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Hi all,

Apologies it's been a while since I was last here, hope you are all well.

One of my summer jobs is to move a computer room, and it's going to require an additional 3 circuits to power the computers. The board nearest this room has an old 3-phase memshield 1 board that is at capacity.

The way I see it is I have 2 options - install a whole new board for all circuits from this location, or install an additional board alongside this older board. I don't want to do the first option for a couple of reasons - first, it's more work (and I'm stowed off), and second, the school is putting in for funding for a site-wide rewire (so spending money without warrant outside of that funding pledge would be unwise).

So, what's the best way to go about this? The MEM1 board is fed in armour. Is it best to pull the armour back and split it in an adaptable (or some such like) before taking a feed back to the old board and then new board (so like a Y formation). Or would it be better to take the new board's feed from the MEM1 incoming terminals? I can see the pros and cons of both methods, but thought I'd weigh in on things before acting.

Thanks,
 
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telectrix

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coming off the old board incoming terminals might be dicey getting 2 cables into a hole made for one. my preference would be to terminate the existing incoming cable into an isolator (1 point of isolation for the whole install), then tails into henleys, then split tails to old board and new board. if incoming is SWA, an adaptable box to gland off would be my preference.
 
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  • #3
Never come across a 4-pole Henley ;)

The installation does have a single point of isolation, albeit not at the location but in the main switchgear cupboard.

I guess another option might be to remove a circuit from the MEM1 board, and use that space to create a single-phase distro circuit to a new box, and the new circuit can be installed in that box alongside the 3 new circuits. I'd rather keep it 3-phase for balancing but time and cost is of the essence.
 

James

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If I was going to do this,
assuming the boards are going to be sited next to each other.
I would take the incoming supply to the original board, remove it and use it to supply the new board.
then make a new circuit from the new board to feed the old board.
if you make the new board big enough, the circuits from the old one can be moved to the new one when the funding is available.
 
Is the new board single phase.
 
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  • #8
If I was going to do this,
assuming the boards are going to be sited next to each other.
I would take the incoming supply to the original board, remove it and use it to supply the new board.
then make a new circuit from the new board to feed the old board.
if you make the new board big enough, the circuits from the old one can be moved to the new one when the funding is available.
I like the idea, but it still means buying a big 3 phase board (when this will be funded when the rewire is approved)
 
If the new board is single phase wouldn't surprise me if you could find a redundant way in the old board anyway to utilise for a new supply.
 
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  • #10
I'd like that very much, but I think from memory the max MCB existing is a 32a type c. That would probably be more than enough actually to feed about 20 computers.
 
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  • #12
That is the problem with the higher rated Memshield 1 stuff a 63A second hand breaker could be £50-60.
I'll have a more thorough look at the board tomorrow and see exactly what it is I'm working with and let you all know
 
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  • #13
Okay, so it's a 6-way MEM1, and about 4 of the MCBs are the double-width RCBO type that are eating in to space. None of the current breakers are redundant.

Best I can think of is to try and pick up a 63A MCB for a distro circuit, moving a circuit for it to the new DB. I can see a 45A single-pole breaker on ebay which I think I would be alright with, but a 63A would be better if anybody had one lying about?

EDIT: There is this: MEM MCB Type 3 63 Amp M6 Single Pole 63A Memshield Circuit Breaker 631MC 631MB3 - Willrose Electrical - Discontinued & Obsolete Circuit Breakers - https://willrose-electrical.co.uk/product/mem-mcb-type-3-63-amp-m6-single-pole-63a-memshield-circuit-breaker-631mc-631mb3/
 

happysteve

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Eh up, good to hear from you again. :)

Quick thought: are you going to be ok selectivity-wise?

If all the circuits in your new board are RCBOs, then you'll probably be alright, but worth checking.
 
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  • #15
Hi Steve, yeah, that was a question on my mind - any distro circuit fed off a standard breaker is going to provide an issue really though, so I don't see what other options I have. All the new circuits will be RCBO.
 
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  • #17
Okay, so I think I've made my mind up and wouldn't mind a sanity check. There's a couple lighting circuits that don't pull much so I'm going to join them in to the same breaker, creating a spare way. Then, C63 MCB as a distro circuit, running in SWA to a little 2-way DB in the room where the new circuits are going, running 2 x B32 RCBOs - they won't be anywhere near 32A at full load, but need 2 circuits as it's computer equipment and would likely trip the RCBO if all lumped together.

Should get away with 10mm SWA for CCC, but was going to install 16mm just to keep the Zsdb as low as possible. Run will be around 8m for SWA from the upstream DB, and then the 2 circuits are RFCs ran in 4mm (again, to keep that Zs down).

All sound tickety boo?
 

Paignton pete

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If your using C type breakers I think I would change this to B type then you’d get away with 10 mm SWA. Probably.

That’s if you where going to use C type.
 

davesparks

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Should get away with 10mm SWA for CCC, but was going to install 16mm just to keep the Zsdb as low as possible. Run will be around 8m for SWA from the upstream DB, and then the 2 circuits are RFCs ran in 4mm (again, to keep that Zs down).
If there is a problem with the Zs of the existing submain then that needs to be sorted out rather than oversizing new cables to try and achieve compliance.
 
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  • #20
If there is a problem with the Zs of the existing submain then that needs to be sorted out rather than oversizing new cables to try and achieve compliance.
If there was a problem with the Zs of the existing submain, I wouldn't be able to get that Zs down no matter what I did. The Zs is fine - I'm just conscious I'm extending on to a long submain anyway. However, it is only a half dozen metres so I'm probably overthinking it with 16mm. I'm going to take some readings this afternoon and then I will do my cable calculations properly to ensure that circuit Zs's will be compliant.
 
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