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ContinuousWave: Small Boat Electrical
Shore Power Cords
|Author||Topic: Shore Power Cords|
posted 04-19-2008 01:32 AM ET (US)
I finally got a slip in Sitka and am little confused how to SAFELY use the 30AMP hook-up. My 25' Revenge certainly doesn't have a shore power package and rumor has it that I need a Ground Fault Circuit at the end of a 30amp extension cord if I use one. There is a great breaker on the dock side, about 25' away. I talked to someone in Juneau today that mentioned a Hubbel connector that may cost $300.00 (ouch). All I need is some 110v. to intermittently run a heater or a few lights to keep any moisture down.
Thanks for your help. If some of you guys up here in the southeast, Anyone know how to best deal with this please advise me.
Still waiting for the Kings in Sitka.
posted 04-19-2008 06:57 AM ET (US)
you can buy a Hubbell 15/30 amp adapter for less than $50. I've used one for years.
posted 04-19-2008 09:08 AM ET (US)
I made my own shore power cord. Here is the procedure:
--go to a big-box hardware supply, like Home Depot or Lowe's
--find a nice 50-foot AC extension cord of suitable conductor size
--find a twist-lock connector to match your marina
--cut off the standard plug on the AC extension and install the twist-lock plug
If you want to run a heater the cord will need to be sized to handle the current. I am guessing the heater will be about 1,200-watts; that is about 10-amperes. Get at least 14-AWG. Get a cord with yellow insulation (so it matches the other boats). Get a cord which has a built in indicator lamp in the receptacle end that shows power is present. I cannot tell you how handy that will be. It will show you when you've found an outlet with power; in some marinas not every outlet is hot. You can buy the cord at the big-box store for about a third of the price of the marina store.
Most marina power outlets use a 120-VAC, 30-A, twist-lock receptacle; it is almost a universal standard. You can buy the mating plug for $15 to $20 at the big-box store. If you do not know how to wire it correctly, abandon this whole project. For the few places where a 30-A twist-lock is not used, you ask to borrow the marina's adaptor.
If you need a ground fault interrupter, you can sometimes find them as part of the extension cord assembly. I have also seen them in short extension cord
In the real world, you do not have to have a cord rated for 30-amperes to plug into a 30-ampere outlet, as long as you don't connect a load that is larger than the cord itself can carry. In my case my load is only a 500-W coffee pot, or about 5-amperes. My cord is just a 16-AWG cord. However, this probably violates the official electrical code, so don't expect the local electrical inspector to bless this arrangement.
posted 04-21-2008 02:16 PM ET (US)
I picked up a 30 amp male to a standard 110V female adapter for about $10 bucks a couple of years back from Home Depot. Match this with a suitable extension cord and you are in business. Most docks have a breaker at the point of connection for each slip, so you probably do not have to worry about overload protection. Check your dock power to make sure. I would use electrical tape and seal any connections that are exposed to keep out moisture.
As far as GFI, I am not aware of any in-line device that is available, but if this is a permanent set up, I would look into it.
posted 04-21-2008 05:37 PM ET (US)
The breaker that the marina provides is for protecting their wiring up to the outlet. If it is a 30-Ampere outlet the breaker is or should be a 30-Ampere circuit breaker. If you attach an extension cord to the marina's outlet which is rated for less than 30-Amperes, you would not be protected against over-current by the 30-Ampere circuit breaker.
One of the reasons the marine grade power cords are rather expensive is because they contain large wire, typically 10-AWG wire for a 30-Ampere rated power cord.
$102 Power Cord
To be really protected against over-current on a power cord with smaller gauge wire, you should have a circuit breaker with a lower rating in your distribution. The usual ratings are:
10-AWG = 30-ampere
A ground fault interrupted circuit breaker is probably a good idea, particularly in a marina environment.
posted 04-21-2008 06:30 PM ET (US)
Ground fault cord set:
posted 04-23-2008 08:58 PM ET (US)
With all due respect, you took my quote out of context. The preceding sentence was "Match with a suitable extension cord" and I was implying that it should be consistent with the dock breaker. Since the breaker on the dock and the load were not specific, I thought it best to be non-specific on the extension cord.
I agree that the extension cord should be matched to the breaker on the dock.
posted 04-23-2008 09:06 PM ET (US)
I agree, too, the extension should be matched to the breaker on the breaker on the dock, but I have to confess that I plug in my under-sized power cord all the time. I just never plug much of a load into it. My coffee pot is the biggest current draw on the end of that 14-AWG cord.
I suppose I should include my own circuit breaker in my lash up.
I will have to investigate further into the GFI cord set. I wonder if it also has a 15-Ampere circuit breaker in addition to the GFI-trip breaker. That would make it the perfect device.
Another thing to worry about around the marina dock with power cords that are not twist lock plugs might be the possibility that a cord could separate and fall into the water. That would be a nasty situation.
posted 04-23-2008 09:23 PM ET (US)
Does anything need to be done to the cord, or the connection at the boat to help isolate or eliminate the stray current that causes galvanic corrosion?
Also, it seems to me that many marinas in the Lake Michigan area are now offering 240v service. Is there an advantage for wiring to accept that?
posted 04-24-2008 12:13 AM ET (US)
When you connect your boat to the 120-VAC circuit at a marina, you can protect against galvanic currents by inserting a device into the GROUND circuit which creates a small voltage drop across itself. The voltage drop is intended to be greater than the galvanic voltage, so it will tend to stop galvanic currents from flowing on the GROUND. However it is small enough and can carry large current, so in the case of a high-current ground fault it does not affect the GROUND circuit or prevent it from saving your life or gear (by blowing a big 30-A circuit breaker).
The device is usually made from very high current diodes wired back to back. For more information visit the Yandina website. I believe they make such a device and also explain in more detail the problem it solves.
THE GALVANIC ISOLATOR EXPLAINED
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