Build a Cruising Tool: Test the Shore Power

There have been questions on our Facebook page about how I test shore power receptacles to make sure there are no issues before plugging the boat into them. Here are my tools (some assembly required—all products are linked to Amazon items). 

15A/20A/30A Tester

For 30A I use a 30A to 20A adapter like this one with a household-type receptacle tester like this one. It works perfectly!

​To test 15/20A receptacles, I separate the adapter from the tester and start testing. 

50A 120/240V Tester

For testing the standard 50A 120/240V (split-phase) receptacles often found at marinas, I built this monstrosity. It works very well. 

Credit where credit is due: I should note that the inspiration for this came from my friend, Sean on MY Vector who built a similar tester that he posted about here. 

Mine comprises a NEMA SS2-50P, marine-grade 4-pin plug, a digital AC voltage indicator, and two NEMA 5-15 female 120V pigtails (18 AWG is fine for this since there will be no real current involved).

• Drill holes for the pigtail wires in the sides of the 50A plug.
• Mount the voltage indicator (see image below) and connect it only to L1 and L2 (do not connect in any way to neutral or ground). 
• For the pigtails: wire ground and neutral to the ground and neutral lugs in the 50A connector; pigtail hots are split—one to L1 the other to L2 on the 50A plug. 
• Once the assembly is otherwise complete, plug the outlet testers into the pigtails.

To use: the outlet testers tell you if either 120v side of the 50A receptacle is  properly wired or not. The voltage gauge will only come on if you have good split-phase 240v power available. If the outlet testers show correctly wired, but there is no 240v reading (the voltage indicator likely will not even light up if there is no ~240v available), you are dealing with a 120v pedestal that does not provide split-phase 240v—you will be able to use 120v devices aboard, but not 240v devices.