The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Photo Upload Tutorial
by DanK
Yesterday at 11:35 PM
Sprinklered equipment 26-008
by bigpapa
12/02/16 04:24 PM
On Delay Relay with Auto Reset
by Potseal
12/01/16 09:59 AM
Wow, that was close!
by jraef
11/28/16 07:06 PM
Earthquake in New Zeeland
by RODALCO
11/27/16 11:25 PM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 13
HotLine1 9
Texas_Ranger 8
sparkyinak 7
Trumpy 6
Who's Online
1 registered (aussie240), 158 Guests and 6 Spiders online.
Key: Admin, Global Mod, Mod
Page 1 of 2 1 2 >
Topic Options
Rate This Topic
#171021 - 11/17/07 08:49 AM What would've caused my power to do this?
Dawg Offline
Member

Registered: 01/06/05
Posts: 58
This morning I was online when all the sudden the computer goes off. Then come to find out my home suffered a power outage.

Ok, no big deal, except my monitor (LCD flat screen) would flash on and then right back off....then on and right back off....un plug it and it would stop...but plug it back in and it would do this all over again.

But wait! How could it do this? The power is out!

Well then I go in to use the rest room, and forget the power is out, when I flip the switch. There is a faint glow.

I look up and low and behold the light was illuminated, but barely. It almost looked as if it were on a dimmer switch on the lowest setting.

I tried a few other lamps in my home. All of the incandescent lamps did the same thing (the fluorescent tubes wouldn't do it)....the filament would glow an orangish color, sorta looked like those old vacuum tubes they used to use in radios.

Went and grabbed my multimeter, flipped it on AC volts and stuck the probes in the 120 volt wall outlet.

I got a reading of 24 volts AC out of my 120 volt AC wall outlet.

I called the power company and reported the outage. I got no explanation on why it happened but in about an hour I had power again.

I'm just curious as to what would've (or could've) caused this to happen? I've been in power outages before, but not ones where there some power still there.

Anyone know?

Thanks.

Top
Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#171023 - 11/17/07 10:16 AM Re: What would've caused my power to do this? [Re: Dawg]
SP4RX Offline
Member

Registered: 10/01/07
Posts: 56
Loc: Edmonton, Alberta, Canada...eh
I can't actually explain what happened, but to me it sounds like there was some kind of back-feeding going on. As though 2 line-side phases of your supply transformer went down, but the third was still live. It would still induce voltage into the secondary windings, but the voltage would be much lower than normal.
This is just an educated guess though, I've never seen this happen before. But I'm sure someone here will have a definite answer as to what would've caused a situation like this.


Shawn.

Top
#171037 - 11/17/07 04:05 PM Re: What would've caused my power to do this? [Re: SP4RX]
wire_twister Offline
Member

Registered: 07/25/07
Posts: 265
Loc: Georgia USA
I have had one hot leg go completly away at my house, due to a transformer failure. Never seen just 24 volts though interesting problem hope someone can explain.
_________________________
Jimmy

Life is tough, Life is tougher when you are stupid

Top
#171051 - 11/17/07 09:12 PM Re: What would've caused my power to do this? [Re: wire_twister]
Sixer Offline
Member

Registered: 08/08/05
Posts: 264
Loc: Canada
We used to have brownouts a lot before the poco upgraded their system. The lowest voltage I got at a receptacle was 42 volts. Across the street would have full power, and other parts of the subdivision would have none. It's been a while but I do remember a lineman telling me it was something to do with a 3 phase distribution transformer. Can't remember what was the exact cause.
_________________________
Sixer

"Will it be cheaper if I drill the holes for you?"

Top
#171055 - 11/17/07 10:23 PM Re: What would've caused my power to do this? [Re: Sixer]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
I suspect an open phase on the primary might get some voltage reflected on the secondaries of the transformers on that missing phase through the other loads if you had a mix of wye and delta connected loads.
_________________________
Greg Fretwell

Top
#171057 - 11/17/07 11:06 PM Re: What would've caused my power to do this? [Re: gfretwell]
Check Pilot Offline
Member

Registered: 11/25/05
Posts: 145
Loc: Edmonton Alberta Canada
I've seen that exact same thing - 24 volts - we had one of the phases crap out and someone in the local area went and started up a genset and backfed the current into the grid without making the proper offlodading from their genset back into the line. Another case of a know-it-all Home owner just getting things back to normal.

Top
#171058 - 11/17/07 11:37 PM Re: What would've caused my power to do this? [Re: Check Pilot]
SP4RX Offline
Member

Registered: 10/01/07
Posts: 56
Loc: Edmonton, Alberta, Canada...eh
The only thing I don't get about the scenario Check Pilot is describing is that the OP mentioned being at his (or her) computer desk when the power went off and seeing his (or her) monitor flashing off and on.

If the 24V were due to a backup power supply back-feeding the supply transformer, wouldn't there be a time delay between the power outage and the appearance of the low voltage responsible for the monitor's erratic behavior? The DIY'er who so ingeniously discovered how to re-supply his house with home-made electricity would surely need several minutes, at least, to acknowledge the power outage and fire up the generator.

Maybe I'm misunderstanding the wording, but didn't the monitor's weird actions begin at the moment of power loss?

Top
#171079 - 11/19/07 07:21 AM Re: What would've caused my power to do this? [Re: SP4RX]
Texas_Ranger Offline
Member

Registered: 12/17/01
Posts: 2343
Loc: Vienna, Austria
Computer stuff can do all sorts of weird stuff... my ex-gfs computer would act off as you turned off the switch on the back of the ATX power supply and pushed the power button on the front. The power LED lit up and the floppy drive started making weird "read error" type noises. Never managed to figure out what was happening there.

Top
#171084 - 11/19/07 08:47 AM Re: What would've caused my power to do this? [Re: Texas_Ranger]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
I agree with Tex
These TSR supplies can build up enough DC voltage with low line voltage to try to power on but as soon as the full load hits it the supply "undervolts" and goes back down.
_________________________
Greg Fretwell

Top
#171085 - 11/19/07 09:40 AM Re: What would've caused my power to do this? [Re: gfretwell]
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
You can get the same thing with the switched-mode (chopper) power supply found in many modern TV sets when fed severely under-voltage. There's enough juice to charge the reservoir capacitor, the start circuit will try to get the oscillator going, but as soon as it draws current the voltage drops too low on the capacitor, so it drops out again, then the whole cycle repeats.

The typical results is a regular flashing of a power/standby light, sometimes accompanied by a regular "ticking" sound, etc.

Top
Page 1 of 2 1 2 >



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals