Melted 110v Outlet

[Sandero]

YIKES!!!!!!!!!!!
I went to check on the boat yesterday and discovered the shore power not working. After checking the cable and forth I investigated the outlets themselves. There were 3 items plugged into 2 of the 4 outlets on board. They were the first two in the series parallel wiring. In the 2nd outlet was a 1500 watt heater which was OFF. In the first outlet was a work light with a 40 watt bulb which was also switched off and a small air purifier. The first outlet was the site of the melt down. I could not even remove the plugs from the socket.

I unscrewed the cover plate to find a melted outlet with obviously shorted wires... what was left of them. Obviously after the heat and the short... the circuit protection kicked in and the heating ended.. but not before it had seriously melted the socket.

I cut the wires and removed the mess. The wiring was multi strand marine grade 3 conductor AC wire. The individual wires DID show evidence of corrosion (green oxidation).

So what happened?

The shore power was on because it powered the batter charger. This also meant that the 4 outlets were energized whether or not they had items plugged in and drawing current. The three items were not drawing current... They were switched OFF.

Was this caused by the corroded wiring creating lots of resistance and heating? Can *faulty* wiring which is not powering anything but nevertheless *live* cause overheating and this sort of meltdown? Should the outlets have had a breaker? The Blue Sea panel only has breakers for battery charger, water heater and AC main (30 amp). So there's no way to de power the outlets and have the battering charger ON.

Any comments and recommendations?

[Teknav]

Hi! High current demands will cause an outlet and its wiring to catch fire and melt. A broken/corroded wiring can cause a short-circuit, leading to a fire. Check all "loads" on the circuit and make sure that the sum total does not exceed the safe load; aim for a much less load. Shore power needs to be checked, as well; not unusual to be corroded and faulty. Good luck!

Mauritz

[JusDreaming]

This is a very common problem with the twist lock set up. We had replaced our's about every year. It is all about resistance, caused by the small surface of blades on the plug. I could always feel the heat when grabbed with my hand. And the heating started almost immediately. And it did not matter what was turned on, current draw was not the problem. I recently replaced the entire system with
SmartPlug Systems - Shore Power Products and Accessories it is a bit expensive but well worth the peace of mind. I have it installed for 3-4 months under constant heavy current draw and have yet to feel any warmth at all at the boat input!!!!!!!!!!!
FYI I have no connection with the company, just a happy customer

smartplug - Google Search

[Lake-Effect]

Was this caused by the corroded wiring creating lots of resistance and heating?

In a circuit with a substantial load, any point of unexpected resistance - a loose or dirty connection, a corroded wire, a loose crimp, etc - will start to heat... and the heat usually makes the resistance higher, which makes more heat, and it snowballs quickly to complete failure, by burning through, or by melting insulation leading to a full short.

The melted outlet would indicate that the problem was hot enough and continued for a while before the short caused the breaker to trip.

Can *faulty* wiring which is not powering anything but nevertheless *live* cause overheating and this sort of meltdown?

It takes a load pulling current to create the heat. If the outlet wiring was previously damaged by heat, I suppose a short could appear in an unused circuit by insulation crumbling away and create more melting, but it's not very likely. Usually a short blows the breaker/fuse before significant melting occurs.

So, faulty wiring doesn't usually fail like that until current is running through it.

Should the outlets have had a breaker?

ALWAYS!

But the only way to guard against melting from resistance is to do the best possible job when wiring - good wire of the correct size, quality connectors, proper crimps, protection from corrosion, tightened screws etc etc. And try to inspect the electric connections annually for signs of looseness, deterioration, damage, corrosion, heating, etc.

[btrayfors]

Sandero,

Lake-Effect has it exactly right. I would note two additional things:

1. In my experience it's never a good idea to run a 1500 watt continuous appliance (like a space heater) from a common 15A outlet, whether or not it has a 15A breaker. On a boat, there are just too many things to go wrong. I have never run space heaters above 900 watts (about 7.5A AC draw) for just this reason, and in over 25 years of heating over winter with electricity have never had a problem.

2. All your outlets are not created equal, at least they're not likely to remain in an "equal" condition over time. Last year I purchased a handy little tester device which puts several different loads on an outlet, measures voltage drop, and calculates the "condition" of the outlet.

