Need Help: AC Powercord (female side) Is Burned

Ross · Dec 4, 2008

I will presume a 30 amp power cord. 2-1500 watt heaters will draw about 25 amperes, the 100 watt lamp ---1 amp, the dehumidifier 4-6 amps. Based on just that I would say that you pushed the limits. I would install a 30 main breaker and then the branch circuit breakers.

J Page · Dec 4, 2008

I think your diagnosis was spot on. Even though the panel breakers never tripped all that power at once is not designed to go through a single shore power inlet. that's the reason larger boats have 2 sometimes 3 inlets feeding different panels to handle the load. The power split off at the panel and , now I'm guessing, dropped enough that any one breaker didn't trip( too bad too as this may have dropped total power too the point to avoid the damage). Good news is you didn't have a fire. Bad news is I would no longer trust the inlet, all wiring that leads to the panel, check the lead into the panel(the bussbar where the main wires comes in) and possibly the panel itself, but I doubt it. Hire a good marine electrician to check it, give you a quote and a guide of what needs fixing, and decied if filing a insurance claim is right or not. BTW if you do file the claim, plan on getting a new company as your will probably get dropped. If it's under a grand or so, bite the bullet and pay it.

Just my opinon, Mainsail or Ross may be helpful people to talk to.

Lugeman

Ross · Dec 4, 2008

A worn power cord connection can over heat without being overloaded. Note how tightly a new power cord fits a new receptical and how sometimes an old receptical will not hold the plug of an extension cord.

Roger Long · Dec 5, 2008

Ross said:
A worn power cord connection can over heat without being overloaded. Note how tightly a new power cord fits a new receptical and how sometimes an old receptical will not hold the plug of an extension cord.

I would second that and check out the whole system before getting too excited. You were drawing too much but outlets around salt water lead a hard life. People drop cords in the water, blow on them (maybe) and push them into the sockets. Corrosion starts and increases resistance. The metal gets hot at that point and corrodes further, raising resistance, creating more corrosion,..... round and round until it burns. Meanwhile, the resistance and voltage drop prevents the breaker from tripping. This is what starts fires.

The good news its that damage is probably limited to the socket and cord. Check everything but you'll probably only need to replace the socket and cord.

sailingdog · Dec 5, 2008

The problem is two-fold.

First, as pointed out above, you were probably drawing far too much power. Running TWO 1500 watt heaters on-board by themselves is a really bad idea if you only have a 30 Amp service. Electrical systems are really not designed to run at above 75-80% of their rated load for extended periods of time. A 15 Amp circuit should generally not have more than about a 12 amp load on it for any extended period of time.

Second, chances are good, especially on a saltwater boat, that there was some corrosion of either the cord end or the shore power inlet on the boat. That adds resistance. Also, in many cases, if the cord is an older one, the connection it creates won't be as tight as it should be, creating even more resistance. These two things combined with the excessively high loads you placed on the shorepower line are probably the cause of the damage to the end of the cord and the inlet.

Replacing your shorepower cords on a regular basis as part of your maintenance routine is not a bad idea IMHO. I would also highly recommend getting a heavy duty shorepower inlet and replacing the inlet, the cord and at a minimum, checking the wiring that leads from the cord inlet to the main AC breaker panel—replacing it if the insulation is at all damaged, or if the wire is not marine-grade tinned wire.

One other possible problem is that the shorepower was running at slightly lower voltage than is normal. If the shorepower voltage is less than 120 VAC coming out of the post, the amperage required to run all the gear would have been higher to compensate... making the situation worse. I'd highly recommend at least checking the shorepower outlet on the dock to see what voltage it is at.

Ross · Dec 5, 2008

Even a 2 volt drop at the cord /inlet connection at 30 amps would be a 60 watt heater. Think 60 watt incandescent light bulb as to the heat that 60 watts can generate.

Bill Roosa · Dec 5, 2008

Saildog!

