The term "surge" tends to get over (or mis-) used. Surges (of the kind you'd expect a surge protection device (SPD) to help with) are very short duration and usually very high voltage - typically measured in kV and micro-seconds. Usually the results of lightning or large switching events. If someone can see lights visibly changing (and not exploding) you're probably looking at something of far longer duration and lower voltage.

There are a number of things that could contribute to that - perhaps the most common is a loose neutral in the 3-phase section of the distribution system (i.e. in the DNO section if your supply is all single phase from the origin) . With the neutral connection lost single phase loads are in effect connected in twos in series across 400V and can see anything from 0V to 400V instead of 230V - all depending on what happens to be switched on on the other single phase loads at any particular moment.

You would need some evidence to present to the DNO though. If you can show voltage readings out of the normal range (216.2 to 253V) or L-N loop impedances out of range or rapidly fluctuating, that would be enough to call them out I reckon.

   - Andy.

The term "surge" tends to get over (or mis-) used. Surges (of the kind you'd expect a surge protection device (SPD) to help with) are very short duration and usually very high voltage - typically measured in kV and micro-seconds. Usually the results of lightning or large switching events. If someone can see lights visibly changing (and not exploding) you're probably looking at something of far longer duration and lower voltage.

There are a number of things that could contribute to that - perhaps the most common is a loose neutral in the 3-phase section of the distribution system (i.e. in the DNO section if your supply is all single phase from the origin) . With the neutral connection lost single phase loads are in effect connected in twos in series across 400V and can see anything from 0V to 400V instead of 230V - all depending on what happens to be switched on on the other single phase loads at any particular moment.

You would need some evidence to present to the DNO though. If you can show voltage readings out of the normal range (216.2 to 253V) or L-N loop impedances out of range or rapidly fluctuating, that would be enough to call them out I reckon.

   - Andy.

Hi Andy,

Thanks for the reply. There is no SPD fitted, and as you said, it will only protect from high voltage; I spoke to Schneider about this, and they do not sell anything protecting from low voltage anomalies. It seems to be a good bit of advice about recording the voltage over a long period. I believe by hiring a Fluke 1736 tester and recording the voltages over time, then I can send a report back to the DNO.

Before that, I will complete an EIC again to ensure I have not missed anything for the third time; I will also replace the main incoming fuse and check the carrier for erosion, etc.

Andy