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ECITA ISE: QS Chapter 6 Plugs and Socket (Safety) Regulations

09 : QS Chapter 6 Plugs and Socket (Safety) Regulations

Thursday, November 6, 2014

Introduction

The Plugs and Socket (Safety) Regulations are arguably one of the most important parts of the regulatory requirements. Electrical items cause a significant number of deaths and injuries, and therefore this must be taken very seriously. Please also see CHAPTER 8 for the WEEE requirements, which will affect mains plugs and chargers, including USB chargers.

A BS 1363 plug has two horizontal, rectangular pins for line (commonly termed "live") and neutral, and above these pins, a larger, vertical pin for an earth connection. Unlike most other types of sockets, the earth pin is necessary for use of the BS 1363 plug, as it is needed to push open a shutter in the socket to allow the live and neutral pins to be inserted. It also polarises the plug, ensuring that the live pin is connected to the correct terminal in the socket. Moulded plugs for unearthed, double-insulated appliances may substitute this with an ISOD (Insulated Shutter Opening Device) which is a non-conductive plastic pin to open the shutters. Most non-fixed domestic equipment is connected using the BS 1363 plugs, the main exceptions being equipment requiring more than 13 amps (e.g. larger electric cookers, which are hard-wired); remotely switched, non-fixed lighting   (which use proprietary or BS 546 plugs); and low-power portable equipment, such as shavers, which may be used in several countries. Many bathrooms, particularly in hotels, have 2-pin standard "shaver sockets", which usually accommodate both European and US 2-pin plugs.

FIgure 1: Detail of an MK Logic Plus wall socket showing shutters which are operated only when all three pins are simultaneously inserted

BS 1363 part 1 is the specification for the plug. As there are no moving parts in a plug it is practicable to define the dimensions of the plug in an absolute manner. BS 1363 part 2 contains the specifications for sockets, to allow some flexibility in design the socket is defined partly in terms of the plug with which it will be used. It therefore follows that the performance of the socket is unpredictable if anything other than a BS 1363 compliant device is inserted into the socket.

Figure 2: BS 1363 plug, with an ISOD and sleeved pins.

What the law requires

•    Any component part which will plug into a mains electricity supply must have credible EU certification (see CHAPTER 3 CE AND ROHS/ROHS2) for, and comply with BS 1363;
•    Amongst other specifications, BS 1363 requires that the following standards are observed:

Pin insulation

The live and neutral pins on modern plugs have insulated sleeves to prevent finger contact with pins and also to stop metal sheets (for example, fallen window blind slats) from becoming live if lodged between the wall and a partly pulled out plug. The length of the sleeves is such that the pins themselves will not make contact with the socket receptacles until the exposed part of the pin is completely shielded by the socket.

Dimensions

The live and neutral pins have a rectangular cross section 6.35±0.13 mm wide and 3.975±0.075 mm height. They are 17.7±0.5 mm long and their centre lines are horizontally 11.115±0.065 mm on either side of the symmetry plane of the plug. The protective-earth pin is centred on the symmetry plane, is 22.73±0.5 mm long and has a cross section 3.975±0.075 mm wide and 7.925±0.125 mm height. The centre lines of the live/neutral pins and the protective pin are vertically 22.23±0.13 mm apart.

(These dimensions may be more easily remembered in the original imperial units, which are not mentioned in the current standard: 1/4±0.005 inch wide by 5/32±0.0025 inch high, and 0.695±0.02 inch long. They are 7/8±0.005 inch horizontally from each other, and the same distance vertically from the earth pin, which is 0.895±0.02 inch long. The pin lengths were presumably originally 0.7 and 0.9 inches, and assigned an asymmetric tolerance of +0.005/−0.015.)

We offer an auditing protocol for mains adapters/chargers, to check for compliance with these measurements. Please note that this does not replace the need for the correct documentation, but is a useful ‘spot check’ to ensure that your plugs have the proper dimensions to comply with the standard. Please contact us for details. (See ANNEX XIII for details of this auditing protocol, which is available to non-members as well as being provided to members as part of their routine auditing.)

Other safety features

The distance from any part of the live and neutral pins to the periphery of the plug base must be not less than 9.5 mm. This ensures that nothing can be inserted alongside a pin when the plug is in use, and helps keep fingers away from the pins. (This was a very early modification to the standard, which was later improved by the use of the insulated pin sleeves described above).

Figure 3: Internal wiring. Owing to the channel design (not shown), there is more slack in the neutral wire than the live, ensuring that if the lead is forcibly removed, the live wire will disconnect first.     #1 Cable grip; #2 Neutral terminal; #3 Earth terminal; #4 Live terminal; #5 Fuse

•    The requirement to fit a fused standard plug does not apply to appliances which are correctly fitted with a non-UK plug complying with the safety provisions of the International Electrotechnical Commission standard IEC 884-1 (1987) and fitted with a conversion plug of a type approved for use with such a non-UK plug which encloses the fitted non-UK plug and can only be removed by the use of a tool:

“Schedule 1 Excluded Electrical Devices 1.

Any plug, socket or adaptor which incorporates any other electrical device (other than a F fuse link, switch or indicator light).”(1)

Given the dangers associated with mains electricity, robust documentation is extremely important for any mains product.

 

Footnotes

1http://www.legislation.gov.uk/uksi/1994/1768/schedule/1/made