I need a good extension cord to plug in my batteries at the dock at night. Been awhile since I shopped for one – what do I need to know in terms of gauge, amp, volts, etc?
Any decent brand/price to recommend? Thx!
You need to know (A)the input amps of the charger (or any item you plan to use with this cord) (B) the length of the cord needed. Then you can calculate the gage wire needed to handle the load. Google ” ac wire size calculator” and you should come up with several calculators to choose from.
When buying an extension cord, besides wire size, looks at the ends for quality construction. If you compare different cords with different prices you will begin to see the differences. (Thicker blades on the contacts) I like a round cable rather than one which is “flat”. The flat ones seem to be three wires plus insulation. The round ones will have a couple strands of paper or fiber filaments woven in and around the conductor wires. These filaments help the cord from stretching and breaking the conductor wires inside. Not all round cable cords will have the extra strengthening filaments. Again sometimes you can just tell when comparing them in hand.
Brand-wise, I’m a fan of the Yellow Jackets
https://www.farmandfleet.com/products/160670-yellow-jacket-14-gauge-power-cord.html
Size-wise, like mentioned above, amp draw (size of charger) and length come into play.
HRG
Just remember to do your AC/DC conversions! I wasted a good chunk of time running around trying to find a cord that would handle 50-100′ of 20 amps, because that’s the DC output of my charger! 
I’m thinking of 50 feet, and for my Minnkota charger for 36 Ultrex 112
5FCAA6AF-D468-43C1-A34C-F375C3439855.jpeg
I’m thinking of 50 feet, and for my Minnkota charger for 36 Ultrex 112
The MK manual for your model says 50′ cord should be 16 gage while a 100 foot cord should be 12 gage wire size. That does not mean you can hook two 50ft 16 gage cords together, if you happen to run into a location where you need more length.
Really never a good idea to string cords together. Too many times, one ends up overloading, too small a wire size for the total length involved.
Thx Dave!!
My extension cord has a built in small light at the recieving end that shows that power is at that end-suprisingly handy sometimes.
I have one of these : http://a.co/1TWVBuO . I originally bought it for an electric snowblower, it’s a bit overkill for an onboard charger, but if you get it you have a nice cord that will work for anything in any weather. I would get a 12AWG 100′ because, like Dave said, stringing them together isn’t good when you do need the extra length. The only bad thing about this one is the weight, it’s a beefy cord and you’ll get a workout spooling it on your arm.
Buy the heaviest outdoor rubber jacket-oil resistant cord that you can comfortably afford in nothing less than 12 gauge with quality heavy duty plugs. The extra $20-40 more in cost will easily pay for itself over time. The most common mistake I see is guys using under sized cords with thin cheap plugs and slowly burning their equipment up. Most don’t realize how hard it is on electronic devices – especially motors – to restrict your A/C draw. Additionally, the cord will last MUCH longer.
Nearly all my 100′ cords are 10 gauge and my 50′ cords are 12. With the exception of my 10 gauge cords designated for my compressors. Try to avoid multiple cords plugged into each other. A continuous cord in a heavier gauge is much better. I have a lot of Century brand cords and they have been pretty good.
Oh, and make sure what ever you buy is UL listed!
Here is some jacket info:
Designation Letter Meaning
S
Indicates a flexible cord designed for general use
W
Indicates the cord is rated for outdoor use
J
Indicates the cord with standard 300 voltage insulation. If there is no J in the designation, the cord has thicker, 600-volt insulation, designed for heavier use.
P
Indicates parallel wire construction, used in air conditioner cords and household extension cords
T
Indicates the cord jacket is made from vinyl thermoplastic
E
Indicates the cord jacket is made from thermoplastic elastomer rubber (TPE)
O
Indicates the cord is oil-resistant
I use a 12ga, 100ft waterproof cord with lights in both ends. Always plug it into the boat first, run it to the power source and then plug it in there. That way if you drop it along the way, you don’t drop a live cord in the water.
