Is the male plug an aftermarket install, I would expect to see a molded plug from the factory. Another thought, did they need to unplug the water heater to make repairs? If so the cheap factory receptacle could have broken. If none of the above I would tend to believe that the cheap stab receptacle could not handle the overcurrent.
It looks to me like contact corrosion, especially on the line blade on the plug. Maybe accelerated with a humid environment. The oxidation increases contact resistance which increases heat which increases the oxidation rate until...things melt and eventually the circuit is opened.
In the original post somebody suggested replacing the receptacle with a traditional one rated for 20 amps. While this seems wise, wouldn't it be against any code ever to replace a 15 amp outlet on a 15 amp circuit with a 20 amp outlet?
Actually, that’s okay according to code. While it’s a violation to replace a 15-amp breaker with a 20-amp breaker, that’s because the 14-gauge wire is only rated for 15-amps and you could overheat it with too much current. But you can install a duplex 15-amp duplex receptacle on 12-gauge wire with a 20-amp breaker due to a code exception. I should write an article on how this works in America. UK code is totally different!
There is a little debate on this. If you read 210.21.B sections 1 & 3 they both say that receptacles should be NOT LESS THAN the branch circuit rating. So I read that as any receptacle of ant least 15A is allowed on a a5A circuit. Come up a lot in the EV world (and somewhat in RV world) where people use 14-50 outlets on 30, 40, or 50A circuits.
210.21 Outlet Devices
Texas Electrical Code 2023 > 2 Wiring and Protection > 210 Branch Circuits Not Over 1000 Volts AC, 1500 Volts DC, Nominal > 210.21 Outlet Devices
Go To Full Code Chapter
Outlet devices shall have an ampere rating that is not less than the load to be served and shall comply with 210.21(A) and (B).
(A) Lampholders
Where connected to a branch circuit having a rating in excess of 20 amperes, lampholders shall be of the heavy-duty type. A heavy-duty lampholder shall have a rating of not less than 660 watts if of the admedium type, or not less than 750 watts if of any other type.
(B) Receptacles
(1) Single Receptacle on an Individual Branch Circuit
A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.
Exception No. 1: A receptacle installed in accordance with 430.81(B).
Exception No. 2: A receptacle installed exclusively for the use of a cord-and-plug-connected arc welder shall be permitted to have an ampere rating not less than the minimum branch-circuit conductor ampacity determined by 630.11(A) for arc welders.
Informational Note: See Article 100 for the definition of receptacle.
(2) Total Cord-and-Plug-Connected Load
Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 210.21(B)(2).
Table 210.21(B)(2) Maximum Cord-and-Plug-Connected Load to Receptacle
Circuit Rating (Amperes) Receptacle Rating (Amperes) Maximum Load (Amperes)
15 or 20 15 12
20 20 16
30 30 24
(3) Receptacle Ratings
Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall not be less than the values listed in Table 210.21(B)(3), or, where rated higher than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.
Exception No. 1: Receptacles installed exclusively for the use of cord-and-plug-connected arc welders shall be permitted to have ampere ratings not less than the minimum branch-circuit conductor ampacity determined by 630.11(A) or (B) for arc welders.
Exception No. 2: The ampere rating of a receptacle installed for electric discharge lighting shall be permitted to be based on 410.62(C).
Table 210.21(B)(3) Receptacle Ratings for Circuits Serving More Than One Receptacle or Receptacle Outlet
I am thinking a loose connection due to vibration while moving. It happened to me on my transfer switch. Cost me a new transfer switch and two days of discomfort until the transfer switch came in. Now I check them every three months.
My guess woudl be a loose connection, either the plug to receptacle interface, a loose screw in the plug wiring, or the insulation displacement connection inside the receptacle. Corrosion in any of those locations.
The receptacle looks like it’s rated for 15A. If the water heater draws more than 15A, then that’s a big problem for sure. I agree with everyone that said the water heater should have a dedicated breaker.
