F204AC-63SLASH0.1 datasheet(41/62 Pages) ABB

41 / 62 page

Residual

Curr

ent

Devices

Low Voltage Products & Systems

16.39

ABB Inc. • 888-385-1221 • www.abb.us/lowvoltage

1SXU000023C0202 Rev. A

Difference between RCD and MCB

Miniature Circuit Breaker (MCB)

A miniature circuit breaker (MCB) is a device designed to isolate a circuit

during an overcurrent event without the use of a fusible element. A

breaker is a resettable protective device that protects against two types of

overcurrent situations; overload and short circuit.

Residual Current Device (RCD)

A residual current device (RCD) is a device designed to provide protection

against voltage leakage to ground. RCD’s are sensitive to a 30-300mA.

RCD’s are mechanical devices that contain a CT and a solenoid. RCD’s

are designed to protect equipment, not wires against overload and short

circuit situations. For this reason, an RCD should always be used in

conjunction with an MCB in order to provide full protection from overload

and leakage to ground.

Ground Fault Interrupter (GFI)

GFI Definition (NEC): A device intended for the protection of personnel that

functions to de-energize a circuit or portion thereof within an established

period of time when a current to ground exceeds the values established for

a Class A device.

A ground fault interrupter (GFI) is a device designed to measure the current

between the hot wire and neutral wire. Like the RCD, the GFI will open the

closed contacts in order to protect against damage. A GFI is sensitive to

5mA and higher and is designed to protect people, not equipment.

A GFI is an electric device that contains a printed circuit board (PCB).

GFI’s have a “pigtail” wire at the end that carries a signal to the PCB that

tells the contacts to open when a current imbalance is detected between

the two conductors.

Application manual

Difference between RCD and MCB

Example of current leakage to ground

Abrasion in wire;

small (mA)

leakage to ground

Current ow

Neutral (N) return path is not

equal to the current in the hot

(L1) path (leakage to ground);

there is an imbalance

between the

L1 and N.

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