Investigating lights dimming intermittently today. I saw the voltage dip from 239v to as low as 205v for a second, several times over the hour I was there.

This is a rural overhead TT supply. I couldn't see any heavy loads in the house but thinking about it now, I didn't check the swimming pool pump, which is fed from it's own separately metered TP supply albeit from the same overhead lines 50 metres away from the house supply.

Any ideas what this could be or whether the pool pump kicking in could cause such a dip?

Have you checked for loose connections on tails?

Dave.

Yes, forgot to mention that I have been though the CU checked all terminations on neutrals and busbar and RCBO terminals. Meter terminations are sound.

In my experience, pool pumps tend to run constantly. Pool heaters might cycle if it's heated with electric.

I'd have a word with the DNO, our local one has a really pleasant chap who spends his time investigating such problems. You might find they will stick a voltage logger in there for a week to help trace the problems.

Stu

Thanks Stu. I did actually call them out before I left the job but as always, start to think I've missed something when in the van!

I'll let you know the outcome.

loose clamp on overhead........

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry

I tend to give the bottom of the poles a gentle kick as I walk past ;-)


Stu

Glad that's not a capital P there!

Regards

Had something similar a while ago (but on an old underground TN-S supply) - turned out to be a loose connection in the cut-out. High current loop tests helped a lot in tracking it down, although in the end it was the "crackling" from the cut-out that pin-pointed it!
- Andy.

I had a customer with the same problem and an overhead pole in the back garden, turned out to be a loose connection on the pole. Flickering lights during peak load times, at breakfast time and in the evening. The customer had previously phoned the supplier, she was advised to have an electrician check out her installation. Let someone else do the leg work!, I told the lady to ask for a refund for my time!, but I wouldn't bank on her getting anything.

BT carry out the same procedure nowadays, they rely on someone else proving it's a BT problem.

Regards

As suspected, loose neutral was found by DNO, although not sure if this was in the head or at the pole. Customer still reporting same problem...the saga continues...will keep you posted!

"I didn't check the swimming pool pump, which is fed from it's own separately metered TP supply albeit from the same overhead lines 50 metres away from the house supply."

What is the Authorised Supply Capacity (ASC)?
Does the motor exceed 0.75 kW?
What motor/welder ratings were on the application form in the section "disturbing loads"?

Regards

BOD

You'd probably be suprised at just how many "loose" connections are out there, particularly where there are non crimped connections - ie line taps.

It wasn't unusual for line crew to deliberatly "back off" a selected number of line taps to ensure a long term "employment" resolving call outs to "flickering lights" - all on garaunteed maximum bonus of course.

Not quite a outrageous as a public lighting guy I knew who used to keep a high powered air rifle in the van - just to ensure there were always enough "outages" to keep the PL crew busy every week !!

I kid you not

regards

OMS

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Failure is always an option

sounds like the retained fire fighter convicted for deliberately starting grass fires...

- Andy.

Yep - when I was a kid you could make an easy 50p for setting fire to gorse bushes during the school hols on the old colliery waste tips - you just needed to know when to hang around selected fire stations which had retained crew - it got out of hand in the summer of 76 when it was so dry, the grass fires got down into the waste - which had a high component of coal in it - the underground fires burned for months - kept FRS busy for sure, and by then we were back in school and away scot free !!

Bloody kids are out of control these days

regards

OMS

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Failure is always an option

Investigating lights dimming intermittently today. I saw the voltage dip from 239v to as low as 205v for a second, several times over the hour I was there.

This is a rural overhead TT supply. I couldn't see any heavy loads in the house but thinking about it now, I didn't check the swimming pool pump, which is fed from it's own separately metered TP supply albeit from the same overhead lines 50 metres away from the house supply.

Any ideas what this could be or whether the pool pump kicking in could cause such a dip?
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TT supply, is the pole mounted transformer close to the dwelling, well maybe not as you have a tap off 50metres away. This sort of problem can surface if they keep adding additional loads on a long run of LV overheads, if you are at the end of the line you could have lighting flickering (like a welder in use) and dipping which is quite annoying. Just for fun, TT so test as TN-C. Take a loop impedance tester, put the earth and neutral clip together on to the neutral and test Ze between live and neutral, this will give near enough the impedance of the supply lines and work out what the natural volt drop should be.
Don't' use any lies or exaggerate to get things attended to, I did not in this genuine case of a overloaded washing machine humming instead of turning ( due to low voltage), the conclusions of which was eventually replacing all the overheads with 90mm bundled aluminium.

Note: I am not sure that it may be a poor connection of the neutral. The current in the neutral conductor should be equal to the phase conductor , a poor connection could be downstream from the TT RCD and may not cause tripping, but you could measure the current in both when the voltage is low to find out if the current is equal. P=I squared R so if you had a poor connection of say two ohms with a current of say 30amps flowing that would be 1.8Kw, and would show up somewhere along the line.

No idea! My customers have only recently moved in to the property, I've only been there twice to look things over and start some investigation work.

The pool house / supply only is only using one phase of the supply and there is some major updating that needs to take place throughout!

Usually, as a matter of course, I will take a Line impedance measurement. For some reason I didn't on this job.

What would that tell me anyway? I could see the voltage 'drop' as the lights dimmed.

The effect is not a flickering but an actual momentarily visible 'dip' that corresponded with the 205v measurement.

I will investigate further when I return in a couple of weeks or so with a couple of kettles and use your load monitoring method!

Primo, I look after a musician who has the same problem as you describe and we have discussed it on here. He too is in a rural setting on a TT and a great distance from the supply transformer. In his case, a three phase.

The fluctuations have an affect on the quality of sound recording and he used to have tripping problems.

Over the years we have tried various things but it seems that the distance from the transformer is the issue. To this day the supply authority are not in the least empathetic. Because he chooses to live where he does and where the rest of us want to.

However, he no longer has tripping problems during the fluctuations since installing a high integrity earth around the studio and the bit which might interest you....completely separating the swimming pool installation from the rest of the house and completely separating the recording studio likewise.

Zs

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'The desk is a dangerous place from which to view the world.'
John Le Carre

I do a bit of work for a client that has a lot of laboratory equipment looking at all sorts of strange things. By nature of the business, they often have equipment that originates in all parts of the world, is often quite specialisist - and equally they have a spread out site with lots of little buildings dotted about - so voltage can, and does, vary quite a bit across the site.

Some of the lab kit has quite close requirements on voltage (in some cases very close) - we have, on a number of locations used voltage stabilizers and or UPS (more as power quality than back up) either for specific bits of kit or to deal with a complete lab or even a complete building

For your music studio, you might want to take a look at these guys:

Claude Lyons

They really do have some good equipment and can usually turn some pretty appalling voltage fluctuation problems into very stable outputs (as good as 0.5% variation over full load)

Worth a look - but not cheap - depends on how much your client wants to "suffer" for his art -

Regards

OMS

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Failure is always an option