ASK THE EXPERTS
From the helpline We continue with our series of answers to some of the more frequently asked questions put to the NICEIC Technical Helpline.
Q
A
I’m making an addition to an existing installation to accommodate a television aerial amplifier in the loft. The amplifier comes complete with a moulded-on BS 1363 13 A plug fitted with a 3 A fuse. According to the manufacturer, the plug must not be removed or this will invalidate the warranty on the amplifier. There is no socket-outlet circuit in the loft. The only circuit up there is a lighting circuit. I have established that this has enough spare load capacity for the amplifier. Can I connect a BS 1363 socket-outlet to the lighting circuit to supply the amplifier? If so, should I label the socket-outlet “TV aerial amplifier only”, so it won’t be used for other purposes?
Connecting a socket-outlet to a lighting circuit is a poor engineering solution, even if it is only to supply a TV aerial amplifier. You should describe the problem to the customer, including the limitations on the amount of load the proposed socket-outlet could supply if it was connected to the lighting circuit. You should also try to persuade the customer to let you connect the socket-outlet to a suitably rated socket-outlet circuit instead, even if this is less convenient and involves more work. If the customer is unwilling to let you connect the socket-outlet to a suitable socket-outlet circuit but is willing to accept that the socket-outlet could supply nothing more than the TV aerial amplifier, you may connect the socket-outlet to the lighting circuit through a 13 A fused connection unit fitted with a 3 A fuse. The fused connection unit should be labelled “Maximum fuse rating 3 A”, or words to that effect. Also, the socket-outlet should be labelled “TV aerial amplifier only”, as you suggest. This is because the coordination requirements of Regulation 433.1.1 would not be met if the socket-outlet was likely to be used for other purposes, such that load current might exceed the rating of the circuit cable or protective device.
Q
A
Does an electric towel rail in a bathroom or shower room require supplementary bonding?
Yes, unless all three conditions at the end of Regulation 701.415.2 for the omission of supplementary bonding in the location containing a bath or shower are met, as would usually be the case for a new installation. The three conditions are given in the table below together with comments. Condition
Comments
(i)
All final circuits of the location comply with the requirements for automatic disconnection according to Regulation 411.3.2
The maximum disconnection times of Table 41.1 apply, such as 0.4 s in a TN system or 0.2 s in a TT system (using RCDs), for final circuits rated at not more than 32 A at 230 V nominal voltage.
(ii)
All final circuits of the location have additional protection by means of an RCD in accordance with Regulation 701.411.3.3
RCDs have rated residual operating current (IΔn) not exceeding 30 mA and operating time not exceeding 40 ms at 5 x IΔn.
(iii)
All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2
The extraneous-conductive-parts have been main bonded, such as near their point of entry to the premises in the case of gas, water or other services (see Regulation 544.1.2).
If one or more of conditions (i), (ii) and (iii) are not met, Regulation 701.415.2 requires supplementary bonding to be established. This must connect together the protective conductor terminal of each circuit supplying Class I and Class II equipment in the room (including a heated towel rail), and the accessible extraneous-conductive-parts in the room, if any.
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