When to use SP, DP, TP, 4P, SP+N, TP+N Circuit Breakers

  1. SP or 1P– Single Pole
  2. SP + N – Single Pole and Neutral
  3. DP or 2P – Double pole
  4. TP or 3P – Triple Pole
  5. TP + N – Triple Pole and Neutral
  6. 4P – Four Pole

1.     Single Pole (SP):

[Single Pole ABB circuit breaker: S201-C]

  • In a Single Pole CB, switching & protection happens over only one phase.
  • AC Voltage in SA is 220/230V between Phase and Neutral.
  • Application: Single Phase Supply, CB is used to break the Phase only.
  • Used for Lighting circuits, plug points, etc..

2.     Single Pole + Neutral (SP + N):[Single Pole + Neutral ABB circuit breaker: S201-C NA]

  • In a Single Pole + Neutral MCB, the switching  happens over the Phase and Neutral. However, no protection is incorporated over the Neutral Phase.
  • AC Voltage in SA is 220/230V between Phase and Neutral.
  • Application: Single Phase Supply, CB is used to break the Phase and Neutral.
  • Used for AC, Heaters, Dryers, etc..

2.     Double Pole (DP):

[Double Pole ABB circuit breaker: S202-C]

  • In a Two Pole or Double Pole MCB, the switching & protection happens over phase-phase or the phase-neutral.
  • AC Voltage in SA is 400V between Phases.
  • Application: Single Phase Supply, CB is used to break the Phase and Neutral.
  • Used for AC, Heaters, Dryers, etc..

3.     Triple Pole (TP):

[Triple Pole ABB circuit breaker: S203-C]

  • In a Three Phase or Triple Pole CB, switching & protection happens over all three phases. The neutral is not switched or protected.
  • As in the image above, the phase indications are often represented as Red-White-Blue.
  • AC Voltage in SA is 400V between Phases.
  • Application: Used in a system with a three Phase Supply.
  • Used for machinery, motors, welders, etc..

4.     Triple Pole Plus Neutral (3P+N):

[Triple Pole + Neutral ABB circuit breaker: S203-C NA]

  • In a 3P+N CB, Neutral phase switching takes place within the CB as a separate pole. However, no protection is incorporated.
  • TPN for Y (or star). The connection between ground and neutral is in many countries not allowed. Therefore the N is also switched.
  • AC Voltage in SA is 400V between Phases.
  • Application: Three Phase Supply with Neutral.

5.     Four Pole (4P):

[Triple Pole + Neutral ABB circuit breaker: S203-C NA]

  • In a 4P CB, Neutral phase switching takes place within the CB and protection is incorporated.
  • In 4-Pole MCCBs the neutral pole is also having protective release as in the phase wires.
  • AC Voltage in SA is 400V between Phases.
  • Application: Three Phase Supply with Neutral.
  • Used in application where the neutral is to be isolated from the earth in case of an earth fault, photo-voltaic installation, UPS, Generator suppler etc…

Difference between TP+N and 4P 

  • For TP+N, protection applies to the current that flows through only 3 poles (Three Phase) only; there is no protection for the current flow through the neutral pole. Neutral is just an isolating pole.
  • For the 4 pole breakers, protection applies to current flow through all poles. However when the breaker trips or is manually opened, all poles are disconnected.

Where to Use TP, TPN and 4P in a Distribution Panel:

  • An MCB is used for protection of the system if fed from a transformer. If the board is fed from a Minisub or is a sub-distribution board, the main incomer can be an Isolator, as the protection takes place up stream.
  • TP MCB: It is the most common type of breaker used in ordinary three phase supply.
  • TP+N MCB: It is generally used where there are dual incomers to the panel (utility source and emergency generator source).
  • 4P MCB: It is used where there is the possibility of high neutral current (due to unbalance loads and /or 3rd and multiple of 3rd harmonics current etc) and Neutral / Earth Protection is provided on Neutral.
  • Normally in a 3 phase + neutral system, it is common practice to use a 3 pole CB while the Neutral is connected to a common Neutral Link.  However, if the application of a 3pole will affect the operation of a protective relay then a 4 pole CB is used.

For more information contact Josh Berman or visit www.switchmanproducts.co.za

Joshb@switchman.com

0118275705

What is the difference between an MCB, MCCB, ACB and RCD?

Understanding switchgear jargon can be daunting, but don’t let it get you down. Here are some of the basic Circuit Breaker (CB) definitions and the characteristics of each type. This will help you better familiarize yourself with the products on the market and decide when to use them.

