For the naysayers, here's what I actually shared with the Battery/Solar companies.
PROPERTY & SUPPLY
- Single-phase 100A supply
- Octopus Go tariff — cheap rate 00:30–05:30
- Smart meter installed
- G99 notification required for Powerwall 3
INSTALLATION LAYOUT
- Tesla Gateway: above electricity meter, right-hand cabinet
- Tesla Powerwall 3: inside garage, opposite side of property from meter
- Hypervolt Home 3 Pro: exterior driveway wall, front of garage
- Critical requirement: Hypervolt circuit to be wired on the LINE SIDE (grid side) of the Gateway, upstream of the Gateway's internal load monitoring CTs. This prevents the Powerwall from ever discharging into the EV. Please confirm your design reflects this and that a dedicated MCB will be provided on the Gateway DIN rail for this circuit.
CABLE SPECIFICATION
Powerwall 3:
- 16mm² (Doncaster Cables), ~17m run, to be clipped to first-floor joists through floor void
Hypervolt (EV Ultra combined cable):
- 6mm² with integrated Cat5 data pairs, ~10m run, same floor void
Ethernet: separate Cat5e runs — router to Gateway, router to Powerwall 3. EV Ultra data pairs serve the Hypervolt.
All cables via rear entry, through blockwork at first-floor joist level into wall cavity, exiting through external brickwork.
THERMAL ASSESSMENT — FLOOR VOID
I mounted remote temperature sensors at joist level near existing heating pipework (worst-case point on the cable route) and ran the central heating at maximum output.
Readings recorded:
- Sensor 1 (near pipework): 29.8°C
- Sensor 2 (mid-void): 25.5°C
Both readings are at or below the BS 7671 30°C reference temperature, so no derating is required. For reference, even if the void reached 35°C, my assessment tells me both cables should remain well within limits:
- 16mm² derated to ~62A vs. 31A actual load (Powerwall charging at 7.2kW)
- 6mm² derated to ~44A vs. 32A actual load (Hypervolt at 7.4kW)
Voltage drop is also within the 3% BS 7671 limit for both runs (~2% and ~1% respectively).
Heating pipework runs through the same void but I will lag the piping prior to the cable installation.
SITE LOADS & MANAGEMENT
Maximum connected loads:
Powerwall 3 charging (7.2kW) 31A
Hypervolt Home 3 Pro (7.4kW) 32A
NEFF double oven (6.3kW) 27A
AEG induction hob (7.35kW) 32A
Immersion heater (3kW) 13A
Background load (~4kW) 18A
Raw total 153A
I envisage this being managed in two layers:
1. Tesla Gateway — monitors all load-side loads via its internal CTs and dynamically reduces Powerwall charge rate if total import approaches the 100A limit.
2. Hypervolt ALM — CT clamp on the full meter tails (upstream of everything, including the EV circuit). Throttles EV charge rate to keep total site import within the 100A service fuse, down to a minimum of 6A.
In practice, these loads will not be achieved but assuming under peak load (cooking + EV + Powerwall + immersion), the Hypervolt ALM would see the loads creep up to 100A and throttle down, whilst the Gateway pauses or reduces Powerwall charging based on loads drawn by the house — this should give absolute priority to fixed cooking and heating loads. Under this setup the 100A fuse would be protected at all times. Immersion heater will be on a timer within the Octopus Go window to avoid peak overlap with cooking.
FUTURE PHASES
- Solar PV may be added later. Please advise now whether a second Tesla Remote Meter or any Gateway pre-configuration is needed to avoid rework at that stage.
- Immersion diversion (Eddi or iBoost) to follow alongside solar.
and have viewed the solar software many times, so I know permitted voltage is +10% - 6% so 216 to 253 volts, outside that range, the solar, or EV charging point is required to disconnect, to ensure if there is a loss of PEN the system must fail-safe. (PEN is the combined earth and neutral before it enters your meter.
but you will not get this until the device is installed, which by time that happens It's too late.
I have looked on Octopus app, it does not show voltage. You can, I think, read voltage direct at the smart meter, but for me that means going outside.