Failure to not hard wire the water heater 120V electoral connection at the water heater to the circuit breaker of the electrical panel board with Romex or suitable electrical wiring in the RV. RV electrical receptacles are not intended for high current appliances due to the electrical connection method (push in connection, not securely clamped) and light duty contacts for plug cap blades of RV receptacles.
I see these outlets used by RV manufacturers every day. Most RV water heater electric elements are rated at 1400 watts (11.6 Amps) which should be OK for a 15 amp dedicated circuit. In theory. I also see this type of outlet fail all the time.
Many outlet strips are rated for 1,800 watts/15 amps and have melted and caused fires when a space heater was plugged into them. My thought is the reason for plugging a space heater and similar high current devices directly into residential wall receptacle is the greater heat dissipation and structural stability of their design. While the plug and receptacle electrical contacts become warm, heat is flowing and dissipating both into the cord and back into the standard residential or commercial receptacle to keep runaway heating and melting from occurring. Not so with with light weight plastic RV receptacles and outlet strips.
The tab of the water heater plug having the larger amount of arcing in the picture appears to be the “neutral” connection. The statement “ plug was secure in outlet“ is probably only true due to the excessive heat generated which was melting the plug’s tab inside the receptacle contacts. Were the wires connecting to the 120v receptacle loose or tight? My guess would be loose!
A short or other over-current fault would have tripped a (good) breaker. Assuming the breaker was proper and working, that kind of heat only comes from poor connections. Either corrosion and/or loose screws.
BUT -- if the breaker were faulty, then a short could also do it. However, that's a double-fault condition, much less likely.
Those stab connections are not designed for high amp draw for extended duration. I have seen similar results from electric heaters plugged into the same make of outlets. Overheated connections eventually cause corrosion and a break down of the wire.
So….what’s the final answer Mike?
I’m posting the list on Saturday. Please Stand By…
Is the male plug an aftermarket install, I would expect to see a molded plug from the factory. Another thought, did they need to unplug the water heater to make repairs? If so the cheap factory receptacle could have broken. If none of the above I would tend to believe that the cheap stab receptacle could not handle the overcurrent.
It looks to me like contact corrosion, especially on the line blade on the plug. Maybe accelerated with a humid environment. The oxidation increases contact resistance which increases heat which increases the oxidation rate until...things melt and eventually the circuit is opened.
In the original post somebody suggested replacing the receptacle with a traditional one rated for 20 amps. While this seems wise, wouldn't it be against any code ever to replace a 15 amp outlet on a 15 amp circuit with a 20 amp outlet?
Actually, that’s okay according to code. While it’s a violation to replace a 15-amp breaker with a 20-amp breaker, that’s because the 14-gauge wire is only rated for 15-amps and you could overheat it with too much current. But you can install a duplex 15-amp duplex receptacle on 12-gauge wire with a 20-amp breaker due to a code exception. I should write an article on how this works in America. UK code is totally different!
My question is: is it permitted to put a 20 amp recepticle on a 15 amp circuit?
There is a little debate on this. If you read 210.21.B sections 1 & 3 they both say that receptacles should be NOT LESS THAN the branch circuit rating. So I read that as any receptacle of ant least 15A is allowed on a a5A circuit. Come up a lot in the EV world (and somewhat in RV world) where people use 14-50 outlets on 30, 40, or 50A circuits.
210.21 Outlet Devices
Texas Electrical Code 2023 > 2 Wiring and Protection > 210 Branch Circuits Not Over 1000 Volts AC, 1500 Volts DC, Nominal > 210.21 Outlet Devices
Go To Full Code Chapter
Outlet devices shall have an ampere rating that is not less than the load to be served and shall comply with 210.21(A) and (B).
(A) Lampholders
Where connected to a branch circuit having a rating in excess of 20 amperes, lampholders shall be of the heavy-duty type. A heavy-duty lampholder shall have a rating of not less than 660 watts if of the admedium type, or not less than 750 watts if of any other type.
(B) Receptacles
(1) Single Receptacle on an Individual Branch Circuit
A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.
Exception No. 1: A receptacle installed in accordance with 430.81(B).
