Advice on RCD Protection for commercial office sockets (earth leakage)

[fordselec]

Hi guys,

I've got a job where I'm installing dado trunking on the floor of an office for sockets and data. Some info on job - In total I will be installing 36 double sockets to supply 40 workstations. Majority of the workstations will be a laptop with dual monitors and phone setup. Some of the workstations will have desktop PCs or the smaller NUC style PCs. Some of the sockets allowed are to be installed between the desk locations due the customer wanting some redundancy and flexibility in moving desks. The rows of desks come out vertically from the wall the dado trunking will be located on and site plan to run extension leads from the sockets to supply all equipment. They've requested this as their current setup with floor boxes has caused them a lot of issues and they want flexibility to move the desks forwards/backwards with cable management installed on the back of desks.

Where I'm looking for advice is the best way to provide RCD protection to all of these sockets without having fault issues due to earth leakage.

I've seen varied information on how many PCs should be connected to one RCD circuit from 3-4 to 8 PCs per circuit. I plan to install a new board and run radials for the sockets however I'm not sure how many workstations I should be wiring for one circuit due to earth leakage and it seems like it could require a lot of circuits needed just to stop nuisance tripping.

Is there a better way to go about this or a standard for larger office installations like this ?

The other option I was considering is installing RCD sockets instead of RCBOs however I'm not sure if this is a common way of doing an installation like this with so many sockets or if it would be considered ‘rough’. Using RCD sockets would allow for two rings to be wired for the whole floor which offset the extra socket costs compared to running lots of radials and rcbos/bigger board. Also the added benefit of not tripping out the full circuit if a fault occurs, not as big of a deal as they mostly use laptops but still helpful. Would using RCD sockets like this be considered good practice?

I was also planning to install high integrity earthing by linking out the last socket of each radial in the dado with a 4mm CPC, from what I can tell this is the correct way of achieving it.

Any thoughts or advice would be much appreciated.

 

[timhoward]

I think that is something that was reverse-ferreted in AM2, but don't have a copy yet.

I've done a bit more research and I think your right. This appears to be a glorious mess-by-committee on several levels and unfortunate timing.

The clue is that there is also a new BS7288 in draft and there are rumours that the fantastic sentence "SRCDs are intended for use in circuits where the fault protection and additional protection* are already assured upstream of the SRCD" .... will be improved to be clear what it means. There seems to be an acceptance that the intent was to mean "additional protection as required" i.e. it won't protect the supply circuit.

The 18th edition couldn't include BS7288 because the then shiny new BS7288 erroneously implied that devices didn't offer additional protection. To compound matters an earlier sentence says "SRCDs are only intended to provide supplementary protection downstream of the SRCD" which is 16th edition language for 'additional protection'.

I think Amendment 2 anticipates the forthcoming draft BS7288 clearing things up.

Anyway, the bottom line is that they are back in Amendment 2 as being suitable for additional protection (even if their own standard is currently as clear as mud) so I say crack on and use them - it would make a nice neat job in dado trunking.

 

[telectrix]

So much depends on the age of the PC's as some more recent ones have external power supplies anyway that are class 2.

Check Amendment 2 risk assessment requirements. From memory you have to be careful who does the RA now. If children / disabled persons are present then an RCD is needed anyway, and it's unlikely they would be able to state they will never employ anyone with disabilities. So I'm not sure this one will fly.

High integrity protective conductor connections are still very much in the regs.
The confusion might be that for socket circuits you don't actually need to do anything if it's wired as an RFC.
But if wired as a radial you can wire the CPC as a loop or provide a bigger cpc. (The 3rd radial option is sharing a larger CPC between circuits but this makes future testing such a pain I'd avoid that at all costs.)
No changes in amendment 2.

Now RCD sockets are in amendment 2 again, and considering the lack of productivity if an entire floor goes out, there's something to be said for fewer circuits with RCD sockets.
Blue sky thinking - I wonder if a higher current 6mm radial circuit with a 13 amp RCD spur in each area might be worth considering, it would cost less.

I look after some buildings that have at least 25 PCs on a 30ma RCBO if that helps at all.

1 point. IMO RCD Sockets are non compliant as there is no RCD protection for the cable itself..correct me if I,m wrong. Senile Dementia will kick in ìf I Don,t get out of this osptal soonest.

 

[davesparks]

1 point. IMO RCD Sockets are non compliant as there is no RCD protection for the cable itself..correct me if I,m wrong. Senile Dementia will kick in ìf I Don,t get out of this osptal soonest.

If the cable doesn't need RCD protection then RCD socket outlets are fine.

In the OP's case they are installing in dado trunking so it is unlikely that the cable, or circuit as a whole, will need RCD protection.

 

[littlespark]

4 months?

You think the job is still ongoing?