Each month, our team of expert, technical engineers answer essential questions from NICEIC-certified businesses – here are a few of the latest queries.
Q. Who should make the recommendation for the interval to the first periodic inspection and test A of a new installation?
A. The designer
Regulation 134.2.2 states that: “The designer of the installation shall make a recommendation for the interval to the first periodic inspection and test as detailed in Chapter 64.”
It is also noted that the requirements of Chapter 34 (Maintainability) should be taken into consideration.
Q. Which of the following is excluded from the scope of BS 7671?
a) prefabricated buildings b) railway signalling equipment c) sauna rooms d) ceiling heating systems
A. The answer is b) railway signalling equipment
Regulation 110.2 Exclusions From Scope states that: “The Regulations do not apply to the following installations: (ii) Railway traction equipment, rolling stock and signalling equipment”.
And Regulation 110.1.1 states that: “The Regulations apply to the design, erection and verification of electrical installations such as those of: (v) prefabricated buildings, (x) rooms and cabins containing sauna heaters, (xxvi) floor and ceiling heating systems“.
Q. In a TT system, can I use just a circuit-breaker to provide protection against electric shock?
A. Yes
Regulation 411.5.2 states that: “One or more of the following types of protective device shall be used, the former being preferred: (i) An RCD (ii) An overcurrent protective device”.
There is also an informative note which states that: “An appropriate overcurrent protective device may be used for fault protection provided a suitably low value of Zs is permanently and reliably assured”.
So, if your Zs has a suitably low value which can be permanently and reliable assured, ensuring that the circuit-breaker will achieve the required disconnection time for protection against electric shock, then you can use a circuit breaker for protection against electric shock in a TT system, without needing an RCD.
There is also a second informative note which states that: “Where an RCD is used for fault protection the circuit should also incorporate an overcurrent protective device in accordance with Chapter 43”.
Catch up on previous ‘NICEIC FAQs’ articles here
