Electrical quantity takeoff glossary: legends, blocks, Xrefs, BOQs and identifiers

Drawing terms

legend

A table explaining drawing symbols, item names, specifications and mounting heights. It is the starting point for a quantity takeoff. How to read the legend

Symbol

A defined graphic used to represent a device, such as an outlet or switch, on a drawing.

Block

A CAD object that groups lines and text into one object. Device symbols are often blocks, which can be counted efficiently by block name.

Layer

A layer groups CAD drawing content by system or purpose. Devices on hidden layers may not be visible.

External reference (Xref)

A feature that loads another drawing as a background. If an electrical drawing uses an architectural Xref, missing reference files can leave the walls invisible. DWG and DXF differences

Model space / paper-space layouts

Model space is the full-size drawing workspace; a layout is a sheet arranged for printing. Several floors may be drawn side by side in one model space.

Revision (Rev.)

A number or label assigned to a drawing revision. Mixing drawings with different revisions can produce incorrect quantities. Drawing revision control

Enlarged views/details

An enlarged drawing of part of a plan. Repeated devices on plans and details are a common source of duplicate counts. Causes of duplicate counts

Takeoff terms

Quantity takeoff

Measuring material counts, lengths or areas from drawings. This guide covers only the number of wiring devices.

Wiring devices

A collective term for wall- or floor-installed devices providing electrical power or communications, such as power outlets, switches and communications outlets.

residential unit

A plan for one dwelling-unit type. Multiply its quantities by the number of applicable dwellings to calculate building totals.

Unit-type schedule

A table assigning a dwelling-unit type to each building, floor and unit. It also identifies mirrored units and first- or top-floor exceptions. Calculate building totals

common area

Areas outside dwelling units, such as corridors, stairs, elevator halls, underground parking, plant and electrical rooms and rooftops. Count them separately from dwelling-unit quantities. Common-area omissions

Identifier

A unique device reference in the schedule, such as 101-K-07, that connects its row to its drawing location.

Evidence

A record of each device’s item classification and the reason for it. It provides the basis for review. Review checklist

Review required

A flag for an item that needs clarification from the designer or site team before ordering because the drawing alone is insufficient.

Estimating and ordering terms

Unpriced BOQ

A bill listing item names, specifications and quantities with unit prices left blank for the bidder to complete. Compare it with quantities counted from the drawing. Unpriced BOQ comparison

BOQ(Bill of Quantities)

The English term for a bill of quantities, used in international projects and documents from overseas clients.

quantity schedule

A schedule of item quantities taken from drawings. These are not necessarily the quantities to order.

Allowance (loss/reserve)

Extra quantities added for damage, loss or site changes. The rate depends on the item and company policy. Drawing and order quantities

Part number

A manufacturer’s unique product reference. Grounded double-socket outlets can have different part numbers depending on manufacturer, series and color.

Units (each, set, lump sum)

Each counts individual items; a set counts a specified group of items; a lump sum counts the entire stated scope as one. Align these units before comparing quantities.

Faceplate

The faceplate covering an outlet or switch. It is often ordered separately from the device itself.

Suggest a term

This glossary collects terms Voltix frequently explains during reviews. Sites and companies may use them differently. To report a missing term or a different usage, Contact. After checking, we will update the article and show the revision date.