Damaged Live Terminal

HI!

VERY INTERESTING !

1. Basically, whenever there is a loose connection , there will be burning due to arcing.

2. If live terminal is loose, arcing energy shall burn live terminal. If neutral terminal is loose, it will happen to the neutral also. ( in single phase ).

3. But, if there is a 5 pin plug, with 3 phase & neutral + Earth, then may be because the energy thru neutral is minimal as balanced load neutral current is almost zero. hence, live terminal shall get burn first under these 3 ohase connections.

Sounds like a classic case of a bad (high resistance) connection between the phase male pin of the plug and the phase female connector of the socket.

It may be wise to get an electrician to check the socket if the plug looks undamaged as this can be a serious fire hazard. If you plug the appliance into another socket does the same thing happen? If so it is likely the appliance plug (or it's wiring connection inside the plug) that is the problem.

In my experience, it is not always the live terminal that overheats, it is much more of a lottery than that, and there are several factors that can lead to overheated terminals.

Incorrect installation practices are often to blame. Here is a pic of a disconnect switch that was wired with steel washers used as spacers between busbars and switch :

The interesting thing here being that despite all terminals being installed in the same way, only one has fizzed up.

On the other hand, it is not unheard of for terminals that have been performing OK for years to overheat, even when they have apparently been installed correctly. I saw the remains of a 3-pole main switch earlier this week that had been removed from the switchboard of a house owned by an electrician. The pole that controlled the night-store heating had burned when the heating was turned on this winter, but the owner was quite sure that it had operated satisfactorily for more than a decade before it failed.

As far as why only the hot lead seems to fail in your application, I suspect that the mechanics of the terminal that happens to be the hot lead maybe difficult to tighten properly. For I've seen, as others here have too, that both the hot and return are just as prone to failures. But I have seen that terminals that bind before properly compressing on the wire (thus giving a false impression of a tight connection) fail far more often on heavily loaded circuits.

Basically, most common cause is the loose connection, overloading the capacity of the electrical equipment/apparatus, wrong cable sizes and due to moisture effect. It may also due to manufacture defect of the plug or socket.

Some may cause by global competition that some of the electrical manufacture has to cut cost and reduce the material quality in which the actual current capacity of these socket and plug are reduce and not able to withstand the actual limit design current.

I have some experience especially with the 13Amp socket outlet and the plug top. With low quality of 13Amp socket and the plug top, you will face that, the socket will be overheating after running your 1 hp air cond forabout 30 minutes. After replacing it with a better quality the problem is solved.

Live terminal on standard 120Vac 15A plug is SMALLER one. Maybe it heats faster and to a higher temperature on high current loads(?) This damages the live plug terminal and corresponding socket terminal as well(?) Try getting BETTER grade plugs and sockets that are rated to handle higher current.

the size of the terminals has nothing to do with the overheating. the size difference is due to double insulating of the intended load. in a double insulated appliance if live energy were supplied to the neutral it would go to the housing because the neutral and ground are bonded together.

It seems from the discussions, that it is very important to check all connections to plugs and sockets on regular basis to ensure good connections. I have found that normal screw terminals seem to 'vibrate' loose after a while, when connected to an AC supply.

Thanks for all your comments.

Ah an interesting question. I like interesting questions. There are several factors involved here.

Primarily terminals fail due to cascade resistive heating. If a terminal is not correctly connected, the resultant resistance will generate heat. The heat will cause the metal to expand, and when the circuit is opened the joint will cool and contract. This cycle will repeat continuously and can begin to loosen the connection. This will in turn increase the resistance which initiates the cascading effect. Arcing creates carbonised surfaces which greatly enhance this effect.

In a 3-phase balanced circuit, little or no neutral current should be flowing thus the effect could occur on any phase terminal. However the effect will normally "run away" on just one terminal.

In a single phase circuit this effect should be equal on either terminal (live and neutral); each carries the same current. However if there is or ever has been a fault, fault current will only flow through the live terminal. This can initiate the cascade effect on the live terminal and of course once started will run away.

