cut out with fuses with the 1000a enclosed ACB mounted directly above, from the top of the ACB enclosure Metal trunking is run to the 2 panel boards( approx 4M away ) off the load side off the ACB a set of conductors run to panel board 1 ( 400a ) and are rated for 400a, also off the load side of the ACB is a set of conductors that run to Panel board 2 ( 600A ) and are rated for 600A, this is a 10 year olf install.
Does thid arangement comply on the basis that each board can only pull 400 A and 600A respectivly thus the conductors can not be overloaded in normal condition, and fault protection is provided by the ACB.
The correct way to install this is to install 1000a rated conductors through a 1000a c/o and then split this supply with 2 MCCBs 400a and 600 A before feeding the panel boards but when I suggested this I was told that there is not enough room, so I would like to know if the arrangement that is installed at present conforms with the regs.

Hope I have explained this better and I agree that photos would help, any advise is apreciated

 

[JIM4179]

Ps
Sorry about the spelling mistakes, I was typing on my phone

 

[Knobhead]

My concern is magnetic repulsion between the tails in the event of a fault. Regarding the size of the tails, are they capable of safely carrying the MPFC? FLC may be, fault current is a different beast, it bites hard!

 

[benji]

the cables fed off the 1000a acb should be about 800mm / 1000mm singles or 2 x 400mm singles in parallel per phase to each panelboard (not checked) what size are the installed cables and what size is the trunking (hope there,s no bends) but i could be wrong

 

[benji]

hmm seems like they don,t list cables above 630mm in trunking wonder why

 

[brookster]

Personally I would have used SWA.

 

[JIM4179]

From what I am told there are no bends.
The set to the 400 A board are 240mm tri rated
For the 600A board there are 2 x 240mm tri rated in parallel
Although these will not cover the 1000A from the ACB they are enough to carry the maximum Current able to be pulled from the respective boards.
As Tony has stated the main issue is the MPFC

The Regs do have a section ( sorry not with me at the moment ) that adds that if mechanical protection is provided and a minimal risk is present then certain safety measures need not be applied, however I still believe that Current Carrying capacities and MPFC have to be covered?

 

[Knobhead]

We're well out of the realm of BS7671 with this.

The ACB out going tails must each be capable of the full fault current. Two 400mm² per phase would be about right if they were run in trefoil formation. The trefoil formation is solidly clamped together to stop magnetic influence causing damage.

Each phase of the ACB out going terminals should have four 400mm² tails per phase. Two to each of the sub panels.

Sorry to spoil you're day but you have to be aware of the danger of this set up.

 

[guest119]

Is the acb to be cranked down? IE .8 .6 etc.
What is to be the type setting IE b,c,d?
Has diversity been applied to the 600 plus 400 to allow the acb to be cranked down?
Having asked the above it dont really matter because the whole idea is just nuts to me.(and others)
The people who are designing it for you dont seem to know what they are doing, from your descriptions.

Boydy

 

[Knobhead]

Is the acb to be cranked down? IE .8 .6 etc.
What is to be the type setting IE b,c,d?
Has diversity been applied to the 600 plus 400 to allow the acb to be cranked down?
Having asked the above it dont really matter because the whole idea is just nuts to me.(and others)
The people who are designing it for you dont seem to know what they are doing, from your descriptions.

Boydy

It's late, try sobering up! Then re-read the thread.