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Old 09-03-2016, 07:41 AM   #1
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shore power cord problems

Two questions:
  1. How do you prevent the condition shown in the pictures below? It used to happen to my sailboat, and it now happens to my trawler.
  2. I hear RVs have surge protectors. Is that something I should add to my trawler?
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Old 09-03-2016, 07:57 AM   #2
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The black carbon deposits are a sign of arcing (sparks). Both your cord and the inlet are beyond repair and should be replaced. Replacing one won't work, the other one will quickly ruin the new one.

How to prevent it? To start with, always, without fail, turn off the breaker on the dock pedestal before connecting or disconnecting the cord. If there's no breaker on the dock pedestal, turn off the main breaker on your boat before connecting or disconnecting the cord. Unplugging the cord when electricity is flowing is sure to generate an arc and that causes what you see.

Sometimes we see this damage on the male end of the cord and that's caused by a faulty outlet on the dock pedestal. That's more difficult to deal with because it belongs to the marina. Use a different outlet or ask them to replace it.

Other things to do: Don't drop the ends of the cord in the water, especially salt water. Don't leave them out in the rain when not in use.

Applying a coat of dielectric grease to the pins and sockets is a good maintenance procedure as it will shield the contacts from corrosion but still allow electrical contact. Dielectric grease is an insulator but the action of plugging in the plug wipes the grease from the actual contact surfaces.

Screwing on the ring helps hold the plug steady so it doesn't wiggle and loosen. Strapping the cord to the boat a foot or two from the plug also helps to remove strain and movement.

In the end, you should plan on replacing these things every several years.


I've never seen a surge protector on a boat or one in a catalog intended for a boat. I wouldn't worry about it.
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Old 09-03-2016, 08:01 AM   #3
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That damage has nothing to do with surge.


The traditional twist lock 30 amp connector has a number of deficiencies in marine use: connector comes loose which reduces contact, contacts are too small to carry full current continuously, salt environment makes connections less reliable.


One solution is the Smartplug, a positive locking, enclosed connector with more contact area. See Home -.


Another is Marinco's EEL connector. See EEL Cordset, 30A 125V, Yellow, 50' | Marinco


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Old 09-03-2016, 08:09 AM   #4
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Here is some interesting reading for you on this subject...
Rod is a very bright guy.
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Shore Power Cords - SmartPlug vs. 1938 Photo Gallery by Compass Marine How To at pbase.com
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Old 09-03-2016, 08:22 AM   #5
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Applying a coat of dielectric grease to the pins and sockets is a good maintenance procedure as it will shield the contacts from corrosion but still allow electrical contact. Dielectric grease is an insulator but the action of plugging in the plug wipes the grease from the actual contact surfaces.
How often do you apply this grease?
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Old 09-03-2016, 08:28 AM   #6
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This is caused by resistance in the electrical connection while trying to draw a heavy load. Resistance can be caused by corrosion, arcing and loose wire connections. I recorded temperatures this summer on my standard 30 amp connection saw a 30 degree temp rise above ambient when carrying a 27 amp load for 30 minutes. Replaced the standard Marinco hull inlet and still had a 19 degree temp rise. Ordered a smart plug inlet $$. Replaced that inlet with a smart plug and had a 3.5 degree temp rise. We cruise full time and have been in about 30 different slips since the first of this year. About 80% of the time the power post breaker is on when we go to connect our cords. Naturally I turn it off before connecting, but this tells me that 80% of the time people are "hot plugging." That leads to arcing, arcing creates burns which have high resistance and that causes heat. I am also amazed at how many people do not close the cover on the hull inlet when under way. that allows salt air/spray etc lead to corrosion. Also am always surprised how few people use the locking ring to seal the 30 amp hull inlet: if you don't use the locking ring water gets in and creates corrosion. I use electric conductive pate on my plug spades if I am forced to plug into a suspect dock power pedestal. I have written about this for SAIL and Chesapeake Bay Magazine. Have a follow up article on the Smart Plug performance due out this winter.