Miniature Circuit Breaker (MCB)

Miniature Circuit Breakers (MCB’s)
MCB Characteristics
  • Generally rated at currents from 6A – 100A.
  • Generally within the fault level range of 3kA-10kA.
  • An MCB usually doesn’t have adjustable Trip Characteristics such as time to trip.
  • Comes in both Thermal or hyrdaulic-magnetic operation.
  • Available in single pole (SP), double pole (2P), triple pole (3P), single pole plus neutral (SP+1), triple pole plus neutral (3P + 1).
  • Small frame size and generally DIN mounted (Clips onto a rail).
Miniature Circuit Breakers Fitted to Steel Surface Enclosure at Switchboard Manufacturers, JHB

MCCB (Moulded Case Circuit Breaker)

Moulded Case Circuit Breakers (MCCB)
Characteristics
  • Rated currents between 32A – 1600 A.
  • Higher fault levels than MCB’s (15kA – 70kA).
  • Available in adjustable and fixed current rating / trip characteristics.
  • Comes in both thermal or hydraulic-magnetic operation.
  • Available in triple pole (3P) and four pole (4P).
  • Larger than MCB’s and fitted on a chassis to support thicker cables or busbars.
Moulded Case Circuit Breakers Fitted to Steel Enclosure at Switchboard Manufacturers, JHB

Air Circuit Breaker (ACB)

Air Circuit Breaker (ACB)
Characteristics
  • Generally rated from currents of 630A up to 10,000A.
  • Trip characteristics are often fully adjustable and include configurable trip thresholds and delays.
  • Usually include auxiliary terminals for external control and tripping.
  • Often contain a motor in order to toggle the breaker.
  • Come in draw-out or fixed mounted versions (Mounted on an angle-iron or Chassis).
  • Often used for main power distribution in larges installations.
Air Circuit Breakers Fitted to Steel Enclosure at Switchboard Manufacturers, JHB

Earth Leakage – Residual Current Device (RCD), Residual Current Circuit Breaker (RCCB)

Characteristics
  • Both the phase wire (line) and neutral are fed through the RCD.
  • The RCD trips the circuit when there is earth fault current by measuring the amount of current that flows through the phase (line) compared to the current flowing through the neutral.
  • Triggers within 30 milliseconds.
  • RCD’s are an extremely effective form of protection against shock.
  • Most widely used are 30 mA (milliamp) and 300 mA devices.
  • RCD will not protect against a socket outlet being wired with its live and neutral terminals the wrong way round.
  • RCD will not protect against overheating that occurs when conductors are not properly screwed into their terminals.
  • RCD will not protect against live-neutral shocks, as the current in the live and neutral is balanced. So if you touch live and neutral conductors at the same time (e.g., both terminals of a light fitting), you may still get a shock.

RCCB

  • RCDs don’t offer protection against current overloads. If a live-neutral fault occurs (a short circuit, or an overload), the RCD won’t trip, and may be damaged.
  • Therefore an MCB is requires in series with an RCD.  A combined MCB and RCD in a single unit is called an RCCB.
For more information on circuit breakers, visit our other articles here.
To purchase these products online, visit our online store at Switchman Products.

Author: Josh Berman

Electrical Engineering at Switchboard Group

joshb@switchman.com

What is a Circuit Breaker?

A circuit breaker (CB) is an essential protection device used in electrical installations. It is used to prevent potential fires or other disasters as a result of faulty wiring or equipment failures. A CB detects when too much current is flowing through it and cuts the power until the problem can be resolved.

How does a Circuit Breaker Work?

A CB consists of a simple switch which makes a connection in the electrical circuit. When the load current in the circuit rises above a certain safety level, the switch in the circuit breaker opens, thus preventing any further current from flowing through.

Flush Distribution Board fitted with Miniature and Moulded Case Circuit Breakers. [Switchboard Manufacturers, JHB]

What are the Fundamental Characteristics of Circuit Breakers?

The fundamental characteristics of circuit breakers include:

  1. Rated Voltage (Ue)
  2. Rated Current (In)
  3. Tripping Current Range for Overload Protection (Ir) & Short Circuit Protection (Im)
  4. Short Circuit Current Breaking Rating (Icu or Icn)

Rated Operational Voltage (Ue)

The rated voltage of a circuit breaker is the voltage at which a circuit breaker has been designed to operate in normal (undisturbed) conditions (i.e 230V/380V/415V). The circuit breaker has also been assigned other voltage levels with which to operate during disturbed conditions.

