UKPN unreasonable charge for 3 phase upgrade, but single phase upgrade free?

[-rick-]

That is my point. The system is running off single phase and transferring the energy between phases (via the DC battery bus). Lose a bit of efficiency but as long as total draw is below the input capacity of the inverter connected to the mains minus the efficiency loss it should run forever. The battery also proivides a reserve for temporary load spikes above the capacity*. Would want soft start on equipment though I'd guess.

 

Anyway I'm not 100% sure Victron can do it but I thought I saw it mentioned in their docs. I know people do similar using big VFDs (instead of one per machine, get a big one and have it generate 3 phases for the shop). But I believe that has downsides, you absolutely need to understand the details and wouldn't be a recommended route.

 

*The Victron Multiplus series can generally run at 2x rated for short periods without sweating.

 

If your compressor is the main draw, why not put it on a VFD and run it off single phase? Even if you put in a way to generate 3-phase for everything else, at least it would reduce the overall load on that system saving cost.

[Alan Ambrose]

@NCXo82ike - if it’s any consolation, I’m finding UKPN laughable. I kicked off our install in January. It’s the simplest install of 5m cable from the verge outside our plot to our kiosk, just inside the plot. We’re on a single track quiet lane. Single phase only. We dug the trench and installed their special duct months ago. It should get installed in early August - that is 8 months later. They’re planning to close the road for 2 days for what will be a couple of hours work max.

 

My most recent conversation:

 

Me: I can’t think it will take two days - the whole route is already dug and ducted all the way to your mains cable and has been ready for months. Your guy on the ground has seen it several times, you really won’t need to start with an excavation team for 1/2 a day.

 

UKPN: is the excavation already open? I advise you to fill it back in so my team can excavate it again on the day.

 

Me: OK. (Thinking, I’ve inadvertently fallen into a major role in a play written by Kafka with help from Beckett, Checkov and Orwell.)

Edited July 19 by Alan Ambrose

[Roger440]

On 19/07/2025 at 08:21, -rick- said:

That is my point. The system is running off single phase and transferring the energy between phases (via the DC battery bus). Lose a bit of efficiency but as long as total draw is below the input capacity of the inverter connected to the mains minus the efficiency loss it should run forever. The battery also proivides a reserve for temporary load spikes above the capacity*. Would want soft start on equipment though I'd guess.

 

Anyway I'm not 100% sure Victron can do it but I thought I saw it mentioned in their docs. I know people do similar using big VFDs (instead of one per machine, get a big one and have it generate 3 phases for the shop). But I believe that has downsides, you absolutely need to understand the details and wouldn't be a recommended route.

 

*The Victron Multiplus series can generally run at 2x rated for short periods without sweating.

 

If your compressor is the main draw, why not put it on a VFD and run it off single phase? Even if you put in a way to generate 3-phase for everything else, at least it would reduce the overall load on that system saving cost.

 

My fundamental issue is that the incoming supply isnt big enough to support the loads i want to apply. The secondary issue is when im using the compressor (and fan sometimes) its its likely to be for several hours or all day, and so batteries are not a realistic option to cover the shortfall. Theres also a 3 bed house on this supply, which is all electric aside from the oil boiler, ie electric cooking and electric shower.

 

For reference we are looking at a peak workshop load at 240v of something of the order of 55amps, give or take, depending on what i actually end up using. Sticking a rotary convertor or a VFD in their pushes that up a touch more.

 

If i turn the house off when i want to use the workshop i could make it work, but im not really seeing that as a sensible solution. The current situation also rules out ever fitting a heat pump or car charger.

 

Its fair to say the high load situation isnt frequent, im not doing this every day by any means. But when i need the power i need it. 

 

A three phase connection was an obvious, easy answer. But as National Grid/Western Power, want me to pay for all of the supply side work, (despite their PR to the contrary) its not remotely a viable option from a cost perspective.

 

Which is why ive arrived at a genset, with batteries to cover the smaller loads, like a vehicle lift. It also means i dont need to change any of the existing infrastructure, such as the house wiring and the supply to the workshop, which in its current form couldnt support much higher loads. To do so will be disruptive and expensive. But id do it if i had the three phase supply as the end result would be far superior.

 

The aditional benefit of the genset route, is if i have batteries, i can connect  solar to them.

 

Ive said it before, but its 2025, theres 3 phase 50ft from where its required, but the only cost effective solution is a diesel generator. Something has gone wrong somewhere............................

