RCD/RCBO in an office refurbishment

[DOKAJM]

Client is having some refurbishment in an office and i am tasked with relocating/removing/adding some sockets due to walls being moved etc.

Currently none of the sockets in the building are protected by any RCD/RCBO. The majority of the cables feeding sockets will be t&e ran under floor grates to floor boxes of 4x twin sockets. Some however will be chased into solid walls. My initial thought was to cover ourselves the best course of action would be to put all circuits feeding sockets onto and RCBO back at the board, however alot of the sockets will have computers plugged into them and this can create induced DC voltages causing the Rcbos to trip which would have a potential to affect the clients work. I am also unaware if they will have a competent i.e maintenance employee who has a knowledge of RCD/RCBOs on site?

Finally with the possibility of any ground floor sockets being used to supply any equipment that may be used outside (highly unlikely but never the less) should then all ground floor sockets be protected by an RCBO? Any advice appreciated.

 

[littlespark]

I think you can leave them on mcb if a risk assessment explains why.

Any cables buried in wall should be protected.

mark the sockets as computer use only. This dissuades anyone plugging in the wrong equipment that could be used outside and covers your behind.

have another rcd protected circuit dedicated for outside use, or cleaners equipment etc.

 

[James]

10 x double sockets per rcbo.
gives 3ma per twin socket of leakage before tripping.

more than that an you CAN get nuisance tripping with computers, screens, photocopiers, printers.
they all have a little earth leakage and what i have found is especially if the supply is a little "noisy" random tripping can occur when the psu's dump the electrical noise.

 

[pc1966]

Most RCBO are type A RCD part so are fine with typical PC faults. As above, you typically see 1-3mA leakage per PC so limiting them to a 10 or so per RCBO is one approach.

If it were servers in a rack (with additional grounding) I would be inclined to keep it on MCBs with appropriate warnings, but if office PCs and other stuff plugged in then definitely RCBOs, just split the circuits in to manageable chunks. Personally I am a fan of the RFC and here the added high-integrity earthing is useful as you are looking at high leakage currents.

As for ground sockets (and sockets in general) then yes, put them on RCBOs as well.

 

[westward10]

A documented risk assessment must be carried out by the client outlining the reason/s for omitting additional rcd protection this is then attached to the certification. This is the only stated way in BS7671 to omit additional protection. Of course you can fit warning notices to the sockets however this alone will not satisfy BS7671.

 

[Mike Johnson]

I have held my tongue long enough to many on here tend to think the fist stage is a "Risk Assessment", before a "Risk Assessment" is carried out a "Hazard Analysis" must be prepared, if that "Hazard Analysis" indicates that the "Risk" is minimal then further investigation is not required, if however the "Hazard Analysis" indicates that a "Hazard" is present then a "Risk Assessment" is carried out and a "Method Statement" is prepared of how that Risk is to be managed the "Risk Assessment" is not a control document.

 

[westward10]

BS7671 requires a documented risk assessment because omitting additional rcd protection leaves for increased hazard.

 

[Mike Johnson]

Yes even British Standards get it wrong, a documented "Risk Assessment" is a "Method Statement" if it includes control methods.

 

[westward10]

BS7671 does not ask for control methods therefore it is a risk assessment.

 

[Mike Johnson]

A "Risk Assessment" is just that it list the risks possible from the "Hazard Analysis" it does not list the control methods as you say, but, if the control methods are not listed in a "Method Statement" the process has not been completed and would be found wanting in Court, been there done that.

Illustrate what you would do after carrying out a "Risk Assessment"?

 

[littlespark]

Risk assessment, hazard analysis, method statement...

*sits back and waits for the outcome*

Its as big an argument as trump / biden...... or even ring / radial!

 

[DPG]

And plug/plugtop!

 

[Mike Johnson]

It is quite a simple structured process, but miss-understood, the sequence is:
1. Hazard Analysis.
2. Risk Assessment.
3. Method Statement.

 

[westward10]

1. Hazard is present, additional rcd protection not being provided.
2. Risk assessment, clients problem.
3. Method statement, clients problem.

 

[Mike Johnson]

Not withstanding if you think it is not your problem, it was the process that I was questioning, most on here seem to go straight into the "Risk Assessment" without any consideration for the required "Hazard Analysis" when the structure of the process is clearly indicated in HSE guidance.

 

[westward10]

Not withstanding if you think it is not your problem, it was the process that I was questioning, most on here seem to go straight into the "Risk Assessment" without any consideration for the required "Hazard Analysis" when the structure of the process is clearly indicated in HSE guidance.

What has this to do with the OPs query. BS7671 asks for a documented risk assessment which the client carries out.

 

[Mike Johnson]

Nothing, it was an observation on the incorrect use of "Risk Assessment" prior to a "Hazard Analysis" being carried out, as I said earlier a "Risk Assessment" by itself is useless, without its correctly documented procedure and being taken to its conclusion with a "Method Statement" if required by the contractor carrying out the work, not the client!

 

[Mike Johnson]

What has this to do with the OPs query. BS7671 asks for a documented risk assessment which the client carries out.

Just thought I would clarify the above: If the installation is on a commercial premises then indeed the Principle Contractor or Principle Designer may well prepare the "Risk Assessment" and then ask each contractor for their "Method Statements" if however the premises are domestic and you as the contractor are the only contractor on site then you are the Principle Contractor and Principle Designer and the process falls to you and not the client. (CDM Regulation 7)

 

[DPG]

I'm not sure this is helping the OP.

 

[westward10]

Just thought I would clarify the above: If the installation is on a commercial premises then indeed the Principle Contractor or Principle Designer may well prepare the "Risk Assessment" and then ask each contractor for their "Method Statements" if however the premises are domestic and you as the contractor are the only contractor on site then you are the Principle Contractor and Principle Designer and the process falls to you and not the client. (CDM Regulation 7)

Nothing needed clarifying. It is commercial the risk assessment is for omitting additional rcd protection carried out by the client. The RAMs required from the OP is for their working methods which are a separate issue.