Q & A of the Day – What is the correct code for reporting socket outlets in a commercial installation?

Question: For a periodic inspection and test of a 15-year old commercial installation that has a TN-C-S system with no RCD protection onsite, the earth fault loop impedance external to the installation (Ze) has been found to be 0.15 ohms and the earth fault loop impedance (Zs) reading of the 32A MCB-protected socket-outlet circuit is 0.19 ohms.

What would be the correct option to report the following:

1. Unsatisfactory certificate with a C2 observation that notes no RCD protection onsite?

Or:

2. Satisfactory certificate with a C3 observation that notes that improvement is recommended to install upgraded RCD protection?

Answer: If the socket-outlets are not likely to supply mobile equipment for use outdoors and the earth fault loop impedance is satisfactory to achieve automatic disconnection for fault protection purposes, the requirement for additional RCD protection of socket-outlets introduced in 2008 is not retrospective to the installation.

It should be noted that BS 7671:2008 (2011) allows an exemption for additional RCD protection for socket-outlets in an installation under the supervision of skilled or instructed persons and the socket - outlets may therefore be satisfactory if this is the case.

If, however, the installation is not under the supervision of a skilled or instructed person, it may be advisable to record a C3 observation which will undoubtedly improve the safety of the installation

Where the socket outlets are likely to supply mobile equipment for use outdoors, they should be provided with additional 30mA RCD protection and a C2 observation would be the most appropriate in this situation.

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