How does a trip unit work?

A trip unit works by sensing an abnormal condition in an electric power circuit and tripping the circuit breaker to protect the circuit from damage. An electronic trip unit, such as the AMP-SAFE PRO is programmable device which will receive inputs, compare them to set points, and provide outputs for circuit breaker operation. In addition to providing a means to open and close its contacts manually, a circuit breaker must automatically open its contacts when an overcurrent condition is sensed.

The lifecycle of a circuit breaker

Circuit breakers are designed to deliver years of reliable, untroubled service. But they don’t last forever.

The AMP-SAFE PRO economically extends the life of circuit breakers and reduce maintenance downtime

During original production

During the time when a circuit breaker is actively marketed and promoted the manufacturer will offer full service, support and parts either direct to end-users or through a network of distributors (the green area on the chart). The manufacturers and their distributors actively support and develop their current product range.

Once a circuit breaker is superseded by a newer model, support continues but it changes (the orange area on the chart).

The end-user is affected by this:

• Spare parts are downgraded from prime stock so stock levels fall and delivery times increase.
• High volume production of spare parts falls so the unit price rises, increasing the cost of maintaining older systems.
• Expertise starts to decline as technical staff switch focus onto newer products and experienced staff leave the industry.

This type of lifecycle is common for most technical products. However, the circuit breaker market is different to others. Whereas the next generation of television or computer offers fundamental improvements, the differences on newer circuit breakers are nominal. Electricity supply has stayed the same so there’s rarely a major technical reason to upgrade from one model to another.
 
After production ends

Most manufacturers offer at least ten years support for circuit breakers after their production run finishes. At this point, end-users enter the red area of the chart. Original units and other spare parts are no longer available from the manufacturer, only in limited quantities from specialist distributors.

The impact can be dramatic for end-users:

• No official support is available.
• Supplies of units and other spare parts decline and are not replenished.
• Spare part prices rise in a classic seller’s market.

In normal circumstances this is the point at which an upgrade is logical.

But it’s hard to justify an upgrade for circuit breakers:

• It can be difficult to identify a technical reason why the end-user needs a new circuit breaker. Electricity, regulations and infrastructure are still the same.
• Many circuit breakers can be perfectly serviceable but it won’t work because one specific – and often small – part has failed. This culprit is often the trip unit. It’s the one part that’s specifically designed to fail to protect the breaker.

The 3rd party after-market will play a part here. This is represented by the blue area of the chart. This is a golden opportunity for end-users to continue using old equipment to its full potential at a fraction of the cost of a full replacement or upgrade.

The implications of replacing circuit breakers

Circuit breaker installations are not simple. They require planning, designing, approvals and certification.

This comes at a price.

Using a trip unit replacement is far more economical than replacing an entire circuit breaker

• Cost. The simple cost of a circuit breaker replacement is the main reason not to do it. The cost of replacement will vary but you can expect a total bill of about £45,000 for a full replacement. The cost of replacing the trip and other components can be a small fraction of that coming in at around £8,000. This could result in a saving of up to £37,000!
• Disruption to customers. Circuit breakers that serve customer-facing resources such as web servers, phone switchboards and IT systems leaves customers affected by a major upgrade. Advance notice helps customers plan ahead but even with notice, customers will not welcome a disruption.
• Extra workload. Your support departments already have a huge project list. Adding circuit breaker replacements does nothing to help project completion. Changing the trip is a minor upgrade by comparison.
• Training. Staff are trained heavily so they can support a new circuit breaker. No training is required for a circuit breaker they’ve been using for the past decade. 

The advantages of using a trip unit replacement to extend circuit breaker life

The advantages of using a trip unit replacement will help to avoid the negatives of an upgrade.

Another key reason in retaining circuit breakers for as long as possible is to avoid needless waste. Circuit breakers are replaced when one critical and usually inexpensive part is unavailable. Trip units are often the culprits because they’re designed to fail. They make sure the circuit breaker stays perfectly serviceable.

There’s plenty of examples when we don’t replace the ‘main unit’ when a component fails. We don’t replace a car when its windscreen breaks or its tyres wear out. We don’t change a light when its bulb blows.

The advantages of extending the life of a circuit breaker by using 3rd party components like the AMP-SAFE PRO are:

• Enhances system reliability by replacing the trip unit and other likely points of failure.
• Reduces maintenance costs by increasing reliability and limiting the scope of the upgrade. A trip unit replacement can cost as little as £8,000. Replacing the whole circuit breaker can approach £45,000.
• Reduces maintenance time increasing reliability and limiting the scope of the upgrade.
• Reduces disruption to internal and external customers by completing an upgrade in minutes instead of hours.
• Maintains compliance by ensuring equipment passes regulatory testing.
• Ensures safety by replacing unreliable components that could trigger a critical system failure.
• Reduce WEEE and recycling obligations by replacing one or two small components instead of a complete circuit breaker.
• Limits equipment overheads by cancelling an expensive circuit breaker replacement.

Bringing new opportunities

Most 3rd-party manufacturers of after-market components promote their products as being ‘as good as the original’. This is not always true. Tey are often much better than the original.

There are many advantages to a component designed and built years after the original:

• Materials or components are superior to those in the original equipment. For example, plastic is a lighter and ideal replacement for metal in many situations.
• Materials or components are much less expensive than those on the original equipment. Almost all electronic components are cheaper now than they were ten years ago.
• Shortcomings identified during the life of the original equipment and overcome in new designs.

Using a trip unit replacement may only be a temporary reprieve – all circuit breakers will have to be replaced eventually. Extending their life simply postpones the expense until the time when it is suits the end-user.

Related products

Product name
Masterpact M trip unit: AMP-SAFE PRO The AMP-SAFE PRO is the only UL and CE-listed replacement for STR breaker protection units and is a direct replacement for a Merlin Gerin Masterpact M breaker protection unit. Find out more