Joint, Britannia.
A joint for uniting the ends of telegraph and electric wires. The ends
of the wires are scraped clean and laid alongside each other for two
inches, the extreme ends being bent up at about right angles to the
wire. A thin wire is wound four or five times around one of the wires,
back of the joint, the winding is then continued over the lapped
portion, and a few more turns are taken around the other single wire.
The whole is then soldered.
Fig. 204. BRITANNIA JOINT.
Joint, Butt.
A joint in belting or in wire in which the ends to be joined are cut off
square across, placed in contact and secured. It ensures even running
when used in belting. Any irregularity in thickness of a belt affects
the speed of the driven pulley. As dynamos are generally driven by
belts, and it is important to drive them at an even speed to prevent
variations in the electro-motive force, butt joints should be used on
belting for them, unless a very perfect lap joint is made, which does
not affect either the thickness or the stiffness of the belt.
When a butt joint is used in wire a sleeve may be used to receive the
abutting ends, which may be secured therein by soldering. This species
of joint has been used on lightning rods and may more properly be termed
a sleeve joint.
Joint, Lap.
(a) In belting a joint in which the ends are overlapped, and riveted or
otherwise secured in place. If made without reducing the thickness of
the ends it is a bad joint for electrical work, as it prevents even
running of machinery to which it is applied. Hence dynamo belts should
be joined by butt joints, or if by lap joints the ends should be shaved
off so that when joined and riveted, there will be no variation in the
thickness of the belt.
(b) In wire lap joints are made by overlapping the ends of the wire and
soldering or otherwise securing. The Britannia joint (see Joint,
Britannia,) may be considered a lap-joint.
Joint, Marriage.
A joint for stranded conductors used for Galende's cables. It is made
somewhat like a sailor's long splice. Each one of the strands is wound
separately into the place whence the opposite strand is unwound and the
ends are cut off so as to abutt. In this way all are smoothly laid in
place and soldering is next applied.
Fig. 205. MARRIAGE JOINT.