Guess what? Many of mine passed OK at the 15A level, and two even passed at the 20A level...more than they were designed for. But, two outlets didn't even pass at the 10A level. That means a fault in the wiring, or more likely the connections at the outlet.

A friend who is on my dock and is also a marine electrician tested his liveaboard sailboat with the same tester and found that many of his outlets failed at the 15A level!

The moral: keep all your outlets and plugs scrupulously clean and don't overload them. Keep total load way below the rated or maximum load. This is particularly true of 30A shorepower connections, too. There's no way the typical one can really carry 30A continuous without overheating, burning, etc. which we see very often in marinas. A good rule-of-thumb is to keep loads below 24-25 amps and, again, keep contacts clean and tight.

FWIW,

Bill

[smac999]

yes your outlets need a breaker.

are they currently just off the 30a main? In a daisy chained system that means you could have 30a going through that first plug. which is a good cause for melting...

no they can't melt and overheat with nothing pluged in. that melting has likely been slowly happening for a while. from the use of the heater and other things pluged in. especily if you've been pulling over 15a through it.

[boatpoker]

Originally Posted by Sandero

YIKES!!!!!!!!!!!
Was this caused by the corroded wiring creating lots of resistance and heating? Can *faulty* wiring which is not powering anything but nevertheless *live* cause overheating and this sort of meltdown? Should the outlets have had a breaker?

Yes, you are absolutely correct.

[wingless]

Originally Posted by btrayfors

Last year I purchased a handy little tester device which puts several different loads on an outlet, measures voltage drop, and calculates the "condition" of the outlet.

Can you please post a link to this load tester?

[nigel1]

Originally Posted by wingless

Can you please post a link to this load tester?

Maybe something like a Extech CT170 AC Circuit Load tester

[btrayfors]

Originally Posted by nigel1

Maybe something like a Extech CT170 AC Circuit Load tester

Close. It's an Extech CT70. Cost was $179.92 from Zoro Tools.

There's one on eBay now for $139.99 new with free shipping from Iowa.

Here's the result of my first tests with it on my own boat last April.

Bill

[Neo]

Originally Posted by smac999

no they can't melt and overheat with nothing pluged in. that melting has likely been slowly happening for a while. from the use of the heater and other things pluged in. especily if you've been pulling over 15a through it.

+1

[Sandero]

Thanks all for the replies! I did a careful job with marine tinned stranded wire rated for I believe 20 or 30 amps. Crimped connections. The install was done 2006 so it's 7 years of corrosion. And no I did not open the outlets... which are Leviton Decora to check for corrosion. I will put a 15amp break in this weekend I don't run a 1500 watt heat. I use the Espar... and rarely use shore power ('cept in winter storage in water).

I will rewire the 4 outlets... It's not a terribly difficult project... just a PITA.

[nigel1]

Originally Posted by btrayfors

Close. It's an Extech CT70. Cost was $179.92 from Zoro Tools.

There's one on eBay now for $139.99 new with free shipping from Iowa.

Here's the result of my first tests with it on my own boat last April.

Bill

Attachment 72637

Thanks Bill, I really did mean the CT70, getting bounced so much out here that typo's are going to happen.
They are available in the UK, as will work on 240V, so one is the xmas list
UK prices about the same as US, looks like a useful bit of kit

[rtbates]

Originally Posted by Sandero

Thanks all for the replies! I did a careful job with marine tinned stranded wire rated for I believe 20 or 30 amps. Crimped connections. The install was done 2006 so it's 7 years of corrosion. And no I did not open the outlets... which are Leviton Decora to check for corrosion. I will put a 15amp break in this weekend I don't run a 1500 watt heat. I use the Espar... and rarely use shore power ('cept in winter storage in water).

I will rewire the 4 outlets... It's not a terribly difficult project... just a PITA.

I'd also add a GFI to ALL your interior AC outlets, as well as a separate breaker for the battery charger and one for the AC outlets.

[FlyingCloud1937]

Originally Posted by rtbates

I'd also add a GFI to ALL your interior AC outlets, as well as a separate breaker for the battery charger and one for the AC outlets.

I only use commercial/hospital grade outlets. They are built in all copper and much higher quality.

On top of that I always use 20 amp outlets for 15 amp circuits.

The builder spec Leveton is cheap and won't last in home use.

Lloyd