burned plug

[B_B_Upch]

can someone tell me what could have caused my plug to burn up? I have an rv with a 50 amp to 30 amp adapter plugged into a 30 amp plus outside. I just noticed the one side of the adapter on the 50 amp side was black & a little melted. so I checked the 30 amp plug at the house & it was melted on the same side. any help? I know I will need a new 30 amp extension cord & 30 to 50 amp adapter but want to figure out what caused it so not to happen again. thanks

[wa8yxm]

Burned plugs on the 50 amp side is rare, 30 amps burn up all the time.

As others have said, bad connections,, the blades on the plug should be bright and shiny, if they are dull or worse yet black they will overheat.

Likewise the contacts inside the outlet.

[DrewE]

There's quite a bit of perhaps inadvertently misleading information here.

Plugs and sockets overheat due to power dissipation at or near the connection. This is nearly always because of high resistance at the connection due to looseness, corrosion, improper or broken attachment of wires to the connectors, or something along those lines. The power dissipation is of course related to the current that's flowing, but a properly seated connection between connectors in good shape is more than able to carry the rated current (30A in this case). If more current were to flow for more than a very brief time, the circuit breaker would trip to protect the circuit.

Low voltage causes many devices to use less current (all resistive devices) and a few to consume more current (switching power supplies, some electric motors in certain applications). But the voltage itself is not the cause of the connector failing.

Similarly, undersized wires are dangerous when used with more current than they can carry (which is what being undersized means), but they do not cause the connector to melt. The wire itself may get hot and start a fire or otherwise be dangerous, but it wouldn't cause the connector to fail in itself. That's a moot point here as the wires involved were apparently all quite adequate for the current.

Note that power dissipation of a resistive connection increases with the square of current. A one ohm connection, which is a very poor one, would drop ten volts at ten amps and need to dissipate a hundred watts; encased in plastic as connectors are, with little chance to dissipate heat, it would melt in short order. A connection with a resistance of one tenth of an ohm, at ten amps, would dissipate ten watts; that would be plenty to get mighty hot internally over time.

[pianotuna]

Hi B.B.Upch,

As little as 15 amps can burn a connector. What often happens is, in a low voltage situation, the air conditioner draws more and more amps. That causing heating--which leads to even greater amp draw.

One solution is to use highest quality connectors (not female Cameco) such as Hubble. But even those may fail.

Using "dog bone" adapters is better. Treat them with deoxit from time to time and keep them bright and shiny.

If you have an energy management system, for 15 amps limit it to 12, 30 to 24, and 50 to 40 amps.

The best solution may involve an autoformer, to boost voltage, and a load support hybrid inverter charger.

Since I started doing the last two I've not had to replace a single plug.

[MrWizard]

you have a 30 amp outlet at home
or do you mean you also used a 30amp rv to 15 amp duplex adapter ?

[donkeydew]

low voltage =high amps check your power supply and the size of the wire in your cord.

[B_B_Upch]

thanks everyone. I was only running 1 A/c unit & nothing else. just running the unit to cool down the coach in order to work on it. I'm guessing it was a bad connection on the 50 to 30 amp adapter which caused it to melt at both the adapter & the house plug.

[Chum_lee]

If I understand what you are saying, you have an RV with a 50 amp service. Yes? It's really two 50 amp 120 volt circuits in the pigtail which you reduce to one 30 amp at the pedestal. (house plug) The main circuit breaker(s) in your RV aren't going to flip until they reach 50 amps. (only one is being used) The house circuit breaker will flip at 30 amps. So, now you have a 50 amp potential draw fed by a 30 amp breaker. Add in a few extension cords, a few bad connections, and you WILL shortly find the weakest link, which you did.

Chum lee

[Executive45]

Yep, electricity is a pretty simple subject. Try to push too many amps through a smaller cord and something's gotta give. Electricity always generates heat. That's what trips the breaker inside the box. Two things generally cause burnt plugs...too much demand on too small a cord/plug and loose connections between the plug and receptacle. Unless the cord itself is damaged, replace only the plug ends....Dennis

[siggyd777]

I have the same problem with the 50 / 30 adaptors , because they are
made dirt cheap and sold for a high price. I would love to see the poorly made connection inside of the molded 30 amp plug.
BTW , I never run more then one AC unit on 30 amp and turn off the
AC when using the microwave.
Siggy

[Sam_Spade]

ScottG wrote:
Only two large items (AC & water heater for example) at a time when on 30A.

Actually that probably should be limited to ONE "large" item.....along with the stuff that you have little control over, like the battery converter/charger.

If your 50 A unit has only ONE air conditioner, just that alone probably comes close to the 30 Amp limit.

An overheated plug usually means a bad connection....or an overload....or a combination of the two.

The original post was a bit unclear about exactly what he has.....mentioning a 30 amp extension cord at the end of the post.
Normally one would use the regular 50 amp cord and the only 30 amp things in the circuit would be the adapter and the outlet.

[Matt_Colie]

Brian,

Save some trouble and money. Only replace what was damaged and don't buy a whole new cord.

The reason things are heat damaged is that they were not capable of carrying the load. Replace just those parts. But if you are not sure which was the bad part, replace both.

It is very easy to do this if you are running a 50 amp coach on a lesser service. You have to be very careful.

Matt

[harold1946]

The most common cause is the connection not being properly installed and tightened.

[Bruce_Brown]

^^^ True, although excessive amp draw could also do the same.

[ScottG]

Only a weak or otherwise poor connection wil cause that. Probably just worn. I would replace both.
You should also be careful how much current your pulling through the 30A adapter. Only two large items (AC & water heater for example) at a time when on 30A.