Protection against Voltage Transients


Thread Starter


Recently a large number of instruments (magflow, optical sensors) were destroyed at the same time because of fault in the 440 V system that traveled into 220 Vac system. We suspect the 220 V rated instruments were subjected to 440 Volts, since there was no UPS for instruments.

what reliable devices are used as industrial standard for protection of 220 V devices against such voltage transients and how are these installed.

pl. suggest best models with recommended ratings.

James... can you forward a simple sketch or Single-Line-Diagram illustrating the connection between the 440 and 220 volt systems?

Phil Corso (cepsicon [at] aol [dot] com)

Amit Manjrekar

Dear James,

What you have described might have been caused due to neutral open condition. In this condition, there is break in neutral line causing, the line voltage shoots upto 440V.

In this scenario all devices get burnt.

We have been successful in providing neutral open protection and have had very good results. Please see our blog
give us a feed back if this is useful.

Amit Manjrekar

Amit Manjrekar

Using a UPS system will only give you power backup in case of power failure. but protection, i really doubt that..
James: rather than go into how or why your high voltage got into your low voltage try installing a constant voltage transformer on the main side of your instrument distribution panel.

it's a device consisting of a transformer and a few capacitors and MVAR's that allow you to over voltage your input (temporary only) to this device while it maintains a constant output voltage (usually 120/240 volts ac). they can be purchased in many sizes from very small .5 VA to very large 1000VA sizes and bigger and several mfg's make them (google 'Constant voltage transformer") for a source to buy from.