Hi Kevin,

I have a problem with my boat’s shore power.

I ran 240 volt, 50 amp service to my dock with appropriate wiring (2 Hots, Neutral and Ground of sufficient size wiring five years ago. In my main house electrical panel, the 2 hots run to a 60 amp double pole breaker. The neutral and ground are on a common bus in the main electrical panel in the house.

I installed a power post at the dock using two Marinco 240 50 A outlets each protected by a 50A double pole breaker.

For 5 years I have had no trouble running any and all devices on my 49′ Gulfstar MY while plugged in. Most current probably drawn on start up of air conditioner with all other systems running was 35 amps. The boat main never blew, nor did shore power breaker at shore power post or main house electrical panel.

A friend is docking his 1997 50′ Carver CPMY at the dock. He has never had issues at any other dock with shore power. Now, when we plug his boat into either 240v 50a outlet at the shore power post using a 75′ 240 50a extension to his Marinco reverse Y (2 125 V 50a) to his boat, his panel indicates 110 on each leg. However, as soon as I try to turn breakers on, shore power one main on the Carver blows.

• I have inspected the wiring at my shore power post including loose and proper connections.
• I have further pulled back the waterproof covers on all of the Marinco male and female plugs to make sure there was no corrosion and no loose connections and each termination is correct (Hot legs where hot legs belong and ground and neutral properly wired.)
• I do measure 10 ohms across Neutral and Ground at the power post with all plugs disconnected which I expected as Neutral and Ground are tied together on a common bus at the main House electrical panel.
• I metered resistance on all four legs of the 240v 50a extension and get fewer than 25 ohms.
• There is no indication of reverse polarity on his Carver electrical panel. At the end of the 240v 50a extension, I measure 240 across the hot legs, and 120 across each hot leg and neutral, and 120 across each hot leg and ground.

Again, neither his 1997 50′ Carver has had this problem at any marina, nor have I encountered this issue with my 1986 49′ Gulfstar MY at any marina from Florida, through the Bahamas and the entire Great Circle.

I am perplexed. The only thing I keep going back to is the common Neutral/ground in my House main electrical panel. Again, it does not matter which 240v 50a outlet the Carver is plugged into – the same net result is shore power #1 blowing on the Carver panel.

I really would appreciate any insight you could offer,

Ken

Hi Ken,

Have you ever used the y adaptor before? Did you take voltage readings after the Y?

Looking in the end of the 30 amp receptacle, the “L” shaped terminal in the Ground. Clockwise to neutral and then continue clockwise to Hot.

What is the reverse polarity protection system on the Carver? Indicator light or Auto trip?

Please me know what you find,

Kevin

Kevin,

I went back to basics.

I assumed that because I had 240 VAC at the end of the extension, and 125 on each leg of the Y across Hot and Neutral that the extension was good. It appeared in good condition, free of corrosion etc.

I metered the 240 VAC extension for continuity across Hot/Hot, Neutral/Neutral, G/G and Hot/Hot. I was amazed to find that there was an open on both neutral and ground. Hot legs were 5.2 ohms. I peeled back the male side of the Hubbel 240 V 50 A plug and was astonished to find that the Neutral and Ground were both intentionally cut short and not connected in any way. The extension (pre-owned) was a new purchase from the local Marine consignment shop and I should have metered it before I purchased it.

After a trip to West Marine for a new 50 A 240 VAC Marinco male plug, I am in business.

I am perplexed why I metered 125 VAC on each leg of the extension, there being no ground or neutral. Likewise perplexed 125 VAC on each leg of the Y adapter.

Big lesson – Carefully check any used boat wiring or marine hardware prior to purchase- this most certainly was a disaster in the making.

Thank you kindly for taking your valuable time to respond.

Ken