Difference between a circuit breaker and a load break switch?

[Manoj Sahu]

Hi.

I am working in on a Ring Main Unit of Siemens make. Today, my senior asked me the same question. As per my understanding, a circuit breaker is make or break switch. I mean, when fault occurs the circuit breaker trips, protecting the equipment connected to the line.
I have no information or knowledge regarding "Load Break Switch (LBS)." This is regarding Ring Main Unit (RMU).

Please tell me the difference between the two with as much detailed explanation as you can.

Thank you.

 

[anorlunda]

I don't know about the specific "Load Break Switch (LBS)." But in power engineering we usually use the word switch for devices that open only when there is zero current. The word breaker is reserved for devices that can interrupt flowing current.

But there are no language police to assure that everyone uses words correctly.

 

[Manoj Sahu]

.

But there are no language police to assure that everyone uses words correctly.

I don't know about the specific "Load Break Switch (LBS)." But in power engineering we usually use the word switch for devices that open only when there is zero current. The word breaker is reserved for devices that can interrupt flowing current.

But there are no language police to assure that everyone uses words correctly.

Thank you for replying. Practically, I have observed few things. When the circuit breaker is ON, the load break switch can be turned ON or OFF but the Earth switch cannot be turned ON. Similarly, when Earth switch and breaker is ON, load break switch cannot be turned ON

 

[anorlunda]

I would need to see a one line schematic diagram to be certain what you are talking about. Use the UPLOAD button to upload pictures to a post.

But once again, there are no language police. What one man calls a switch, another may call a breaker (perhaps incorrectly). So is your question about design, or about the meaning of words?

 

[Manoj Sahu]

I would need to see a one line schematic diagram to be certain what you are talking about. Use the UPLOAD button to upload pictures to a post.

But once again, there are no language police. What one man calls a switch, another may call a breaker (perhaps incorrectly). So is your question about design, or about the meaning of words?

 

[anorlunda]

No. A one line schematic looks like this.

 

[Manoj Sahu]

I have this only @anorlunda

 

[Windadct]

AN LBS is designed for interrupting the max rated load - and doing it multiple times... a CB is designed for interrupting the max Interrupting Current (IC) - that will be experienced in a fault, and this is often for a limited number of times.

Example - large switch max load 1200A - do not exceed this! But the Max IC rating for a 1200A CB ( Medium Voltage) may be 36,000A... The issues being faced are like night and day.

Consider a 15 A Light switch, in your house- it is fed by a 50,000 or 100,000 A interrupting breaker - bot also rated at 15A.

 

[Manoj Sahu]

AN LBS is designed for interrupting the max rated load - and doing it multiple times... a CB is designed for interrupting the max Interrupting Current (IC) - that will be experienced in a fault, and this is often for a limited number of times.

Example - large switch max load 1200A - do not exceed this! But the Max IC rating for a 1200A CB ( Medium Voltage) may be 36,000A... The issues being faced are like night and day.

Consider a 15 A Light switch, in your house- it is fed by a 50,000 or 100,000 A interrupting breaker - bot also rated at 15A.

This is very helpful. Can you please suggest me few sources or references to read more about this topic?

 

[Windadct]

Unfortunately I can not think of any condensed textes on the topic. For each there are two clear issues, use and specification, and then comstruction.

A PE that designs the systems "only" calculates the voltages and most critically the load, overload and represents to define the elements necessary to build a safe system.

The equipment designer, manufacturer independently has to test their products to validate that they meet the specs.

There are IEEE books, The Color Books, that help define the standards and equipment ratings, but I am not a sadist so I can't recommend you go and read these!

 

[sparkie]

Make it really simple. Look up about disconnects. A device that mechanically interrupts energy to a utilization device. This device must open feeder power, just opening control power isn't acceptable.

Overload device. This device is meant to open the circuit automatically once a certain power threshold has been met for a certain amount of time. Often, especially in motor circuits, they open by breaking a control circuit.

SCPD. Short circuit protection device. This device opens in the event of short circuit.

OCPD. This device opens in the event of excessive current for a specified time.

GFCI. Ground fault circuit interrupter. These devices open when there is a difference between line current and load current that exceeds a specified threshold.

AFCI. Arc fault circuit interrupter. These a fairly new devices that open a circuit when an arc is detected in the circuit.

Different devices can be combinations of these. One example, you can have an Arc fault gfci circuit breaker. This device is an OCPD, GFCI and SCPD as well as an AFCI.

You can have a fused disconnect that is a disconnect, OCPD and SCPD. In practice we specific names for equipment that serve specific purposes. The important thing is to recognize all the different types of circuit protection and what functions each device serves. Also, remember, there is a difference between load (which is more about power) and ampacity. Once you think about these types of devices and circuit protection in this manner, I think it will clarify things a bit.

 

[jim hardy]

In transmission world a circuit breaker can interrupt fault current or load current and is very fast.
A disconnect is less robust, slower, and usually designed to handle just charging current, like this


see the arms swing away to interrupt the circuit ? Not much power there..

The potentially huge arc in a circuit breaker is contained.