There are a lot of non functioning outlets on docks. Many times they just need a breaker reset. Lights in the end of the cord are really helpful for knowing if you are going to be happy in the morning.
I don’t know the brand but my 100 foot cord is yellow and black and has lighted end. Have used it a lot for 12 years. Just rolled it in from the dock an hour ago. Ground prong broke off so I need to repair or replace.
Ok I hate to blanket everyone with information but power on docks and by the water is a big issue and seldom done correctly. There are very definite rules that apply and electric shock drownings are becoming more frequent now with the big lake homes and dock systems that seem to be appearing. I will copy and paste some information to give everyone something to read and keep everyone safe.
Shore Power Cords — Proper Use and Maintenance
• All shore power cords should be rated suitable for Marine Use, or better still, “UL-Marine”
listed for marine shore power applications.
• CAUTION — Never use ordinary “outdoor use” extension cords to provide electrical shore
power to the boat or any equipment, such as a battery charger on board the boat. These
cords are not rated for and are not suitable for the severity of a marine environment. They
can deteriorate and/or overheat causing electrical shock, a short circuit or a fire.
• All shore power cords should have male (plug) and female (connector) ends of the locking
type. Make sure that plugs and connector are turned to the full locked position by pulling on
them. If they are properly locked, they will not pull out. A plug or connector not properly
locked will become loose, causing arcing (sparks) on the contacts, resulting in a failure, and
possibly a fire.
• All male (plug) ends must be molded on or have weather-proof boots in order to provide a
weatherproof seal when plugged into a receptacle.
• All female connector ends must have a locking ring to secure the power cord to the inlet on
the boat and provide a weatherproof seal.
• Adapters should always be used at the shore end of a power cord.
• Always make sure that the “Main” circuit breaker on the boat is turned “OFF” before
connecting or disconnecting the shore power cord,
• Always connect the female end of the cord to the boat before plugging the male end into
shore power receptacle. Always disconnect the male end from the shore power receptacle
before disconnecting the female end from the boat.
• Never leave a shore power cord on the dock with only the plug end connected. A live cord
end is dangerous, especially if it accidentally falls into the water.
• Periodically check shore power cords for the following:
• Cuts, cracks or severe abrasions on the yellow cord covering.
• Bent, broken or loose plug blades.
• Plug blades or connector slots that show signs of overheating or arcing, such as:
• Brown or black discoloration on insulation around blades or slots.
• Discoloration and/or erosion of blade material
• Faulty locking rings due to cracking or damaged threads.
• Do not allow cords to be pinched by a closed door or hatch. Pinch points create resistance
and generate heat that can result in a fire.
• Never coil a cord tightly on the dock. Such a coil acts as a heat generator and can cause a
fire. Hang the cord loosely on a hook or support or lay it out in a loose coil of only a few
turns.
• Spray all contacts monthly with an electrical contact cleaner, corrosion inhibitor and
lubricant, such as LPS-1 made by Holt Lloyd Corp. Please note that “WD-40” or silicone
sprays are not appropriate because the film they leave increases contact resistance. The
proper spray types can be found at electrical supply houses or stores such as Radio Shack.
• If a shore power cord should become immersed in water, it should be immediately sprayed
with fresh water, THOROUGHLY dried, and blades and contact slots sprayed with a
moisture displacement before re-using.
From United States Coast Guard Boating Safety Circular 81, December 1999
Extension Cords on Docks and at the Lake
The following safety guidelines should be carefully considered wherever extension cords of any type are
considered for used in, on, over, or near lakes, rivers, or other bodies of water. Compliance with these
recommendations will significantly reduce the risk of an electric shock drowning or in-water electrocution.
Compliance does not, in any case, result in a condition where it may be deemed “safe” to be in the water.
Application and Usage
• General purpose/utility extension cords are designed, intended, and listed for use where connected to 15-
or 20-Amp, 125-Volt convenience receptacles.
• General purpose/utility extension cords should not be connected to any receptacle where the overcurrent
protection is greater than 20 amperes, even though adapters might be available for the purpose.