Exception No. 2: A receptacle installed exclusively for the use of a cord-and-plug-connected arc welder shall be permitted to have an ampere rating not less than the minimum branch-circuit conductor ampacity determined by 630.11(A) for arc welders.
Informational Note: See Article 100 for the definition of receptacle.
(2) Total Cord-and-Plug-Connected Load
Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 210.21(B)(2).
Table 210.21(B)(2) Maximum Cord-and-Plug-Connected Load to Receptacle
Circuit Rating (Amperes) Receptacle Rating (Amperes) Maximum Load (Amperes)
15 or 20 15 12
20 20 16
30 30 24
(3) Receptacle Ratings
Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall not be less than the values listed in Table 210.21(B)(3), or, where rated higher than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.
Exception No. 1: Receptacles installed exclusively for the use of cord-and-plug-connected arc welders shall be permitted to have ampere ratings not less than the minimum branch-circuit conductor ampacity determined by 630.11(A) or (B) for arc welders.
Exception No. 2: The ampere rating of a receptacle installed for electric discharge lighting shall be permitted to be based on 410.62(C).
Table 210.21(B)(3) Receptacle Ratings for Circuits Serving More Than One Receptacle or Receptacle Outlet
Circuit Rating (Amperes) Receptacle Rating (Amperes)
15 15
20 15 or 20
30 30
40 40 or 50
50 50
I am thinking a loose connection due to vibration while moving. It happened to me on my transfer switch. Cost me a new transfer switch and two days of discomfort until the transfer switch came in. Now I check them every three months.
My guess woudl be a loose connection, either the plug to receptacle interface, a loose screw in the plug wiring, or the insulation displacement connection inside the receptacle. Corrosion in any of those locations.
Tiffin uses push connect outlets throughout the coach. My guess is one of the wires worked loose and created an arc, causing meltdown.
The receptacle looks like it’s rated for 15A. If the water heater draws more than 15A, then that’s a big problem for sure. I agree with everyone that said the water heater should have a dedicated breaker.
Failure to not hard wire the water heater 120V electoral connection at the water heater to the circuit breaker of the electrical panel board with Romex or suitable electrical wiring in the RV. RV electrical receptacles are not intended for high current appliances due to the electrical connection method (push in connection, not securely clamped) and light duty contacts for plug cap blades of RV receptacles.
I see these outlets used by RV manufacturers every day. Most RV water heater electric elements are rated at 1400 watts (11.6 Amps) which should be OK for a 15 amp dedicated circuit. In theory. I also see this type of outlet fail all the time.
Many outlet strips are rated for 1,800 watts/15 amps and have melted and caused fires when a space heater was plugged into them. My thought is the reason for plugging a space heater and similar high current devices directly into residential wall receptacle is the greater heat dissipation and structural stability of their design. While the plug and receptacle electrical contacts become warm, heat is flowing and dissipating both into the cord and back into the standard residential or commercial receptacle to keep runaway heating and melting from occurring. Not so with with light weight plastic RV receptacles and outlet strips.
Loose connection
The tab of the water heater plug having the larger amount of arcing in the picture appears to be the “neutral” connection. The statement “ plug was secure in outlet“ is probably only true due to the excessive heat generated which was melting the plug’s tab inside the receptacle contacts. Were the wires connecting to the 120v receptacle loose or tight? My guess would be loose!
I believe the current draw was too high for the circuit, causing this.
A short or other over-current fault would have tripped a (good) breaker. Assuming the breaker was proper and working, that kind of heat only comes from poor connections. Either corrosion and/or loose screws.
BUT -- if the breaker were faulty, then a short could also do it. However, that's a double-fault condition, much less likely.
Those stab connections are not designed for high amp draw for extended duration. I have seen similar results from electric heaters plugged into the same make of outlets. Overheated connections eventually cause corrosion and a break down of the wire.
I had to choose "something else" because I believe it was a failure of the self contained receptacle outlet which was not a choice on the survey.
Whether it is lose screws or another lose connection, some type of lose connection is my guess.