(Can copper?) Homework Question for a Co-worker

It might help to know what class he is taking. I can think of a lot of reasons not to do it; but most of them have to do with what kind of heater and what is being connected by the copper wire.

Unlogical.
It is not in practice for Power Devices like Heaters,Motors etc. As you can see in power distribution & House_Wiring that Aluminum conductors are used in Transmission Lines while Copper conductor is used in house-wiring & also in Windings of most of Motors, Transformers, etc. Power cables of almost all domestic appliances, like kitchen tools, TVs etc are of copper.

The heaters are normally NiChrome but all the connector to these are of copper.

However it is of utmost-consideration in connectors of Sensor-like devices [say Thermal sensors Type T, K etc] which are Bi-Metallic Junctions where a very small voltage is generated. There the connectors are of similar metatls to avoid on the contacts [both] bi-metallic-volage to off-set the sensor signal.

There is no reason why a copper wire can not be connected to the heater. On the contrary most of the heater manufacturers prefer copper wire to aluminium due to specific advantages. Ofcourse, there are certain areas where copper wire is discouraged such as places where corrosion of copper is expected. Secondly, if the heater already has leads which are aluminium then copper wire can not be connected to aluminium wires directly. It is also an industry practice to connect alumium wire with copper wire through crimped connections some times. Unless, the problem is defined in more specific details, an answer to this question may not be possible.

My guess would be that the heat cycling of the copper would cause fatigue in the metal, resulting in hot spots from ohmic heating, and potential fires.

As I recall, copper has some very different heat cycling characteristics.

Thks Bruce. Good thought. The heavy duty industrial heaters are designed to run on copper wires. In fact in hazardous areas where the sparking or hot spot fires are expected, it is copper that is specified. In refineries, it is manadatory to use copper cables and aluminium is not allowed. I will cheack on the metal fatigue phenomenon in copper and lets discuss more. Have a nice day.

Copper oxidizes rapidly with heat and can cause crimped connections to degrade to the point that heater current density at the joint can become so hot that the wire melts. Same for aluminum. Usually, unstranded, copper wires are plated with cadmium (or some other wire with low oxidation properties) to make the connection.

Not anymore, Cadmium is only allowed in 0.01% in any single component for RoHS standards. Not sure what they are replacing it with.

I'm glad I'm not far from retirement . . . I know it's a bad attitude, but I'm glad the next generation are the ones who will have to deal with RoHS, etc. Platinum wire ought to work O. K. I'd bet it'd never make it to the dump. :-)

I know what you mean. The scary thing is the twin guns of RoHS and WEEE. Let me get this strait; you want me to use lead substitutes that I know are going to shorten the products life span and then I'm responsible for paying for the recycling of those crappy products that you forced me to make in the first place?
I'm all for recycling and the removal of toxic waste from landfills, but tell me to make better products or tell me to make environmentally sound products. What's that old adage; Fast, cheap and reliable, pick any two.

Some heating elements have internally a steel wire welded to the nicrome heating element. The steel wire provides an unheated segment across which a temperature gradient is developed in order that you are not attempting to terminate to a glowing hot wire. Once you get down to a reasonable temperature, it would seem that copper would be the preferred conductor.

While copper is certainly the preferred conductor it is normal to isolate the worst of the heat as rcapper says. In items such as toasters spot welding is used. In the days when these were regarded as repairable, repairs were made with silver solder (probably some cadmium in it. For large furnace elements I've worked on we used to TIG weld a stainless threaded connecting rod to the inconel bars used as the actual heating element this isolated the worst of the heat and was apparently reasonably compatible with copper . Some degradation of the insulation often occurred as copper conducts the heat away from the termination (some of the heat being from the actual contact). These connections were made using a hydraulically crimped lug and lock nuts on the rod. I'm talking large sizes here, cables from 120 sq mm to 240 sq mm and the inconel bars 25 x 6 mm and 50 x 8 mm.