 

 

[Kelvin]

On 19/07/2025 at 08:42, Alan Ambrose said:

@NCXo82ike - if it’s any consolation, I’m finding UKPN laughable. I kicked off our install in January. It’s the simplest install of 5m cable from the verge outside our plot to our kiosk, just inside the plot. We’re on a single track quiet lane. Single phase only. We dug the trench and installed their special duct months ago. It should get installed in early August - that is 8 months later. They’re planning to close the road for 2 days for what will be a couple of hours work max.

 

My most recent conversation:

 

Me: I can’t think it will take two days - the whole route is already dug and ducted all the way to your mains cable and has been ready for months. Your guy on the ground has seen it several times, you really won’t need to start with an excavation team for 1/2 a day.

 

UKPN: is the excavation already open? I advise you to fill it back in so my team can excavate it again on the day.

 

Me: OK. (Thinking, I’ve inadvertently fallen into a major role in a play written by Kafka with help from Beckett, Checkov and Orwell.)

Bloody hell. That’s frustrating. The install team will take 2 hours to do that if it’s anything like ours. The only difference was no road closure and the cable was longer. I backfilled the trench but left it open at the bottom of the pole which was in my neighbours field so put a bit of plywood over the opened trench and a cone. 

[-rick-]

Edit: replying to Roger

 

Peak load and continuous are usually quite different (and by this I mean the continuous load when you are actually in the workshop). Inverter/battery system could easily act as a buffer and smooth out peaks. If the 55A is motor start load, then soft start or vfd reduces that a lot also.

 

How big is this compressor? What are you doing with it? 10HP compressor/7500W should do 40-50CFM continuous. That's a lot of air to use for one person. An awful lot of workshop tools are now available in battery versions that are easily equivalent to the air versions and use a lot less power. (Air power is 50% efficient at best, battery ~90%). The 18V tools can deliver many KW power to the tool during use. Obviously there is a cost to buying them but the cost of a generator or inverter system is also high.

Edited July 20 by -rick-

[Roger440]

37 minutes ago, -rick- said:

Edit: replying to Roger

 

Peak load and continuous are usually quite different (and by this I mean the continuous load when you are actually in the workshop). Inverter/battery system could easily act as a buffer and smooth out peaks. If the 55A is motor start load, then soft start or vfd reduces that a lot also.

 

How big is this compressor? What are you doing with it? 10HP compressor/7500W should do 40-50CFM continuous. That's a lot of air to use for one person. An awful lot of workshop tools are now available in battery versions that are easily equivalent to the air versions and use a lot less power. (Air power is 50% efficient at best, battery ~90%). The 18V tools can deliver many KW power to the tool during use. Obviously there is a cost to buying them but the cost of a generator or inverter system is also high.

Sorry, should have been clearer. That continuous max load. I've not concerned myself with start up currents. As you observed, a battery will take care of that 

 

Primarily, aqua blasting, but of sand)grit blasting. And painting. Which will mean running the extractor and the same time, which is close to 3kw on its own. I've currently got a noisy 7.5hp petrol compressor, which is marginal if using an air fed mask at same time. So was looking to bump up to 10hp. And, ideally I'd like to have some infras red drying lamps too. But not included those as I can use oil heating.

 

There's obviously lighting and other minor loads. The previous owner had some electric heating but that bonkers so I've switched that off and reverted to oil. 

 

I've swapped many of my air tools to battery 

[Alan Ambrose]

Actually, I think that £6.7K for 3P isn't bad, I would have leapt at that. Can you do some or all of the digging yourself (contestable work) - by which I mean get a one-man-band to dig it more cheaply?

 

Re gensets, I recently bougt a Hyundai one which does 3P ~6kW for £1.6K new.  Any size bigger than that starts getting a lot more expensive - then you're maybe looking at 2nd hand industrial sets which are physically quite big. They're all properly noisly even the 'whisper quiet' ones. By your calcs, you're looking at 13kW for the workshop. Unless you have big CNC, you won't substantially be using more than one machine at once. Also, the laws of entropy say that your power use all ends up as heat, so that makes 13kW for more than a few minutes unlikely. Also, 13kW is 17HP - that's a lot of big-arse workshop machinery - a bridgeport is still only 1.5-2HP.

 

I think if you look at the average demand carefully, you may find some scheduling / battery time shift will make it all work. Failing that, suggest investigate 'contestable work' and ante up the funds - that's by far the easiest solution. If you have time on your side, you may be able to negotiate the amount - there are some good examples here on 't 'ub of people doing just that.