In addition a lot of circuits can carry an appreciable earth leakage current. Computers, solid-state transformers and fluorescent lighting are the usual culprits. This figure may be small for individual devices, but of course may add up to several hundred amps in the main earth risers of buildings.

It is good practice to install "clean" earths to IT suites as the normal earth may carry these large currents.

These leakage currents are also carried through the live terminal only, in addition to the circuit load. Again any imbalance will preferentially heat the live terminal over the neutral.

I have had a lot of experience with electrical. I agree with Harry Potter with his answer. I would like to see a photo of the affected terminals, as well as have some more information. Is this a 120V appliance, single phase or 3 phase, current draw, what type of appliance, has this happened with the same piece of equipment or different ones, have the cord end or the receptacle been replaced?

What I am looking for is a pattern. I have in my experience (40 years as an electrician) seen a good looking connection, but there could be a small resistance that could cause heat with a large current draw. Something else i should ask is this, what is the current rating of the equipment and of your cord end and receptacle and wire?

Actually being an electrical engineer practitioner, I agree about the technical comments of Mr. Simon Wan, that in most cases the user overlooked the quality of electrical devices they intend to use. We can't put the blame on them may be becuase of lack of budget or ignorance of electrical principles such as

1. Fail to use good quality and may be under size capacity of power recetacle.

2. Loose terminals due to lack of preventive maintenance that cause the arcing sparks when load is energized.

3. In addition to a good quality of electrical materials you choose to buy in stores, check also for the rated capacity if it can handle the load. Note that its not a tail that wave the dog, but its dog that wave the tail.

______________

BRUTUS , Northrop Grumman, SA

I was just reading all of the replys to this post and noticed that the major point was still unaddressed. The point is that in an electricla circuit the neutral only carries the unbalanced current; which explains why it is not overheating.

To the point of the live or hot terminal the result is either that there is a high resistance resulting in high current flow or that possibly the circuit breaker has been oversized defeating the trip point fro the branch circuit.

I have been reading and thinking on this some more. Without good basic information (what appliance is, how used, photo of terminal, voltage, single or 3 phase,) it is difficult to troubleshoot this problem. We are "shooting" in the dark. The responses are good, and all are possible solutions, however, we need more information. Another cause could be dis-similar metal connection. For example, copper to aluminium.

Great response, thank you. I have a few other things to add to this. Many years ago, I had a friend who had a short in his wiring in a lamp socket. I checked the socket, replaced the fuse and boom, the fuse blew again. This went on for a couple of hours and to say I was frustrated. I would remove the socket, fuse stayed, install socket, boom. I measured across the socket with my ohm meter, infinity. To make the story short, I discovered a discoloration similar to the discoloration of a gasoline slick on water. This went between the terminals. This is what I determined, a carbon trace. When I scratched out this trace, the circuit was fine. Since then, I have come across this a couple of times. You have to hold the suspected part just so in the light to see the trace.

Thanks for the words of wisdom on the site.

AND WHERE IN THE HECK IS LEWIS THE BEAR!! LOCATION IS IMPORTANT!! Especially in the case of Electrical Systems. IF he is located in North America, and IF the circuit is 120v 20 amp, he might want to replace the wall socket with a 20 amp socket, and one of good quality. Most houses are wired with 15 amp sockets (and cheap ones at that). For that matter, most line cords are wired with 15 amp connectors. If the device is used in only one location, in addition to changing the wall socket, I would change the connector on the power cord to 20 amp also. 15 amp plugs will still fit in a 20 amp socket.

Bill

Changing the outlet or plug to 20A is not accomplishing anything. The branch circuits in the US for residential convenienance outlets are 15A circuits. they have a 15A breaker and most often 14awg wire. If yiou are going to change to a 20A circuit you need to replace the wire with 12awg and a 20A breaker.

Most of the times that I've seen situations like this; someone has changed the breaker to a larger size than the wiring because of overloading. If the terminals are burning just imagine what the wire inside the walls looks like. This is a potential housefire waiting to happen.

That is why I specified a 20 amp circuit... meaning 20 amp breaker, AND 12 awg romex (or what ever local code calls for). I gather some local codes don't allow Romex.

