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

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?

A

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

Does an electric towel rail in a bathroom or shower room require supplementary bonding?

A

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.

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.

Condition (i) All final circuits of the location comply with the requirements for automatic disconnection according to Regulation 411.3.2

(ii) All final circuits of the location have additional protection by means of an RCD in accordance with Regulation 701.411.3.3 (iii) All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2 Comments 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. RCDs have rated residual operating current (IΔn) not exceeding 30 mA and operating time not exceeding 40 ms at 5 x IΔn. 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).

Q

When inspecting and testing an electrical installation, what determines whether items of current-using equipment should be included in the inspection and test or whether these should be covered by PAT testing? . A During initial inspection and testing of an installation The initial inspection and testing of an electrical installation should also include fixed items of current-using equipment forming part of the building services installations, such as luminaires, extractor fans, electric space heaters and water heaters, and any permanently-connected items of kitchen or laundry equipment that are present at the time. Permanently-connected items installed after the installation is completed If any permanently-connected items are installed after completion of the electrical installation, the electrically competent persons responsible for installing them should carry out the appropriate inspection and testing. During periodic inspection and testing of an installation In the case of periodic inspection and testing of an electrical installation, the fixed and/or permanently-connected current-using equipment should be included unless otherwise agreed in advance with the client, the implications first having been explained by the inspector. PAT testing Inspection and testing of mobile or stationary equipment fitted with a plug, such as white goods, personal computer equipment, electric tools, electric irons and table lamps, should be subjected to so-called “PAT testing”, in accordance with the IEE Code of Practice for In-Service Inspection and Testing of Electrical Equipment, and is not normally part of a periodic inspection report.

PAT testing may also be necessary for permanently-connected items of kitchen or laundry equipment where these have not been covered during inspection and testing of the electrical installation or where they need more frequent inspection and testing than the electrical installation. Precautions to prevent damage or influence on test results In all cases, precautions should be taken where an item of equipment could influence a test result or be damaged by a test, such as an insulation resistance test. This may necessitate disconnecting the item for the duration of the test concerned.

Q A

Does BS 7671 permit the installation of a non-UK socket-outlets, such as the CEE type (used in some EU countries) or the NEMA type (used in the USA) in a low voltage circuit, e.g. 230 V or 120 V?

CEE 7/4 socket This would be a departure from the requirements of BS 7671 in the majority of cases. For most applications, socket-outlets for low voltage circuits are required to be of the types listed in Table 55.1 of BS 7671. These include 13 A socket-outlets to BS 1363, and socket-outlets of specified current ratings to BS 546, BS 196 and BS EN 60309-2. The use of socket-outlets of other types is permitted by Regulation 553.1.5 for the connection of an electric clock or shaver (sockets of the specified types), or for a circuit having special characteristics such that danger would otherwise arise or it is necessary to distinguish the function of the circuit. No less important than complying with BS 7671 is to need to comply with the Plugs and Sockets etc. (Safety) Regulations 1994 (PSSR). Any person who supplies, in the course of a business, socket-outlets ordinarily intended for domestic use at a voltage of not less than 200 V is legally obliged to ensure these meet the requirements of the PSSR. Amongst other things, the PSSR require the sockets-outlets to comply with BS 1363, BS 546 or, for shaver sockets, BS 4573. As an alternative, however, regulation 3(3) permits socket-outlets conforming to a standard or specification recognised for use in a member State of the European Economic Community or another State within the European Economic Area, provided these give an equivalent level of safety. UK hotel rooms are sometimes fitted with European socket-outlets, such as the CEE 7/4 or 7/7 types, or with 120 V NEMA socket-outlets (not covered by the PSSR, as they are rated at less than 200 V), for the benefit of overseas guests. This is a departure from the requirements of BS 7671, as such socket-outlets are not listed in Table 55.1. The departure must be noted on the Electrical Installation Certificate, as required by Regulation 120.3, and the resulting degree of safety of the installation must be not less than that obtained by CEE 7/7 socket US 120 V NEMA socket compliance with BS 7671 Parts 3 to 7.