Switchboard Wire is most often referred to in the electrical industry as simply SIS wire. It is also at times called out by electricians and end users as UL3173. SIS wire, although simple in construction, is a very versatile cable used in many different applications. Some of those applications range from its obvious name, switchboard wiring, to panel boards, distribution boards, industrial control panels and many other applications up to 600 volts.
The construction of SIS wire is fairly simple to say the least. SIS wire is available in a large number of gauge sizes ranging from 4/0 to 18awg. It consists usually of a stranded copper conductor that is tin coated with XLP (cross-linked polyethylene) insulation. Although this construction is standard you will sometimes find it with bare copper conductors rather than the tinned. A note to consider when either selling or installing SIS wire is to determine the stranding needed or preferred. SIS is available with a coarse strand count as well as a flexible strand count. The installer should determine what is suitable for the job at hand. Obviously the SIS coarse strand will be less expensive at the cost of flexibility. The flexible stranded version, SISF as its known, is by far the most popular due to the fact that many of its applications require more of a flexible cable. An additional reason for the SISF being much more popular than the coarse stranding is the flexible version of switchboard wire is more readily available.
Another thing to consider with SIS wire is that it is rated at 90 Celsius as standard. Also, the majority of SIS wire will meet the VW-1 (vertical Flame test) rating although not all. Both temperature and flame test requirments are important to clarify when looking for the type of SIS wire that is best for your project or job.
Lastly, when considering SIS for a specific need it is good to know that the most common color of the cross linked polyethylene insulation is gray but can also be found in other colors as well. The reason for this is that at times there is a need to make multiple runs of the same item and it is useful for clear and easy identification. If multiple colors are not available, another option is having the SIS wire striped with different colors to distinguish the runs needed.