Bill

Bill,

I haven't worked in any jurisdiction that didn't allow Romex in a single-family dwelling.

personally, if it were my house; I would run 12AWG and then still use 15A breakers.

That way the wiring that is embedded in the wall is sufficiently oversized t and wil generate far less heat; and the circuit is sufficiently protected for just about any appliance that I own. (even my air compressor)

A friend of mine from Southern California told me that where he was, they had to run conduit... no romex... but I don't know details there though.

Another friend of mine needed some painting done so I loaded my air compressor in the back of the truck and off we went... only to find out that his whole bloody house was wired for 15 amp. There was no way I could get sufficient power to the air compressor, so we ended up painting by hand.

Like the guy from NY, I wire lighting for 15 amp, and outlets for 20 amp, although I use 12 awg wherever possible. I buy #12 by the roll, but if I have to use #14, it requires a trip to the hardware store.

Bill

Wiring does need to be properly rated for the load and the breaker to prevent a major fire hazard.

Only dedicated light fixtures and wall switches should be wired with 14 gauge and 15 amp breakers. In this area, most outlets are wired with 12 gauge and 20 amp breakers.

When you use one of those cheap 15 amp sockets(10/$3.50) with a 15 amp space heater, it should be no surprise that problems arise. A good quality 15A or 20A rated socket (1/$3.50) can make a BIG difference.

noshorts:

Your post brings to mind a scene in the movie "A Christmas Story", the movie about the kid with a Christmas desire for a BB gun.

The Ol' Man plugs in a lamp, along with the twenty-three strings of tree lights. After a generous release of magic smoke and ozone, he opines "... well, I guess there are just one too many."

People in the herd will overuse and abuse anything. I discourage plug multi-taps at every turn for this very reason.

Thus, to the original post: Are there other items being powered by the same outlet/line/branch/breaker?

I am pleasantly surprised about the feedback and comments about the asked question. I would like to supply more information: The location is South Africa where the line voltage is 220V 50Hz. The problems normally occurred in single phase 16A plugs and sockets and with high current appliances such as a clothes tumble dryer (2200W), an electric heater(2000W), a small inverter type arc welder (3000W) and a rotary angle grinder(2000W. The plugs and sockets used were normally of fair quality with a certification of quality mark. I think most of the problems occur because if the typical construction of the plug and socket. (see picture of plug below, detail socket pic to follow).

The South African standard plug and socket is a round type. To make good contact on a round pin in a round socket, I think, is difficult and only a small contact surface area is possible. Is that a possible problem?

The comments about poor quality plug and sockets is very valid but a little preventative maintenance (checking fasteners and screws) have solved some problems of overheating of connections. More info to follow.

I have experience with the European, not in North America, style of cord ends and sockets. You hit the nail with the round connection. With the round connection, on the socket side there are two blades that have a curved top that the round (post) cord end slides into. There is probably less contact actually on the connection because of the curves than there is on a blade style of connection. If there are small variances in the circumference of the round "post" then there may be less actual contact surface and therefore there is more current flowing through the actual physical connection than there should be. This of course causing heat, creating more resistance, more heat and the cycle (pun intended) continues.

You might have a recurring problem if you are using new cord ends with an old (by this I mean you have never replaced the wall socket. If you keep burning the "live" terminal, then I would say that the socket should be replaced as well. On a different note, I replaced just yesterday a male cord end on a 220 line as aluminium wire was used on a non copper/aluminium cord end. The cord end was plugged into a generator and this was supplying 120 / 240 to the house as well as charging a battery bank. (there is no electricity at this location in Guatemala). The lights would go on, then off, then on, as the cord end connections would heat up and cool off.

Sorry for late response, I am catching up on old posts after being away. My guess is the switch contributes to the heating, it doesn't conduct heat away as well as the neutral conductor and may heat up itself if the contacts are loose or dirty. This will result in the live pin running hotter than the neutral.

If your plug were a British style 13A rectangular pin plug I would suspect a loose or dirty contact with the fuse in the plug.