Location of PME Links

[maddog]

Hey pepes.
I'm a bit new to Ryefield boards, so maybe an obvious one.
While installing the Ryefield boards in the risers to feed the flats in a tower block (40 floors), we were told to remove the PME links from within the boards.
Should there only be a link at the supply, as it is a PME system.
What difference does it make?

Thanks for any help you can give me.

 

[Knobhead]

I don’t know physically where you’ll find the N→E in a Ryefield board other than the obvious place, connected to the neutral bar.

As to what difference it makes, as an electrician you should know the theory of PME and the reasons there should only be one N→E link in a system.

 

[Engineer54]

Hey pepes.
I'm a bit new to Ryefield boards, so maybe an obvious one.
While installing the Ryefield boards in the risers to feed the flats in a tower block (40 floors), we were told to remove the PME links from within the boards.
Should there only be a link at the supply, as it is a PME system.
What difference does it make?

Thanks for any help you can give me.

As Tony stated, only the one N-E connection and that would normally be at the service head. But maybe this large tower block is supplied via it's own DNO TX into a switchboard...

BTW, how many rising mains does this 40 storey tower block have??

 

[maddog]

Im a bit of a Newby to this kind of thing. I'm normally a flat rat.
There is a ryefield every 3 floors to feed around 27 flats, and each swa will feed 3 ryefield boards. About 400 flats in all.
I guess this would be a PNB system. I've never been in the substation.
Obviously removing the PME link was very simple. But why? The swa comes from the main panel with a seperate bond.

 

[Engineer54]

Im a bit of a Newby to this kind of thing. I'm normally a flat rat.
There is a ryefield every 3 floors to feed around 27 flats, and each swa will feed 3 ryefield boards. About 400 flats in all.
I guess this would be a PNB system. I've never been in the substation.
Obviously removing the PME link was very simple. But why? The swa comes from the main panel with a seperate bond.

Never heard of a tower block distribution system being laid out like that. So what size are these SWA cables feeding 3 X 9 or 10 way Ryefield boards?? Got a photo of one of these completed Ryefield boards??

 

[Knobhead]

It sounds a bizarre way to do it to me. God help who ever has to get the SWA’s in.

 

[maddog]

they're 185's. Cable gang put them away. Can't get any pics at the mo, not working in that area for a while. Will be going back to it after xmas.
The ryefields are 3 rows of 10 ways.

 

[Knobhead]

they're 185's. Cable gang put them away. Can't get any pics at the mo, not working in that area for a while. Will be going back to it after xmas.
The ryefields are 3 rows of 10 ways.

Per floor?

 

[Engineer54]

Per floor?

No, he stated one Ryefield per 3 floors and stated 27 flats per ryefield so i'm assuming one 10 way row for each floor...

All i know is, that definitely wouldn't be the way i'd go about providing a distribution system for a 40 floor residential tower block!!

Just think about it for a moment or two, 1 X 185mm 4 cores plus bonding cable feeding supposedly a busbar chamber that then feeds local ryefield panel and another 2 X 30 way Ryefield panels located at 3 floor intervals. At each Ryefield panel 20 smaller 16/25mm 3 core SWA to supply apartments over the next two floors, ..All sounds bloody ridiculous to me!!

Why is not each floor being utilised as the distribution point for the apartments located on that floor, rather than a distribution point that can be located 3 floors distant??


The more i think about it, the more problems i can see...

 

[Knobhead]

I’d have thought they would have gone for busbar risers with tap-offs on each floor. 81 flats on each feed is going to be pushing it.

 

[Farmelectrics]

throw a sicky lol

 

[Engineer54]

I’d have thought they would have gone for busbar risers with tap-offs on each floor. 81 flats on each feed is going to be pushing it.

That would be the sensible way of doing things!! I just hope these riser cupboards have plenty of room in them!!

 

[Knobhead]

1 x 4c185mm[SUP]2[/SUP] + 81 x 3c16mm[SUP]2[/SUP] in one cubical just doesn’t bear thinking about. It would be funny to watch them sort it out. 16mm[SUP]2[/SUP] being a rough guess.

Added to which I don’t think 185mm[SUP]2[/SUP] would be up to the job.

Personally I think the OP has got things mixed up a tad.

 

[maddog]

Sorry for the delay, been away for a bit.
The landlords DB's are also every 3 floors, for corridor lighting and sockets, stairway lighting and what have you. These are fed by busbar trunking, Tapped off every third floor. This is because the Landlord's power requirements is not so substantial. But to supply 400 flats off of busbar trunking (that's 400x100A fuses), is going to be very expensive. Space is tight in the risers, so forget about putting multiple busbar trunking, it takes up too much room.
At each Ryefield board, there will be a maximum of 30 flats being supplied. That's 10x3c25mm cables out of the header trunking, running up the riser to the floor above, 10x3c25mm cables out of the header trunking and out through a letterbox to feed this floor, and 10x3c25mm cables from the bottom of the ryefield board and down to the floor below.
Each header trunking is over 150mm2 and over a meter long. Each Ryefield board is about 600/700mm wide and about 1000mm in height.

 

[maddog]

Just done a search and Eaton's range only goes up to 6300A, shneiders to only 5000A.
So we are talking about 6 or 7 busbars to feed that lot. Just isn't the space for that.