Buchholz Relays

We are PENTA. A multinational industrial leader, pioneer and expert manufacturer of electrical safety solutions, committed to ensuring your safety with every intervention, committed to ensuring your life!

The PENTA Buchholz Relay is one of the few true cast body types in the world, developed in conjunction with the British Central Electricity Generating Board (CEGB).

PENTA was established in 1937 to manufacture electrical instruments.

In the mid 1940s the company identified a requirement for gas and oil operated (Buchholz) relays to protect oil filled transformers and the first production units were designed and installed at that time. A continual development programme, in conjunction with the Central Electricity Generating Board, led to the production of the Mk10 Buchholz relay with its revolutionary displacement operating principle.

Today PENTA offers a range of Buchholz relays for small and mid-size transformers, many of which are used in substations across the world with an excellent track record of service. Many units remain in service after 50+ years of satisfactory monitoring.

PENTA offer a range of single and double-element type relays as well as a range of Buchholz relays accessories such as dry air pump, oil and gas sampling kits and diode protection units.

PENTA maintains a quality assurance system certified in accordance with BS EN ISO 9001.

Customer Benefits

Contact us for the full technical details using the button below.

Testing and Operation

Switch Data

Single Element Diagram

Dry Air Pump

Double Element Diagram

Oil & Gas Sampling

Performance Data

Diode Protection Units


PENTA is the leading designer, manufacturer and supplier of quality electrical safety products.

PENTA is a globally recognised designer, manufacturer and supplier of temporary portable earthing, voltage detectors, Buchholz relays and electrical safety products.

With a heritage spanning over eighty years, and world-class experience in equipment designed for the safe maintenance of power systems, PENTA provides customers with high-quality service, reliable solutions and technical expertise.


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