Q: What is the reason for/difference between the flashing (R-3W) and non-flashing (R-3W-SR) voltage indicators?

A: The only difference between the two is that the R-3W-SR is solid on or solid red, hence “SR”. This comes down to personal preference by the end user. It was created for the oil and gas industry since flashing meant that there is something wrong. The R-3W-SR will still flash at lower voltages due to the internal circuity, see the following for voltage levels vs indication: 32-159V (FLASH); 160-329V (SHIMMER); 330V+ (SOLID).