Options in selecting the right circuit breaker

A Siemens Automation and Drives product story

Edited by the Engineeringtalk editorial team Aug 9, 2000

Choosing the right type of residual current circuit breaker is an important element in ensuring protection from electric shocks.

Andy Scragg, Product Marketing Manager at Siemens Automation & Drives discusses selecting the right circuit breaker.

Making the right choices in electrical safety can mean the difference between life and death.

Choosing the right type of residual current circuit breaker is an important element in ensuring protection from electric shocks.

Several factors have to be borne in mind when choosing the right device, particularly the way the breaker operates.

The two most common types of residual current circuit breaker in use in the UK are voltage dependent and voltage independent residual current circuit breakers (RCCBs).

These may be operated with or without overcurrent protection (RCBOs).

The two units trip the switches in different ways, and should be used appropriately to gain the right level of protection.

In this respect it is important to look at the manufacturers' specifications and reliability data.

Voltage dependent RCCBs are reliant on the line voltage to trip the switch through an electronic control device.

Voltage independent devices are electromagnetically operated and depend on the unit detecting a current imbalance.

The imbalance is detected through the secondary winding of the current transformer.

Hence the RCCB or RCBO will trip and isolate the circuit.

When looking at safety, potential users need to look at other less well known issues.

There are important differences when using the single pole RCBOs, most commonly used in the UK, as opposed to two pole RCBOs, used elsewhere in Europe.

With Single pole RCBOs, even when they have tripped, the neutral wire is not interrupted so operators may still risk getting an electric shock.

Two Pole RCBOs provide a much safer solution as they interrupt both the live and neutral wires.

Another strand to the safety issue is protection against overloads.

Primarily, the RCBO, a Residual current Breaker with overcurrent protection, will both act as a circuit breaker and will prevent damage if there is an overload situation.

For any business or operation, where safety is a top priority, a two pole RCBO is the circuit breaker of choice.

The use of this type of RCBO in Europe is the standard, apart from in the UK and Ireland.

Equally, the UK Government is reportedly coming under increased pressure to conform to the much safer European Standard.

The present British Standard is in place until July 2005.

So looking to the future, if safety standards for RCCBs were to become stricter in the UK, investing for the future by choosing the safer option makes good business sense, especially when making long term investments.

In a world that is becoming more safety conscious with increasing cross border legislation users need to plan for the future.

There are cost implications in using two-pole as opposed to single-pole devices but operators need to be secure in the knowledge that they are safe at work.

Looking at costs over the long term, an investment for safety now will bring dividends in the years to come.

Siemens' has an extensive range of RCCBs that can sense, smooth DC current faults (Type B), as well as AC (Type AC) and pulsating DC (Type A) currents and are highly reliable.

There is also a range of Type A and Type AC two pole RCBOs.