Floor and Ceiling Heating Systems

As a registered Devi (Gaia) Floor and Ceiling Heating installer we were most interested to see this, not much new. but informative nevetheless

The 17th Edition of the Wiring Regulations (BS 7671:2008) introduced additional sections on special locations in 2008 that were not previously included in the 16th Edition. Among the special locations introduced were requirements for floor and ceiling heating systems contained in section 753 of BS 7671:2008.

Risks
The obvious risks associated with floor and ceiling heating systems are penetration of the heating element by nails, drawing pins, screws, etc., pushed through the ceiling surface.
Similarly, there are concerns that underfloor heating installations can be damaged by carpet gripper nails, etc. To protect the building structure and provide precautions against
fire, there are requirements to avoid overheating of the floor or ceiling heating system.
Protection against electric shock

As you would expect the protective measures of obstacles, placing out of reach, non conducting location and protection by earth-free local equipotential bonding are not permitted. These measures are contained in Sections 417 and 418 of BS 7671:2008 and are not for general application. The protective measures of section 417 provide basic protection only, and are for application in installations controlled or supervised by skilled or instructed persons. The fault protective provisions of Section 418 are special and, again, subject to control and effective supervision by skilled or instructed persons. In addition the protective measure of electrical separation (section 413) is not permitted.

Regulation 753.411.3.2
Where the protective measure is automatic disconnection of supply, heating units without
exposed-conductive-parts, must have a metallic grid, with a spacing of not more than 30mm, (as an exposed conductive part) installed above the floor heating elements or under the ceiling heating elements. The grid must be connected to the protective conductor of the electrical installation and the heating system protected by an RCD with a rated residual operating current not exceeding 30mA for fault protection. A note below regulation 753.411.3.2 limits the rated heating power to avoid unwanted tripping of the RCD.

Regulation 753.415.1
A circuit supplying heating equipment of Class II construction or equivalent insulation must be provided with additional protection by use of an RCD with a rated residual operating current not exceeding 30mA.
RCDs

An RCD is a protective device used to automatically disconnect the electrical supply when an imbalance is detected between live conductors. In the case of a single-phase circuit, the device monitors the difference in currents between the line and neutral conductors. If a
line-to-earth fault develops, a portion of the line conductor current will not return through the neutral conductor. The device monitors this difference, operates and disconnects the circuit when the residual current reaches a preset limit, the residual operating current (IΔn). An RCD on its own does not provide protection against overcurrents. Overcurrent protection is provided by a fuse or a circuit-breaker. However, combined RCD and circuit breakers are available and are designated RCBOs.

hope this helped