Health and Safety data on Constant Voltage Transformer based power conditioners


These notes apply to all ferroresonant transformers made by Advance Electronics Ltd. at Wrexham.


The transformer consists of insulated copper wires wound onto an insulated former subsequently assembled onto steel laminations.

Advance power conditioners are double-wound transformers with tested secondary isolation from the mains. In addition high voltage capacitors are added into a resonant circuit configuration.


Advance provides detail installation instructions for all models and care should be taken to use them.

It is practical to meet the fundamental safety needs and yet retain a high level of earth integrity with a little care at the planning and wiring stages.


High voltage

The transformer must be correctly installed according to the requirements both of the latest edition of local wiring regulations and manufacturers recommendations.

Specifically proper in-line fusing or other suitable protection must be installed. Output voltages can be as high as 650 volts and suitable RCCD protection and proper insulated fittings must be used in accordance with the needs of the application. The internal capacitors may run at 660 volts ac and are lethal when operating. The capacitors are safe when the unit is switched off SO LONG AS THE'CAPACITOR TO WINDING' CONNECTIONS are SOUND. Only authorised and trained personnel should attempt repair.


The unit is incapable of delivering more than 2 or 3 times its rated current in a failed mode and a maximum of less than 75% of its rated output voltage.


The steel stack of the unit may reach 120 Deg C (60-80 Deg C above ambient) in normal air flow and precautions must be taken when repairing or testing exposed units.

The exposed stack on small units does not reach an unsafe temperature but may feel quite warm to touch. All units should be well ventilated as power ratings assume natural air cooling.


Once completed and all solvents have been burned off the transformer is chemically benign.

The capacitors contain paper insulation soaked in transformer oil which is relatively odourless and harmless to human skin. Although messy this oil is only found if a capacitor leaks through some internal electrical fault in the capacitor. If the capacitor is leaking the transformer is faulty and should be switched off. Historically PCB's have been used in the capacitors but Advance has not used any since about 1972.


All the transformers have a high density and suitable precautions should be taken in respect of the size under consideration.


Audible noise at 50 Hz is emitted at different intensities depending on unit size. Levels range 45 - 65 dBA. If other higher frequencies are present - checks should be made for potential faults.

Multi phase systems

Advance power systems can be wired in several different configurations.

In cases where more than one 240 volt phase is to be connected into one enclosure attention must be given to external safety labelling. The wiring regulations demand that 415 volt warning labels be affixed in visually prominent positions after installation. Suitable labels are enclosed if appropriate and replacements are available on request from Advance at no charge to systems customers.

Self setting power supplies

During recent months an application problem has arisen with some types of UPS.

The problem specifically relates to customer loads which have self-adjusting voltage power supplies. This type of power supply looks at the incoming mains and typically sets itself to either 115 or 230 Vac. If driven with any current limiting source such as a CVT or CVT based UPS the power supply sets itself to 115 V and then is promptly supplied with 230 V which usually means destruction of the customers' power supply.

Customers who have selected products with a load using this kind of SMPS should select a CVT which corresponds to the lower voltage input rating of the power supply or ensure that the CVT/ UPS is switched on before the load. Most of the equipment we have seen with this type of 'world wide' power supply is small and rated below 1 kVA for razors and portable TV sets.