Burned Shore Power Connector

[Nancyc7]

Can anyone tell me why one of the breakers or the EMS did not shut off the power before such a catastrophic melt down of the connector occured.

Cord end note "that is the male connector welded to the female end of the cable"



Coach plug-in prior to removal for repair



Schematic of my shore power configuration (to the best of my knowledge). This configuration has been working well for 20 months in 30 different RV parks.



Hughes Autoformer 30 Amp Model # RV2130-SP
Voltage Regulator and Surge Protector 2400 Joules



Progressive 30 Amp Electrical Management System
EMS-PT30X Portable EMS with Surge Protection



2016 Forest River Sunseeker 24ft MBS WS

10/27/19 - Arrived and hooked to shore power Washington DC.

10/30/19 - Approx. The clock on the microwave reset to "0". Once in the night and twice in the daytime. We took note of that but there was absolutely no other electrical anomaly, no smoke or odd electrical smell, no breaker to reset. We reset the clock and took no other notice. I did not check the EMS because the outage was a blink noted only by the microwave clock.

10/27/19 - 11/13/19 Weather in DC was 60s to upper 20s we ran 1 small space heater many evenings and nights. We also ran the water heater and coffee pot. Not all at the same time and did not blow a 30 amp breaker, or any other house breaker. The Dometic heat pump/air conditioning worked well when we tried it several cold mornings. No anomalies at all were noted. We are quite careful not to draw more amps than allowed. We have only blown a breaker 3 times in over 20 months of full time travel.

11/13/19 - I unplugged the shore power cable. I heard a crunching noise when I twisted the cable end loose from the coach. I discovered the burned cable.

11/13/19 - Drove to Hamilton VA and parked the MH at our reserved space. We did not hook up any of the services and we did not run the generator. We stayed in a motel for 5 nights until new OEM parts arrived and repairs could be completed by a professional.

11/14/19 - Service tech reviewed the damage and ordered a new OEM 30 Amp male connector. We purchased a new 30 Amp 30 Ft cable with a 90 degree head and screw on locking ring.

11/17/19 Parts arrived and repairs were begun.

11/18/19 Repairs and testing were completed. We drove the MH back to our reserved space. Service Tech stated "when he unscrewed the plug from the MH he was able to pull the plug directly out of the hole, as if the wires were not screwed to the rear of the plug" On further review the tech assured me that none of the 3 wires was ever fastened by a screw to the back of the plug. Just stuck in and held by some friction. I do not believe this is a situation where a screw came loose on the connector by either hot and cold weather changes or road vibration.

11/19/19 - The MH is connected to shore power and seems to be working as expected.

My usual electrical connection process is as follows:
1) Check the park power pole with a voltage detector.
2) Use the voltage detector to determine that the lower left hole is hot and no other hole is electrified
3) Confirm the 30 A breaker on the pole is OFF
4) Turn OFF refrigerator, fans or lights that may be on while traveling
5) Turn OFF the battery switch on MH
5) Connect Autoformer to pole and power cable to MH confirming that I lock both the plug and the outer screw on ring
6) Turn ON 30 A breaker on power pole
7) Watch EMS display to confirm the Voltage, Amp Draw, Hz, and EMS Connection Test is Error Free
8) Turn ON battery switch in MH, turn ON refrigerator
I am strict about the above procedure.

My usual electrical disconnect process is as follows
1) Turn OFF refrigerator, fans or lights
2) Turn OFF the battery switch in MH
3) Turn OFF the 30 A breaker on the pole
4) Disconnect the Autoformer from the pole and power cable to MH
5) Turn ON battery switch in MH, turn ON refrigerator
I am strict about the above procedure.


This view could show the screws were tightened at least a little ???





I dont know for sure if the strain relief was ever installed but it looks as if it was



If you have an answer as to why one of the breakers did not trip, please respond.

[MtBiker]

I would agree that the screws for the wire hold downs on male side were likely not tightened correctly. Bad connection created resistance (heat) which melted down the casing.

[BandJCarm]

It didn't shut off the power because the malfunction occurred past the point that either/both device(s) were in play.

[Darryl Honda]

MtBiker is correct in what he stated. The breaker did not blow because it is an over current device. In your case the amount of resistance wasn't creating enough heat because you had minimal load. Had the plug melted more it could of shorted out to either the neutral or the ground. In that case the breaker would of blown. I have to say that that was probably a good thing (the slow melt) because it could have first resulted in a fire. Sorry for your bad luck, hope this helps.