Rated Current (In)

The rated current of a circuit breaker is the maximum value of current that a circuit breaker, fitted with a specified over current tripping relay, can carry indefinitely at an ambient temperature (stated by the manufacturer) (i.e. 60A/80A/100A). An increase in ambient temperature will result in the circuit breaker being de-rated (see Hydraulic Circuit Breakers).

De-rating a circuit breaker is achieved by reducing the trip-current setting of its overload relay and marking the circuit breaker accordingly.

Overload & Short Circuit Relay Trip-current Setting (Ir & Im)

Short circuit tripping relays (instantaneous or slightly time-delayed) are used to trip the circuit breaker rapidly when high values of fault current are detected.

 

Performance curve of a circuit breaker thermal-magnetic protective scheme (left); Performance curve of a circuit breaker electronic protective scheme (right) [engineers-practical-knowledge]

Definitions:

  • Ir: Overload (thermal or long-delay) relay trip-current setting.
  • Im: Short circuit (magnetic or short-delay) relay trip-current setting.
  • Icu: Breaking capacity.
  • Ii: Short circuit instantaneous relay trip-current setting.

Rated Short Circuit Breaking Capacity (Icu or Icn)

The short circuit current-breaking rating of a circuit breaker is the highest value of current that the circuit breaker is capable of breaking, over a short period of time, without being damaged (i.e. 6kA/10kA/25kA). The current value found in the standards is the rms value of the AC component of the fault current; this is usually given in kA rms (see the meaning of kA ratings here).

Conclusion

These are the basic characteristics of Circuit Breakers. For more info on finding the right breaker visit our Interesting Articles Page.

Author: Terry Berman

Biomedical & Electrical Engineer at FNB.

How Do Hydraulic Magnetic Circuit Breakers work?

Hydraulic magnetic circuit breakers combine overload and short circuit protection features into a single mechanism. The operation is completely independent of temperature allowing them to be used in environments subjected to extreme temperatures, without fear of failure.

Introduction:

The main advantage of using a hydraulic magnetic circuit breaker is that its operation is independent of temperature and thus, can be used in environments where extreme or volatile temperatures are present. Hydraulic magnetic circuit breakers also allow for a large range of delay times in which the overload condition will trip the breaker.

General Operation:

The hydraulic magnetic circuit breaker combines both the overload and fault protection into a single mechanism rather than using separate thermal and magnetic mechanisms as with the thermal magnetic circuit breaker. The circuit breaker contains a single solenoid coil which is combined with a spring-loaded actuator that is housed inside a cylinder filled with a dampening fluid.  Figure 1 below shows the inner workings of a hydraulic magnetic circuit breaker.

Figure 1: Hydraulic Magnetic Circuit Breaker [1]

A magnetic field is produced by the current flowing through the breaker. The magnetic field strength varies depending on the amount of current flowing through the solenoid. At normal operating currents the magnetic field will not be strong enough to cause the switch trip [2].

Normal Overload Operation:

When an overload condition arises, i.e. the current drawn through the breaker is greater than the rated current, the magnetic flux within the solenoid produces a magnetic field that is strong enough to move the core to the pole position. The hydraulic fluid within the cylinder dampens this movement thereby creating a time delay in the breaking of the current. This time delay is important provided it is short enough to not damage the devices connected to the breaker. This time delay allows for a moment of inrush current that many devices, such as motors and lights, require on start-up without tripping the breaker.  However, if the overload condition persists the core piece will reach the pole position which significantly drops the reluctance of the magnetic circuit causing the armature to be attracted to the pole face with sufficient force to collapse the latch mechanism which in turn trips the breaker [3].

[Photo Taken at Switchboard Manufacturers Johannesburg]

Short Circuit Operation:

When a short occurs in the system, a very large amount of current is drawn through the solenoid which creates a strong magnetic field. The strong magnetic field attracts the armature to the pole face even without the core having moved. This is known as the instantaneous trip region of the circuit breaker. Unlike thermal circuit breakers, the trip point is unaffected by the ambient temperature and thus the hydraulic magnetic circuit breaker can immediately be reset without requiring a cool down period [3].

Conclusion:

In conclusion, hydraulic magnetic circuit breakers use a single solenoid coil which is combined with a spring-loaded actuator housed inside a cylinder that is filled with a dampening fluid to achieve the overload and short circuit fault protection. These circuit breakers make use of varying strength magnetic fields to break the circuit when a fault occurs. They are especially suited for environments where the temperatures vary as their operation is independent of temperature.

