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Old 07-27-2015, 06:53 AM   #1
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Hot power cord

Looking for electrical coaching SVP !

I have just noticed an electrical issue that I am quite concerned about. My 30 amp shore power cord has scorched one of the three prongs while at the same time, I have two on-board electrical heaters (new) and both cords are quite hot after being plugged in for a short period of time. I have since stopped using them until I get to the bottom of this.

Any ideas would be most welcome

Thanks in advance

Zoom
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Old 07-27-2015, 06:59 AM   #2
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If cheapo heaters....their cords are barely adequate to begin with and will get hot no matter what you do, except rewire with heavier wire as I have done occasionally.

A 30 Amp circuit will not usually handle 2 - 1500 watt heaters on full and much of any other load like a hot water heater. All 3 at one time will usually trip the breaker.

Once a plug is scorched, and the dockside receptacle should be replaced as both may be compromised enough that it will always be a higher resistance connection now.

That's why I upgraded to a 50 amp setup...I think the 30 amp plugs are almost dangerous in design and having spare juice is better than not enough.
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Old 07-27-2015, 07:06 AM   #3
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Thanks for the quick reply sir. I have considered going to the 50amp side, however, I need to understand the problem before making that move. Concur with your heater comment, nonetheless, this does not answer the hot power cord issue. Thanks again.
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Old 07-27-2015, 07:22 AM   #4
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Smart plug is a good way to go on shore power cords. Twist lock receptacles are old technology, and by design will cause failures.

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Old 07-27-2015, 07:37 AM   #5
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Thanks for the quick reply sir. I have considered going to the 50amp side, however, I need to understand the problem before making that move. Concur with your heater comment, nonetheless, this does not answer the hot power cord issue. Thanks again.
Zoom
Take the heaters home and plug them in and see if the cords get hot.

If not then the issue is that they are on the verge of over loading the circuit on the boat. And you may have other resistance issues with the wiring on your boat.
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Old 07-27-2015, 07:43 AM   #6
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Here is a link to a good discussion of the shore power cord problem.

Shore Power Cords - SmartPlug vs. 1938 Photo Gallery by Compass Marine How To at pbase.com
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Old 07-27-2015, 07:51 AM   #7
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Cold at home, suspect you are on the right track with your analysis. Not sure where to start. Someone mentioned outlets are old and need replacing. I might swap one out and see what results yield.
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Old 07-27-2015, 08:34 AM   #8
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Low voltage will cause excessive current on the fan motor causing hot cords. Bad connections are one of many reasons .
You could try a different dock connection and measure the voltage
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Old 07-27-2015, 08:37 AM   #9
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First unplug the boat from dock power. Next pull the receptacle out of the boat and look for scorch marks on the wires, It is usually the white on that burns. If burned, get a new receptacle. It is looks OK tighten each screw. What normally causes hot plugs is loose wires in the plugs, especially the one on the boat. The heating and cooling as heaters and A/C's go on and off cause the connections to expand and contract which over time will cause the screws to work loose and get hot as they arc.

Best is to replace both the boat receptacle and the cord plug and then check the tightness of the screws every few months.
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Old 07-27-2015, 12:13 PM   #10
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Low voltage will cause excessive current on the fan motor causing hot cords. Bad connections are one of many reasons .
You could try a different dock connection and measure the voltage
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First unplug the boat from dock power. Next pull the receptacle out of the boat and look for scorch marks on the wires, It is usually the white on that burns. If burned, get a new receptacle. It is looks OK tighten each screw. What normally causes hot plugs is loose wires in the plugs, especially the one on the boat. The heating and cooling as heaters and A/C's go on and off cause the connections to expand and contract which over time will cause the screws to work loose and get hot as they arc.

Best is to replace both the boat receptacle and the cord plug and then check the tightness of the screws every few months.
Great advice! If the dock receptacle is scorched, replace it. If the boat receptacle is scorched, replace it. Replace the scorched plug end and be sure to cut back into the good wire on the cord if replacing the end only.

High resistance from a bad or corroded connection can cause a drop in voltage. A voltage drop will result in more amps being drawn which can cause overheating. Fix your resistance problem and you'll more than likely fix your overheating problem.

