I know these shouldn't look like this.

[guy99]

This is the female plug on the 30 amp extension I use to connect to power.

The is the male end of the 30 amp cord from the MH.

This is the inside of the male plug. If you look carefully you can see a bulge of insulation on the black wire and some discoloration on the white wire.

What I can't figure out is why this is happening. I have been plugged into a 50 amp connection via a 'dog bone' but since the main breaker in the MH is 30 amp, I don't see how I could be drawing more than 30 amps long enough to do this.

I's been hot and the AC has been running almost constantly.

[Inland RV Center, In]

Originally Posted by guy99

Attachment 63479 This is the female plug on the 30 amp extension I use to connect to power.

Attachment 63480 The is the male end of the 30 amp cord from the MH.

Attachment 63481 This is the inside of the male plug. If you look carefully you can see a bulge of insulation on the black wire and some discoloration on the white wire.

What I can't figure out is why this is happening. I have been plugged into a 50 amp connection via a 'dog bone' but since the main breaker in the MH is 30 amp, I don't see how I could be drawing more than 30 amps long enough to do this.

I's been hot and the AC has been running almost constantly.

The problem is the "dog bone."

Look at it's rating and you will see why it burned what it did.

Dog bones are usually rated at 15 amps, and then only if there is a few inches of wire between the plug and socket.

The dog bones that do not have those few inches of wire, will burn up every time you use your AC.


If you want to run the AC, you must plug the trailer directly into an outlet, without any type of dog bone.

Andy

[TomW]

Contacts are rated for a particular load just like wire size.

My first thought is that inferior contacts were used in the female connector.

A good contact for high current loads needs to have plenty of surface area to transfer power.

If you get bored, purchase a 33 cent, 15 amp, household outlet, and a $3.79 certified 20 amp household outlet from the your local home improvement store. Then smash each with a heavy hammer.

You will find that the 15 amp outlet has knife-like connectors instead of the 20 amp outlet's sleeve-like connectors.

More surface area means better contact.

Tom

[john hd]

oxidation on the blades and internal parts can cause heating. were the connectors green before use?

another culprit could be low voltage at the source. the load does not change, the voltage drops and the current goes up!

watts = volts x amps if you decrease the voltage the current rises to meet the demand.

john

[guy99]

Originally Posted by Inland RV Center, In

The problem is the "dog bone."

Look at it's rating and you will see why it burned what it did.

Dog bones are usually rated at 15 amps, and then only if there is a few inches of wire between the plug and socket.

The dog bones that do not have those few inches of wire, will burn up every time you use your AC.


If you want to run the AC, you must plug the trailer directly into an outlet, without any type of dog bone.

Andy

The dog bone is a 50 amp to 30 amp device. The 30 amp extension then plugs into the dog bone, then the MH plugs into the 30 amp extension.

The pictures I posted are of the female end of the extension (male end is plugged into the dog bone) and the male end of the MH power cord.

There is no sign of over heating where the extension plugs into the dog bone or where the dog bone plugs into the 50 amp outlet.

[guy99]

Originally Posted by john hd

oxidation on the blades and internal parts can cause heating. were the connectors green before use?

another culprit could be low voltage at the source. the load does not change, the voltage drops and the current goes up!

watts = volts x amps if you decrease the voltage the current rises to meet the demand.

john

The connectors were not green, they were not shiny either, pretty much a tarnished brass.

Unless the utility power had low voltage (could happen) I don't think there was low voltage at this outlet. I have had friends with big motorhomes with fancy power management systems report that it supplies good voltage even at heavy load.

I do have an autoformer in the motorhome. Is it possible for it to draw more than 30 amps even though it is supplying 30 amps or less?

[Andrew Selking]

John hd Give us some more good advice is the dog bone the problem or is as you suggested a problem with the cord or the ends of the cord?