• General purpose extension cords are intended for use only for temporary, task-oriented applications.
They are not to be used as a substitute for permanent wiring, or for semi-permanent or long term use.
• General purpose extension cords are not be attached to building surfaces or other structures.
• General purpose extension cords intended for use outdoors are specifically identified and marked for
such use. A permanent tag attached to the cord when purchased will indicate the uses permitted.
• General purpose extension cord conductors should be adequately sized to the load served (i.e. 12-, 14-,
16-gauge). 18-gauge extension cords are no longer manufactured and should not be used.
• Where used near water, it is recommended that general purpose extension cords be connected (plugged
into) receptacles that include integral GFCI protection, or receptacles that are marked as being protected
by an upstream GFCI device (receptacle or circuit breaker).
• Do not place extension cords over sharp edges (such as the metal framing on docks) or where they could
be pinched or crushed.
• Where used near water, it is recommended that the GFCI protection be tested, and reset, before each use.
• General purpose extension cords and their plugs and connectors should never be permitted to dangle in
the water or placed in any way that could enable them to fall into the water.
• General purpose extension cords should always be disconnected, removed, properly coiled, and stored
upon completion of the task for which the cord was required.
• General purpose/utility extension cords are not permitted to be used for shore power applications and
should never be used to establish the connection between any shore power outlet and a boat’s shore
power inlet, with or without adapters, when the boat is afloat.
General Condition
• Where used, extension cords must be in good repair; free from modifications, splices, excessive wear,
damage, cracks, abrasion, burns, etc. Do not use cords that have had plugs and connectors replaced.
• Extension cords with worn, damaged or missing grounding terminals should not be used.
• Avoid the use of two-wire, non-grounding type extension cords.
• Do not use “home-made” or user-repaired extension cords.
• Daisy-chaining of extension cords is discouraged, and may be prohibited by the cord’s instructions.
• Damaged extension cords should be removed from service, destroyed, and properly disposed.
Review the Electric Shock Drowning Prevention Association brochure and other electrical safety materials available
at http://www.electricshockdrowning.org and http://www.electricshockdrowningmn.com .
DISCLAIMER
These materials are for informational purposes only and not for the purpose of providing professional advice or instruction. The
information expressed in these materials is not necessarily an exhaustive list of precautions. The author does not guarantee the
accuracy or reliability of the information provided herein. Users of this information are fully responsible for any consequences
resulting from their use of the information.
Sorry to put so much out here but safety is a big thing and none of us want our kids, friends or grand kids jumping in the water and having something horrible happening. Note the code article that says we need an insulated ground to these receptacles feeding power to our docks. Most every dock out there has a UF wire underground form the house to the dock and that is no longer code compliant, as well as how many have their aluminum docks bonded to the power equipment? Non of us?
Not trying to scare anybody but in our profession we see this a lot and get called out several times a year to places claiming to feel a tingling in the water to find bad cords etc. causing the issue.
Sorry for the long articles but be safe everyone. Adds a whole new dimension to getting power to our docks to charge our batteries doesn’t it.
20amp_wd.pdf
NEC-Article-682.pdf
Periodically check shore power cords for the following:
• Cuts, cracks or severe abrasions on the yellow cord covering.
God me on that one!
Most chargers are below deck and sometimes someone will step on a cover with the 110v power cable leading to it.
I found out the hard way when I was disconnecting the power from the charger and slid my hand down the cable just far enough to get a tickle from the exposed hot wire. Apparently I make a good ground because I could see the cut but couldn’t see the bare wire.
Some would tape that up. I recycled it after cutting off the ends. 
Randy is right on with his post. Always buy the heaviest cord you can. If you need to use it for something else in the future you have the peace of mind of not restricting the power and harming your item.
Suzuki, I am not sure why but OSHA will not let you use a cord with a replacement end on it. Might want to get a new cord since it will be around water.
Looks like Kabekonacrazy post answered my question.
First part of the article has to do with marine environment, so saltwater, lots of good information, but not all applicable.
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