Floor heating unit
A heating cable or flexible mat with its cold tails, laid in or under a floor. BS 7671's Section 753 covers it, and every circuit supplying one has additional protection by an of 30 mA or less with no time delay, even for Class II units. Nobody can see it once the floor's down, so the owner gets a plan of the layout and instructions on what can go on or into the floor.
Using Floor heating unit in context
Reviewed
A distinction worth remembering
An RCD's type tells you which kinds of residual current it will reliably respond to. It doesn't tell you how much leakage trips it, which is the mA rating. And it's nothing to do with MCB curves. A Type B RCD and a Type B MCB share a letter and nothing else, because MCB Types B, C and D describe how a breaker responds to overcurrent.
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- How can I revise Floor heating unit beyond the definition?
- Explain what Floor heating unit describes, compare it with a related term and use it in a topic question. State any assumptions and what evidence you would need before applying the idea to real work.
Sources
- Professional Electrician: understanding RCDs and their application (Scolmore) — A maker's article, 23 June 2022, written for Amendment 2. Regulation 531.3.3 on Types AC, A and B, blinding, 6 mA smooth DC on Type A, S types and the 3:1 selectivity ratio.
- Professional Electrician: RCD types for EV charging installations (Hager) — A maker's article, 18 December 2024, written for Amendment 3. Type B or Type A or F with an RDC-DD, the 6 mA threshold and why it was chosen.
- Voltimum: Type A or F RCDs? (Doepke) — A maker's article, 20 December 2018, written for the 18th Edition before its amendments. Mixed-frequency current, the 10 mA smooth DC limit on Type F, and three-phase inverters needing Type B.
- IET: initial verification technical webinar questions — Webinar of 5 April 2022. Whether to code a Type AC RCD on a condition report where electronic equipment is installed takes engineering judgement.
- IET: RCD selection, types and testing — Residual-current waveforms, device selection and the distinction from overcurrent protection.
Where Floor heating unit fits in the learning path
The Special Locations section covers these units:
- Wet locations
- Sites, farms and shows
- Moving and temporary
- Heating, lighting and the outdoors
Curriculum mapping: C&G 2382-26 (BS 7671 Part 7).
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- RCD TypesInstallation
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A protective device that detects an imbalance between the currents in the live conductors passing through it. In a single-phase circuit this usually means comparing line and neutral current. It disconnects when the residual current meets its operating conditions. A 30 mA RCD can provide additional shock protection, but it does not prevent every kind of electric shock or replace safe isolation.
Compare related terms
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RCD — Residual Current Device
A protective device that detects an imbalance between the currents in the live conductors passing through it. In a single-phase circuit this usually means comparing line and neutral current. It disconnects when the residual current meets its operating conditions. A 30 mA RCD can provide additional shock protection, but it does not prevent every kind of electric shock or replace safe isolation.
Read the RCD entrySpecial location
A place or type of installation where the risks are higher or different, so BS 7671's Part 7 adds to or changes its general rules. Bathrooms, swimming pools, construction sites, caravan parks and EV charging all have their own section there. Read that section before designing or testing, because the general parts still apply unless it changes them.
Read the Special location entryA definition is a start. Using it in a real question is where it sticks.