A lot of people don’t know how to calculate the number of the LED drivers that can be connected to an MCB, this article explains how to do that. First we have definition of MCBs, then we describe how it works.
Definition of Miniature Circuit Breaker (MCB)
A miniature circuit breaker is an electromagnetic device that carries a complete molded insulating material. The primary function of this device is to switch the circuit. It means to automatically open the circuit (which connects to current) when the current passing through the circuit goes beyond a set value or limit. MCB is designed to protect the cable downstream of the device against overloads and short circuits, preventing damage to cables and equipment. The device can be manually switched ON or OFF, just like standard switches whenever necessary.
Types of MCB
There are 3 MCB types, Type B, Type C, and Type D, and the speed at which they trip depends upon the level of overload and is usually determined by a thermal device within the MCB. A typical MCB tripping curve shows the amount of time required for a circuit breaker to trip at a given overcurrent level as below.
These curves differ from manufacturer to manufacturer and from type to type. Typically, the B type MCB curve has the operating range of 3 to 5 In, C type has 5 to 10In, and D type has 10-14 In according to the datasheets of most commonly used ABB S201M series.
MCB Working Principle and Work Conditions
MCB works by tripping when a circuit is overloaded or when a short circuit has occurred in the system and has a current rating such as 6A or 10A depending upon its intended use, i.e., for residential, commercial, industrial or public buildings. The MCB is tripped in two conditions, steady-state current and instantaneous current, also called inrush current.
What is inrush current?
It refers to the input current of tiny duration that flows into the LED driver, which can be regarded as a capacitive device during the power on stage. The figure below shows the typical inrush current with capacitive load from 230Vac 50Hz AC line input.
If there are multiple LED Luminaires powered on at the same moment, the max peak inrush current and its duration might trigger the MCB.
Formula to Calculate
The formula to calculate the LED driver load number is Min(Itrip /Idriver ,Ihold/Iinrush). The value is the minimum between two values.
Itrip: N x MCB rated current (N depends on different types of MCB).
Idriver: the maximum input average current of an LED driver.
Ihold: the instantaneous rated current of the MCB.
Iinrush: the maximum inrush current of an LED driver.
And the most critical curve to calculate how many pieces of LED drivers you could parallel is the one below.
A typical example to calculate MCB loads is presented bellow.
Maxium Upowertek LED drivers that can be connected to a MCB at 230Vac.
- Users need to be very careful when selecting MCB for proper usage.
- Tripping MCB needs either steady current overload or Instantaneous current overload.
- The MCB selection service is provided by sales.
Here are some related standards.
- IEC 60947-2 (GB14048.2)
LOW-VOLTAGE SWITCHGEAR AND CONTROLGEAR
PART 2 CIRCUIT BREAKERS
— Mainly for Industrial Use
— related to low voltage CB for use in industrial (Car assembly, Petrochemical, steel production, food processing) and similar installation. Inside UK these are traditionally known as MCCBs or ACB, MCB according to construction.
- IEC 60898-1 ,-2(GB 10963.1,.2)
Electrical accessories. Circuit-breakers for overcurrent protection for household and similar installations
— Mainly for House and Commercial
— Related to low voltage CB use in household, retail, schools, offices and similar installation. These are traditionally known as MCB’s.