100 Amp Shore Power Cable
Shilshole Bay Marina added 100 amp, 3-phase power to our slip on A dock in June of 2007.
We are hoping to replace our two 50-amp 240V cables with a single cable, as one of our 50 amp cables is 130' long to allow us to draw from two power pedestals on opposite ends of our 100' slip. The 50 amp shore power cables are long, heavy, and difficult to store in the lazerette when leaving our home dock, and long, heavy, and difficult to deploy when returning home. We often left the two cables on dock when cruising for the day - hoping no one would steal them.
The first option we considered was to purchase and install two
Glendinning 50-amp cablemaster units to automatically extend, retract and store our shore power cables. It would make our lives easier today, and in the future when we are too old to lift the heavy cables. I estimated the cost to purchase two units and install them to be about $15,000. Installation would involve running a conduit through the fresh water tank, associated cable glands, paint repairs, 24V DC power feeds, DC circuit breakers, etc. In addition to avoiding the mess of construction (and violating the marina's rules against welding in our slip), we really didn't want to spend $15,000 right now.
The previous owner left us a collection of parts to build a 100 amp 3-phase shore power cable, approximately 130' long. Well, almost all of the parts. The cable contained four 2-gauge wires, not five. One connector was missing a cable strain relief, and other other was missing the locking ring. Finally the 100 amp. cable is black - black cables leave marks when pulled around corners, over decks, through hawseholes, etc. We have a 100-amp 3-phase shore power inlet on the boat, but since it is not connected to an isolation transformer, we only use it while hauled out. Could we use a Y-cable/splitter to feed two 50-amp 240V inlets on the boat? I've seen splitters to service two 30-amp 120V cables from a single 240V 50-amp outlet. Someone must certainly build a 100-amp 3-phase splitter to service two 50-amp 240V feeds! We could permanently attach the 100 amp. cable to the dock, and only use the 50-amp cables when visiting a guest marina.
I searched and searched but failed to find one. Charles Marine does not make one, neither does Marinco or Hubbell. I located 100-amp reverse Y adapters, but not splitters. I would have to build one. I needed:
1 non-metalic NEMA enclosure (10"x8"x6") & SS subpanel
1 splice block
1 3-phase 100-amp receptacle
10' of #4 wire
25' of 4 conductor #6 wire
2 50-amp 240V connectors
2 50-amp weatherproof covers
5 #4 x #10 lugs
8 #6 x #10 lugs
shrink-wrap
2 cable glands
miscellaneous fasteners
We've spent about $1600 thus far. We still need a strain relief and a locking ring.
Since the original cable contained 4 wires, not 5, I left out the neutral leg, attached cables to the 3 hot feeds + ground, and the two isolation transformers will supply the neutral service for our 120V service.
I am not a certified marine electrican, but I managed to assemble the splitter over an 8 hour period. Now, the exciting moment! 100 amps of 3-phase power is a scary monster. I turned off the circuit breaker on the pedestal, plugged in the honkin' 3-phase plug, turned on the circuit breaker, and ran back to the box (130' away) to see if anything was smoking. I reached the box, nothing is smoking. Using my trusty multimeter, I checked the voltage across the each of the 3 hot legs - each should be about 208V AC. All of them were 0 volts! 0 volts? After checking the breaker on dock, it disconnected the 3-phase plug from the pedestal. I metered the receptacle on the pedestal directly. Everything was working properly: 208V hot to hot, and 120 hot to neutral! Again I inserted the plug, but this time I noted that it was too easy to insert. I recalled that a 3-phase plug is usually difficult to insert into the receptacle. I opened the shore power pedestal and discovered that the force required to insert the plug broke the inner workings of the receptacle. This is the first time this pedestal was used. I reached into the pedestal, held the receptacle in place, and partially inserted the plug.
After turning on the pedestal circuit breaker, I again ran back to the box to see if anything was smoking. As I was running back, I could hear a really loud hum. What the heck is going on? As I was approaching, I was trying to figure out what could be humming. The two output 50-amp cables were not plugged into anything, so it couldn't be the isolation transformers. As I reached the back deck, I noticed that my neighbor was using a power tool which was the source of the humming. Using the multimeter, checking the voltage across the each of the 3 hot legs confirmed that each was about 208V AC. Success!
I reported the malfunctioning 3-phase outlet on the pedestal to the marina staff. Hopefully they will replace it soon. Until then, we get to look at my hard work and $1600 worth of parts laying on the aft deck....
Update:September 2007
We have successfully connected to the 3-phase 208V / 100 amp service on A dock! You will remember that while attempting to insert my plug into the receptacle, I applied too much force and disassembled in inner workings of the receptacle. I immediately reported this to the marina staff, and a new saga began.
I believed that Hubbell was the gold-standard in marine shore-power connectors; products from other manufacturers should be compatible with Hubbell; hence my Hubbell M5100P9 plug should work with the marina's receptacle. I began to suspect that my plug was damaged, thus preventing it from successfully mating with the marina's receptacle. Or perhaps was the new 100 amp receptacle on A6 was defective?
Apparently the new 3-phase, 100 amp receptacles installed on A dock are not compatible with a Hubbell M5100P9 plug. The marina staff, their electrician, and I were all surprised. I verified the incompatibilty after purchasing a new M5100P9 plug from Fisheries Supply, walking around the marina with Shilshole support staff, and attempting to (unsuccessfully) mate it with various newly-installed 100 amp 3-phase receptacles.
After successfully working with the Marina staff for a few weeks, they swapped out the incompatible 5-pin receptacle for a Hubell model M5100R9 receptacle and we were able to sucessfully mate our plug with the marina's pedestal.
