| S ➠ Apparent power in volt-amperes |
| s or p ➠ Laplace operator in mathematics, for transfer functions |
| S ➠ Slip of a rotating machine with respect to 1.0 pu |
| SAW ➠ Surface Acoustic Wave |
| SB ➠ Switch Board |
| SBM ➠ Single buoy mooring |
| SC, S/C ➠ Short circuit |
| SCADA ➠ Supervisory control and data acquisition system |
| SCF ➠ Standard cubic feet of a gas |
| SCIM ➠ Squirrel Cage Induction Motor |
| SCK ➠ Serial Clock |
| SCR ➠ Silicon Controlled Rectifier |
| SCS ➠ Silicon Controller Switch |
| SCSI ➠ Small Computer System Interface |
| SDR ➠ Single discipline review |
| SEB ➠ Service End Line Box or Service Electrical Box |
| SECT ➠ Skin effect current trace heating |
| SELV ➠ Safety extra-low voltage |
| SFU ➠ Switch Fuse Unit |
| SF6 ➠ Sulphur hexafluoride |
| SI ➠ System International of Unit’s |
| SIM ➠ Subscriber identity module |
| SIO ➠ Serial Input and (serial) Output |
| SIPO ➠ Serial In Parallel Out |
| SLDB ➠ Secondary Lighting Distribution Board |
| SLI ➠ Double-ended, linear arc tube |
| SMD ➠ Surface Mount Device |
| SMPS ➠ Switch-mode power supply |
| SMSB ➠ Sub Main Switchboard |
| SMT ➠ Surface mount technologies |
| SNR ➠ Signal-to-Noise Ratio |
| SoC ➠ System on a Chip |
| SOIC ➠ Small Outline Integrated Circuit |
| SOLAS ➠ Safety of life at sea, a document relating to marine practice |
| SON ➠ Diffused ellipsoidal outer bulb, single-ended lamp |
| SONAR ➠ SOund NAvigation and Ranging |
| SON-T ➠ Clear tubular outer bulb, single-ended lamp |
| SON-TD, – L ➠ Clear tubular outer bulb, double-ended lamp |
| SON-R ➠ SON lamp, with internal reflector |
| SOL CU ➠ Solid copper |
| SOP ➠ Small Outline Package |
| SOT ➠ Small outline transistor |
| SOX ➠ U-shaped arc tube, single-ended lamp |
| Sox ➠ Sulphur based gas emissions |
| SP ➠ Single phase |
| SPDT ➠ Single Pole Double Throw |
| SPI ➠ Serial Peripheral Interface |
| SPICE ➠ Simulation Program with Integrated Circuit Emphasis |
| SPMSM ➠ Surface Permanent magnet Synchronous Motor |
| SPST ➠ Single Pole Single Throw |
| SPT ➠ Stranded Parallel Thermoplastic |
| sq ➠ Square, e.g. sq mm is square millimeters |
| SR ➠ Shift Register, Slew Rate |
| SRAM ➠ Static Random Access Memory |
| SRF ➠ Self-resonant frequency |
| SRIM ➠ Slip Ring Induction Motor |
| SRM ➠ Switched Reluctance Motor |
| SSB ➠ Single SideBand |
| SSI ➠ Small Scale Integration |
| SSR ➠ Solid State Relay, Synchronization check protection relay |
| ST ➠ Super Tension, Shunt Trip |
| STA ➠ Steel Tape Armoure |
| STG ➠ Steam turbine generator |
| STP ➠ Shielded Twisted Pair |
| STR ➠ Statimax Trip Release |
| STR CU ➠ Stranded copper |
| SW ➠ Switch, Shortwave, as in the case with shortwave bands |
| SWA ➠ Steel wire armour |
| SWBD ➠ Switchboard |
| SWG ➠ Standard Wire Gauge |
| SWGR ➠ Switchgear |
| SYNC, Sync ➠ Synchronizing |
| SYM ➠ Symmetrical |
| SYRM ➠ Synchronous Reluctance Motor |