What is a Shorepower Y-Cable, and why would you use one? A Y cable is an adapter cable used to parallel two shorepower circuits. They come in a variety of configurations, including two 30Amp female to one 50Amp male, two 30Amp female to one 30Amp male, and others. Most cruisers have one of three cabling configurations, depending on its size and electrical requirements; One 30Amp service, one 50Amp service, or two 30Amp service.
Docks on the other hand may or may not have the same outlet configurations for your boat. This is especially true when you transient into public marinas, where they may only have a single 30A service. Most private marinas - at least in my area - offer two 30A or one 50A service, or a combination of the two. For this reason, when travelling, it is a good idea to have a couple different Y cables on board, albeit they are quite expensive.
My marina for instance has two 30A services available dockside. But you get an additional $300 bill at the end of the year for using two circuits. Luckily, I have found that I can satisfactorily power the boat from a single 30A service providing I use a bit of power management. In other words, if I don't turn every thing on all at once, I won't exceed 30Amps. For instance, I can power both air conditioners, and either the Microwave or Stove and stay under 30Amps. But if I attempt to power all 4 devices at once, I'll exceed the 30Amp limit. This is manageable, especially if it means saving $300 a season on dock fees. And the side benefit is I can use the Y-Cable at marinas only having one 30Amp service.
The cable shown here is a Marinco 157AY shorepower Y-Cable adapter. It has two 30Amp female connections for the boat, and a single 30Amp connector for the dockside. These cables are also available from several other manufacturers. This Y-cable enables the entire boat to operate on a single 30Amp service.
But isn't there some danger in using this approach? Yes, there can be. It is possible to draw up to 60Amps through the single 30Amp shorepower cable before tripping a circuit breaker on the boat. However, the dockside breaker should prevent this from happening. However, you should not rely solely on the dockside breaker as you don't know what condition it is in, or whether or not it is sized correctly from marina to marina. So the safest bet is to add a 30Amp breaker to the Y-Cable.
For this project, I have selected a NEMA 6x enclosure (IP67), waterproof cord grips for the cable, a 30Amp circuit breaker for the box, and a waterproof cover for the circuit breaker.
Marine shorepower hardware is very expensive! I found the cheapest solution for marine rated wire and connectors is to simply buy a 12Ft shorepower cable and cut it in two. Man, it just doesn't seem right cutting into a new $50 cable.
Wiring the box is pretty simple, so I won't go into much detail. While you can probably use a single 30A breaker, the proper method to safeguard against reverse-wired shorepower pedestals is using two 30A breakers (one on the black wire and one on the white wire). If you use a single breaker, make sure you pay attention to the shorepower reverse indication on your shorepower panel.
Wiring the breaker to the boat is as simple as finding a suitable location for the enclosure, then connecting it to the Y-cable. A nice piece of 3/4" Starboard makes for a good mounting base. I also used rubber-clad cable clamps so that I did not mar the stainless railing. This becomes a semi-permanent installation, but can be removed if needed.
The finished project, showing the Y-Cable and the breaker box I built. I left about 4ft of cable on the left side of the breaker. This cable can either connect to the dockside shorepower, or to my Honda EU2000 generator I sometimes carry aboard (with the proper 15A to 30A adapter).
Isn't that dangerous as well? Not really. The Honda generator will supply about 13Amps of current, and when connected to a 30Amp shorepower system, the 30A breaker will not trip. However, the function of the 30Amp breaker in the shorepower system is to protect that system, and will do so regardless of the source current from the generator. The generator itself has its own breaker which protects it. Therefore, there should never be a condition where an overcurrent that exceeds the wiring can exist.
While this might not look too pretty, it at least is all temporary, so it can be removed if needed. Also, I have terminated the shorepower cable, water line, and TV cable all at the same point to make it easier to disconnect everything when we want to take the boat out.