What a charger survey is actually checking
An electrician visiting to quote for a home charger isn't just picking a spot on the wall. They're checking whether your electricity supply, the cable run from your consumer unit to where the car parks, and the earth connection into your house can carry the extra load without becoming a fire or shock risk. Some of that only a qualified person can confirm with test equipment on the day. Some of it you can work out yourself, standing in your own driveway, before anyone comes round.
Knowing which is which means you turn up to the survey with answers ready, and you can read the quote that follows with a better idea of what each line is for. The installation quote worked example shows how those survey findings turn into the items on an invoice.
Your main fuse and consumer unit
Your main fuse is the service fuse or cut-out, the sealed unit before your meter that only your network operator (the DNO, or Distribution Network Operator) is allowed to touch. It sets the maximum current your whole house can draw at once, and a charger adds a steady extra load on top of everything else running in the home. The rating is usually printed on the fuse carrier itself, often 60A or 80A on an older domestic supply.
Your consumer unit is the fuse box or breaker panel that splits that supply into the circuits around your house. An electrician will look at its age, its rating and whether it has room for another circuit, because a charger is normally wired in as its own dedicated circuit.
What you can check yourself
- The rating printed on your main fuse carrier, if it's visible without opening anything sealed
- Roughly how old your consumer unit is, and whether it's a modern box with labelled circuit breakers or an older fuse board
- Whether there's a spare way, or empty slot, in the consumer unit
What only the survey settles
Working out whether your existing fuse rating can take a charger alongside everything else in the house, such as an electric shower or immersion heater, needs a load calculation. That's the electrician's job, not a guess from the fuse rating alone.
Earthing arrangement
Every home has an earthing arrangement, the system that gives fault current somewhere safe to go. There are three types an electrician will identify: TN-S, where the earth comes back along a separate conductor from the network; TN-C-S, where the earth is combined with the neutral for part of its journey (this is also called PME, protective multiple earthing); and TT, where the house has its own earth rod.
The type matters because PME supplies (TN-C-S) carry restrictions on outdoor equipment, including chargers fitted where the car parks away from the house, such as a driveway separated by a path or pavement. In those cases the installation often needs its own earth rod regardless of what the house itself uses, known as a cross-pavement solution when the supply crosses a public footway. The full detail of each type, and why PME changes what's allowed outdoors, is set out in the guide to earthing types and looped supplies.
You can't identify your earthing type by looking at the consumer unit alone. It's confirmed by testing at the survey, though your electricity bill or a previous electrician's paperwork sometimes gives a clue.
Looped supply, or shared service
Some houses, particularly older terraces and some semis, share a single network connection between two properties, with the cable looping from one house to the next. This is called a looped supply, or a shared service. It affects whether a TT earth rod is required and can affect how a cross-pavement solution is run, because work on a looped supply sometimes needs the network operator involved before any charger wiring starts.
Whether your supply is looped is usually something your network operator's records show, though a second meter box close to your own, or a neighbour's cable running through your property, is worth mentioning to the electrician regardless.
Parking position and the cable run
Where you park the car, relative to where your consumer unit sits, decides how far the cable has to run and whether it crosses a path, a garden or a public pavement on the way. A charger fitted a few metres from the consumer unit, on the same wall as the meter, is a simpler job than one run to a driveway at the front of a house with the meter at the back.
If the cable has to cross a public footway to reach a driveway, that's the cross-pavement case referred to above, and it brings both an earthing question and, in some cases, a street-works notification. You can measure the distance and note any obstacles, such as a drain or an existing duct, before the survey. Whether the run needs ducting, surface trunking or buried cable, and whether permission from a local authority is needed for any pavement work, is for the electrician and installer to confirm.
Single-phase or three-phase supply
Nearly all UK homes are supplied with a single-phase connection, and that's what almost every domestic charger is designed to work with. A three-phase supply is unusual in a house, but where one exists it changes which chargers are compatible and how the installation is wired. An electrician will confirm which you have from the supply itself; it isn't something to work out by eye.
What you can find out before the survey, sorted
Before the survey, you can reasonably gather:
- The rating marked on your main fuse carrier, if visible
- The age and spare capacity of your consumer unit
- Where you intend to park the car, measured against where the consumer unit and meter are
- Whether the cable run would cross a path, driveway boundary or public pavement
- Any other high-draw appliances already on the supply, such as an electric shower, electric heating or an immersion heater
The electrician's survey settles:
- Your earthing arrangement (TN-S, TN-C-S or TT) and whether an earth rod is needed
- Whether your supply is looped with a neighbouring property
- A load calculation confirming the main fuse can carry a charger alongside existing demand
- Whether a cross-pavement solution needs network operator or local authority involvement
- The Part P building regulations notification route for the completed work
Working through a checklist in this order, before the electrician arrives, sorts what you already know from what you're waiting on them to tell you.
Common mistakes before a survey
The most common one is assuming the main fuse rating alone answers the question. A high rating doesn't guarantee spare capacity if the house already runs an electric shower and storage heating; a lower rating doesn't automatically rule a charger out, because a load calculation looks at what's actually drawn at once. Guessing the earthing type from the age of the house is another, since TN-C-S supplies have been installed into older properties during network upgrades and TT setups turn up in newer ones with a weak network earth.
A third is choosing a parking spot for convenience without checking what the cable run to it would cross. A driveway at the opposite end of the house from the meter can be fitted, but it changes the quote, and knowing that before the survey means the figure you're given isn't a surprise.
Where this fits with the rest of the decision
The survey findings feed directly into the charger you can fit and what the installer quotes for. A tethered charger with a shorter cable run costs differently from a socketed one run further from the consumer unit, a comparison covered on the charger comparison table. Once the survey has confirmed your earthing arrangement and supply type, the quote itself should set out each of these items as its own line, which is what the installation quote worked example walks through.