How much voltage drop is normal?

[DetlefSchmitz]

I have no argument with that in principle. And it there is a definate promise that there will not be an unexpected bill (from the DNO in the area in question) then recommending a visit is definately the way to go.

I have a feeling that not everyone instinctively believes that a call-out will not cost anything. There are certainly situations where the conditions are that the call-out will be free if a fault is found but not otherwise. I believe check meters in some areas work this way.

I have recent experience from BT (OK nothing to do with electrical supplies I know!) where a phone line was vandalised outside, and we were told it would be repaired free of charge. In the event the engineer said it would be a better repair if he entered the building and terminated to our master socket rather than making a join. Result? A bill for £200 and a threat to cut off all 4 lines and the internet if we didn't pay.

The utilities are ruining customer trust in these ways. I understand why (difficult times) but I don't have to like it.

 

[westie101]

Ah charging the customer, lots of experts on that in the pubs of the UK.

We as a DNO have NO mechanism to charge the customer directly for this sort of advice! We have monies allowed in our budgets by the regulator to do this work and offer advice.

The only time we may raise a charge (except for additional loads, no supplies, service alteration or diversions) is if we a called out to faults on a customer's installation (we normally advise customers of simple checks they need to do before we attend) or repetitive calls to main fuses operating owing to overload.
The only way we can recover our costs is by charging the supplier who may add it to the customer's account.
We never bother as it costs nearly as much to raise the charge as we will recover.

The old electricity boards did have service electricians who would attend to repair customer faults which was chargeable, I doubt any of them have any more

I believe check meters in some areas work this way.

They are installed by the suppliers who are a whole different ball game!!

 

[DetlefSchmitz]

I believe check meters in some areas work this way.

They are installed by the suppliers who are a whole different ball game!!

Yes, good point.

 

[JohnW2]

I don't really follow the argument. Everyone has a Ze (or Zn) of some value (~0.20 ?) but not everyone's lights dim when the shower is turned on.

[I somehow lost track of this thread]. As DetlefSchmitz said, it's nothing more than Ohm's Law. If Ze in 0.2Ω, the Zn is going to be at least 0.2Ω (probably slightly more, given PME) - so turning on a 40A shower has simply got to reduce the voltage at the origin of the installation by at least 8V. If Ze were 0.3Ω, the the inevitable voltage drop would be at least 12V. As has been said, whether or not such falls in voltage result in 'noticed' dimming of lights presumably depends upon (a) the lights, and (b) one's eyesight/ perception.

Kind Regards, John

 

[JohnW2]

I have recent experience from BT (OK nothing to do with electrical supplies I know!) where a phone line was vandalised outside, and we were told it would be repaired free of charge. In the event the engineer said it would be a better repair if he entered the building and terminated to our master socket rather than making a join. Result? A bill for £200 and a threat to cut off all 4 lines and the internet if we didn't pay.

Interesting - experiences obviously vary. About 4 months ago, I had a very similar problem - rodent destruction (not for the first time!) of outside BT wire. As with you, they said they would repair it FOC and, again as with you, the engineer said it would be better if he ran new cable to the master socket rather than joining it. He assured me that it would still be FOC - and it was. The impression I get is that BT engineers have a lot of individual discretion as to whether or not to record what they do as chargeable work.

Kind Regards, John

 

[EFLImpudence]

As DetlefSchmitz said, it's nothing more than Ohm's Law. If Ze in 0.2Ω, the Zn is going to be at least 0.2Ω (probably slightly more, given PME) - so turning on a 40A shower has simply got to reduce the voltage at the origin of the installation by at least 8V. If Ze were 0.3Ω, the the inevitable voltage drop would be at least 12V. As has been said, whether or not such falls in voltage result in 'noticed' dimming of lights presumably depends upon (a) the lights, and (b) one's eyesight/ perception.

Yes, I realise that but my point was that everyone has a Zs (some relatively high - e.g. flats) but not dimming lights.

What I did/do not grasp is why you are blaming the OP's Zs for the problem.

 

[JohnW2]

Yes, I realise that but my point was that everyone has a Zs (some relatively high - e.g. flats) but not dimming lights. What I did/do not grasp is why you are blaming the OP's Zs for the problem.

The OP did not just tell us that his lights dimmed, but also that voltage fell by 10V (from 238V to 228V) when a ~40A shower was switched on. I'm not sure that 'blaming' is the right word, but what I'm saying is that the observed voltage drop (not necessarily the dimming lights) is exactly what one would expect when switching on a 40A load if the Ze were 0.25Ω (far from an impossible figure).

As I wrote recently, whether or not a 10V drop will necessarily produce a 'noticeable' dimming of light is a different matter, dependent on a number of factors.

Are you considering the possibility that the dimming of the OP's lights may be due to something other than (just) the installation's voltage reduction - and, if so, I wonder what sort of things you had in mind? [I guess that the very hypothetical possibility of the lights being fed from the downstream end of the shower circuit might well do it ]

Kind Regards, John

 

[westie101]

So, back to work today! A colleague told me of an odd one whilst I was off.

Reports, proven with a voltage recorder, of fluctuating volts. Ze/Zn (PME system) was .35 so acceptable.

System checks of other Ze/Zn figures found that ir dropped fairly quickly to .1.

The network is interconnected with a normal open point on the live conductors but with the neutral connected through which is normal on our system.
Further investigation found an open circuit neutral!

So as I said never just rely on a calculated or measured value to prove or disprove an issue without further information!
How the DNO LV systems operate is often far removed to an electrical installation!