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Topic Title: Mains supply to sockets intermittent.
Topic Summary: 3 phase supply RCBO control on all phases supplying wall sockets.
Created On: 24 April 2013 02:25 PM
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 24 April 2013 02:25 PM
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roberts

Posts: 26
Joined: 18 January 2003

Users of my village hall complained that their music player(s) went off for a short time and then came on again on many seperate occasions on different days and when connected to any of the 3 phases.
I checked all sockets on all 3 phases with a 60w lamp load and wiggled the plug and banged on the wall socket in case it was an intermittent connection. As the fault seemed to happen on all phases it was not likely to be a connection fault.
I have never seen the fault for myself.
After much chat on many occasions I decided to check all connections in the fuse board and tightened all 50 connections of which only one needed half a turn and that connection was not loose.
I did a check on all circuits with a 10kohm resistor to earth from live in a plugtop. All RCBOs worked on all 3 phase circuits.
When I tried to reset one of the RCBOs it would not reset until I gave it a tap. I have had this happen before on another simple circuit breaker and tapping it effected a cure to its not resetting.
Since I have made these tests I have as yet not had a complaint about an intermittent supply.
I am now thinking that the fault might be with the RCBOs not making good connection inside and that making them trip with the earth leakage test may have cleared the fault on them.
I also suspect the company supply may be faulty but inspection of the overhead cable connections revealed no obvious fault and tapping the neutral overhead cable did not produce any 'crackles' from an AM radio connected to the the red phase wall socket circuit.
I have connected a wall clock that, once disconnected even for a very short time, will not start up without manual starting. This to see if the mains fails at any time as would be indicated by the stopped clock.
I re-wired this village hall in 1999 and all has worked well and been tested by an independent electrician in 2010 with no faults found.
The cut-outs and RCBOs are of well known French manufacturer.
Has anyone had similar problems and particularly with intermittent RCBOs ?
Any other clues please!
Bill (MIET)
 24 April 2013 02:36 PM
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AJJewsbury

Posts: 10963
Joined: 13 August 2003

Sounds like the supply to me - could be anywhere on the distribution network, LV or HV. (I think I'd be a bit wary of tapping overhead lines!)

Are there any neighbours who might have noticed a power fail at about the same time?

- Andy.
 24 April 2013 04:47 PM
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roberts

Posts: 26
Joined: 18 January 2003

Hi Andy
Thanks for the reply. Yes I am on the same 4 wire overhead system in the same road as the village hall and I have had short breaks in the supply but did not think they were as frequent as the hall users complained about. I have also written to Seeboard with a list of things that I have observed wrong with our overhead system (broken and missing insulators on a pole and wires that are too long between poles and can clash together in windy weather. They say they will replace the 4 single wire system with a multicore, sometime !
Point taken about tapping the overhead wires but the 3 live ones are insulated on the premises but not so in the street. But I tapped the bare neutral in particular (with a good dry stick) because the fault seemed to affect all phases.
I'm hoping the electric clock will tell me when the incoming mains supply fails but that is connected to one of the phases.
I gave the company fuses and meter tails a tap too but didn't hear any crackles from the AM radio.
It is a bit of a coincidence that there have been no complaints since I did the inspection and tests.
Have you had any experience with RCBOs giving this sort of trouble ?

Bill
 24 April 2013 05:02 PM
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AJJewsbury

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If the supply N goes open circuit it doesn't just kill the supply to all three phases, but you get strange effects as the loose end of the N is dragged towards the voltage of the most heavily loaded line conductor - with the result that some single phase equipment suddenly gets presented with anything up to 400V - usually with a lot of burning and dead electronics.

Have you had any experience with RCBOs giving this sort of trouble ?

Not that I recall. They tend to trip, but stay tripped - not coming back on again without intervention.

Some supplies are much worse than others. We've got UPSs that complain regularly about the supply (at least once a week) and the lights flicker noticeably at least once a month on average - and this is a commercial building in an urban area with underground LV & HV. The day YEDL tried to locate a fault on one of the underground LV cables by repeatedly replacing the fuse in the substation and trying to listen for the bang from under the pavements (dozens of times) kept the UPSs very busy - and we apparently weren't even on the faulty LV circuit!