[cavie]

Originally Posted by Nancyc7

It absolutely 100% was turned and tightened.

My brain is calling you bad names but I’m not writing them down, it’s not helpful.

I edited my responce but now I'm just gonna leave. Have a nice day!!!

[Photo Lab]

As already mentioned by others, the actual problem was a poorly tightened neutral (white) wire connection.
This situation is more common than it should be, and I think it is due to an assembler not tightening the screws properly, and a cheap connector, which in practice requires care in assembly. Personally, I prefer Hubbell brand connectors on both ends of the cord, and on the coach end of the cord.

I hate to admit it, but in practice,I have used the Hubbell connectors for far in excess of the rating, using #8 wire on 30 amp connectors, and drawing a tad over 50 amps. Temporary of course, but it didn't burn up. Sometimes on a job site, you have to work with what is available! (Not code, but according to "Temporary Harry".

[Larry-NC]

Originally Posted by Nancyc7

Can anyone tell me why one of the breakers or the EMS did not shut off the power before such a catastrophic melt down of the connector occurred.

Nancy, Very detailed report and photos. It helps everyone.

I agree with all that has been stated. The fault occurred before (upstream in the power delivery) the EMS and autoformer, so they never saw it.

I did Failure Analysis for a few years and complete answers are important to me. You also asked about breakers, and the pedestal breaker was upstream from the fault. No one else has addressed that.

The heat and resulting occurred due to arcing. The arc was sustained at a current level lower than the breaker's trip threshold. The reason for the current limitation is that all of the current had to flow through the RV as well as the arc. This is true of a single-pin arc at the plug.

If there were an arc between two pins in the plug (technically called a "short circuit" because the current takes a short path (circuit) through the plug pins and not the longer path through all the appliances in the trailer), the breaker would certainly trip in less than a second.

It might also be helpful to know that in newest construction, "arc-fault breakers" are used. Today's breakers detect overcurrent. Some also detect a "ground fault" where current flows in the correct wire but out the wrong wire which indicates that an appliance could be dangerous. You could get a shock from the case of that drill, saw, toaster, or mixer.

The newest breakers detect detect overcurrent AND ground faults AND arc faults. They are still pretty expensive and I imagine they will only be seen in new construction until the price drops. Once the price drops, as old breakers fail, arc-fault breakers could be used, including the breaker at the pedestal. So your damage is caused only because it happened too soon. If you had been plugged into an arc fault breaker due to the failed cord, the RV socket would not have been damaged. You could have diagnosed the problem and bought a new cord and been on your way!!

Diagnosis steps:
1) Arc-fault breaker trips and won't reset
2) Unplug from pedestal
3) Reset breaker. It stays reset. Conclude that breaker is working okay
4) Unplug cord from RV. Now plug cord into pedestal. Breaker trips. Conclude that cord is bad. (It has to be. It is the only thing that was added to a working condition. The RV is unplugged and out of the picture)

Sorry if this post is too long and boring.

[SailorSam20500]

I noticed at this years International Rally, FR is using a different connector on some rigs. Replacing the twist-lock connector with a straight push in similar to the Smart Plug. I couldn't tell if the blades were larger as they are on the Smart Plug brand products.

When/if I replace my connector setup, I will use a Smart Plug or something similar. I think it is way too easy to not properly connect using a twist/lock connector.
https://smartplug.com/rv/

[TitanMike]

Best way I know to prevent problems like this is regular inspections. Look for signs of heat at the connections when "de-camping" and putting cord away.

Also not a bad idea to check the connector periodically during high current use times like Summer with A/C and Winter if using space heaters.

To me the main issue is that the connector is rated for 30 amp as well as the circuit breaker. To me it would be more ideal for the connector to be rated higher, like 40 amp is such a connector were to exist.

Running a plug in connector at it's max will always generate heat and in my experience they will fail eventually.

On my trailer I have a shore power monitor that shows voltage, amperage, Kw flowing, and Kwh consumed. When the current approaches 30 amp I take note of what's running and unless it's something temporary like the microwave I start looking for items to shut down (like turning a heater down to a lower power setting).

[Larry-NC]

Originally Posted by TitanMike

Best way I know to prevent problems like this is regular inspections. Look for signs of heat at the connections when "de-camping" and putting cord away.

