IDEN­TI­FY­ING THE PROB­LEM

Passage Maker - - News & Notes -

So what is hap­pen­ing when you plug into shorepower, the pedestal trips, and sud­denly you have no air con­di­tion­ing? We know from th­ese illustrations that an im­bal­ance ex­ists be­tween the hot and back to ground through the green wire and through the wa­ter. Here are the pos­si­bil­i­ties:

1. At least one piece of AC equip­ment has a dan­ger­ous short be­tween the hot and the equip­ment, in which case the black wire is mak­ing con­tact to ground where it shouldn’t. You haven’t been shocked ei­ther be­cause you haven’t yet touched the wrong thing at the wrong time or be­cause the green ground­ing wire is safely car­ry­ing away the bulk of the cur­rent.

2. You have at least one con­nec­tion some­where—and maybe sev­eral—be­tween neu­tral and ground, al­low­ing enough cur­rent im­bal­ance to trip the ground fault de­vice. 3. Both of the above. By plac­ing a sen­si­tive am­me­ter around the hot and neu­tral wires (fig. 7), ex­clud­ing the green ground­ing wire, an im­bal­ance can be de­tected. In the boat­yards, we plug the shorepower cord into an adapter that we make up, with the green wire sep­a­rated out. The am­me­ter must be ca­pa­ble of mea­sur­ing cur­rent flow as lit­tle as .004 amps, and those me­ters cost some­where in the range of $500 to $600. The test can be­gin by plug­ging into shorepower, turn­ing on all AC break­ers, and ac­ti­vat­ing all AC loads. In other words, its not enough to turn on the air con­di­tion­ing breaker; you must make sure the com­pres­sor runs. This test will pro­vide a snap­shot of the over­all con­di­tion, and any read­ing above 4 mA in­di­cates a prob­lem. Of course, plug­ging in sounds eas­ier said than done. It won’t be pos­si­ble to run the test at a pedestal that im­me­di­ately trips.

Be­fore go­ing down this rab­bit hole, re­mem­ber that the ground fault de­vice on the pedestal trips when the to­tal im­bal­ance ex­ceeds the rat­ing. Let’s as­sume a de­vice rated at 30 mA (even though some mari­nas have those eas­ily tripped GFEPs rated at 5 mA). You ar­rive at the ma­rina, plug in, and just like that, the de­vice trips and sev­eral other boats lose power be­cause of you. You’re the prob­lem child and oth­ers on the dock glare at you. It is quite pos­si­ble, how­ever, that some if not all the other boats also have small neu­tral-to-ground leaks. Per­haps those leaks add up to 25 mA, or just un­der the trip thresh­old. You add

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