Direct current distribution

There exist copies of newspaper and magazine ads for home radio receivers (RCA and others) that were built specifically for the DC residential distribution of New York's Central Business district. The ones I've seen were from the 20's and 30's.

I'm not sure when this DC service was discontinued, although I seem to recall that Con Edison provided DC service for elevators well into the

50's and maybe beyond.

I'm sure someone here has the details...

Beachcomber

Didn't NYC originally get a portion wired in DC by Edison?

The London cinema/theatre area had a 220VDC supply for years, to power the arc lamps used. The University College London Physics Department also took this and the building was wired with 220VDC outlets (in addition to 240VAC and 12VAC outlets) throughout, for powering experiments. I recall using the 220VDC supply for an experiment to measure the temperature of a carbon arc. In 1980 when I was there, the 220VDC supply was generated in the basement as the external supply had been discontinued by then, but I believe that only happened 2 or 3 years before, which would be late 1970's.

"Beachcomber" wrote

They still do supply DC in NYC. but I think they are trying to phase it out. As a first step:

my guess is within 10 years they will try to have all DC systems supplied as AC to the customer and then customer rectified.

Yes- The Pearl street station was the first "central station". However, the DC system at "user" voltage levels was very limited due to voltage drops with reasonable sizes of conductors -say 1/2 mile radius so multiple small stations had to be used. The transformer invented by Gaullard & Gibbs made AC practical for longer distances and Tesla's polyphase system and motors put the dirt on the grave of DC distribution (as opposed to HVDC transmission which wasn't viable 'til much later). --

Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer

Thanks for the information. I was pretty sure someone here would know.

I have been away from New York City, except for short visits, for over 50 years. I do remember motor-generator sets for running x-ray machines. I also was aware that buyers of sewing machines in the New York needle trades needed to worry about ac and dc. IIRC, especially with my limited knowledge of that time, dc machines would use some form of resistor speed control and start-up. I think that ac machines had their motors running continuously and engaged by clutches.

I have a suspicion that it may take well over ten years to complete conversion to ac.

Bill

The last 25Hz rotary converter substation on the Subway was shut down in 1999, this would have been the last low frequency supply, and I have a feeling that I read somewhere that Con Ed stopped supplying their last customers with d.c. at about the same time.

I may be wrong, but I thought there was an article in one of the IEEE magazines a couple of years ago about the last DC feeder being removed. It was a big deal at the time. I will see if I can find it.

Ben Miller

Someone previously posted an article

November 14, 2007 "Today, Con Edison will end 125 years of direct current electricity service that began when Thomas Edison opened his Pearl Street power station on Sept. 4, 1882. Con Ed will now only provide alternating current..."

That looks the one I was thinking of. Thanks!

Ben Miller