Half‑Hourly Electricity Meters in the UK: CT vs WC — and How Low‑Usage Businesses Can Save

Why Half‑Hourly (HH) Settlement Exists

Since 2017, Ofgem has pushed larger business supplies onto Half‑Hourly settlement so the energy system sees exactly how much power you use every 30 minutes. The benefits are accurate bills and a grid that can balance demand in real time. The drawback? Extra kit, extra data, and extra fixed charges that can dwarf the energy cost for light‑users.

The Two Flavours of HH Meters

Whole‑Current (WC) HH meter

Sometimes called a direct‑connected meter.

• Fuse limit: up to ≈ 100 A per phase (≈ 69 kVA total).
• The supply tails run straight through the meter — no external current transformers.
• Normally installed where the service head already has 100 A fuses or smaller.
• Physically similar to a smart meter; fits on a DIN rail or meter board.

Current‑Transformer (CT) HH meter

The heavy‑duty option.

• For loads above 100 A/phase (shopping centres, big chillers, machinery).
• Current flows through external CTs; the meter reads a tiny secondary current and multiplies by a CT ratio (e.g. 200/5 A).
• Requires a CT chamber, test links, and often a separate cubicle.
• Enables supplies up to hundreds of kVA but drags in extra compliance and standing charges.

Typical Cost Stack for Each Type

Paying four‑figure standing charges for a

site that uses less than a domestic house?

Book a free 15‑minute Capacity Review with our energy engineers

and get a personalised savings report.

When a CT Meter Stops Making Sense

1. Peak demand consistently < 50 kW (about 80 A/phase) for six months or more.
2. Agreed capacity (MIC) is far above what you need — you’re paying to reserve headroom you’ll never use.
3. Standing charges + capacity charges are > 30 % of your total electricity bill.
4. You’re closing production lines, sub‑letting floors, or moving to low‑energy equipment.
5. The CT meter cabinet is taking up valuable wall space you’d love to clear.



If three or more points ring true, downgrading is worth investigating.

How to Downgrade from CT to WC (and Save)



1. Measure today’s peak load. Download HH data or ask your supplier for a maximum‑demand report.
2. Ask the DNO to cut your capacity. Aim ≤ 69 kVA (100 A fuses). Paperwork is usually free; physical works may cost £300–£1 500.
3. Get supplier buy‑in. Explain the permanent load drop and request a Change of Measurement Class from HH (class 00) to a WC smart meter (class 03/04). Shop around if they refuse.
4. Book a joint visit. DNO isolates and removes CTs; Meter Operator installs the new WC smart meter. Power off 1–2 hours.
5. Check your first bill. New standing charges should land in the £0.50/day zone, MOP/DC fees gone, capacity charge reset.
6. Stay under the new limit. Exceeding 100 kW in any half‑hour can trigger an automatic re‑upgrade.

Worked Example

A print shop in Leeds
Old setup: 200 kVA CT HH supply, peak demand 25 kW.

⚡ Recurring saving: ~£4 100 per year. Payback on a £1 000 DNO/meter swap = < 3 months.

Caveats & Future‑Proofing



• Market‑wide Half‑Hourly Settlement (MHHS) will make all smart meters HH‑settled by 2026, but not all will attract CT‑level standing charges.
• If your load might climb again (EV chargers, new kit), factor the cost and lead‑time to re‑upgrade.
• Suppliers differ — get quotes from at least three for profile‑class tariffs before committing.

Conclusion

Half‑Hourly data is here to stay, but oversized infrastructure isn’t. If your business’s electricity demand has shrunk, a quick capacity review and meter right‑sizing can slash four‑figure fixed costs — money better spent on your core operations.