RCD's in office

[csm86]

Hi. I have been asked to change a DB in an office that is going to be used as a call centre. The original wiring (which isn't being altered) is T+E in partition walls.

With amendment 3 coming in and the removal of "under the supervision of skilled and instructed persons", would I be right in saying that all the circuits will have to have an RCBO?

However due to the call centre's use of computers this could cause an issue with tripping, so would I have to install RCD sockets throughout and write a risk assessment to explain why the cables for the sockets aren't RCD protected?

I appreciate any advice on this.

Thanks

 

[davesparks]

How much earth leakage do you anticipate on each circuit?

 

[csm86]

How much earth leakage do you anticipate on each circuit?

Potentially there could be 15 computers on each circuit, due to the original configuration.

 

[malcolmsanford]

An old rule of thumb is 6-8 terminals per circuit. But that would take into account that there is a tower/monitor perhaps a small router on the desk . So a belts and braces approach was 6-8 positions. But now most offices use laptops/tablets there is a view of coming away from that.

As Dave as said have you checked what your protective conductor current is? Most 30mA RCDs will hold 18-20mA quite comfortably without tripping.

Personally I would invest in a clamp meter that will detect PCCs and see what you have. Then you can do a more educated assessment of what is required.

I agree if I was designing a circuit I would want to split the load up better than it is now. But you are not doing that and so you need to identify the best way you can do the job

 

[davesparks]

Potentially there could be 15 computers on each circuit, due to the original configuration.

Allowing an average 3.5mA per computer gives 52.5mA design leakage, well and truly over the 10mA limit before you must apply high integrity earthing to the circuits!

 

[Darkwood]

Hi. I have been asked to change a DB in an office that is going to be used as a call centre. The original wiring (which isn't being altered) is T+E in partition walls.

With amendment 3 coming in and the removal of "under the supervision of skilled and instructed persons", would I be right in saying that all the circuits will have to have an RCBO?

However due to the call centre's use of computers this could cause an issue with tripping, so would I have to install RCD sockets throughout and write a risk assessment to explain why the cables for the sockets aren't RCD protected?

I appreciate any advice on this.

Thanks

How would the rcd socket option protect the cables though, you may have to fit larger board and sub divide the circuits unless you run a trunking system meaning RCD sockets could be a reality.

 

[malcolmsanford]

Allowing an average 3.5mA per computer gives 52.5mA design leakage, well and truly over the 10mA limit before you must apply high integrity earthing to the circuits!

Are you being serious here Dave? You honestly believe that a healthy PSU will leak 3.5mA while running?

I agree that there is a certain leakage on inrush start but a healthy PSU will not leak nowhere near that. Again I agree a faulty one that is breaking down will leak

If this was the case then a healthy 30mA RCD will ramp test anywhere between 20-25mA, I would average that to 22mA. If each computer did leaked 3.5mA then you would be lucky to have 8-9 on any circuit covered by that RCD.

I'm totally amazed then that there are not thousands of 16th edition boards in homes all over the country not tripping every day. Nearly every household appliance will be controlled with micro controllers, have LCD Displays etc and will all need a AC/DC power supply

With the configuration of laptops, televisions, xboxes, playstations, sky boxes, blueray players, dvd players, routers etc in a home all with PSUs all running at let us just say 1.5mA to 2Ma

This then don't also take into account boilers, washing machines, dishwashers, tumble dryers, mircowaves CCTV Systems, burglar alarms and the list goes on and on in a modern home, even the humble refrigerator/freezer all with varying degrees of switch mode equipment all leaking to earth.

Again this is something that manufacturers put out, why I'm not sure but a computer will not leak that much

 

[davesparks]

Are you being serious here Dave? You honestly believe that a healthy PSU will leak 3.5mA while running?

I agree that there is a certain leakage on inrush start but a healthy PSU will not leak nowhere near that. Again I agree a faulty one that is breaking down will leak

If this was the case then a healthy 30mA RCD will ramp test anywhere between 20-25mA, I would average that to 22mA. If each computer did leaked 3.5mA then you would be lucky to have 8-9 on any circuit covered by that RCD.

