Introduction
If you’re still sizing domestic electrics the way you did five years ago, you’re already on the back foot. EV chargers, heat pumps and time-of-use tariffs are stacking new loads onto 60–100 A single-phase supplies. What’s changing? Smart consumer units, dynamic load control and flexible DNO connections are moving from “nice to have” to standard practice. Why it matters: without load management, peak demand can exceed the main fuse and derail jobs with nuisance trips or DNO delays. How to respond: tighten your survey, design with dynamic control, set clear proposal assumptions, and get in front of clients with simple packages they can sign quickly.
Table of Contents
Key Takeaways
- EV chargers (commonly 7.2–7.4 kW at 32 A) plus heat pumps (often 2–6 kW with defrost peaks) can push domestic peak demand beyond a 60 A main fuse without management.
- Smart consumer units and EV dynamic load balancing typically cap total current, preventing main-fuse trips while prioritising essential circuits.
- DNO upgrades and approvals commonly add 2–8 weeks; export-limiting and load-shedding designs can keep projects moving within existing limits.
- Contractors often report that capturing loads and assumptions on site and turning them into a proposal the same day saves 2–3 hours and reduces back-and-forth by half.
Where We Are Now: Domestic Load Is Changing Fast
Many contractors are walking into homes with 60 A supplies, undersized meter tails and packed consumer units—then being asked to add a 7 kW EV charger and a heat pump. The old diversity assumptions struggle when two big loads run together.
The Problem
- It’s common for older homes to have 60 A main fuses and limited spare ways.
- EVs at 32 A continuous + heat pumps with defrost cycling can exceed available headroom during evening peaks.
- Relying on “it’ll probably be fine” leaves you exposed to nuisance trips and unhappy clients.
The Solution
- Calculate After-Diversity Maximum Demand (ADMD) with the new loads in mind and stress-test worst case (evening peak, cold snap, EV plugged in).
- Identify DNO constraints early; plan for load management or staged upgrades.
- Offer smart load control as a standard option, not an afterthought.
Example
A typical 3-bed semi with a 60 A fuse: existing ADMD around 35–45 A. Add a 7.4 kW EV charger (32 A) and a 5 kW heat pump (approx. 10–18 A depending on COP/defrost). Without control, peak demand can nudge beyond 60 A. With a smart consumer unit or EV load balancing clamping the total to 55–58 A, you avoid main-fuse risk while keeping heating priority.
The Big 2025 Trends To Watch
Smart Consumer Units And Dynamic Load Control
- What’s changing: connected RCBOs, CT clamps on incoming tails, and controllers that throttle EVs or hot water when the main current approaches a set limit.
- Why it matters: In general, dynamic control preserves essential circuits (heating, lighting) and shaves non-essential loads first.
- Contractor view: Many installers report fewer callbacks for tripping once smart clamping is set around 90–95% of main-fuse rating.
Technical Details
- Single-phase domestic supplies are commonly 60/80/100 A; set clamp thresholds 5–10 A under the fuse rating for margin.
- EV dynamic load balancing can modulate from 6–32 A in real time, preventing overloads without customer intervention.
Time-Of-Use Tariffs And Demand Response
- What’s changing: more households switch to time-of-use (TOU) tariffs. It’s common for clients to ask for schedules that charge EVs off-peak and pre-heat homes ahead of peak bands.
- Why it matters: Shifting loads off-peak cuts bills and flattens demand, reducing main-fuse stress.
- Contractor move: Provide programmable schedules and explain “priority rules” in plain English in your handover pack.
Batteries, PV And Export Limiting
- What’s changing: Export-limiting (G100-type control) and “flexible connections” help projects proceed where DNO capacity is tight.
- Why it matters: Storage can cover EV top-ups during peaks; export limits keep within DNO constraints while enabling solar and heat pump synergy.
- Practical note: In general, export limiting and flexible connections shorten DNO timelines versus reinforcement.
Data Visibility And Remote Diagnostics
- What’s changing: Home energy apps now show live current per phase and per load category.
- Why it matters: Clients see cause-and-effect—turn on cooker, watch current spike—making your design value obvious.
- Contractor benefit: Many pros find that live data reduces “mystery trip” callouts and supports chargeable optimisation visits.
What It Means For Your Business
Pricing And Packages
- Problem: Custom one-off designs slow you down and confuse clients.
- Solution: Bundle clear packages with assumptions.
- Essentials: Consumer unit upgrade, 25 mm tails, 100 A switch, bonding checks, EV with dynamic balance.
- Smart Load Management: Above + smart unit with CT clamp, priority rules, app setup.
- Battery Ready: Above + CTs and isolators pre-fitted, export-limit capable.
- Outcome: Contractors commonly report faster yes/ no decisions when clients see three tiers with plain benefits.
Skills And Compliance
- Stay aligned with BS 7671 (IET Wiring Regulations 18th Edition, AMD 2) for selection of protective devices, RCD/RCBO use and circuit design.
- EV installs: ensure PME earthing solutions or open-PEN protection within the EVSE where applicable.
- PV/battery: recognise G98/G99 notification versus application paths and where export limiting applies.
Lead Times And Expectations
- Problem: DNO upgrades and approvals commonly take 2–8 weeks; clients expect instant installs.
- Solution: Offer designs that work within current limits (load shedding, export limiting) with a priced option to upgrade to 80/100 A when approved.
- Example outcome: Keeping the job moving with load management can avoid month-long stalls and protects your schedule.
