222 The N.Z. Journal of Science and Technology. [July 
destruction of insulation by vermin, and the objectionable and dangerous 
use of temporary connections. 
A badly made or dry joint in any conductor constitutes a most serious 
fire hazard, because it offers a resistance to the passage of the current and 
generates heat. The resistance may be sufficiently high to cause the wire 
to become red-hot, and it is then only a question of time till the rubber 
insulation is set on fire and a conflagration possibly started. Such a joint 
is bad enough when enclosed in steel conduit, but it requires no effort of 
imagination to figure out what will happen if it were enclosed in wood 
casing. In a well-designed installation there should be no joints at all, the 
lights being “ looped ” in one from the other ; but in long runs there is 
sometimes a temptation to make joints to save a few feet of wire. The 
same principle which causes heat to generate in a faulty joint applies to a. 
wire that is overloaded. Conductors of a certain diameter can transmit 
only a definite amount of current with safety, and heat will be generated 
according to the amount of overloading put on to the conductor, which 
may be sufficient to burn the insulation and everything combustible in 
contact with it. Where it is necessary to make a joint it should be in a 
metal box, the joint being properly soldered and insulated with rubber 
and adhesive tape. The insulation resistance round the joint should be at 
least equal to the insulation on the rest of the wire. 
The generation of heat due to resistance is not confined to joints, but 
will occur in switches, fuses, ceiling-roses, lamp-holders, or any other 
electrical apparatus where there- are bad contacts or loose screws at the 
terminals. 
Fuses are installed to protect the wiring and different apparatus con¬ 
nected to the system, but under certain conditions they may themselves 
become a hazard. They should be designed so that an increase of 50 per 
cent, of the normal current will cause them to “ blow, 5 ' and so disconnect 
that portion of the installation. They should also be enclosed, to prevent 
the hot fused metal from falling on any inflammable material and setting 
light to it. I have frequently found that when fuses blow, due to a fault 
developing, and not on account of an increase in the load, instead of locating 
and removing the fault the size of the fuse has been gradually increased 
until the fuse would remain intact. Such a case happened in our own city, 
where a No. 16 copper wire was used as a fuse on a circuit wired with No. 18 
wire. An incipient fire broke out, and at the investigation the man 
responsible for putting in the fuse innocently stated that he could not get a 
smaller wire to “ stop in.” It never occurred to him what the possible 
result of overfusing might, be ; in fact, he did not know what the fuse was 
for. He simply wanted his lights going, and that was the only thing that- 
concerned him. 
Cord flexibles, unless used with discretion, are always a source of danger. 
As drop pendants in dwellings, offices, and certain classes of shops and 
factories they are quite safe, but in other situations may be a serious hazard. 
They should not be used in butchers 5 or confectionery shops, hotel-kitchens, 
public dining-rooms, bakehouses, stables, fellmongeries, or any situation 
where subject to the action of flies and other insects. In such places the 
flexibles should be covered with a tough rubber compound, or, better still, 
stiff metal pendants or batten holders should be used. The use of flexibles 
for extensions, or as we often see them used in shop-windows, should be 
prohibited, because the constant handling causes the insulation to become 
