UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Roger Ramjet · 28th Jan 2023, 5:35 pm

In the 70's the company I worked for imported several USA made yarn spinning machines, each with multiple 3 x phase motors & dedicated control gear.

The control contactor worked on 24VAC & to facilitate this a 415V > 24V step down transformer was installed, the secondary winding of which was floating.

After a while, several transformer started to "break down" resulting in a phase voltage of 415 appearing on the control circuit. Each one was replaced with a UK match but as a precaution I tied one leg of the 24V secondary down to the machine earth & then retrospectively modified the remaining USA made ones.

Made me sleep easier at night.

Rog

28th Jan 2023, 5:35 pm	#52
Roger Ramjet Heptode Join Date: Feb 2022 Location: Leicestershire, UK. Posts: 690	Re: Isolator Transformer Query In the 70's the company I worked for imported several USA made yarn spinning machines, each with multiple 3 x phase motors & dedicated control gear. The control contactor worked on 24VAC & to facilitate this a 415V > 24V step down transformer was installed, the secondary winding of which was floating. After a while, several transformer started to "break down" resulting in a phase voltage of 415 appearing on the control circuit. Each one was replaced with a UK match but as a precaution I tied one leg of the 24V secondary down to the machine earth & then retrospectively modified the remaining USA made ones. Made me sleep easier at night. Rog