References

[1] Cbi-lowvoltage.co.za. (2017). Energy Efficiency | CBI-electric (Circuit Breaker Industries). [online] Available at: http://cbi-lowvoltage.co.za/content/energy-efficiency [Accessed 14 Dec. 2017].

[2] Chan, L. (2017). Hydraulic Magnetic Circuit Breaker Theory. [online] https://www.linkedin.com. Available at: https://www.linkedin.com/pulse/hydraulic-magnetic-circuit-breaker-theory-lily-chan/ [Accessed 14 Dec. 2017].

[3] Cbi-lowvoltage.co.za. (2017). Hydraulic Magnetic Principles | CBI-electric (Circuit Breaker Industries). [online] Available at: http://cbi-lowvoltage.co.za/content/hydraulic-magnetic-principles [Accessed 14 Dec. 2017].

Author: Brendon Swanepoel

2nd Year Electrical Engineering Student, University of the Witwatersrand

Brendon is completing Switchboard Group’s 6 week Learnership and Training program offered to students looking to further their practical skills.

Switchboard Manufacturers, Empowering South Africa’s youth.

How to Select the Right Circuit Breaker for your Installation?

Selecting the correct Circuit Breaker (CB) for your distribution panel is crucial  for the longevity of the installation as well as the safety of those maintaining and occupying the premises. This article addresses the selection of key breaker attributes such as voltage, current and kA rating.

Rating Considerations:

Circuit Breaker Voltage Rating

The voltage rating of a CB is determined by the highest voltage that can be applied  across any two conductors in the circuit.  It is important to select a circuit breaker with enough voltage capacity to meet the end application. A single phase AC circuit in South Africa is generally rated at 230V  and a single pole CB rated at 230V can be used. A 3 phase AC circuit operates at 400V and requires a Triple Pole CB rated at 400V.

Circuit Breaker Current Rating

The next rating to consider is the amperage or ‘operating current’ of the breaker. CB’s are designed to operate at 100 percent of the required load . However,  in order to offset the effects of heat generated by the system, it is good practice to select a CB at approximately 125 percent of the required load.

For example: If a supply of 250A is available from the transformer, the breaker of choice for the main incomer should be rated at 250A in order to protect the transformer. However, the feeder breakers feeding a 25A load should be rated at 32A.

[Photo Taken at Switchboard Manufacturers Johannesburg]

Circuit Breaker kA Rating

Finally the ‘kA rating’ or ‘fault level’/’rupturing capacity’ of the CB should be taken into account. The kA rating of the CB indicates the maximum short circuit current that the CB can withstand without arcing or catastrophic failure. This current can be upwards of 100 times the required load and has the potential to  cause major damage to property and personnel.

For Example: A circuit breaker rated at ‘6kA’ means that the circuit breaker can withstand 6,000 amps of current during the brief time it takes to trip.

Why is it so important to choose the correct kA rating?

If the short circuit current is greater than what the CB can withstand, the contacts in the CB can weld together,  preventing it from tripping.  Another possibility is that the CB can explode, spewing dangerous plasma.

Under Rated Circuit Breaker

[Breaker fitted to a DB with an Under rated fault level]

So how do I calculate the correct kA?

The maximum current that can flow through a circuit is determined by the size of the transformer feeding the circuit as well as the length of the cable run from the transformer. This is often called the downstream short circuit current. This will determine the maximum kA rating required for the main circuit breaker.

For example: A 500kVA transformer that has a short circuit current of 35kA at its terminals. The cable run from the transformer to the main breaker is 10m and is run with 90mm2 cable. The resistance in the cable limits how much current comes from the transformer, and so after calculations it was determined that the short circuit current at the end of the cable would be 26kA. In this case, a 20kA circuit breaker cannot be used in the installation.

Switchboard Manufacturers
Distribution Panel

[Photo Taken at Switchboard Manufacturers Johannesburg]

SABS Approved Dealers:

When selecting a CB, it is vital for it to be SABS or IEC approved. This provides the assurance that the CB’s have been tested to strict quality standards and will operate in a safe manner as required. Well known brands such as ABB, Schneider and CBI are all SABS approved and are regarded as high quality devices. Switchboard Group is a registered supplier of these products and the leading manufacturer of LV panels is South Africa.

Conclusion:

In conclusion a CB should be selected based on the nominal current, kA rating, number of poles required and whether the CB is SABS approved.

Author: Brendon Swanepoel

2nd Year Electrical Engineering Student, University of the Witwatersrand

Brendon is completing Switchboard Group’s 6 week Learnership and Training program offered to students looking to further their practical skills.

Empowering South Africa’s youth.