Variac refurb

I purchased a Yokoyama 5A Variac quite some years ago which was unsafe as purchased (with a current Test’nTag tag) and boxed up for repair / restoration.

It is needed for a current project, so time to fix it!


Above is the terminal block of the Variac. The defects include exposed input active and neutral terminals, exposed single insulated conductors, and the earth terminal has no spring washer or like and the screw also secures the resilent plastic P clip so it does not provide a reliable low resistance independent connection to the frame. There is no sign that there was ever a cover for this terminal block. It is noted that the terminal markings have been somewhat defaced.

The terminal screws are M5 and an exploratory pair of 2.5mm holes tapped to M3 to hold a cover on was successful.

Screenshot - 17_05_16 , 08_45_31

Above, a drilling template for the back of a 70x70x50mm PVC electrical junction box was designed to fit around the existing terminal posts and pickup the M3 tapped holes. The side of the box was drilled for a pair of M16 cable glands for the input and output cables, and a hole in the back to connect the protective earth to the frame.


Above is the prepared Jbox.


Above, the interior of the Jbox with cables fitted. A bead of silicone sealant was laid on the original black terminal block to further secure the Jbox to the Variac. A 3m 10A fitted extension cord was cut 1/3,2/3 to provide the input and output cables. The 230V LED pilot was a later addition.

The Variac was tested on a PAT for insulation, earth resistance and earth continuity… all good.


Above is the completed terminal box, electrically safe and reasonably robust.