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From the helpline We continue with our series of answers to some of the more frequently asked questions put to our Technical Helpline.

QUESTION

Are there any specifi c requirements given in BS 7671 that need to be considered when carrying out work in a dental practice?

QUESTION

Aft er carrying out either an addition or alteration to an existing installation, is it necessary to affi x a periodic inspection and testing notice?

QUESTION

Is it permitted to extend an existing main protective bonding conductor? ANSWER

Yes, dental practices are to be considered as medical locations, as defined in Section 710 – Medical Locations. While complying with the general requirements of BS 7671, it is likely that parts of Section 710 will amend or add to some of those general requirements. Prior to any decisions taken on the particular regulations that may apply, the contractor will need to agree with the client the nature of the work that will be carried out: such work will indicate both the classification and the group. Annex A710 provides guidance on group numbers and classification for safety services of medical locations (Regulation 710.3 refers).

ANSWER

It may be appropriate for a notice advising the user of the recommended date of the next inspection and testing of the circuits that have been subjected to additions or alterations to be fixed at or near the origin of the installation, as required by Regulation 514.12.1; for example, where no current notice exists. However, there is a risk of confusion for the user, where more than one periodic inspection and testing notice is aff ixed. Where there is an existing notice and such confusion could arise, the contractor should err on the side of safety and not aff ix a second notice.

ANSWER

Yes. However, the connection must be a ‘permanent connection’, such as a connection made by soldering or a compression tool. This is to minimise the risk of the connection becoming detached with a consequent loss of continuity. This eff ectively precludes making the connection by an earthing and bonding clamp to BS 951 (Regulation 528.3.3 refers).

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QUESTION

When connecting an item of class II equipment having no earth terminal to an existing wallmounted outlet, is it still necessary to provide a circuit protective conductor (cpc) from the outlet to the equipment?

QUESTION

Is it permissible to use the circuit protective conductor (as indicated by the insulation colour green/ yellow) within a 3 core fl exible cable as a switch-line conductor to supply the item of equipment in the previous question?

QUESTION

Is it acceptable to make the ‘loop-in’ and ‘loop-out’ connections (line, neutral and earth) for a lighting circuit at the switching point, rather than at the ceiling outlet? ANSWER

No, such an item of equipment is neither a point (in wiring) nor an accessory (Regulation 411.3.1.1 refers).

ANSWER

Yes, for this particular situation. Regulation 514.3.2 permits an insulated core to be oversleeved to identify the intended function of the core. However, because of the risks of mis-identification associated with this practice, it is recommended that where practicable this should be avoided.

ANSWER

Yes. However, where ‘loop-in’ and ‘loop-out’ connections are made at the switching point, the enclosure should be of appropriate depth, such as a back box having a depth of 25 mm or greater, and the conductors correctly identified and terminated in appropriate connectors.

Flashback! Ask the Experts…. from 1959

From its earliest inception, the NICEIC has responded to concerns raised with regard to electrical installations.

The half-yearly newsletter No.1 issued in November 1959 by Brigadier Thompson as the CEO and secretary highlights many of the issues that NICEIC still deals with. In particular, from its inception the NICEIC provided guidance to the industry regarding certain technical issues.

One question from a contractor dealt with the need to “bond to earth” the metal box enclosures at switch positions and it not being suff icient to cover the screw heads with wax!

Another question still sounds familiar, even when the type of cable or height measurements may not: “Nearly all lighting fittings having metal suspension chains or rods, provided for erection in domestic premises where the usual ceiling-floor height is 8’6” to 9’6”, are wired in unsheathed lightly insulated flexible cord of the “twisted” or “flat-twin” type. All such fittings must be bonded to the earth-continuity conductor per Regulation 402. Needless to say this requirement applies also to metal wall brackets or fixtures for lighting purposes.”

While the regulation number has changed, the need to connect a protective conductor to class I equipment remains to this day – Regulation 411.3.1.1 requires that every exposed-conductive-part is to be connected to a protective conductor.