When designing a system that will utilize a terminal block, you will likely know your overall system voltage and current requirements. While these are very important, there are other factors to consider in your design as detailed below.
Current Rating
The current rating is often the most important parameter to consider in terminal block designs. The current rating is based on the conductivity of the terminals, cross-sectional area, and the corresponding heat rise. Operating at too high of a current can cause overheating and damage to the terminal block, leading to major safety concerns. It is best practice to use a terminal block that is rated for at least 150% of the max current that is expected in the system.
Voltage Rating
The voltage rating is in part determined by the dielectric strength and pitch of the terminal block housing. The maximum system voltage of the application must be less than the voltage rating. Any voltage surges in the system should also be evaluated when selecting the terminal block.
Pole Count
The number of individual circuits within the terminal block is also known as the pole count. This can be as few as a single pole, and as high as 24 poles, based on how many individual circuits are needed in the specific application.
Pitch
A terminal block’s pitch is defined as the center distance from one pole to the next. The pitch of the connector is often determined by the overall rating of the terminal block where factors like voltage/current, creepage, and clearance are considered. Common industry pitches would be but are not limited to, 2.54 mm, 3.81 mm, 5.0 mm, and 7.62 mm.
Wire Size/Type
The minimum and maximum wire size that the terminal block can accept would be a function of the voltage/current rating. In addition to making sure the wires used will physically fit into the terminal block, the type of wire should also be considered. The stranded or multi-core wire is typically used for screw terminals, and the single-core is typically used for push-in-style terminal blocks. In North America wire size is specified in units of American wire gauge (AWG).