Yup! I'm changing many of the outlets in my 53-year-old house because many get warm when I run the vacuum or washing machine. The importance here is that if I don't, I will bake off the insulation of the wiring behind the outlet.

My son asked me to diagnose an outlet that caused light flicker occasionally. (He actually didn't care about the flicker--he asked because his DVR kept losing its settings.) I told him to plug nothing into the outlet before the weekend.

We traced it back to the circuit breaker panel. The neutral for that circuit had been placed in the bus bar but never tightened. The insulation on that 7" wire was cooked completely off for six inches. As I told him, "If we hadn't found this, it would have burned right through the strain relief and inside the wall."

[ependydad]

Originally Posted by SailorSam20500

When/if I replace my connector setup, I will use a Smart Plug or something similar. I think it is way too easy to not properly connect using a twist/lock connector.
https://smartplug.com/rv/

I've had the SmartPlug since August 2018 and it's been great.

Installation video:

https://www.youtube.com/watch?v=6yvAdM28x6w

[Darryl Honda]

Excellent video on the Smart Plug.

[santara]

Simple that was the ground not netural whichwzs carrying the netural load not design to carry that on 30a plug 1 hot 1 netural 1 ground which dosent go thru any overlaod brk.-ground just for safety noLOAD

[Nancyc7]

Originally Posted by Larry-NC

Nancy, Very detailed report and photos. It helps everyone.

I agree with all that has been stated. The fault occurred before (upstream in the power delivery) the EMS and autoformer, so they never saw it.

I did Failure Analysis for a few years and complete answers are important to me. You also asked about breakers, and the pedestal breaker was upstream from the fault. No one else has addressed that.

The heat and resulting occurred due to arcing. The arc was sustained at a current level lower than the breaker's trip threshold. The reason for the current limitation is that all of the current had to flow through the RV as well as the arc. This is true of a single-pin arc at the plug.

If there were an arc between two pins in the plug (technically called a "short circuit" because the current takes a short path (circuit) through the plug pins and not the longer path through all the appliances in the trailer), the breaker would certainly trip in less than a second.

It might also be helpful to know that in newest construction, "arc-fault breakers" are used. Today's breakers detect overcurrent. Some also detect a "ground fault" where current flows in the correct wire but out the wrong wire which indicates that an appliance could be dangerous. You could get a shock from the case of that drill, saw, toaster, or mixer.

The newest breakers detect detect overcurrent AND ground faults AND arc faults. They are still pretty expensive and I imagine they will only be seen in new construction until the price drops. Once the price drops, as old breakers fail, arc-fault breakers could be used, including the breaker at the pedestal. So your damage is caused only because it happened too soon. If you had been plugged into an arc fault breaker due to the failed cord, the RV socket would not have been damaged. You could have diagnosed the problem and bought a new cord and been on your way!!

Diagnosis steps:
1) Arc-fault breaker trips and won't reset
2) Unplug from pedestal
3) Reset breaker. It stays reset. Conclude that breaker is working okay
4) Unplug cord from RV. Now plug cord into pedestal. Breaker trips. Conclude that cord is bad. (It has to be. It is the only thing that was added to a working condition. The RV is unplugged and out of the picture)

Sorry if this post is too long and boring.

It's not long and boring at all. It's what we needed to know.

I worked as a RN in hospitals and the only committee I enjoyed was the Root Cause Analysis committee. Failure Analysis sounds the same. Very useful and enlightening.



Can one install an "arc fault breaker" in your motor home? Or are you already saying this? The way I read it, the park pedestal would have this.

[Larry-NC]

Originally Posted by Nancyc7

It's not long and boring at all. It's what we needed to know.

I worked as a RN in hospitals and the only committee I enjoyed was the Root Cause Analysis committee. Failure Analysis sounds the same. Very useful and enlightening.

I'm never sure if the detailed responses are appreciated. Thanks!

Failure Analysis (FA) and Root Cause Analysis (RCA) are very closely related.

• FA looks at the component that failed and determines how/why it failed. It could be an internal flaw or speculation about some external stimulus.
• RCA starts there, but then investigates the external conditions until the initiating stimulus (root cause) is found.

