Electrical design drawings in London

Part P: the safety rules behind the layout

Part P of the Building Regulations is the electrical safety requirement for dwellings, and Approved Document P (edition: 2013 edition; takes effect 6 Apr 2013) lists the work that has to be notified: new circuit; consumer unit replacement; additions or alterations to circuits in a special location.

A certificate for notifiable work must be given within 30 days of completion, by the registered installer or the building control body. That is the electrician's duty, and our drawings do not stand in for the certificate.

What we add is advance information. If the plan shows the new circuit, its protection and the special locations such as bathrooms, the installer can prepare the notification without redesigning on the day.

Lighting, and the efficiency figure it must meet

Fixed lighting has a minimum efficacy under Approved Document L. The current edition asks for 75 lumens per circuit watt, and the later edition raises it to 105.

In practice that means LED fittings throughout, and the lighting schedule on our sheet names each type against the figure. Dimmers, scenes and feature lighting are drawn as separate circuits, so a fault in one does not darken the house.

Charge points and solar panels

A new dwelling with parking needs a charge point. Approved Document S defines it as a universal (untethered) socket, BS EN 61851 with a nominal output of at least 7 kW. We draw the position, the cable route from the consumer unit and the spare way reserved for it.

The newest energy guidance adds a solar target for new homes. The calculation assumes panels covering 40 per cent of the ground floor area, rated at 0.22 kW peak per square metre, facing south-east to south-west at a pitch of 45 degrees.

Those are assumptions for the notional calculation, not a design you must copy. We use them to size the inverter position, the isolator and the roof cable route, and we say plainly where a real roof differs.

Price, scope and what we do not do

There is no published starting price for electrical design drawings. A one-room extension and a whole-house rewire are far apart in scope, so we run a free constraints check, agree what you need and give a fixed quote.

We draw and schedule the work. We do not install, test or certify, and we do not replace an installer's calculations for loads, cable sizing or fault levels. If a project needs an electrical specialist beyond a domestic scope, the quote names who covers it.

Because the drawings stay in the model, later changes such as a moved kitchen are updated once and carried through every sheet.

A good brief helps. Tell us how you cook, where the television goes, whether anyone works from home and what you plan to charge or run in the garden. Those answers decide how many circuits the house needs and where the spare ways should be, and they are cheap to settle now and expensive to chase after plastering.

Where electrical drawings fit in the sequence

Rewires and extensions behave differently. In an old house the first task is learning what exists, so we mark the existing consumer unit, the age of the wiring where it is known and anything that looks unsafe, and we say what we could not see. A new extension is simpler: the circuit is drawn from the unit to the room and the loads are added up.

We start once the layout is stable, so sockets are not drawn twice. A second technologist checks each sheet, and the set is cross-checked against the architectural plans: no switch behind a door, no light centred on a beam.

The sheets then join the technical set sent to building control and your contractor. The building regulations drawings page describes how that wider package is assembled. Where heating and hot water are also being redesigned, the MEP design service covers them in the same model.

Electrical design drawings by borough

Electrical work is national, but access to a house is local. Listed and conservation-area buildings restrict visible external items such as meter boxes, cameras and outdoor lighting, and Article 4 directions can bring small alterations under control. Our council pages list the designations that apply in each borough.

Start with the borough where the house stands. Architectural drawings in Westminster shows the format, and architectural drawings by area lists every place we cover.