[Tom Nugler]

How tight were the screw clamps in the housing? Like John said, resistance = heat. The more current, the more heat. Heating causes the contacts to weaken, loose tension and cause more resistance. Resistance creates a voltage drop and the cycle repeats.
I had to hit a customer yesterday for over $400 for a new starter and cable. Reason? Loose nut on the cable terminal.

Tom.

[guy99]

Originally Posted by Tom Nugler

How tight were the screw clamps in the housing? Like John said, resistance = heat. The more current, the more heat. Heating causes the contacts to weaken, loose tension and cause more resistance. Resistance creates a voltage drop and the cycle repeats.
I had to hit a customer yesterday for over $400 for a new starter and cable. Reason? Loose nut on the cable terminal.

Tom.

The screw clamps were very tight (I had to use a socket to loosen them).

Most of the heat seemed to be around the 'blades'.

[bkahler]

Guy,

I had to replace the male connector on our motorhome this past weekend as well. It did the EXACT same thing yours did although the melting wasn't quite as bad. I ended up buying a plug from Lowe's although while installing it I realized the quality was very poor so I'm going to shop around for a good quality replacement and put that on in its place.

I also like you don't understand why the breakers aren't tripping.

Brad

[Tim A.]

I looked at the photos and read what Andy said and I think he is on the right track. Most of the melting seems to be around the female plug of the extension with the heat transmitted by the male prongs into the male plug. In other words, the female plug of the extension appears to have generated the heat.

Whether or not the rating of the extension was adequate, it looks like it was the part of the connection which began to heat up while trying to carry the constant load of your AC. As it heated up, its resistance increased which reduced its effective load-carrying ability. The breaker did not blow because you were within its 30-amp rating, but the female plug of your extension could not carry the 30 amps for an extended period of time.

[guy99]

Originally Posted by bkahler

Guy,

I had to replace the male connector on our motorhome this past weekend as well. It did the EXACT same thing yours did although the melting wasn't quite as bad. I ended up buying a plug from Lowe's although while installing it I realized the quality was very poor so I'm going to shop around for a good quality replacement and put that on in its place.

I also like you don't understand why the breakers aren't tripping.

Brad

Brad,
I don't get it either. I guess that since the heat is being caused by high resistance, the current flow never gets high enough to trip the breaker.

In my situation, the breaker for the receptacle is 50 amp so I would expect the 30 amp breaker in the MH to trip if the current got too high.

The male plug that failed is a replacement. I searched and found the highest quality I could. One concern was that it wasn't water proof. So I just replaced the male end of my power cord by splicing a molded 30 amp plug onto the power cord. I then replaced the extension with a brand new one. I noticed that when I plugged the MH in to the extension, it went in very easily. Doesn't seem like a nice tight fit. I would if this is part of the problem?

[guy99]

Originally Posted by Tim A.

I looked at the photos and read what Andy said and I think he is on the right track. Most of the melting seems to be around the female plug of the extension with the heat transmitted by the male prongs into the male plug. In other words, the female plug of the extension appears to have generated the heat.

Whether or not the rating of the extension was adequate, it looks like it was the part of the connection which began to heat up while trying to carry the constant load of your AC. As it heated up, its resistance increased which reduced its effective load-carrying ability. The breaker did not blow because you were within its 30-amp rating, but the female plug of your extension could not carry the 30 amps for an extended period of time.

Just to clarify, Andy was pointing to the "dog bone". It shows no heat effects. I think you are correct however, high resistance between the male plug from the MH and the female plug of the extension cord caused the failure. I now realize that it isn't clear in the pictures but the damage was actually worse on the male plug.

[2airishuman]

hi guy'

have u checked the voltage?

have u checked the voltage while using the a/c?

while the bone may be rated for 30 amps and u might expect the breaker inside to trip...

they often don't before the cord/contact is toasted.

i too had a 30 amp male cord end melt during one brief session of a/c and low voltage...

the lineman has given you the good advice in post 4.

cheers
2air'

[guy99]

Originally Posted by 2airishuman

hi guy'

have u checked the voltage?

have u checked the voltage while using the a/c?

while the bone may be rated for 30 amps and u might expect the breaker inside to trip...

they often don't before the cord/contact is toasted.

i too had a 30 amp male cord end melt during one brief session of a/c and low voltage...

the lineman has given you the good advice in post 4.

cheers
2air'

Voltage inside the coach reads good (115-118) anytime I check it - but that is the job of the autoformer.

