✨ Electrical Wiring Regulations
2424
THE NEW ZEALAND GAZETTE.
[No. 48
TABLE XIV.—APPROXIMATE FUSING CURRENTS OF LEAD-TIN ALLOY
(LEAD 75 PER CENT., TIN 25 PER CENT.) WIRES IN FREE AIR.
| Diameter of Wire. | Equivalent S.W.G. Size. | Fusing Current. | Maximum Safe-working Current (see Note). |
|---|---|---|---|
| In. | Amps. | Amps. | |
| 0·020 | 25 | 3 | 2·0 |
| 0·022 | 24 | 3·5 | 2·3 |
| 0·024 | 23 | 4 | 2·6 |
| 0·028 | 22 | 5 | 3·3 |
| 0·032 | 21 | 6 | 4·1 |
| 0·036 | 20 | 7 | 4·8 |
| 0·048 | 18 | 10 | 7·0 |
| 0·064 | 16 | 16 | 11·0 |
Tables XIII and XIV refer to wires in free air and of the following lengths: Copper, 2½ in. to 3½ in. for wires up to 0·018 in. diameter, and not less than 4 in. for larger wires; lead-tin alloy, 2½ in. to 3½ in.
The values given in the tables may be taken to be correct where the fuse wire passes through an asbestos tube and does not closely touch the tube, but they do not apply where a substantial length of the wire is in contact with a porcelain holder. The tendency of the latter design is to increase the working-capacity of the fuse—i.e., more current is required to melt the fuse—and if great accuracy is required the fusing current should be determined for the fuse-holder in question.
For copper wires, the values of the currents given in Table XIII are those necessary to fuse the wire in one minute, and are not appreciably different for other periods (the current required to fuse the wire in two hours being, in general, over 90 per cent. of that required to fuse the wire in one minute).
For the lead-tin alloy the currents given in Table XIV are those necessary to fuse the wire in two minutes.
In every case the relation between the fusing current and the maximum safe-running current is based on values which will not produce an excessive temperature under normal running conditions. The actual temperature-rise at the hottest part of the fuse wire will be from 212 to 302 degrees F. for copper and 122 to 167 degrees F. for the lead-tin alloy.
TABLE XV.—FLEXIBLE CORDS : TYPES TO BE USED.
| Use. | Type of Covering (Regulation 93). | Grade of Insulation (Regulations 91 and 92). |
|---|---|---|
| Type. | Twisted, Oval, or Circular Section. | |
| Pendants in dry places (domestic) | (a), (b), (c), (d), (e), (f), or (g) | T., O., or C. |
| Portable lamp-standards in dry places | (a), (b), (c), (d), (e), (f), or (g) | T., O., or C. |
| All shops, public dining-rooms, and kitchens, if flexible conductors are likely to be exposed to the action of flies or other insects, and in all premises such as stables, hide and tallow stores, and in all such other places where flies or other insects are prevalent | (d),* (e), or (f) | O. or C. ... |
| Pendants in damp places or over earthed floors | (d)* or (f) | O. or C. ... |
| Portable lamp-standards over earthed floors | (d),* (e), or (f) | O. or C. ... |
| Portable appliances in dry places (domestic) | (d), (e), (f), or (g) | O. or C. ... |
| Portable appliances in dry places (industrial) | (d), (e), or (f) | O. or C. ... |
| Portable appliances in damp situations or over earthed floors (domestic and industrial) | (d)* or (f) | O. or C. ... |
| Trailing cables for lifts ... ... | (f) | O. or C. ... |
| Where subject to hard or rough usage | (d),* (e),† or (f) | O. or C. ... |
- Provided the insulation is not pure rubber when used in damp situations.
† Not to be used in damp situations.
(i) The use of flexible cords made up to a circular or oval section is recommended for all portable fittings. (ii) Portable appliance includes portable hand-lamp.
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VUW Te Waharoa —
NZ Gazette 1927, No 48
NZLII —
NZ Gazette 1927, No 48
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Electrical Wiring Regulations, 1927
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🏗️ Infrastructure & Public Works11 July 1927
Regulations, Electrical Wiring, Safety, Compliance, Conductors, Cables, Current-carrying Capacity, Insulation Resistance, Tables