I don't know where you got your electrical engineering degree but when you DESIGN an electrical circuit to handle 30 amps that implies that you would have a factor of safety so that it can in fact handle it's designed current. I think that is why they put (in this case 30 amp) circuit breakers in them (and not 25 amp ones). That way the CB pops BEFORE you get to the actual current handling capabilities of the cabling.
With that said, circuits on boats are subject to corrosion to a much greater degree than house/industrial circuits. Like Ross said "a 2 volt drop is like a 60 watt heater concentrated right at the plug"
I have 2-1500 W heaters on a 30 amp plug and have been running them full time for the past month. I did have some initial corrosion issues which caused some concern but after repairing them they work fine.

sailingdog · Dec 5, 2008

Bill-

I'm not talking about the cabling. I'm talking about the breakers and connections. In an ideal case, you could run 30 amps through it all day long... however, most marinas don't have ideal conditions for their wiring. The power post usually has less than ideal voltage coming out of it, the connection at the post end of the shore power cable is usually less than perfect, the connection at the boat is usually less than perfect, etc... Add up all the voltage drops and unintended resistance, you usually end up with lower voltage on the boat, which in return leads to higher amperage draws than intended.

In your case, you qualify running the two 1500 Watt heaters with:

I did have some initial corrosion issues which caused some concern but after repairing them they work fine.

However, most people don't do that... hell, most don't even inspect their shorepower cable or inlet before connecting the two.

Also, in the US at least, most of the Electrical code calls for derating a breaker to 80% for continuous loads—ie, a 20 Amp breaker should only be run with 16 amps of continuous loads, where the maximum load is on for a duration of three or more hours. A cold boat, stored outdoors in sub-freezing temperatures would probably considered a continuous load situation. See HERE for more information regarding this.

Advising them that running two 1500 Watt heaters is going to be fine is foolish at best, unless they've gone and replaced all the questionable portions of their shore power setup.

tommays · Dec 5, 2008

You dont need a degree to know that 80% is a well know safe level for circuts

As far as heaters anything over 1000 watts puts a lot of stress on any 15 amp plug and receptiacle which is why they burn so many houses down and portable electric heaters are NOT LEGAL in comercial buildings in this area

walt · Dec 5, 2008

An unimportant correction to useful posting.

A resistive load such as a space heater will have lower current if the voltage drops (ohms law). Voltage drop = current drop = power drop (power drops off with the square of voltage).

It is generally switching type electronics which can preserve output power so if voltage drops, current is raised.

As I mentioned, a completely unimportant detail..

sailingdog · Dec 5, 2008

Good point.. inductive loads generally increase amperage with voltage drop... resistive loads decrease amperage... I should have clarified that...

walt said:
An unimportant correction to useful posting.

A resistive load such as a space heater will have lower current if the voltage drops (ohms law). Voltage drop = current drop = power drop (power drops off with the square of voltage).

It is generally switching type electronics which can preserve output power so if voltage drops, current is raised.

As I mentioned, a completely unimportant detail..

Bill Roosa · Dec 5, 2008

I'm hip saildog!

I don't think there are many folks that give 120 volt current its proper respect. We can probably thank the code guys for that BTW.
I guess I feel that if you understand the situation you can get better (and cheaper) performance out of it. Having an AC volt and amp meter so you can tell what you are getting when you plug in are key to not setting yourself on fire. When I see the voltage drop off on a circuit I begin to start looking for a hot spot or listening for someone up the dock using his power tools.
On another note, how does lower supplied voltage result in higher amps in a purely resistive (heaters not motors) circuit? For the record, most of my AC loads are resistive and not inductive. In fact I think the only inductive load I have is the battery charger.

Dan Johnson · Dec 5, 2008

Good diagnoses, now a solution...

You're in luck, Joe. I'm replacing the male end on the spare shore power cord on the boat I race on. Defender has these the parts for the male and female ends on page 296-7 of their current catalog. Under $40 plus shipping--a lot cheaper than a new cord, assuming the cord itself is still safe to use.

Cut off the old end about a foot back to get away from any fried wiring. Replace both the socket and cover with lock ring with new units for peace of mind.

Seriously consider replacing the boat side male connector unit too, given the circumstances of your problem. Check the wiring connected to it to be sure you didn't fry it as well.

