When was this last done?

[securespark]

I have a copy of the 13th Ed. on order.

What it will tell me I'm not sure but I'll let you know.

Right. I have got a copy of the 13th now, 1955.

The numbering is completely different to the 14th, so I don't even have a clue which areas of the book to look it, but I'll be reading most of it anyway (sad git!).

What was the question?

 

[securespark]

This is a quote from the 13th Ed, 1955.

402 When earthing is adopted as a means of compliance with the requirements of Regulation 401, the installation shall include a consumer's earth terminal, or the equivalent, to which the following shall be connected by an earth-continuity conductor:

(A) All metalwork associated with wiring systems (other than current-carrying parts), including cable sheaths and armour, conduit, ducts, boxes and catenary wires.

(B) etcetera.........................


403 The application of Regulation 401 (iv) which exempts from the requirement of earthing metal which is so isolated that it is not liable to come into contact with live parts or with earthed metal, shall be restricted to the apparatus detailed in the following Clauses (i)-(ix):

(i) Short isolated lengths of conduit used for mechanical protection of tough-rubber- or p.v.c.-sheathed wiring.

(ii) Short unexposed isolated lengths of metal conduit used for the mechanical protection of cleated wiring where it passes through floors, walls, partitions or ceilings.

(iii) Short isolated lengths of catenary wire used with tough-rubber-sheathed or p.v.c.-sheathed wiring.

(iv) Clips used for fixing cables.

(v) Metal boxes used with tough-rubber-sheathed or p.v.c-sheathed wiring systems, if screened by non-conducting materials.

(vi) Lamp caps.

(vii) Small parts such as screws or nameplates isolated by insulating material.

(viii) Metal chains for the suspension of lighting fittings, not in contact with flexible cord of the twisted type.

(ix) Lighting fittings using filament lamps installed in a room having a non-conducting floor, mounted at such a height that they cannot readily be touched and are out of reach of earthed metal.



So it is suggesting that maybe capping is not included in the list.

Although the list is not exhaustive: it says "all metalwork associated with wiring systems".

Then 403 excuses "short" lengths of conduits and catenary wires. What classes as "short"?

The capping may well be in contact with "earthed metal" (the accessory box if indeed it was earthed).

It may even be that the installer was covering his back by earthing the capping.

 

[EFLImpudence]

SS, what exactly are the requirements of 401?

Just generally, not word for word.

 

[mfarrow]

It does seem like backside covering. Our house was done in 1958 with Ashathene. Very good cabling of which I found intact lengths of when digging the extension footings. None of the capping is earthed.

 

[securespark]

Ashathene is bloody good stuff. I came across it in 1990 when doing a board change. Sound as a pound.

AFAIK, it's still going strong. Probably outlive that old 15th Ed.board too!

 

[securespark]

Here are Regulations 401-403 in full:


401 Electrical apparatus operating at a voltage exceeding extra-low voltage shall be protected against dangerous earth-leakage currents by one of the means described in Clauses (i), (ii), (iii) or (iv) below:

(i) Insulation which encloses the apparatus and is durable and substantially continuous, i.e. of "all-insulated" construction.
Note.--Fixed apparatus, which although not shrouded in insulating material is nevertheless otherwise so guarded that it cannot be touched and cannot come into contact with exposed metal, may in certain circumstances be regarded as of "all-insulated" construction (see Exemption 3 to the Electricity (Factories Act) Special Regulations 1908 and 1944, and Form 928).

or (ii) Double-insulation of an appliance in conformity with a British Standard which has been recognized for the purposes of these Regulations;

or (iii) Earthing of exposed metal parts in accordance with the requirements of this Section;

or (iv) Isolation of metal in such a way that it is not liable to come into contact with live parts or with earthed metal (see Regulation 403).


402 When earthing is adopted as a means of compliance with the requirements of Regulation 401, the installation shall include a consumer's earth terminal, or the equivalent, to which the following shall be connected by an earth-continuity conductor:

(A) All metalwork associated with wiring systems (other than current-carrying parts), including cable sheaths and armour, conduit, ducts, boxes and catenary wires.

(B) Exposed metal of apparatus required to be earthed in accordance with the requirements of Regulation 401.

