# Third-source panel

A third-source panel is the control panel of a medical gas cylinder manifold system with three sources of supply, the number that HTM 02-01 (2026), the NHS England guidance, asks for in line with BS EN ISO 7396-1: primary, secondary and tertiary.

In HTM 02-01 (2026), the primary source is the main source and should be permanently connected; the secondary supply should automatically supply the system if the primary cannot; tertiary supplies provide a third level of resilience, for example mobile cylinders used by clinical staff and backfeed kits used by engineering staff. The HTM classifies a manifold as a single source of supply, one operating unit, and acknowledges that classifications differ.

Portugal's ACSS ET 03/2006, revised in 2024, names the three sources primary, secondary and reserve: changeover from primary to secondary is automatic with alarms, changeover from secondary to reserve automatic or manual with alarms, and the reserve source should be sized for 24 hours of hospital operation.

Ultra Controlo lists a three-source control panel for medical gas cylinder manifold systems and a control panel for four-source systems; see [third and fourth source panels](https://library.ultracontrolo.com/answers/what-is-a-third-or-fourth-source-panel/).

## Sources

- [NHS England, HTM 02-01 (2026) Part A, paragraphs 2.23, 2.25, 2.26, 2.31, 2.32, 2.38 and 5.80](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)
- [ACSS, ET 03/2006 v.2024 Gases medicinais e aspiração, section 4](https://www.acss.min-saude.pt/wp-content/uploads/2016/10/ET-03_2006_v2024-Gases-medicinais_VF.pdf)
- [ultracontrolo.com: third source control panel page](https://www.ultracontrolo.com/accessories/third-source-control-panel)
- [ultracontrolo.com: fourth source control panel page](https://www.ultracontrolo.com/accessories/fourth-source-control-panel)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/glossary/third-source-panel/