110V Site Power in the UK: Yellow CEEform, Why It Exists and What Plugs In

In this guide:What it is · Where it is used · The connectors · In practice · Picks · FAQ

Anyone working in exhibition halls, on construction sites or in television will meet yellow connectors, and they are not blue connectors in a different colour. The supply behind them is a different voltage arranged in a different way, and nothing crosses over between the two.

This guide explains what the system is and how the connectors are arranged. Anything involving designing, installing or testing a supply is work for a competent electrician.

What 110V site supply actually is

A site transformer takes the 230V mains and produces 110V, with the secondary winding centre-tapped to earth. The consequence of that centre tap is that the voltage between either live conductor and earth is roughly 55V rather than 110V.

That is the whole point. If a cable is cut or a tool fails, the voltage a person can be exposed to is halved again, which substantially reduces the severity of a shock. It is a risk reduction measure, not an efficiency one.

Where you will meet it

• Construction sites, where it is the long-standing convention for portable tools.
• Exhibition halls and some venues, particularly for build and break periods.
• Television and film locations, where practice varies.
• Anywhere a risk assessment has concluded that reduced low voltage is appropriate for hand tools.

It is not used for the show itself. Stage lighting, audio and video run on the normal 230V supply. The 110V world is about the build, and about hand tools.

Yellow CEEform, and the colour code

CEEform connectors, also called commando connectors, are colour coded by voltage, and the colour is the fastest way to know what you are looking at.

Within yellow, the pin configuration tells you the rest. A 2P+E connector has two poles and an earth, which is the standard single-phase site arrangement. The rating, 16A or 32A, is fixed by the connector body, so a 32A plug will not enter a 16A socket.

Working with it sensibly

• Match the rating through the whole chain. A 16A tool, on a 16A lead, from a 16A outlet.
• Keep 110V leads visibly separate from 230V leads. Yellow cable as well as yellow ends is the usual convention.
• Transformers are rated in kVA and get warm. Size for the tools in use, not the tools you own.
• Test plugs and sockets exist for proving a supply and are worth carrying.
• The 230V event side of the subject is covered in event power distribution explained.

Anything involving the design, installation, alteration or inspection of a supply is work for a qualified electrician. This guide describes the system so you can identify and buy the right parts.

Frequently asked questions

Why is site power 110V and not 230V?

To reduce the severity of an electric shock. The supply is centre-tapped to earth, so the voltage to earth is around 55V rather than 230V, which is a substantially lower risk with hand tools in a hostile environment.

Can I plug a 110V tool into a 230V socket?

No, and the connector system is designed to make it impossible. The colours and pin arrangements differ specifically to prevent it.

What does 2P+E mean?

Two poles plus earth: a single-phase connector with two current-carrying conductors and a protective earth. It is the standard arrangement for single-phase site power.

Do I need 110V for a gig?

Normally no. Stage equipment runs on 230V. You will meet 110V during build and break in exhibition halls, and on construction sites, mainly for hand tools.