The SH-500-50 is a current shunt that is required by the the TM-2030 battery monitor by Bogart Engineering to measure electricity usage. A shunt is the component that measures how much current flows into or out of the battery bank. The SH-500-50 shunt is recommended for most medium size RVs with a 160-300 Ah battery banks and loads not exceeding 400 A. In most typical RVs the greatest loads develop when a microwave is used. Since most RV microwaves will pull approximately 100-120 A of 12 volts, the 500 ampere shunt is the appropriate size. If you never use a microwave or any other high power device, a 100 or a 200 ampere shunt may be sufficient. Depending on the shunt specification it may also provide a higher resolution picture of power draw in your RV.