Proof Engineering, in collaboration with an end-user, has developed a tamper proof spindle that prevents the restrained plug from being removed without first isolating the circuit.

“As specialists in the design and manufacture of innovative flameproof, explosion proof and non-flameproof plugs, sockets, adaptors and cable couplers for the mining and tunneling industries, we listen and respond to our customers’ requirements,” says Director, Donovan Marks. “So when a customer encountered a problem with the removal of the restrained plug from the socket which posed a safety risk to underground mining personnel, we immediately looked at finding an optimum solution.”

According to Marks, the previous design consisted of a standard lock which went through the end of the socket housing once the plug was inserted, in affect stopping the plug from being removed without first isolating and removing the lock. “However, it became clear that this design was not tamper proof so another solution simply had to be found.” 


“By giving each handle its own unique serial number, we have ensured that the handle supply is strictly controlled; the end user is able to log and issue these handles only to authorised personnel.”“Following research and consultation with our team of specialists, we, together with a large end user, engineered the perfect solution with the development of a tamper proof spindle for our restrained plugs and sockets.” Marks explains that the design is similar to what is used on wheel nuts. “In the new design we have fitted the female section in the spindle and the male sprocket on the handle which is now loose. Thanks to this innovative design, the plug can only be removed once the circuit has been isolated.”

Powermite’s restrained plugs and sockets, available in 300A-425A 1.1kV, 200A 1.1kV and 120A 1.1 kV are flameproof certified to SANS IEC60079-0-1 & SANS 1489 making them ideally suited for power supply to underground as well as surface-to-underground machines. The products feature copper grub screw or crimp type connectors, individually screened insulators and complete phase segregation. 

Marks also notes that the restrained plugs and socket range is available in Pro-Alloy anti-theft material. In addition to being lighter in weight, the patented non-theft ProAlloy material is a mix of zinc, copper and aluminium which holds no resale value, thereby reducing the risk of theft.

Proof Engineering supports its products with a complete after-market solution that includes coupler repair services, locally manufactured spares (ex-stock), product training as well as country-wide technical back-up and support 24/7 from certified Proof Engineering technicians. Services extend to the terminating of plugs and couplers onto cables.