The importance of enclosing electrical connections

The importance of enclosing electrical connections

The team at Elecsa discuss the requirements for enclosing connections in live conductors.

To protect against electric shock and/or thermal effects, BS 7671 requires every electrical connection in a live conductor to be enclosed in a suitable accessory or equipment enclosure, or in an enclosure partially formed or completed with non-combustible building material. However, Area Engineers continue to observe departures from this requirement.

The aim of this article is to draw attention to the requirements for enclosing connections (joints and terminations) in live (line and neutral) conductors. Information is also given on the associated requirements for enclosures and on departures frequently observed by Area Engineers.

Enclosures are intended to prevent inadvertent contact with live parts. However, they also serve to protect electrical connections against certain external influences, and the surroundings against the effects of faulty connections.

Faulty joints and terminations in live conductors can attain very high temperatures due to the effects of resistive heating.

They can also emit arcs, sparks or hot particles. Consequently, there is a risk of fire or other harmful thermal effects to adjacent materials.

To prevent such risks, Regulation 526.5 of BS 7671: 2018 requires every joint and termination in a live conductor, irrespective of the nominal voltage, to be contained in one of the following, or a combination thereof:

  • A suitable accessory complying with the appropriate product standard
  • An equipment enclosure complying with the appropriate product standard
  • An enclosure partially formed by or completed with building material that is non-combustible when tested to BS 476-4: Fire tests on building materials and structures. Non-combustibility test for materials.

A typical example of non-compliant installation work is unenclosed compression joints, such as those shown in Fig 1.

Protection against external influences

Enclosures for joints and terminations, as with all electrical equipment, should be selected and erected to provide suitable protection against any foreseeable external influences, such as the presence of water or high humidity (Section 522 refers).

For example, electrical equipment installed in zones 1 and 2 of a room containing a bath or shower is required to have at least the degree of protection IPX4 (protected against splashing water). However, if such equipment is expected to be exposed to water jets, at least the degree of protection IPX5 is required (Regulation 701.512.2 refers).

Basic protection against electric shock

With certain exceptions for SELV and PELV circuits, enclosures for joints and connections must provide basic protection (protection against direct contact with live parts) for persons and livestock. SELV and PELV circuits of nominal voltage up to 12 V AC or 30 V DC or, in normal dry conditions, up to 25 V AC or 60 V DC, are exempt, provided the relevant conditions of Regulation 414.4.5 are met. Nevertheless, joints and connections in such circuits must still be enclosed for reasons of thermal effects and external influences.

To provide basic protection, Regulation 416.2.1 requires live parts to be inside enclosures (or behind barriers) providing at least a degree of protection IPXXB or IP2X.

Where a larger opening is required for replacement of parts (such as certain lamps) or for the functioning of equipment, all the following requirements apply:

  • Suitable precautions shall be taken to prevent persons or livestock from unintentionally touching live parts.
  • It should be ensured, as far as practicable (such as by a warning notice), that persons will be aware that live parts can be touched through the opening and that they should not be touched intentionally.
  • The opening is as small as is consistent with the requirement for the proper functioning and replacement of a part.

Furthermore, where an enclosure is readily accessible (such as is the case with many consumer units), the horizontal top surface is required to provide a degree of protection of at least IPXXD or IP4X (Regulation 416.2.2 refers).

Example of enclosing connections

Fig 2 shows how a repair (joint) to an insulated and sheathed cable might be made in accordance with the requirements of BS 7671 for enclosure suitability and basic protection. When the front cover plate is fitted, such an arrangement will, amongst other things, also satisfy the requirements of Regulation 416.2.4 (access by use of a tool) and Regulation 526.8 (enclosure of exposed cores).

Specific departures observed by Area Engineers

Some examples of departures observed by Area Engineers relating to enclosure of electrical connections are listed below:

  • Joints and terminations for ELV recessed luminaires and transformers not enclosed
  • Joints and terminations for repairs, additions and alterations to an installation not enclosed (see Figure 1),
  • Blanking-off covers omitted from distribution boards, making it possible to touch hazardous live parts
  • Readily accessible consumer units with the horizontal top surface with holes not providing a degree of protection to IPXXD or IP4X, and
  • SELV recessed luminaires installed in zones 1 and 2 of a location containing a bath or shower, with IP ratings not meeting the requirements of IPX4 or, where required, IPX5.

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