(C) Earth terminals of socket-outlets.
Note.--Earthing of exposed metal of portable apparatus required to be earthed should be effected through a flexible cable or flexible cord and the earthing-pin or earth-contact of a plug.

(D) One point of the secondary winding and of metalwork (other than current-carrying parts) of any transformer used in a consumer's installation.
Exemptions to Clause (D):
(i) A transformer contained in an item of apparatus, eg a mains-operated radio receiver, which taken as a whole conforms with the requirements of Section 6.
(ii) The secondary winding of a "high-reactance" transformer serving solely to energize a tesla coil or the heating element of a discharge lamp.
(iii) A transformer in which each winding is mounted on a separate limb of an earthed core, or in which the windings are separated by an earthed metal screen.


403 The application of Regulation 401 (iv) which exempts from the requirement of earthing metal which is so isolated that it is not liable to come into contact with live parts or with earthed metal, shall be restricted to the apparatus detailed in the following Clauses (i)-(ix):

(i) Short isolated lengths of conduit used for mechanical protection of tough-rubber- or p.v.c.-sheathed wiring.

(ii) Short unexposed isolated lengths of metal conduit used for the mechanical protection of cleated wiring where it passes through floors, walls, partitions or ceilings.

(iii) Short isolated lengths of catenary wire used with tough-rubber-sheathed or p.v.c.-sheathed wiring.

(iv) Clips used for fixing cables.

(v) Metal boxes used with tough-rubber-sheathed or p.v.c-sheathed wiring systems, if screened by non-conducting materials.

(vi) Lamp caps.

(vii) Small parts such as screws or nameplates isolated by insulating material.

(viii) Metal chains for the suspension of lighting fittings, not in contact with flexible cord of the twisted type.

(ix) Lighting fittings using filament lamps installed in a room having a non-conducting floor, mounted at such a height that they cannot readily be touched and are out of reach of earthed metal.

 

[JohnW2]

401 .... the following shall be connected by an earth-continuity conductor: .... (D) One point of the secondary winding .... of any transformer used in a consumer's installation.

Am I missing something here? What if it is an 'isolating transformer' (e.g. in a shaver socket, if they had such things then!)?? In that situation, to earth 'one point of the secondary winding' would appear to defeat the whole point of having an isolating transformer, wouldn't it?? (at its worst if that 'one point' were at one end of the secondary winding).

Kind Regards, John

 

[securespark]

Could it be that said transformer is covered by the exemptions?

 

[JohnW2]

Could it be that said transformer is covered by the exemptions?

I considered that possibility, but wasn't convinced that any of those exemptions necessarily applied (at least, not in all cases). It certainly would not come under exemption (ii), and nor would it necessarily come under exemption (iii) (which is about the method of construction of the transformer). That only leaves (i), and I really don't think that an isolating transformer would really fall into that category, either, would you?

Kind Regards, John

 

[333rocky333]

Here are Regulations 401-403 in full:


401 Electrical apparatus operating at a voltage exceeding extra-low voltage shall be protected against dangerous earth-leakage currents by one of the means described in Clauses (i), (ii), (iii) or (iv) below:

(i) Insulation which encloses the apparatus and is durable and substantially continuous, i.e. of "all-insulated" construction.
Note.--Fixed apparatus, which although not shrouded in insulating material is nevertheless otherwise so guarded that it cannot be touched and cannot come into contact with exposed metal, may in certain circumstances be regarded as of "all-insulated" construction (see Exemption 3 to the Electricity (Factories Act) Special Regulations 1908 and 1944, and Form 928).

or (ii) Double-insulation of an appliance in conformity with a British Standard which has been recognized for the purposes of these Regulations;

or (iii) Earthing of exposed metal parts in accordance with the requirements of this Section;

or (iv) Isolation of metal in such a way that it is not liable to come into contact with live parts or with earthed metal (see Regulation 403).


402 When earthing is adopted as a means of compliance with the requirements of Regulation 401, the installation shall include a consumer's earth terminal, or the equivalent, to which the following shall be connected by an earth-continuity conductor:

(A) All metalwork associated with wiring systems (other than current-carrying parts), including cable sheaths and armour, conduit, ducts, boxes and catenary wires.

