G99 knocked back by DNO - trying understand proposed "reinforcemen"

Qyburn

JC_Derby said:

95Wavecon is an underground cable....i think they probably meant 95 ABC.

I don't know why it's four core either. Nor why they don't want to do it all underground, considering they've specified all excavation, blinding and backfilling "by others". When I looked at cable spec it came up as aluminium so I presumed it was aerial. But Wavecon is what they said.

As for why, originally we wanted to go with the Tesla battery as it had the best functionality, and islanding was one of the benefits.

I can't predict power cuts of course, but if you define "lengthy" as long enough to worry about the freezer and run out of hot water, then we had three in Winter 21/22 but only one in 22/23. Nobody is sxpecting this to improve and local authority and government guidance is that households should try to plan for three days before needing external assistance. We have generator backup but only run that for a few hours a day. Battery backup would be far superior for running light (fridge/freezer) or intermittant (water supply) loads.

But when it comes down to it, if SSEN won't permit the ideal design the we will have to make the best of it with DC coupled battery. I just got a bit excited when told over the phone that SSEN could upgrade our service cable, before I saw the detail on the crap way they proposed to do so.

Reed_Richards

Qyburn said:

... originally we wanted to go with the Tesla battery as it had the best functionality, and islanding was one of the benefits.

But probably also the highest price per kWh of capacity?

QrizB

There's a regular poster here (I won't name them, for reasons that will become apparent) with a large solar PV array. Someone asked how they had persuaded their DNO to approve it. Their reply was along the lines of, "I asked the DNO informally how they would respond to an application. The DNO replied that, if I applied, they would turn me down. So I didn't apply."

In your particular case, as you're the only subscriber on your transformer and the only household who will be inconvenienced if your inverters malfunction and overvolt the supply, you might want to consider a similar approach.

JC_Derby

4 core for three phases and neutral - presumably they want to bundle two phases together and one phase and neutral or think that the larger area of the core size would reduce impedance.
Also Qyburn presumably they would be charging you for the privilege of upgrading your service?

Qyburn

JC_Derby said:

4 core for three phases and neutral - presumably they want to bundle two phases together and one phase and neutral 

I did wonder about that, but it still doedoesn't snt make sense. They need three conductors, so using two each for L and N leaves us without an Earth. Maybe a real bodge, two for L, one each for N and E? But it's a bodge anyway.

Yes there would be a charge and that excludes excavation etc. Their notes give all sorts of requirements suggesting we wouldn't be allowed to DIY that.

Qyburn

QrizB said:
you're the only subscriber on your transformer and the only household who will be inconvenienced if your inverters malfunction and overvolt the supply, you might want to consider a similar approach.

I've considered that, but presumably you lose the MPAN, export payments and eligibility for special tariffs. But maybe I could quietly add an AC coupled battery without telling anyone. 

I understand the DNO has the right to inspect the installation at any time, but do they ever do so? 

QrizB

Qyburn said:

JC_Derby said:

4 core for three phases and neutral - presumably they want to bundle two phases together and one phase and neutral 

I did wonder about that, but it still doedoesn't snt make sense. They need three conductors, so using two each for L and N leaves us without an Earth. Maybe a real bodge, two for L, one each for N and E? But it's a bodge anyway.

If your supply is TN-C-S (also called PME), which is common for domestic supplies in the UK, the earth and neutral conductors are combined. So only two conductors required for a single-phase supply, four for three-phase.

https://en.m.wikipedia.org/wiki/Earthing_system

Qyburn

QrizB said:
If your supply is TN-C-S (also called PME)

The supply is TNS. N and E join on the LV side of the transformer then are separate within the service cable (split concentric). What SSEN call CEW. They specifically checked this for me when I was wiring the outbuildings as it determines the earthing and bonding requirements.

Just as a point of pedantry I don't think a single property TNCS LV supply should be called PME, since there won't be multiple earths.

1961Nick

An old fashioned spike costs about a tenner & means you can monitor it's condition locally.

1961Nick

There must be 1000's of AC coupled storage systems out there without DNO approval. If DNOs think they can regulate what's actually happening through the approval system then they've got their heads buried firmly in the sand. A better way forward would be blanket approval of systems with export limiting of say 3.68kWh... or just publish the export limit for each location.