SER Cable Vs. SEU Cable
Type SE, Style R (SER) and Type SE, Style U (SEU) cables often draw a lot of confusion as to which one is more suitable for the task at hand. These cables are service entrance cables that are available with copper or aluminum conductors, Type XHHW-2 or Type THHN/THWN-2 insulation, and a polyvinyl chloride (PVC) jacket. SER and SEU cables both offer the same voltage rating (600 volts), temperature rating (up to 90°C), and sunlight and heat-resistance, but there are some fundamental differences in their construction that sets them apart.
Type SEU cable has two phase conductors surrounded by a concentric neutral wire. Type SEU is more commonly found in residential applications to connect utility power to the meter base. SEU cables require the user to unwind the neutral wires in order to begin to terminate the conductors. Then, the neutral wires need to be re-twisted back together for termination.
Type SER cable is most commonly used to connect a sub-panel to the main distribution panelboard. Type SER cable includes two, three, or four insulated phase conductors and a bare neutral wire. Type SER cables are sometimes preferred over SEU cables because there is no need to untwist and re-twist the neutral wire to terminate the cable. The National Electric Code specifies that the neutrals and grounds from branch circuits in a sub-panel need to run on the same cable assembly. With the option of up to five conductors in the cable, the Type SER cable allows for more grounded connections while staying within the parameters of NEC requirements.