I recently noticed that my shore power cord was a bit warm near the dock box. The prongs were just starting to show signs of corrosion. I sanded the prongs, cleaned them with an electrical contact cleaner and reconnected. All is well.

I run electric ceramic heaters but only operate them on the low setting which is 600W. The higher setting (1200 or 1500W) is too high for my 30A service.
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Old 07-27-2015, 02:43 PM   #11
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Thanks, sage advice. I will try that
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Old 07-27-2015, 05:25 PM   #12
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All good advice. I would also add: do you have a fridge? Do you have a battery charger? Hot water tank? All of these will overload your 30 amp service. When you have the boat plugged in AFTER you repair the plug, an easy test is to plug your multimeter into a 120 boat socket. I'll bet your voltage is down under 100 volts, which is an easy way to test for overloading. If you do not have 120 volts, you are looking for trouble beyond burnt connections.

Sadly, 30 amps is very small.
Heater 1500
Water heater 1500
Battery charger 1500
Fridge 500
Toaster?
Water pump?
Kettle?
Lights?
Cell phone charger?
USB sockets?
5000/12=42 amps plus. Altogether it would blow the breaker. Unfortunately, as you've seen, the breaker does not blow at precisely 30 amps and there is a lot of room for overloading before it does.

The Smart Plug is great for the boat connection but it is only useful for the dock connection if the marina will allow you to have it installed in their equipment. Visiting many marinas, you will have to use a conventional cord.
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Old 07-27-2015, 08:20 PM   #13
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The problem with a Smart Plug is that it connected to the boat exactly the same way as a regular boat inlet plug. It is better at the cord/boat connection point but the wires from inside the boat attach to the Smart Plug the same way they attach to a regular plug and thus are subject the same arcing caused by a loose connection at that point.
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Old 07-28-2015, 06:19 AM   #14
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Resistance from any part of the circuit causes heat and voltage loss.

Chop the ends of the power hose and use Hubbel ends to replace the molded on cheap junk.

Use a VOM ( $ 7.00 in Wallmart) to measure the Volts at the power post , then measure the V at each heater. A big drop is a problem.

Use a temp sensing lazer gun to see if any connections you can find are hot.

To live well on 15 or 30A of 120 can be easily done , but a load shedding system will need to be installed.

Heating with electric is only worthwhile if the dock does not charge for electric.

Full 30A draw could cost 75c to a buck an hour , 24 hours a day!
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Old 07-28-2015, 10:09 PM   #15
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With all this heating, have you asked yourself why you are not blowing breakers? Think about it.
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Old 07-29-2015, 08:15 AM   #16
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Great note. Thank you for your input
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Old 07-29-2015, 08:20 AM   #17
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Thanks for all of the input.

I have narrowed it down to a poor connection on the 30amp house side and have now switched over to the 50 amp side with clean and stable power.

As for the heaters, we have determined cheep heaters with cheep wiring. No more too it than that. Reworded one with a bit heavier cord, and it works very well.

Thanks for all of the replies.

Best regards

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Old 07-29-2015, 08:52 AM   #18
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Many great mentions here.

With our 30 amp system that has amp and volt meters on electric panel we simply make sure to keep it down to 20 amps max for a very short period (usually we have it under 15 amps) on meter by alternating boat items on/off while utilizing electric features... whether on dock plug or running gen set.

Wally World cheap electric heaters should never be placed on high heat setting - IMO, because they are actually not designed to well-handle that amperage for long periods.

Stay appraised of the amp draw, keep it at least 33% below boat's max, and make sure electric connections are clean/tight. That's how I play it!

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Old 07-29-2015, 09:00 AM   #19
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Cannot agree that you need a safety margin on power cords, it is already built in...just keep them clean, corrosion free and snug.

That's from over a decade of living aboard and a lot of it in Mid Atlantic winters.

Depending what heater from Walmart or any box store.... have been using them for decades on high without fire or more than slightly warm cords. Again, it may be another reason...but not the heater themselves.
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Old 07-29-2015, 09:22 AM   #20
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Cannot agree that you need a safety margin on power cords, it is already built in...just keep them clean, corrosion free and snug.

That's from over a decade of living aboard and a lot of it in Mid Atlantic winters.

Depending what heater from Walmart or any box store.... have been using them for decades on high without fire or more than slightly warm cords. Again, it may be another reason...but not the heater themselves.
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