Voltage at the 50 amp receptacle read 119 -121 whenever I check.

Of course it is possible that there was a brown out when I wasn't in the coach. It's been hot but the power seems to have been stable. But since I wasn't recording ...

[ROBERTSUNRUS]

Originally Posted by guy99

Brad,
I don't get it either. I guess that since the heat is being caused by high resistance, the current flow never gets high enough to trip the breaker.

In my situation, the breaker for the receptacle is 50 amp so I would expect the 30 amp breaker in the MH to trip if the current got too high.

The male plug that failed is a replacement. I searched and found the highest quality I could. One concern was that it wasn't water proof. So I just replaced the male end of my power cord by splicing a molded 30 amp plug onto the power cord. I then replaced the extension with a brand new one. I noticed that when I plugged the MH in to the extension, it went in very easily. Doesn't seem like a nice tight fit. I wonder if this is part of the problem?

Hi, Guy 99. You answered your own question; A poor or loose connection will generate heat and melt; And will not trip breakers. Loose recepticals at campsites can and will do the same thing. I always check for a good tight fit at campsite recepticals.

[guy99]

Originally Posted by ROBERTSUNRUS

Hi, Guy 99. You answered your own question; A poor or loose connection will generate heat and melt; And will not trip breakers. Loose recepticals at campsites can and will do the same thing. I always check for a good tight fit at campsite recepticals.

The interesting thing is that the old connection (which melted) did feel snug. The new one - new male plug into new extension cord - slides in very easily.

Perhaps the old one was corroded internally and caused high resistance and a snug fit.

[RoadKingMoe]

There's nothing "automatic" about an autotransformer. It is simply a fixed transformer where the primary and secondary share winding (although they typically have different taps you can use for different output voltages). If input voltage is adequate, using an autotransformer in a step-up configuration will provide excess output voltage.

In a voltage step-up configuration, it does input more current than it outputs, so if the trailer's 30 amp breaker is on the output of the autotransformer, the input can draw more than the breaker rating, and the 30 amp cord is not protected at the 30 amp level.

The pictures you show support the high-resistance point hypothesis, either blade to blades or wire to blade(s).

[guy99]

Originally Posted by RoadKingMoe

There's nothing "automatic" about an autotransformer. It is simply a fixed transformer where the primary and secondary share winding (although they typically have different taps you can use for different output voltages). If input voltage is adequate, using an autotransformer in a step-up configuration will provide excess output voltage.

In a voltage step-up configuration, it does input more current than it outputs, so if the trailer's 30 amp breaker is on the output of the autotransformer, the input can draw more than the breaker rating, and the 30 amp cord is not protected at the 30 amp level.

The pictures you show support the high-resistance point hypothesis, either blade to blades or wire to blade(s).

The autofomer sold for RV's Hughes Autoformers :: RV 2130 has some control circuitry which only provides boost when the input voltage drops below a point. Some models have variable boost (5%, 10%, 15%). Mine only has 10%. I can watch it operate if I plug in to a source with a borderline voltage. At first I get the lower voltage - say 110, if I turn on a heavy load - a microwave or a toaster, the voltage dips briefly then goes up to say 115. As the device was explained to me, the increase in voltage is the autoformer detecting a low voltage and beginning to boost its output voltage.

[john hd]

another idea to prevent this from happening again is to eliminate the less than quality male connectors and the extension cord.

you can do this by purchasing a canadian spec power cord from an airstream dealer. they have molded ends and are 10 feet longer if i remember correctly.

call a dealer and check it out.

the other route is to by a 20 foot generic cord, cut off the female end and install into your junction or breaker box. at least you will get a molded end. however, the quality may be dubious if it is imported.

john