Lastly, consider running the heaters on a lower setting or acquiring new ones that are rated at 1,200 watts max.

tommays · Dec 5, 2008

And if you fix up say your kitchen watch out when the bring it up to current code

Which requires a circut for everthing fridge ,micro ,dishwasher ,ect ,There is now more power in my kitchen than (5 20 amp and 1 15 ) than the house had when it was built with a 50 AMP service

I somehow now have 26 breakers in a pretty small house

Bill Roosa · Dec 5, 2008

3000 watts on 30 amps

My advice about running 3000 watts on 30 amps is indeed dangerous for anyone who does not know what he is doing. By my calculations I am pushing my circuit (the shore plug to panel one not the branch lines) to 91 percent RATED capacity. I also know that the actual capacity of the cabling and plugs is more than that because I tested (heaters, coffeepot and microwave on at the same time) the circuit so I would know. In the process I saved myself the cost of installing an additional shore circuit and the marina the cost of an additional shore outlet.
I would also not run my car at 6000 RPM unless I was sure that it was in good working order.
I believe my problem with this whole issue is people are becoming more and more ignorant about just about everything you can think of. They don't understand and so can't take the proper precautions. But worse than that, they don't want to understand. They do want someone else to take the responsibility for them and that smacks against what I call "being a sailor". No one is going to pull your arse from the fire when you are way out in the middle of the ocean so you had better be prepared.
If you are going to start plugging high wattage devices into a low wattage circuit you better know what you are doing. The fact that smart folks burn down their homes every winter using their space heaters proves my point.

Bill Roosa · Dec 5, 2008

3000 watts on 30 amps

Just another form of natural selection

As John Wayne said in "True Grit": "Life is tough, it is tougher if you are stupid"

For the record, I don't think anybody on this posting is stupid. The guy that burns down his boat by plugging in 3000 watts of heaters into his under maintained 30 amp electrical system however.....
The guy that takes his Plymouth Speck to 25000 RPMs in first gear however....
The guy that lets his kids stick their hands under the running lawn mower however....
The guy that does not look both ways before crossing the street however...

I don't know how to identify stupid people. I assume that folks will use an abundance of caution when they don't KNOW what they are doing.

sailingdog · Dec 5, 2008

Bill-

The problem is that a lot of people don't know that they "don't know". And as such, can't figure out what the problem is. Someone who doesn't have a clue reading your posts is likely to do something that will get them in trouble. I generally write for the lowest common denominator and assume that the person isn't as knowledgeable about the system as I may be. You apparently don't share that concern.

I'd also point out that whether or not a circuit is designed to handle 30 amps, and whether it can handle 30 amps in the real world are two totally separate things. Many times, the circuit is designed to handle 30 amps, but in the real world, asking it do so would be less than wise.

Bill Roosa said:
Just another form of natural selection

As John Wayne said in "True Grit": "Life is tough, it is tougher if you are stupid"

For the record, I don't think anybody on this posting is stupid. The guy that burns down his boat by plugging in 3000 watts of heaters into his under maintained 30 amp electrical system however.....
The guy that takes his Plymouth Speck to 25000 RPMs in first gear however....
The guy that lets his kids stick their hands under the running lawn mower however....
The guy that does not look both ways before crossing the street however...

I don't know how to identify stupid people. I assume that folks will use an abundance of caution when they don't KNOW what they are doing.

Ross · Dec 5, 2008

There are seveal factors to consider when designing a circuit. For example No. 10 wire is rated for 25 amps load. But No. 10 wire has a resistance of 1 ohm per 1000 feet. So if the distance from your circuit box to your shop is 1000 feet and you feed the distribution panel with No.10 wire from the box and draw 25 amps you will find that you are only getting 95 volts at your machine. Your motors won't last long that way. For this reason you run 220 volt service at 12 amps or you go to No. 6 or 8 wire.
A friend ran a string of small christmas lights from a 300 foot long No. 16 extension cord. Someone cut the end off the extension cord and stole the lights. Cutting the extension cord of such long length didn't trip the circuit breaker because the drop in the wire limited the current.