Let's try some examples:
The TV/microwave/converter in your trailer fails within warranty. The manufacturer sends you a new one and gets the old one in return. His lab takes the device apart. They might find an internal component, isolated from external connections, has failed and would cause the symptoms you reported. They might even replace that component to see if everything works or there's other damage. Instead, it might not a single internal component. It might be several components. The analyst observes that they are electrically all closely coupled to where the powerline enters the product. He speculates that failure is due to a lightning strike and writes his report. This is FA,

A fire breaks out in a home when no one is present. There's lots of damage. The fire department is able to identify a general area where the fire started. The insurance company sends a forensic investigator (perhaps to see if he can determine a product at fault). He goes through the RCA chain to see that B caused C to fail, and A caused B to fail. A's failure caused the entire event. That's RCA.

Here's a simpler RCA. B is stopped at a stoplight/sign. C slams into the back of B pushing him into the intersection where he "T-bones" A. A jumps out of his car and accosts B, "You hit me! It's all your fault!" B calmly replies, "My car hit yours, but the root cause is C." That's RCA, too.

Originally Posted by Nancyc7

Can one install an "arc fault breaker" in your motor home?

Yes, you can install an arc-fault breaker in your trailer. It's probably more customary to install one on each circuit. If you replaced the main breaker with an arc-fault breaker and it tripped, you wouldn't know where to start looking for the fault. Microwave? Water heater? Converter? Toaster? Coffee pot? If you put one on each circuit, that isolates the problem substantially.

Originally Posted by Nancyc7

Or are you already saying this? The way I read it, the park pedestal would have this.

Very perceptive! You are exactly right! Since the previous post indicated that the fault could be diagnosed with the cord plugged into the pedestal but not the RV, an arc-fault breaker would not have helped. It would have had to be in the pedestal.

This is the standard breaker used in just about every RV and many residential homes. It sells for $3.94.

This is the arc-fault breaker that would replace each of those breakers in just about every RV and many residential homes. It is $42,98.

[TitanMike]

Originally Posted by Larry-NC

If you had been plugged into an arc fault breaker due to the failed cord, the RV socket would not have been damaged.

In reading and refreshing my memory on how arc-fault breakers work (I had to install some back in 2003 during some construction in my Colorado house) they don't work on High Resistace Connections also known as "Glowing Connections". There has to be an arc that creates the detection frequency.

I'm guessing that most RV power cords fall in the "High Resistance" category and IF they were to ever trip an Arc-Fault breaker it would only be when the connection actually fails under load and creates the necessary arc.

According to the literature the only way to protect against "glowing connections" (also known as hot plugs by some) is to install Power Fault Circuit Interrupters in the actual receptacle. As I understand they are merely a thermal device that detects the high heat of the "fault" and opens the circuit much like an overheat element in a furnace, etc.

In short, broken wires --- yes. Crappy connections ----- no (unless actually arcing).

PS: If I'm wrong, blame this:

https://en.wikipedia.org/wiki/Arc-fa...ting_principle

(see section on Limitations)

[Larry-NC]

Originally Posted by TitanMike

In reading and refreshing my memory on how arc-fault breakers work (I had to install some back in 2003 during some construction in my Colorado house) they don't work on High Resistace Connections also known as "Glowing Connections". There has to be an arc that creates the detection frequency.

I'm guessing that most RV power cords fall in the "High Resistance" category and IF they were to ever trip an Arc-Fault breaker it would only be when the connection actually fails under load and creates the necessary arc.

According to the literature the only way to protect against "glowing connections" (also known as hot plugs by some) is to install Power Fault Circuit Interrupters in the actual receptacle. As I understand they are merely a thermal device that detects the high heat of the "fault" and opens the circuit much like an overheat element in a furnace, etc.

In short, broken wires --- yes. Crappy connections ----- no (unless actually arcing).

PS: If I'm wrong, blame this:

https://en.wikipedia.org/wiki/Arc-fa...ting_principle

(see section on Limitations)

Not sure about the official terminology, but I would call this a low-resistance connection. A high-resistance connection would not conduct enough current to heat anything. A toaster (8-10 ohms, 1200-1500 watts) is a low-resistance in my world, and gets plenty hot. Concentrate that much power in a tiny connection surface like the plug and it would really glow.

That said, you raise an interesting point. I assumed arcing took place--mostly due to prior experiences. It could have been merely resistive as you suggest. I agree with your conclusion that an arc-fault breaker may not have detected this situation.

Thinking about this: Two pieces of copper in so-so contact with one another,
--Is that stable? will it go from arcing to conducting and back? Thermally?
--Will the connection erode and transition from one state to the other?
In this case, we have something that could go on for hours. That's what led me to consider the thermal situation.