 

[Roger440]

41 minutes ago, Alan Ambrose said:

Actually, I think that £6.7K for 3P isn't bad, I would have leapt at that. Can you do some or all of the digging yourself (contestable work) - by which I mean get a one-man-band to dig it more cheaply?

 

Re gensets, I recently bougt a Hyundai one which does 3P ~6kW for £1.6K new.  Any size bigger than that starts getting a lot more expensive - then you're maybe looking at 2nd hand industrial sets which are physically quite big. They're all properly noisly even the 'whisper quiet' ones. By your calcs, you're looking at 13kW for the workshop. Unless you have big CNC, you won't substantially be using more than one machine at once. Also, the laws of entropy say that your power use all ends up as heat, so that makes 13kW for more than a few minutes unlikely. Also, 13kW is 17HP - that's a lot of big-arse workshop machinery - a bridgeport is still only 1.5-2HP.

 

I think if you look at the average demand carefully, you may find some scheduling / battery time shift will make it all work. Failing that, suggest investigate 'contestable work' and ante up the funds - that's by far the easiest solution. If you have time on your side, you may be able to negotiate the amount - there are some good examples here on 't 'ub of people doing just that.

 

 

Mine wasnt £6.7k. Mine was nearer £20k. Contestable work was about £1.5k. So no meaningful savings to be had there. The big costs are new double pole arrangement and 3 phase transformer they want to charge me for. Despite the existing pole only being held up by the wires!But hey, lets get the customer to pay for our knackered assets.

 

At £6.7k i would have just done it.

 

The compressor will be outside in its little compressor house, so yes, it will generate heat, but its wasted to atmosphere, but it will run for several hours on the days i use it. 

 

When you work it out, my actual requirement for significant power is probably only 200-250 hours a year.

 

Its fair to say the biggest negative of a genset solution will be noise. Like you, ive got one of those hyuandai ones, but thats just way to noisy to be any kind of solution.

[-rick-]

23 minutes ago, Roger440 said:

When you work it out, my actual requirement for significant power is probably only 200-250 hours a year.

 

It really doesn't seem like this is enough to spend an awful lot of money on.

 

Deploying a 15KW single phase inverter/battery combo will be more expensive than generator but will be silent and if you add solar might start paying for itself, making it 3 phase adds cost*. 30kwh of battery doesn't cost much these days (Fogstar, Pylonttech, etc) and would likely keep you going for hours if you allocated the additional 20A you are getting from UKPN from your upgrade to supplement the battery. Victron can definitely work in a way that it limits draw on a grid/generator to a set number of amps and provides the rest from the battery. Still a generator would likely be cheaper.

 

* Sounds like you'd need a new electric compressor anyway. Chinese VFDs are cheap these days to convert existing machines if you have the knowledge or know someone that does, though not all machines are easily convertable.

Edited July 20 by -rick-

[Roger440]

1 hour ago, -rick- said:

 

It really doesn't seem like this is enough to spend an awful lot of money on.

 

Deploying a 15KW single phase inverter/battery combo will be more expensive than generator but will be silent and if you add solar might start paying for itself, making it 3 phase adds cost*. 30kwh of battery doesn't cost much these days (Fogstar, Pylonttech, etc) and would likely keep you going for hours if you allocated the additional 20A you are getting from UKPN from your upgrade to supplement the battery. Victron can definitely work in a way that it limits draw on a grid/generator to a set number of amps and provides the rest from the battery. Still a generator would likely be cheaper.

 

* Sounds like you'd need a new electric compressor anyway. Chinese VFDs are cheap these days to convert existing machines if you have the knowledge or know someone that does, though not all machines are easily convertable.

 

Its certainly the case that i wont be spending 20k on it, thats for sure.

 

I dont, technically "need" 3 phase for a compressor, but options in single phase are rather limited, and theres lots of "cheap" used 3 phase equipment about. 3 phase was just an obvious and easy solution, on face value. Until i got a price.

 

I need to spend some time to understand your suggestions re the victron unit. If that means i can get it all to work off my single phase supply, whilst it might not be a bargain, not having a genset has benefit too.

[dpmiller]

If you're doing a lot of blasting, would a honking big diesel compressor (like a towable ex-council tarmac one) be worth considering?  

[Roger440]

2 hours ago, dpmiller said:

If you're doing a lot of blasting, would a honking big diesel compressor (like a towable ex-council tarmac one) be worth considering?  

 

I have. Its essentially where i am with my petrol one. Rather a pain in reality. Needs starting and stopping at the compressor (outside), very noisy, runs when you are not using air (very wasteful) and generally inconvinient. 

 

Its a worst case scenario, and the one i already have.