I'm totally amazed then that there are not thousands of 16th edition boards in homes all over the country not tripping every day. Nearly every household appliance will be controlled with micro controllers, have LCD Displays etc and will all need a AC/DC power supply

With the configuration of laptops, televisions, xboxes, playstations, sky boxes, blueray players, dvd players, routers etc in a home all with PSUs all running at let us just say 1.5mA to 2Ma

This then don't also take into account boilers, washing machines, dishwashers, tumble dryers, mircowaves CCTV Systems, burglar alarms and the list goes on and on in a modern home, even the humble refrigerator/freezer all with varying degrees of switch mode equipment all leaking to earth.

Again this is something that manufacturers put out, why I'm not sure but a computer will not leak that much

Yes I am being serious here, they are allowed to leak up to 3.5mA which is why the upper limit for a PAT pass is 3.5mA.
As long as the equipment is supplied via standard sockets we cannot really use anything other than this figure. If the equipment is permanently connected then using the actual leakage is fine, but equipment plugged in to standard sockets can be changed without needing a skilled person to be involved who could reassess the suitability of the circuit

 

[Andy78]

I came here to say that there is no apostrophe needed in the thread title.

 

[steve.b]

Agree----------- (Note that posting a message to the forum will remove this message for you)

 

[Deleted member 26818]

With amendment 3 coming in and the removal of "under the supervision of skilled and instructed persons", would I be right in saying that all the circuits will have to have an RCBO?

No, you would not be right.
Circuits which require RCD protection, are those of a location containing a bath or shower, circuits which supply socket-outlets in Agricultural/Horticultural installations, and some circuits in medical locations.
There are other circumstances where RCD protection is required, such as for socket-outlets intended for general use.

From the information you have provided, there is nothing which requires you to provide any RCD protection.

 

[davesparks]

No, you would not be right.
Circuits which require RCD protection, are those of a location containing a bath or shower, circuits which supply socket-outlets in Agricultural/Horticultural installations, and some circuits in medical locations.
There are other circumstances where RCD protection is required, such as for socket-outlets intended for general use.

From the information you have provided, there is nothing which requires you to provide any RCD protection.

It might be an idea to check the regulations before posting advice like this!
411.3.3 is somewhat at odds with your advice

 

[Deleted member 26818]

Have you considered reading 411.3.3?

 

[davesparks]

Have you considered reading 411.3.3?

Yes, it makes no reference to general use sockets.
It requires all sockets below 20A to have RCD protection except where a documented risk assessment is in place to allow there omission or where the socket is restricted to use for a specific piece of equipment.

 

[Deleted member 26818]

The exception for socket-outlets intended for a specific item of equipment, indicates that any socket-outlet which is not intended for a specific item of equipment (in other words socket-outlets intended for general use) are required to be provided with RCD protection.
If you really are unable to understand, I suggest you speak to Kirchoff.

 

[Leesparkykent]

No, you would not be right.
Circuits which require RCD protection, are those of a location containing a bath or shower, circuits which supply socket-outlets in Agricultural/Horticultural installations, and some circuits in medical locations.
There are other circumstances where RCD protection is required, such as for socket-outlets intended for general use.

From the information you have provided, there is nothing which requires you to provide any RCD protection.

Apart from the installation method! How do you get round that one?

 

[infinity]

How about if they were labelled up for 'computer use only' ?

 

[Leesparkykent]

How about if they were labelled up for 'computer use only' ?

Yeah but the installation method would also have to be suitable for not having RCD protection. The OP says it's T&E in a partition.

 

[Deleted member 26818]

The OP intends changing a DB, not installing cables or socket-outlets.
The work which the OP conducts, should comply with the current Regulations.

 

[Darkwood]

The OP intends changing a DB, not installing cables or socket-outlets.
The work which the OP conducts, should comply with the current Regulations.

A very good point made, I think the thread started to go away from the actual work he was doing, and as long as he doesn't reconnect any obvious dangerous circuits and he hasn't made the existing circuits installed under previous regualtion any worse off then he can just not it on the cert' imho.