I really don't know much about this. There's lots published in reliability of contacts in switches, relays, contactors, and high-energy circuit breakers, but they are transitory. There's a measurable period (often a few hundred milliseconds) while this could take place.

[TitanMike]

Originally Posted by Larry-NC

Thinking about this: Two pieces of copper in so-so contact with one another,
--Is that stable? will it go from arcing to conducting and back? Thermally?
--Will the connection erode and transition from one state to the other?
In this case, we have something that could go on for hours. That's what led me to consider the thermal situation.

I really don't know much about this. There's lots published in reliability of contacts in switches, relays, contactors, and high-energy circuit breakers, but they are transitory. There's a measurable period (often a few hundred milliseconds) while this could take place.

I think that much of what you mention is why the Smart Plug is being promoted. Rather than "contacts" that need to be downsized so there's room to twist to lock them, they use full size contacts and lock them in place with a separate locking mechanism.

In my experience all high current connections using plugs don't "Twist to Lock" but are usually relatively large pins mating with equally large sockets, held in a large cast body, and secured with a lock ring or hook on cover like these:



Kind of ugly for RV use though

[TitanMike]

Originally Posted by Larry-NC

Not sure about the official terminology, but I would call this a low-resistance connection. A high-resistance connection would not conduct enough current to heat anything. A toaster (8-10 ohms, 1200-1500 watts) is a low-resistance in my world, and gets plenty hot. Concentrate that much power in a tiny connection surface like the plug and it would really glow.

That said, you raise an interesting point. I assumed arcing took place--mostly due to prior experiences. It could have been merely resistive as you suggest. I agree with your conclusion that an arc-fault breaker may not have detected this situation.

Thinking about this: Two pieces of copper in so-so contact with one another,
--Is that stable? will it go from arcing to conducting and back? Thermally?
--Will the connection erode and transition from one state to the other?
In this case, we have something that could go on for hours. That's what led me to consider the thermal situation.

I really don't know much about this. There's lots published in reliability of contacts in switches, relays, contactors, and high-energy circuit breakers, but they are transitory. There's a measurable period (often a few hundred milliseconds) while this could take place.

I think they mean "higher than zero" which is ideal for a connector. The heating effect increases as the resistance does. At some point the resistance will grow to the point insufficient current will flow to sustain the heating. By that time the damage is usually done to the connector body.

[Nancyc7]

Thankx to: MtBiker, Darryl H., Photo Lab, Larry-NC, TitanMike. I'm convinced the screws holding the wires on the backside of the male connector were not tightened properly at the factory. Especially because the tech that did the repair said the plug came right out in his hand once he unscrewed it from the motor home wall.

Darryl H. is also likely correct that the plug did not melt enough to allow current to flow from the HOT wire to either the neutral or the ground. (a condition I didn't initially think of) However the arcing certainly made enough heat to melt both the male and female connectors and weld pins of the 2 connectors together. That seems hot to me, in fact hot enough to start a fire.

Photo Lab mentions the likely possibility of a poorly tightened neutral wire....a situation more common than it should be...with the possible resolution of a better connector.



Larry-NC explains single-pin arcing well and even explains that single-pin arcing can be sustained creating heat but not a short circuit that would certainly have tripped the breaker.

TitanMike suggests it would be a good idea to actually check the connector during times of high load. I'm assuming he means go outside and touch the connector when I am using appliances that I know draw a relativity high amount of current, especially during weather extremes of (hot or cold). I could have easily been running near the plug/cord limit of 30 amps during the cold weather in DC at the time.

To sum up what I have learned here, I would say the failure is human and, as is so often the case in the RV industry, poor workmanship. A human failed to do the job correctly and in doing so put other people's lives in danger. A fire could have easily been the result here, instead of just a burned plug.

I think your best defense against this type of poor workmanship is to take TitanMike's advice physically check the plug when it is under heavy load. Go outside put your hand on the plug and feel for heat. If it is hot it is a problem. I never thought of this, although it is such a simple thing. I am quite sure I did not see any discoloration of my plug as I connected or disconnected it several times a month. I think my problem occurred only once, during my stay in DC.



I have also read a recommendation to remove the male connector from the RV and inspect and\or tighten the screws in the back side that hold the wires in, as they can be loosened over time by road vibration.


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