(B) Exposed metal of apparatus required to be earthed in accordance with the requirements of Regulation 401.

(C) Earth terminals of socket-outlets.
Note.--Earthing of exposed metal of portable apparatus required to be earthed should be effected through a flexible cable or flexible cord and the earthing-pin or earth-contact of a plug.

(D) One point of the secondary winding and of metalwork (other than current-carrying parts) of any transformer used in a consumer's installation.
Exemptions to Clause (D):
(i) A transformer contained in an item of apparatus, eg a mains-operated radio receiver, which taken as a whole conforms with the requirements of Section 6.
(ii) The secondary winding of a "high-reactance" transformer serving solely to energize a tesla coil or the heating element of a discharge lamp.
(iii) A transformer in which each winding is mounted on a separate limb of an earthed core, or in which the windings are separated by an earthed metal screen.


403 The application of Regulation 401 (iv) which exempts from the requirement of earthing metal which is so isolated that it is not liable to come into contact with live parts or with earthed metal, shall be restricted to the apparatus detailed in the following Clauses (i)-(ix):

(i) Short isolated lengths of conduit used for mechanical protection of tough-rubber- or p.v.c.-sheathed wiring.

(ii) Short unexposed isolated lengths of metal conduit used for the mechanical protection of cleated wiring where it passes through floors, walls, partitions or ceilings.

(iii) Short isolated lengths of catenary wire used with tough-rubber-sheathed or p.v.c.-sheathed wiring.

(iv) Clips used for fixing cables.

(v) Metal boxes used with tough-rubber-sheathed or p.v.c-sheathed wiring systems, if screened by non-conducting materials.

(vi) Lamp caps.

(vii) Small parts such as screws or nameplates isolated by insulating material.

(viii) Metal chains for the suspension of lighting fittings, not in contact with flexible cord of the twisted type.

(ix) Lighting fittings using filament lamps installed in a room having a non-conducting floor, mounted at such a height that they cannot readily be touched and are out of reach of earthed metal.

I assume that answers the case of the unearthed brass lampholders in the other post

 

[securespark]

Depends on the floor, I suppose...

 

[SimonH2]

I considered that possibility, but wasn't convinced that any of those exemptions necessarily applied (at least, not in all cases).

I guess, if those regs were in use today, then isolating transformers would all have to comply with 402(D)(iii) and either have separate bobbins on separate limbs, or have an earthed screen between the windings. The latter would not take much doing if designed in from the outset.

 

[JohnW2]

I guess, if those regs were in use today, then isolating transformers would all have to comply with 402(D)(iii) and either have separate bobbins on separate limbs, or have an earthed screen between the windings. The latter would not take much doing if designed in from the outset.

The former is certainly highly desirable, but I'm not at all sure of the latter (alone). Whilst an earthed screen would usually result in a protective device operating in the event of a defect arising in the primary, it would (unbeknown to user) result in the 'isolating' functionality being lost if a fault developed between the secondary and the earthed screen.

Kind Regards, John

 

[SimonH2]

As would a fault developing between the secondary and primary, or between secondary and frame, in a similar transformer without screen. In that respect, there's little difference between an isolating transformer without a screen but with "good insulation" between windings; and a similar transformer with screen but with "good insulation" between secondary and everything else.

 

[JohnW2]

As would a fault developing between the secondary and primary, or between secondary and frame, in a similar transformer without screen. In that respect, there's little difference between an isolating transformer without a screen but with "good insulation" between windings; and a similar transformer with screen but with "good insulation" between secondary and everything else.

I don't think that really alters what I said.

With a single bobbin, so long as the "good insulation" in intact, the presence/absence of an earthed screen obviously makes no difference. However, if the 'good insulation' ceases to be intact, then an earthed screen would be a good thing if there was a fault just in the primary, but a bad thing if the fault were just in the secondary - and, as I said, the worry with the latter is that the user would be unaware of the hazard resulting from the output of the transformer no longer being isolated.

A non-earthed (ideally non-conductive) 'screen' (in addition to the standard insulation) between primary and secondary would probably be preferable.

Kind Regards, John