Author Topic: How to get rid of stuff?  (Read 2243 times)

Offline klugesmith

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Re: How to get rid of stuff?
« Reply #20 on: June 11, 2020, 04:40:05 AM »
Came to share a thing learned from looking up "grounding" switches, whose green screw is in fact there for safety ground connection to the mounting tabs and cover plate screws.

In most old house wiring, the cable to a light switch on wall has only 2 wires, "Hot" and "Switched Hot". 

Later codes required a safety ground wire.
In NEC it's formally identified as the equipment Grounding conductor (green, or bare copper, or metallic tube protecting the other wires).
Generally there is no need for a Grounded conductor (white "neutral" wire) at a light switch.

That's changing, because of the proliferation of active light switches, for example with Occupancy Sensing, and now fancy dimmers and color controllers.

The control electronics in those switches requires some standby current, customarily not more than 0.5 mA.  For years, the makers provided connection points and instructions to use the Grounding conductor as "neutral" connection for the control circuit. 

The two or three NEC revisions in past decade have been playing catch-up.  First by mandating that Grounded wire (neutral) be routed to new light-switch boxes, except listed cases that are unlikely to ever get an occupancy-sensing switch.  Then phasing out the permission to intentionally put current (even 0.5 mA) into the equipment grounding wire system.  It adds up when every room in a building has an active switch.

It's consistent with the general principle, after more than 130 years of electrical code evolution, that the Grounding conductor is not for current except under fault conditions. 

Kind of like changing rules about connections between electricity and metal water pipes. 
Long ago, a water pipe was a place you could divert electricity into,  to protect users of faulty electric appliances.  Not any more.  In new work, the only intentional ground connection to a water pipe is to take electricity out of the pipe, to protect plumbers and plumbing fixture users.

What's the story in jurisdictions outside of USA?

Offline klugesmith

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Re: How to get rid of stuff?
« Reply #21 on: September 03, 2020, 06:51:21 PM »
All 7 months of electronics flea market were cancelled this year because of the pandemic.  Need to find other ways to move things along.
Some items saved for projects are finally being abandoned, but that is hard to do.  It's easy to give them more time than they deserve.

Fluorescent lamps, set out with recyclables for weekly collection, were separated from their electronics.
An electric heating pad made for gardening was discarded, after becoming dry and stiff.


A dead microwave oven was reduced to metal frame (for ordinary recycling) and a pile of guts.
This specimen has a short section of conventional rectangular waveguide between magnetron probe and cooker box.


The heart from gut pile was able to beat, after I remembered need for ground connection between transformer core and magnetron yoke.  Not a demonstration to be undertaken by beginners; there are hazards other than electrocution.



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Re: How to get rid of stuff?
« Reply #21 on: September 03, 2020, 06:51:21 PM »

 


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