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So I have bought a new light fitting for our shower room (This is the bulb.)

On the instructions it says if fitting in a bathroom a 30mA RCD is required. We have a fairly old fuse box, so wired fuses no RCDs. I see the lighting circuit has a 5A fuse on it. Does this actually equate to a 5,000mA RCD?

Does this mean the light fitting is no good for our circuit? Would I need to wire up a whole new circuit just for this light? Why would fitting it in the bathroom affect the size of RCD required?

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  • Can I presume you are in a 240V country?
    – ThreePhaseEel
    Commented Dec 29, 2015 at 15:36
  • Yes - United Kingdom
    – Mongus Pong
    Commented Dec 29, 2015 at 16:34

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My understanding of UK law (I am not a lawyer) is that like-for-like replacement does not require you to bring an electrical installation up to current standards.

I'd interpret that to mean I can change an incandescent lightbulb to an LED bulb, of same or lower real wattage (not equivalent wattage), in the same fitting, without needing to worry about RCD protection.

I would make sure that the fitting is properly earthed (assuming it has metal parts) and that people using the bathroom cannot reach the light fitting.

I would also make sure that the fitting allows for adequate flow of air around the bulb as LED-based bulbs seem to need cooling much more than incandescent bulbs do.

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  • Thanks, I have fitted the light. Reading around about RCDs they do sound quite useful. We will probably update our fuse box shortly.
    – Mongus Pong
    Commented Jan 4, 2016 at 13:27
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An RCD is different from a fuse. An RCD (residual current device) is known as a GFI (ground fault interrupter) or GFCI (ground fault current interrupting) device in the US.

In non-technical terms, if the RCD device sees current "missing" on a circuit - more leaving than returning - it shuts down power, based on the idea that that missing current may be starting a fire or shocking someone.

A 30ma RCD trips when 30ma of current is "missing." In some locations, a 30ma trip is the maximum allowable for personal protection, prevention of electrical shock injuries.

RCD / GFCI are especially important in bathrooms because people are in contact with water and pipes, which increases electrical hazards.

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  • I see. So would you use an RCD in place of a fuse? Would you generally keep your bathroom lights on a different circuit to the rest of the lights because of this?
    – Mongus Pong
    Commented Dec 29, 2015 at 16:42
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    In the US, if the panel isn't too old, you can usually buy a GFCI circuit breaker to replace the plain one in the panel. I believe similar devices are available for not-too-old panels in the UK. In the states, another option is to install a GFCI device somewhere in the circuit, wired to add GFI protection downstream. This can be a "deadface" GFCI, or a GFCI receptacle. I do not know if that's an option for you, hopefully someone better versed in the rules and products in the UK will chime in.
    – batsplatsterson
    Commented Dec 29, 2015 at 17:39
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    In the UK, an MCB in a CU can only be replaced by an RCBO, not with a plain RCD. The RCBO combines both functions - residual current detection (e.g. earth leakage) and, crucially, overcurrent detection to prevent fires starting in circuits e.g. due to too-many high-power appliances simultaneously operating on a ring circuit. If you buy a new CU it is likely to include one or two RCDs that each protect a group of MCBs (AFAIK)
    – RedGrittyBrick
    Commented Jan 4, 2016 at 15:11
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Ok this is a very nice question to every electrician and Electrical personals but I would like to say that you can choose to ignore the rcd if only u have proper and quality earthing system to all your exposed metal workenter image description hererccb

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  • Welcome to Home Improvement! I'm not sure how this answers the question. Would you please add something to explicitly show how this addresses the original question. Also, feel free to take the tour and spend some time in the help center to get a feel for how things work around here.
    – FreeMan
    Commented Dec 3, 2019 at 19:44

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