half a power cut - Page 1
Forum section: electronics / general

author: jpb
author_rank: Super Contributor
timestamp: May 09, 2013, 07:18:36 pm
content: Came home today to find the internet down and no amount of turning the modem on and off seemed to restore it. It would turn on, then try to find the internet and then give up.The lights in the house seemed a bit dim as well.Then I tried to heat some milk up in the microwave and it came out warm but not hot. The computer and tv were working ok. The electric hob rings would glow red when turned on.I finally looked at my plug-in mains power meter and switched it to Volts. Instead of 230-240V it was reading just 175V.We have power cuts from time-to-time but I've not experienced this half-a-power-cut before, all rather weird.Ringing the electricity company revealed the information that there was an incident with an overhead cable.Thankfully it is now restored and the meter is reading 235V.

author: Monkeh
author_rank: Super Contributor
timestamp: May 09, 2013, 07:21:42 pm
content: Volt drop caused by a damaged or missing cable.

author: G7PSK
author_rank: Super Contributor
timestamp: May 09, 2013, 08:59:33 pm
content: Always getting power cuts here, the wind picks up and the power goes out, despite all the wind turbines in the area, never had a brown out though. And the internet goes down on average every six days.

author: tom66
author_rank: Super Contributor
timestamp: May 09, 2013, 09:08:20 pm
content: I had a brownout down to 90V for a couple of seconds, and the computer PSU rode through it like a charm. I do like PFC circuits sometimes.

author: jpb
author_rank: Super Contributor
timestamp: May 09, 2013, 09:30:11 pm
content: What was strange about this one was there was enough power for things to work or almost work. Like the modem, it looked like it was trying to work but didn't quite have sufficient power to connect to the internet. All the lights did what they normally do so it looked like it was working so I wasted time telephoning my internet provider. The microwave worked but at low power with a dimmer light.It lasted a few hours - plenty of time for me to blunder around trying to work out what was wrong (I'm a bit slow).My desktop computer was fine, so it was happy with an in-between voltage (halfway between 90-110V and 220-240V).Normally the power goes off completely when it goes, such as when a tree brings down one of the cables. I guess this time a cable was damaged but didn't quite break or else there was more than one cable in the supply chain.

author: Rufus
author_rank: Super Contributor
timestamp: May 09, 2013, 09:42:16 pm
content: Quote from: Monkeh on May 09, 2013, 07:21:42 pmLoosing 50 or 60v across a fault? It would melt.Most likely they lost neutral and the voltage you get depends on the load on your phase. The OP was probably lucky his neighbours might have been popping things with 300v on their phase.

author: Monkeh
author_rank: Super Contributor
timestamp: May 09, 2013, 09:58:27 pm
content: Quote from: Rufus on May 09, 2013, 09:42:16 pmThis is also a possibility. However with a lost neutral, they would kill the supply rather than leave it like that.And no, cables wouldn't melt if a ring main dropped a leg. Probably right about a damaged conductor failing entirely though.

author: eKretz
author_rank: Frequent Contributor
timestamp: May 09, 2013, 10:06:05 pm
content: Quote from: G7PSK on May 09, 2013, 08:59:33 pmYowza! That sounds like 3rd world stuff! Are you out in the country somewhere? Where I'm at I usually only lose power for a few seconds maybe a few times a year. The very longest was about 6 hours when we had a massive nasty snowstorm that knocked down utility poles and power lines about 10-12 years ago. I am right next door to the utility company's maintenance HQ though, lol. I don't think I ever lose internet access though.

author: Psi
author_rank: Super Contributor
timestamp: May 09, 2013, 11:43:36 pm
content: More likely one of the phases was dead and the remaining two were being pulled down due to feeding back through the 3phase transformers onto the missing phase.It's supposed to trip all phases out if one fails but sometimes it doesn't happen.

author: G7PSK
author_rank: Super Contributor
timestamp: May 10, 2013, 08:55:59 am
content: Quote from: eKretz on May 09, 2013, 10:06:05 pmYes I am out in the wilds of Norfolk UK. The forgotten region. Full of cell phone black holes as well. And I am nearly 3.5 KM from the nearest telephone exchange so the internet drops if a bird lands on the wire.

author: jpb
author_rank: Super Contributor
timestamp: May 10, 2013, 09:09:08 am
content: Quote from: G7PSK on May 10, 2013, 08:55:59 amI'm in Cambridgeshire and it is not a lot different! I'm 5.5km from the exchange and it took ages before we were even allowed broadband of any sort. Now we have to pay a lot for a slow service but compared to dial-up it is magic. I also can't use my mobile phone at home though other members of the family on different providers can.I suppose on the positive side we get less electrical interference - similar to being down a salt mine!

author: rsjsouza
author_rank: Super Contributor
timestamp: May 10, 2013, 09:40:00 am
content: Quote from: Psi on May 09, 2013, 11:43:36 pm+1 to this. I have seen this before as well - everything dim, some things still working on the house but not the building elevator (the only true three phase machine close to home). I have seen worse, though: if the three phase distribution transformer close to the house is star with a non-grounded neutral, the neutral voltage is raised and some older and/or cheap equipment simply blows away.