- Andy.
 24 April 2013 09:11 PM
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sparkingchip

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"Users of my village hall complained that their music player(s) went off for a short time and then came on again on many separate occasions on different days and when connected to any of the 3 phases. "

So the common feature is the music players and any extension lead that may be used to plug them in, I'd start by PAT testing the players and their leads before getting in touch with the DNO about the incoming overhead cables to the village hall. What are these music players, are they mains operated or plugged into a socket with a mains adapter transformer?

Andy
 25 April 2013 05:43 PM
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roberts

Posts: 26
Joined: 18 January 2003

Hi Andy
Yes the music players have been checked out and there are about 3 of them, including a new purchase.
I managed to annoy the hall user by insisting that I see the fault and the players. They didn't like that idea as it meant that I didn't believe what they had described to me as the fault.
From what you say about the supply neutral becoming disconnected I think it safer to get the supply company to come and check it out.The users also have said they could smell burning at the socket. Which I took with a pinch of salt; and even at 440 volts across live and earth (assuming the Neutral goes diss for a bit it isn't very likely to cause arcing or tracking is it ? And anyway the neutral and earth are connected at the fuse box, no seperate earth rod. We don't have any 3 phase loads so line to line volts can't be applied to any one piece of equipment.
So far they haven't sent a bill for blown up music players !!!
Incidentally the electric clock has not stopped in the last 48 hours, which it does very readily if the juice drops out for a tick.
If the neutral gets disconnected I suppose the neutral and the sink unit goes up to line volts WRT earth if there is anything connected to the supply.
Not good if the company decides not to come out and check it out for me.
Thanks !
Bill
 25 April 2013 05:49 PM
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AJJewsbury

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We don't have any 3 phase loads so line to line volts can't be applied to any one piece of equipment.

Oh yes it can! With N floating and a "big" load on one line (L1 say) and a small (electronic) load on another (say L2), N gets pulled towards L1's voltage (and phase) - so single phase equipment notionally on L2 gets L2 on L but almost L1 on N - hence 400V between the two!
- Andy.
 25 April 2013 07:41 PM
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sparkingchip

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So what are these music players?

Andy
 26 April 2013 09:44 AM
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tattyinengland

Posts: 767
Joined: 23 November 2006

Have you checked your own incoming Neutral?

I've certainly had the supply banging in and out on a three phase system before; the first flickers happening weeks before complete failure.

One particular fault was on a wylex board where the solid neutral bar was not connected to the second half of the board. From the front it looked connected, but when a dentists mirror was used, it was in fact behind the bar, so tightening the screws alone was never going to connect the bar to the neutral block.

Worth a look......
 26 April 2013 11:48 AM
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sparkingchip

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Are you sure there isn't a issue with the players rebooting themselves?

Andy
 27 April 2013 02:50 PM
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roberts

Posts: 26
Joined: 18 January 2003

Hi All
I don't know anything about the players but apparently the owner was told that there is a protection device on one of them. They are only small portable players not the professional things.
I've seen one of them but know nothing of its make or characteristics.
Anyway, yesterday the power company electrician made an instant response to my call for a check to be made on their side of our mains supply. He tightened all the screws, all were tight, pulled out the fuses and inspected them and checked the Re which was 0.18 ohms. He didn't get up and look at the overhead wiring connections but said that if the Re was O.K. then all was well. But Re has increased since it was measured on two occasions from 1998, 0.11ohm and 2010, 0.15 ohm.
So far since Monday 22nd when I checked everything on our side of the system and tripped the (Hagar) RCBOs a few times there have been no complaints about the player going off in 2 days the hall was used. And apparently it used to go off at least once in every session at the hall.
Interesting about the open neutral shoving lots of volts onto the other phases. Its a long time since I did the '3 phase faults analysis' at college and was employed most of the time on electronics. I must take a look at my old note book !
Thanks for your help !
Bill
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