Practical Steps: A Load Management Playbook
A 10-Point Site Survey That Pays Off
- Photograph main head, meter, tails and consumer unit (inside and out).
- Note main fuse rating (60/80/100 A) and earthing/bonding condition.
- Count spare ways and space for CTs, gateways and isolators.
- List fixed loads: oven, hob type, showers, immersion, EV, heat pump, hot tub.
- Understand client routines: EV arrival times, laundry habits, comfort expectations.
- Ask about tariffs and smart meter status; TOU intent changes design choices.
- Check broadband/wifi strength where smart kit will live.
- Sketch cable routes for EV, heat pump, battery and PV isolators.
- Run an ADMD check and a “worst-case” demand snapshot.
- Identify DNO actions: notification, export limit, or fuse upgrade request.
In general, a thorough on-site capture saves 30–45 minutes of office rework and multiple client follow-ups.
Proposal Language That Prevents Disputes
- Assumptions: “Design limited to a maximum import of 58 A to protect the existing 60 A main fuse using dynamic load control.”
- Priorities: “Heating and lighting are prioritised. EV charge rate will reduce automatically during peak demand.”
- DNO: “Works proceed within current DNO limits. Optional upgrade to 80/100 A priced separately subject to DNO timeline.”
- Handover: “Includes app setup, schedules for off-peak charging/heating, and client walkthrough.”
Using Donizo, you can speak these points on site—voice, text and photos—and generate a branded PDF proposal the same day. Contractors often find that sending it with e‑signature enabled gets decisions within 24–48 hours, and accepted proposals convert to invoices in one click.
Commissioning And Handover Essentials
- Prove: demonstrate current clamp operation by starting EV charge then turning on kettle/cooker; show EV throttling.
- Set: configure TOU schedules and explain override.
- Document: export screenshots of clamp thresholds and priority rules in your handover notes.
Real-World Scenarios
Small Terrace With EV Only
- Problem: 60 A main fuse, full board, client wants a 7.4 kW charger.
- Solution: Mini CU for EV, CT clamp on tails, dynamic load limit at 55 A. Replace tails to 25 mm, verify bonding.
- Outcome: No DNO delay; EV charges off-peak at full rate, throttles during cooking. Commonly cuts peak import by 10–20 A when the kitchen is active.
Rural Home, Heat Pump + PV (Future Battery)
- Problem: 80 A supply, 5 kW heat pump, 4 kWp PV. Client wants future battery without rework.
- Solution: Smart CU with priorities (heating first), PV export limit set to DNO letter, CTs and isolators prepped for battery.
- Outcome: Seamless later battery install; winter peaks held under 75 A; summer export stays within limit.
Apartment With Limited DNO Headroom
- Problem: Block-wide capacity constraints; DNO won’t uprate quickly.
- Solution: 7 kW EV with building-import clamp at 48–50 A, off-peak schedule only, clear proposal clause on shared capacity.
- Outcome: Install proceeds within weeks instead of months; client understands charge-rate variability.
| Feature | Current State | Improvement |
|---|
| Consumer Unit | Basic RCD/MCB, no visibility | Smart CU with CT clamp and priorities |
| EV Charger | Fixed 32 A | Dynamic 6–32 A with import clamp |
| Tariff | Flat rate | TOU schedules aligned to off-peak |
| Meter Tails | 16 mm² | 25 mm² with 100 A switch |
| DNO Constraint | 60 A, upgrade pending | Operate at 55–58 A until uprate approved |
Frequently Asked Questions
Do I Need A 100 A Upgrade For EV Plus Heat Pump?
Not always. In general, a 60 or 80 A supply with smart load management can support both by throttling non-essential loads at peaks. Offer two options: operate within existing limits with dynamic control now, and price an 80/100 A upgrade separately if the client wants full-speed everything at once.
How Do Smart Panels Actually Prevent Trips?
They monitor import current on the main tails using a CT clamp. When the total approaches a threshold (say 55–95% of the main fuse rating), they automatically reduce or pause non-critical loads—commonly the EV charger or immersion—keeping the total under the fuse rating. Essential circuits remain active.
Are AFDDs Required In UK Homes?
BS 7671 recommends AFDDs in certain higher-risk premises; for typical single dwellings they are not universally mandated. Many contractors adopt AFDDs selectively (e.g., sleeping areas, high-risk circuits) based on client budget and risk appetite. Always apply the latest edition and manufacturer guidance.
How Long Do DNO Actions Take?
Commonly, notifications and straightforward approvals take a couple of weeks, while capacity upgrades can take several weeks more depending on region and scope. Designing with export limits and load management often allows you to proceed sooner while the upgrade is queued.
What Should I Include In My Proposal To Protect Myself?
State the main fuse rating, import clamp threshold, priority rules (what sheds first), DNO assumptions, TOU setup scope, and any optional upgrades. Include photos and a one-page narrative so the client understands variability (e.g., EV may slow during cooking). With Donizo, you can send a signable PDF with these assumptions clearly listed and convert an accepted proposal to an invoice instantly.
Conclusion
Domestic electrics are shifting fast. EVs, heat pumps and TOU tariffs make load management the new normal—not a bolt-on. If you tighten your survey, standardise smart control, and write clear assumptions, you’ll avoid trips, shorten DNO delays and win trust. Capture everything on site, talk it through, and send a clean, signable proposal the same day. Donizo helps by turning voice, text and photos into a branded PDF, enabling e‑signatures, and converting accepted work to invoices in one click—so you spend more time installing and less time typing.
