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.

 

[Guest111]

If I were you I'd be very wary this doesn't come back and bite you, as Tony stated magnetic repulsion under heavy fault current can do some nasty things. Think about what happens when a steel cable snaps under load,then imagine that level of force as a whip being cracked,a bit of thin trunking is not going to hold it,that's why busbar chambers are thick steel and the busbars are clamped down tight.

 

[benji]

the only current ratings i can find for tri-rated are for installing in free air so trunking seems out,you could use tray with parallel feeds to both boards all in trefoil or equally spaced

 

[Engineer54]

So no protective sub-main (distribution) devices after the 1000A ACB then, oh dear!! As stated above, this sounds like a lash-up job, and one that you need to be very careful about!! This installation is crying out for a main switchboard arrangement, that can also incorporate the change over switch, which i'm assuming now, is for a stand-by generator?? Is this proposed C/O, Auto or Manual operation?? To go any further, I / we need photo's of this existing installation.

 

[brookster]

Sometimes the C/O is part of the generator set up (doesn't matter if its not really), there would always be a main switchboard (fused) which could provide normal service, direct mains and to kill the gen so you can maintain the stuffs.
Cant imagine there would ever be a case of a standy being installed without the necessary means to control it!
SWA is much more friendly with gen set ups bin the trunking :smart:

 

[Engineer54]

Several ways of combining a changeover switch into an existing system. In this case i'm pretty dammed sure, that this is going to be a manual system. lol!! which in itself is going to call for some sort of captured key system, as it stands at the moment!!

 

[Hants-Spark]

I really do think a picture of the current layout would assist here, as Eng54 has mentioned if a manual C/O is to be used then a castel key system or similar is a must. From the previous post IMO this has trouble written all over it, and possibly someones A*&e on the line when things go wrong.

 

[Knobhead]

The better system is Fortress keys. I’ll be amazed if E54 hasn’t got Castell master keys, mine are locked away. I’ve never worked out how to make a master Fortress Key.

 

[Hants-Spark]

The better system is Fortress keys. I’ll be amazed if E54 hasn’t got Castell master keys, mine are locked away. I’ve never worked out how to make a master Fortress Key.

Thats' fair enough, I've only ever worked with a Castell system so my knowledge of other keys systems is limited.

 

[Engineer54]

The better system is Fortress keys. I’ll be amazed if E54 hasn’t got Castell master keys, mine are locked away. I’ve never worked out how to make a master Fortress Key.

I haven't as it happens!! In fact i can only just about remember the last time i worked on a manual key interlocked system. ..lol!!

All the main MV/LV Switchboards i've worked on for many years now, have been fully auto control, (with load shedding facilities when required) be they dual source mains supply or otherwise, and with or without stand-by generators. A far cry from my training day's when most dual source supplies were in the main, manual. Certainly on the MV side of things anyway, it was a real pain going round switching and releasing captured key's on those old oil filled RMU's we had around the plants!! lol!!

 

[Hants-Spark]

We're still using Castell's on our site, it is a pain releasing keys etc but keeps you fit, and do I need the exercise
Nothing new for the OP then, has he given up on this one??

 

[Knobhead]

Last time I used one of my master keys was fault finding on a 660V single phase 2.6MVA supply.

Before that I was paralleling 1.6MVA transformers. I’d only just started with the company and was asked if there was a way of defeating the locked key system! As I said my keys are locked in a chest at home.
Close the Bus Section ACB at the same time another guy has his finger on one of the incomer ACB’s trip.
Shout CLOSED
He shouts OPEN.
If it took 2 seconds we were slow!

Yes it’s dangerous (we were exceeding the maximum fault current 50 KA) but at times needs must, RoB2 will tell you how long it takes to go through a kiln controlled shut down, what took 2 seconds would have resulted in two days down time!

Time to hold my hand up. I’m a rotten barsteward!
I closed the BS after I’d checked the feeder currents.
My mate opened the incomer under near 700A load.
If it had gone wrong, he would have copped the full blast!

I’m a rotten barsteward?

I’ve been next to a 3.3KV 1600A ACB when it opened under fault. I needed new underepants!

 

[Knobhead]

I have never seen a room lit like the arc in a 3.3 KV ACB opening under fault!
It is f***ing frightening!

A brilliant blue flash, then everything goes quiet the plant has shut down!
Then it’s think time. Open feeder 1 close BS 1-2 in three 11KV substations! All back and running within ½ an hour!



The brilliant blue flash!
I hold more qualification in photography as I was sponsored by Kodak and Bowens for 10 years.
I couldn’t light a room like that bloody ACB opening!

 

[Hants-Spark]

Tony - Sounds like you've had some fun (is that the right word) in your day, we have a 3.3 & 11KV ring at our place, I've been there when its popped but never within the switchroom itself, a cable fault twice in the same place, joiners didnt have a good day I suspect. Tried to close as fault was unknown to start with but just fired straight through. Out come the diggers

 

[Knobhead]

It wasn’t fun!

I was ---- scared closing the ACB! It would hold, then trip when the system was on light load?

It took me damn near 6 moths to track the fault down. A faulty OLTC unit was causing a 15% voltage rise at the weekends.

 

[Bobster]

I've been in a sub for 2hours with me jamming main contactor for the kiln main drive before.

As you know leaving a hot kiln not turning for longer than 15-20 min starts causing real problems.

 

[Bobster]

And my I really don't like castell key systems. I've always thought anybody with half a brain would figure how to make one.

I've always stuck to fortress systems where I can. Even then I've never had but have seen master keys for fortress systems.

 

[Knobhead]

I've been in a sub for 2hours with me jamming main contactor for the kiln main drive before.

As you know leaving a hot kiln not turning for longer than 15-20 min starts causing real problems.

Bent like a banana!

You wouldn’t believe 1000T of steel and refractory could bend, it does!

 

[Knobhead]

And my I really don't like castell key systems. I've always thought anybody with half a brain would figure how to make one.

I've always stuck to fortress systems where I can. Even then I've never had but have seen master keys for fortress systems.

Simple reason, you can’t get a Fortress Master Key.

I’ve got Castell Master Keys. I made them. As said they are locked away in one of my big tool chests.

They are bloody dangerous! Under no circumstances will anyone else ever get their hands on them. I would be responsible!

 

[Hants-Spark]

Reading the last few threads, it appears masters are obtainable for both Fortress & Castell key systems, a major flaw for both manufactures by the sounds of it. Maybe one system is better than the other but they both serve a purpose, safety, these systems are then complimented by a robust control management system to ensure accidents are prevented. Everyone goes to work happy and leaves work even happier.

 

[brookster]

Reading the last few threads, it appears masters are obtainable for both Fortress & Castell key systems, a major flaw for both manufactures by the sounds of it. Maybe one system is better than the other but they both serve a purpose, safety, these systems are then complimented by a robust control management system to ensure accidents are prevented. Everyone goes to work happy and leaves work even happier.

I don't know about that , not sure I have read and signed the risk assessment for a happiness so until I have I will remain a grumpy bast**d!