https://dl.dropboxusercontent.com/u/...ng%20along.pdf
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Old 09-03-2016, 08:33 AM   #7
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Have found that this problem is caused by using to many heavy amp devices,a/c and water heater on one circuit. Would replace both ends and try to regulate your loads so you don't draw too many amps. The ground wire cannot take the load of two heavy devices. Since watching my loads I have had no problems since.
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Old 09-03-2016, 08:44 AM   #8
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Have found that this problem is caused by using to many heavy amp devices,a/c and water heater on one circuit. Would replace both ends and try to regulate your loads so you don't draw too many amps. The ground wire cannot take the load of two heavy devices. Since watching my loads I have had no problems since.
That plug is used exclusively for the air conditioner (which died 3 weeks ago) so there is no way to regulate the amperage draw through that circuit.
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Old 09-03-2016, 08:53 AM   #9
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Is there any information comparing the EEL plug to the Smart Plug? Casual observation shows more EEL Plugs around our local docks than Smart Plugs. They seem easier to use as you don't need to replace the boat or power post plugs. Thoughts?
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Old 09-03-2016, 09:40 AM   #10
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One solution is the Smartplug, a positive locking, enclosed connector with more contact area. See Home -.
Works for me!
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Old 09-03-2016, 09:42 AM   #11
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Note the "thermostat" feature
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Old 09-03-2016, 09:44 AM   #12
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That plug is used exclusively for the air conditioner (which died 3 weeks ago) so there is no way to regulate the amperage draw through that circuit.
Why did the A/C die? Could it have been pulling a very high amp load before it died?

After you replace the cord (30a cords are cheap) and boat side receptacle, you need to meter the loads on that cord. If it's consistently at or over 80% of the 30a max load rating of you current cord, you should consider changing over to a 50a 250/125v cord system.
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Old 09-03-2016, 09:47 AM   #13
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If you stick with the 30a cord, unplug both ends and check them regularly and spray all the contact points with Boeshield or something like it as needed. Or at least a few times a year.
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Old 09-03-2016, 10:02 AM   #14
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Is there any information comparing the EEL plug to the Smart Plug? Casual observation shows more EEL Plugs around our local docks than Smart Plugs. They seem easier to use as you don't need to replace the boat or power post plugs. Thoughts?
The EEL plug is certainly easier to use than the standard threaded ring plug, but it suffers from the same limited contact area of a NEMA L5-30 connection. See attached.
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Old 09-03-2016, 10:04 AM   #15
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Originally Posted by hmason View Post
Is there any information comparing the EEL plug to the Smart Plug? Casual observation shows more EEL Plugs around our local docks than Smart Plugs. They seem easier to use as you don't need to replace the boat or power post plugs. Thoughts?

The Eel plug has exactly the same "Guts" as the standards 30 amp hull inlet and cord end. So far as I can tell, his design was simply a way to make it easier for people to lock the plug to the hull inlet. It has no improved load carrying ability.
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Old 09-03-2016, 10:06 AM   #16
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Why did the A/C die? Could it have been pulling a very high amp load before it died?
Yes, that is very possible. The a/c tech who examined the dead Lunaire air conditioner said that the compressor was shorting to ground. There were also some scary melting wires in back of the control panel. It was not a happy a/c. I now have a new Ocean Breeze a/c sitting on the floor of my main cabin, waiting for me to install it this weekend.
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Old 09-03-2016, 10:08 AM   #17
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If you stick with the 30a cord, unplug both ends and check them regularly and spray all the contact points with Boeshield or something like it as needed. Or at least a few times a year.
So, inspect the shore power connector and re-apply the spray twice a year. Is that correct?
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Old 09-03-2016, 10:15 AM   #18
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Yes, that is very possible. The a/c tech who examined the dead Lunaire air conditioner said that the compressor was shorting to ground. There were also some scary melting wires in back of the control panel. It was not a happy a/c. I now have a new Ocean Breeze a/c sitting on the floor of my main cabin, waiting for me to install it this weekend.
Before you install the new AC, You really need to check and maybe replace wire and breaker between the dead 30 amp receptacle and the AC unit. If you cooked the receptacle and power wires within the AC, good chance there is overload damage elsewhere.

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Old 09-03-2016, 10:22 AM   #19
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Two questions:
  1. How do you prevent the condition shown in the pictures below? It used to happen to my sailboat, and it now happens to my trawler.
  2. I hear RVs have surge protectors. Is that something I should add to my trawler?
Newer boats have a breaker right after next to the boats shore power out let between the out let and the main panel selector switch to protect the cord and out let. Older boats do not have the breaker. We updated our electrical with a smart plug for addition safety.
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Old 09-03-2016, 10:27 AM   #20
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If you stick with the 30a cord, unplug both ends and check them regularly and spray all the contact points with Boeshield or something like it as needed. Or at least a few times a year.
This is good advice, and we consider it standard practice. If you cruise a lot you will sometimes get to marinas with questionable dock receptacles. Eventually one of them will overheat and damage your cord end despite the care you take of your own cord.
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