Mainly, they can go bad, with no means of fixing, nor inpecting, nor means of actually detecting prolems early:

What was that cord connected to? It looks like you were close to flames with that one.

My Barth came complete with a melted dogbone. It put the frighteners on me wondering if there was some electrical problem. Electrical is fine but I agree about the molded plugs keeping secrets.

Not sure if this is heater-related, but I will repeat my winter caution about using an electric heater on the 1500 watt setting.

This is a full load for many 120V outlets and plugs. My rec is to do a temp test with an IR gun or with your fingers or lips. Any heat detected at all is a warning. Any outlet that sees a heat gun or heater in my stuff gets a high grade outlet. That means from an electrical supplier or similar. I use Grainger.

I keep a good plug with only one flat blade for testing. This allows me to feel how tight the fit is, which relates to how good the contact is. There is a spec for so many ounces of pull, but a good feel can be developed after feeling a few.

In addition, the plugs should be clean with no corrosion. Cheaper plugs with folded metal contacts should be replaced with solid brass contact plugs.

Plugs should never be connected or disconnected with a load on them. This causes arcing and pitting, which will add to overheating and burn your house down while you are sleeping without pajamas. If you can find one, a point file or a flexstone can sometimes improve a pitted or oxidized receptacle.

My neighbor, the fireman, says every cold snap brings fires and fatalities caused by space heaters overloading wiring. We both agree that UL did a disservice by allowing 1500 watt heaters to be sold to consumers. They are safe only when used with connections and wiring that are in perfect condition. A neighboring trailer burned down a few winters ago just before we got there. The preliminary investigation concluded that it was overloaded wiring or outlet from a space heater. I didn't get the final report, though. The good news is that (it was an Irish festival)rain had wetted everything down so no other RV caught fire.

I never turn my back (or close my eyes) on a 1500 watt heater. Generally, we use the high setting only for initial warming-up.

Most instances in which I have encountered a problem like Rusty displayed were combined with compromised connection on the other side of the mating plug. I had this happen on my boat and saw it with several others or at the supply post. Remove or replace the connections, clean the tinned leads on both sides and properly tighten the connections and the problem was resolved.
It is also a good idea to add tightening all accessible connections to the Spring commissioning list. (Any not accessible need to be accessed if they are 10 ga. and up, these seem to heat, expand and dance more that others. Don't forget the DC side also.)
When operating at a normally high Summer load check connections with an IR temp gun. I find mine essential for checking all manner of things including tires for hot tread or sidewalls, bearings and other special items on the boat that are more fun to employ preventive maintenance than repair.

quote:

Originally posted by Bones:
My Barth came complete with a melted dogbone. It put the frighteners on me wondering if there was some electrical problem. Electrical is fine but I agree about the molded plugs keeping secrets.

Hospitals have transparent plugs that allow visual detection of overheating or arcing. Transparent molded connectors offer that advantage, as well. Overheating really discolors them. Usually long before melting temperatures.

quote:

Originally posted by ccctimtation:
Remove or replace the connections, clean the tinned leads on both sides and properly tighten the connections and the problem was resolved.

Tinned can mean different things for different people:

1. For some, it means a tin plating on the copper strands. This is very good at resisting corrosion.

2. For others, it can mean a bit of solder on the end of a stranded wire, coating and making all the strands into one solid wire. For high amperage connections, this can compromise current carrying ability. This is because the screw connections cannot force the soldered end into total and intimate contact with all the flat surface of the underside of the screw head and the mating surface underneath. Only the high spots make contact. ..........A stranded end of the same wire would be forced into a much greater contact area, owing to the flexibility of the individual strands.

This was doctrine at the airline.

The usefulness of this advice will depend on the amount of current carried by the connection.

Yes, the individually tinned strands or more precisely, the overpriced wire that doesn't come from China.

Why I LIKE Molded Plugs:

They are less subject to internal corrosion.

IF properly made, they are unlikely to work loose.

They seem not to suffer as much if jerked out by the cord.

They fit in between wall warts and large plugs on busy receptacles or power strips.

They are easy to cut even narrower with a pocket knife.

All of this is fine if current is low.
________________________________________________

Why I DON'T Like Molded Plugs:

See all previous posts by everybody.

In addition, polarity can be fiddled. People with old outlets or extension cords will narrow the wide neutral blade to fit.

The socket (on the right) is transparent. The plug is from a 20A-30A adaptor. The socket is from a Rigid 100' 10 ga extension cord, powered by a 20A (not the Wal-Mart $0.97 kind) GFCI duplex in a weathertight box. That receptacle was wired by me, 12-2-G. One other duplex and a bench light are on the circuit, and neither is in use.

I've measured current draw on most of the appliances, including the high and low settings on the space heaters.

So I know this connection wasn't overloaded - and I make the connection in a little shelter to keep the it out of the weather.

The resistance in a 100' extension cord may be dropping the voltage enough to heat up appliances and therefore the cable. The stranded cables used in extension cords also increase resistance. The connector ends up being the weak link, or fuse, for the system. If this were the issue, try bringing power out on a heavier gauge wire.

I know you don't do this Rusty, but power should be off or at least minimized when unplugging to decrease the chance for arcing and plug deterioration.

Most of the devices that I run here are resistive loads - so the current can be accuragtely measured (but with nichrome, the load takes a short time to stabilize).

Actually the culprit in the above photo is the plug, which had an internal connection come loose.

quote:

Originally posted by Rusty:

Actually the culprit in the above photo is the plug, which had an internal connection come loose.

Out of curiosity, I have cut a few failed ones apart, and the failures were poor spot welds. All of the strands were not carrying the current.

"it can mean a bit of solder on the end of a stranded wire, coating and making all the strands into one solid wire. For high amperage connections, this can compromise current carrying ability."

Yes it can the reason being that in elect. conductivity it is the outer "valence" electrons that conduct MOST of the power, hence the advantage of stranded wire... When you "tin", "sloder", or "spot weld" the conduntor you have essentially made a single conductor out of that wire which then has only ONE set of outer valence electrons, versus 17 sets with your average "stranded" wire...

quote:

Originally posted by Patch1st:
"it can mean a bit of solder on the end of a stranded wire, coating and making all the strands into one solid wire. For high amperage connections, this can compromise current carrying ability."

Yes it can the reason being that in elect. conductivity it is the outer "valence" electrons that conduct MOST of the power, hence the advantage of stranded wire... When you "tin", "sloder", or "spot weld" the conduntor you have essentially made a single conductor out of that wire which then has only ONE set of outer valence electrons, versus 17 sets with your average "stranded" wire...

The tendency of electricity to travel on the outside of a solid metal conductor (AKA Skin Effect) occurs as the frequency rises. At DC, there is little Skin Effect.

All atoms of a conductor have valence electrons, whether they are on the surface or inside. At DC, they really don't know or care where they are.

Skin Effect doesn't come into play until well above 60 hz. Into hi freq welding and radio frequencies, radar, microwave, etc.