Grounding pin on Type E socket is warm to the touch

Question

I live in an apartment building built about 40-50 years ago, with aluminium wiring and Type E power plugs.

I noticed that the grounding pin on one of the sockets is somewhat warm to the touch, I would say about 35°C. I have experienced that on some high-powered appliances such as electric kettles, one of the plug pins gets hot during operation, but this plug has nothing inserted into it, yet is still warm.

Does this mean that the wiring in the building is done incorrectly, or is this a fairly normal condition?

Note: Since this is aluminium wiring in a somewhat old building, I suspect that a contact got loose and needs tightening and the reason why an unoccupied plug would get warm is that all the outlets are wired in series.

Answer 1

Safety ground pins never carry current except during fault conditions. Therefore they should not be getting hot.

Quite likely something else is getting hot and causing problems. Most likely either the plug contacts due to being loose, or the hot or neutral terminal where they attach to the aluminum.

The American experience with aluminum wiring taught us 2 very critical lessons:

1. The terminal needs to be properly rated for aluminum wire. North America had a lot of trouble when "receptacles made for copper wire" were hastily and carelessly certified for aluminum. The key to aluminum terminal design is the thermal expansion of the metals. Aluminum expands more than copper. An aluminum lug (aluminum wrapped around copper) works favorable. A copper lug works disfavorably, as the aluminum is crushed as it expands, so when it shrinks again it is now loose (under-torqued).

2. This was a copper-wire issue, we weren't even looking at aluminum wire for this one. We found out that first, screw torque matters even on small terminals, and poor torque causes series arcing failures that overheat and start fires. And second, based on lab testing at trade show booths, electricians are positively awful at guessing torques - getting the same "25% in spec, 50% low, 25% high" score as their spouses. As such, NEC was amended in 2014 to require torque screwdrivers. Again this was never about aluminum, but it sure explains a lot about North American aluminum troubles, because nobody was using torque drivers on the small stuff, yet everyone was doing it on large feeder lugs (which have proven reliable).