G99 and Three-Phase Grid Connection for Fabrication Shops

Almost every fabrication shop we survey runs on a three-phase 415V supply, and almost every solar array we design for one is big enough to need formal grid-connection approval. That approval, the G99 application to your Distribution Network Operator (DNO), is the single longest item in the whole programme. Get it moving on day one and it runs quietly in the background while the survey and design happen. Leave it until contract and it can add months to a project you were hoping to have generating before the winter bills land.

This guide explains why fabrication sits firmly in G99 territory, what the DNO timelines really look like, and how export limitation lets a heavy-motor shop connect even where the local network is tight.

Why fabrication is a three-phase, G99 job by default

A domestic solar system on a single-phase supply can often connect under the simpler G98 notification because it sits below 16A per phase, roughly 3.68kW. Fabrication is nowhere near that. A metal-fabrication workshop, structural-steel shop or laser-profiling house draws heavy motor and process loads that only a three-phase supply can carry: rotary-screw compressors, fibre-laser chillers and servo drives, CNC spindles, press-brake power packs, shot-blast plant and welding sets.

That same three-phase 415V supply raises the threshold before G99 kicks in, but only to about 11kW across the three phases (again, 16A per phase). A typical fabrication array runs from 60kW to 500kW, so you clear that threshold many times over. In practice, commercial fabrication solar is essentially always a G99 application. There is no fabrication-scale array that avoids it.

The good news is that the same heavy three-phase supply that forces the G99 is also what makes fabrication such a strong solar site. Your welders, plasma cutters and lasers are spiky, high-power loads, but they sit on top of a large, near-constant daytime baseload: the compressor cycling to hold line pressure, the legally-required LEV weld-fume extraction running whenever anyone welds, the laser chiller and the CNC coolant. Solar feeds that steady baseload smoothly. Because you run a single day shift, 70 to 90 percent of everything the array generates is consumed on site at your full 25 to 30p import rate. That load match is the reason paybacks land between three and seven years, and you can see the numbers for your own shop on our cost page.

What G99 actually is

G99 is the Energy Networks Association engineering recommendation that governs how generation equipment connects to the distribution network. Any inverter output above 16A per phase must be applied for and approved by the local DNO before it energises. The DNO’s job is to confirm your proposed array will not push local voltage or fault levels outside safe limits or overload the network in your area.

For a fabrication shop this is not a formality to fear, but it is a process with a clock, and the clock is what catches people out.

The DNO timeline, honestly

There are two broad routes, and which one you fall into depends mainly on array size and how much spare capacity the local network already has.

Connection type	Typical array	First response	Formal connection offer
Standard G99	Smaller commercial arrays	Within days	Around 45 working days
Full network study	Larger arrays, constrained network	Roughly 12 weeks	Typically 16 to 24 weeks

A standard smaller G99 connection usually gets a connection offer within about 45 working days. A larger array, or one on a network with little headroom, needs a full network study: expect roughly 12 weeks to a first response and typically 16 to 24 weeks to a formal offer, occasionally with reinforcement costs attached if the DNO needs to upgrade local infrastructure.

Set against the rest of the programme, the pattern is clear. From contract to commissioning most fabrication installs take three to six months. Physical installation is only one to four weeks on the roof. The grid connection is the long pole in the tent, which is exactly why we submit the DNO application alongside the structural survey, so the connection clock starts on day one rather than after everything else is settled.

Apply on day one, not at contract

This is the single most important scheduling decision in a fabrication solar project, so it deserves stating plainly.

The moment your load profile and a candidate system size exist, the G99 application can go in. That is weeks before final panel selection, before scaffolding, before anyone touches the roof. If you wait until the contract is signed to start the DNO clock, you have simply bolted 45 working days, or up to 24 weeks, onto the front of your generating date. On a competitively tendered fabrication business where power is the biggest controllable cost after steel and labour, every month without the array is a month paying full grid rates you did not need to.

Most contractors wait until contract. We do not, and neither should whoever you appoint. When you request a quote, the DNO application timeline is part of the plan from the outset.

G100 export limitation: connecting where the network is tight

Sometimes the DNO comes back and says the network cannot accept your full potential export. This is common on older industrial estates with tired local infrastructure. It does not have to kill the project.

G100 is the export limitation scheme that sits alongside G99. It uses a certified control system to cap how much power the array can ever push back onto the grid, guaranteeing the DNO that you will never exceed an agreed export limit. For a single-shift fabrication shop this is often a non-issue in practice, because you consume most of what you generate on site anyway. Limiting export to a low figure, or even to zero, still lets you self-consume the full array output during working hours.

Where export headroom is genuinely constrained, G100 export limitation, sometimes paired with a battery to soak up any midday surplus, is what gets the connection approved. It means a heavy-motor shop on a weak part of the network can still install a properly sized array and capture the self-consumption value, rather than being forced down to a token system or turned away.

Checking your supply has headroom

Before we finalise a design, we check that the incoming three-phase supply and the site transformer can carry both your existing fabrication load and the new generation. Heavy motor loads matter here: welder inrush, compressor starts, laser servo drives and large CNC spindles all draw hard, and the connection design has to account for power factor and transient current, not just steady-state kW.

On a CNC or laser shop where sensitive controls share the supply, inverter selection and power-quality also come into the assessment, so the PV does not introduce harmonics onto a supply feeding precision equipment. Where transients are heavy, power-factor correction is specified. None of this is exotic, but it is the difference between a clean connection and a surprise partway through commissioning. It is also why the connection question is tied to the same structural and roof-load survey that any heavy-lifting shop needs, covered in our structural steel fabrication sub-sector guide.

How the grid connection fits the wider project

For an owner-manager weighing solar against a new fibre laser or press brake, the honest headline is that the grid connection governs your timeline more than anything else, and it is almost entirely front-loaded. Deal with it first and the rest of the project is predictable.

A working checklist:

• Confirm the supply. Three-phase 415V, with the incoming capacity and transformer headroom checked against your real load.
• Submit G99 on day one. In parallel with the structural and roof-load survey, not after contract.
• Expect the timeline. Around 45 working days for a standard connection, 16 to 24 weeks where a network study is needed.
• Plan for G100 if needed. Export limitation, with a battery where it helps, keeps the project alive on a constrained network.
• Size to self-consumption. With 70 to 90 percent used on site, export limits rarely cost a single-shift fab shop much real value.

Grid connection sounds like the intimidating part of a commercial solar project. In truth it is the most predictable, provided it starts on day one. The genuinely site-specific work is the roof survey, the load modelling and designing the array around your LEV extraction and crane rails. If you want to understand how your single-shift daytime load drives the economics, our guide on why fabrication is a strong solar fit sets out the self-consumption case in full.

For the authoritative detail on the connection process itself, the Energy Networks Association connection guidance sets out how DNO applications are handled. And once the array is sized, our grants and funding page covers the Annual Investment Allowance and the Smart Export Guarantee so you know exactly what the numbers look like before you commit.