What is Unit 1: Location and Avoidance of Underground Apparatus (Cat &; Genny)?

Key facts

• Unit 1 trains the operative to locate buried services (gas, water, electricity, telecoms, fibre) before digging.
• Uses a Cable Avoidance Tool (CAT) and a Signal Generator (Genny) in combination.
• Mandatory for any operative excavating in or near a UK public highway.
• Underpinned by HSE guidance HSG47 (“Avoiding danger from underground services”).
• Typically 1 day, with a theory test and a practical assessment.
• Card is valid for 5 years alongside the rest of the operator’s NRSWA units.

Why Unit 1 exists

Buried services are the highest-frequency, highest-consequence hazard in UK highway work. A gas main strike can kill people; an electricity cable strike can kill the operative on the tools; a fibre strike can cost a contractor six figures in third-party damages. The HSE publishes HSG47 (“Avoiding danger from underground services”) as the standard for safe excavation. NRSWA Unit 1 is the formal training that proves an operative knows how to apply HSG47 in practice. No competent client will accept an operative on a UK highway excavation without it.

What CAT and Genny actually do

The Cable Avoidance Tool (the “Cat”) is a hand-held receiver that detects electromagnetic fields from buried services. It runs in three modes:

• Power mode. Detects the 50 Hz field around live electricity cables.
• Radio mode. Detects the radio-frequency signal radiating from long metal services (some water mains, telecoms ducting).
• Genny mode. Detects a signal applied by the Signal Generator (the “Genny”) to a specific service the operator wants to trace.

The Genny is the active counterpart. The operative connects the Genny directly to a service (where possible) or induces a signal into a service from above the surface. The Cat then traces that signal along the run of the service, mapping where it is in the ground before the trench is opened. Unit 1 training teaches operatives the three modes, the right mode for each service type, and how to interpret the readings on the Cat display.

Course content

Unit 1 covers six broad areas:

• The legal and regulatory framework. NRSWA, HSE HSG47, employer duties under the Construction (Design and Management) Regulations 2015.
• Buried services overview. What is typically buried under a UK highway and at what depth.
• Statutory undertaker plans. How to request, read and interpret service drawings from the utility companies (the gas, water, electricity, telecoms and fibre operators) before going to site.
• CAT and Genny operation. Setting up, calibrating, running the three Cat modes, applying signals with the Genny, interpreting the readings.
• Safe digging practices. Hand-digging in the proximity of located services, tool selection, exposing services without damage.
• What to do if a service is struck. Incident response, isolation, reporting, statutory notifications.

Training is delivered by SQA-registered instructors on real equipment, with practical exercises on a buried-service training rig.

The test format

Unit 1 is assessed by a short theory paper (multiple-choice, covering HSG47, the operating modes, statutory plans and the legal framework) plus a practical assessment using the CAT and Genny on the training rig. Both must be passed to be issued the card unit. Results are confirmed on the day. The NRSWA Streetworks card carrying Unit 1 follows from SQA in the standard processing window.

NRSWA Unit 1 versus NPORS N304 Cable Avoidance Tool

The same core competence is offered under two card schemes:

• NRSWA Unit 1. SQA-administered. The standard route for utility, civils and highway operatives who need the unit as part of an NRSWA Streetworks card.
• NPORS N304 Cable Avoidance Tool. NPORS-administered. The standard route for plant operators who need the CAT and Genny competence as part of an NPORS plant card portfolio, without the wider NRSWA Streetworks card framework.

Both are accepted by most utility contractors. The right route depends on which card scheme your other site credentials sit under. Operators who already hold NRSWA units almost always take Unit 1; plant operators with no other NRSWA needs usually take N304. There is also a CITB-accredited Cat & Genny short course for operators whose employer prefers the CITB route.

How often do I need to renew it?

Unit 1 renews on the standard NRSWA five-year cycle, alongside the rest of the operator’s NRSWA units. Renewal is by retest. Best practice is to book the retest six weeks before card expiry; full detail in our card validity and renewal FAQ.

Why employers often train wider than just the operatives

Many employers train surveyors, project managers and design staff on Unit 1 even though those roles do not strictly need an NRSWA Streetworks card. The underground services awareness is useful site-wide, and the cost of a one-day course is low compared to the risk of an undetected service strike on a project where the design or survey work missed a buried line. Booking project staff alongside operatives on the same Unit 1 attendance is straightforward.

Related questions

• What units does NRSWA training cover?
• What is NRSWA?
• Who needs NRSWA training?
• How long does NRSWA training take?
• How long is the NRSWA card valid for?

Quick answers to related questions

What does Cat & Genny stand for?

CAT = Cable Avoidance Tool (the hand-held receiver). Genny = Signal Generator (the active counterpart that applies a signal to a buried service). Used in combination to locate buried services before excavating.

How long is the Unit 1 course?

Typically 1 day, including the theory paper and the practical assessment on the CAT and Genny. Delivered at our centre or on-site for group bookings.

Is NRSWA Unit 1 the same as the NPORS N304 course?

The core competence is the same, but the card scheme differs. Unit 1 sits on an NRSWA Streetworks card; N304 sits on an NPORS plant card. Choose the scheme that matches the rest of your card portfolio.

Last updated: 2026-05-21. Reviewed by the MPTT NRSWA training team, SQA-registered instructors and assessors.