Questions tagged [circuit-breaker]

An automatically operated electrical switch designed to protect an electrical circuit.

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1answer
39 views

20 amp to a 40 amp circuit [closed]

On the back of my house is the breaker box. It has an open 40AMP fuse (not connected to anything any more). There is also a 20AMP fuse connected to my shed. When the shed was originally built, it was ...
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2answers
145 views

Why does adding one more extension cable turn the MCB on again?

I found a strange phenomena when I tried to use a metal cutter that consumes about 2000 watt. See the following illustration. If I just use one extension cable, the MCB will trip when I turn on the ...
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3answers
113 views

Why can't circuit breakers close across a large phase angle difference?

In power systems I understand that breakers have mechanisms preventing their closing if they detect the phase angle (and voltage) across them to be too large. This is usually called a 'sync check'. ...
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1answer
81 views

Connecting a 120V/30A variac to a 240V circuit

I have a variac rated for a maximum output of 30A. The problem is it takes 120V on the input and all of my 120V circuits are 15A, as expected. I unfortunately cannot just add an additional 30A circuit ...
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4answers
101 views

Is there a device to prevent a main circuit breaker from tripping and give an added layer of protection?

I would like to install some additional appliances in a room that already has a couple of heavy equipment machines running in it. These are sensitive machines, so instead of having the main circuit ...
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1answer
62 views

How to create a break away to cut the board

I am not a expert with Eagle 9.6 but I created a nice PCB. A friend of my is going to assembly the part with a pick and place machine. He asked me to enlarge my PCB to be able to fix the board and ...
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2answers
128 views

Fault current indicator - what should I do?

Part of the power plugs in my flat stopped working this morning. I checked the breakers box and one of the breakers was in OFF position, with a yellow indicator. After checking the producer's website, ...
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10answers
9k views

What causes a fuse to blow, the current or the power?

Fuses and circuit breakers are often specified at a certain current they will 'blow'. Increasing the current will also increase the power. So if a fuse is rated for 12V DC and 20 A, this would be ...
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0answers
42 views

Are breakers polarized?

I would like to know if a circuit breaker is polarized if it looks like this. I would also like to know how I can manually turn off these breakers and how to reset them Thank you!
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77 views

Can I avoid tripping my breakers with an superinductor?

I was thinking about creating a circuit with a large inductor to avoid tripping my breakers when I turn on an iron. When I use the iron, if I slowly start it with minimum heat and gradually increase ...
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2answers
38 views

How do TVSS and Circuit Breakers (thermal-magnetic) interact with each-other?

In EU you can find thermal-magnetic circuit breakers all other the places in buildings and it's not uncommon to have daisy chains of them (meaning a main panel will have one, which is connected to ...
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1answer
84 views

Why location of CT is different for the two Circuit breakers in same substation layout?

This is a schematic diagram of a traction substation. In this traction substation protection system schematic diagram, at point marked 'A', CT is located after the 25kV CB. However, at point marked 'B'...
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109 views

What does this switch do?

Also, what is that circuit element symbol (an arrow leaving a rectangle) called, in the diagram next to the switch?
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17 views

Tripping threshold question

The tripping threshold is between 0.5 and 0.7 times the rated voltage I will like to confirm the above statement. If my rated voltage is 215V, assuming we picked 0.5 setting, does this means that the ...
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1answer
64 views

Can I replace a 32 A switch with a 32 A MCB?

A switch for a water heater in my apartment is broken (image attached). It is an "Anchor Roma 32 Amp 1-Way Switch with indicator". Can I replace it with this or this switch? Would the installation ...
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2answers
40 views

3-Pole Circuit Breaker with GPIO

I'm starting a small project involving 3-pole circuit breakers and 3-ph motors. There's this custom built machine with multiple 3-ph motors, each connected to circuit breakers. The purpose of the ...
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1answer
138 views

Generator to Main changeover issue RCCB not moving up

RCCB not moving to up position while DG to EB ( generator to mains) changeover. I live in a community where we have almost 1200 apartments in India which will serve power through generators when the ...
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0answers
30 views

What is the NEMA and IEC schematic symbols for a Variable Current Circuit Breaker or Adjustable Trip Circuit Breaker?

I really need a depiction of a variable current circuit breaker (VCB) for a single line drawing of a new MCC cabinet. We are putting in a 40 to 100 amp 3 phase 480 Volt circuit breaker and this is ...
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4answers
8k views

Why can an AC circuit breaker not be used in DC circuits?

Let's assume that I want to use a 20-amp GE AC circuit breaker in a DC circuit. So, after testing it in a DC circuit with some loads and ammeter + clamp DC amp meter I find the current at which the ...
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1answer
59 views

I'm looking for a circuit breaker that interrupts the circuit when current drops to zero

I am looking for a switch that only keeps contact while current is running. Once the current drops to zero the switch opens contact. Something like a circuit breaker that trips with no current. It ...
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1answer
63 views

Are ground fault currents shown as RMS or Peak in GFCIs?

When a GFCI (Ground Fault Circuit Interrupter) states that it trips for example at 30 mA, is this value RMS or Peak?
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1answer
35 views

GFI Breaker on a three line 240V circuit

I need to add GFI to an existing 240V 30A circuit your use an electric home brewing system. The system uses an electric heating element that is immersed in a kettle of water. The manufacturer ...
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2answers
179 views

How does the arc extinguisher work in a miniature circuit breaker?

In a miniature circuit breaker, as shown below, the distance between open contacts is much less than the distance between metal bars in the arc extinguisher part (the gap gets progressively longer ...
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1answer
78 views

What symbol to use for a electronic circuit breaker in a schematic?

What symbol should I use to electronic circuit breaker in a schematic?
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1answer
106 views

Safety switch “breaking capacity” vs. voltage

In the context of safety switch rating (fuses, circuit breakers, etc.), the concept of breaking capacity refers to the maximum electric current which can be safely interrupted by a tripping safety ...
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1answer
105 views

Does a 5A Car Fuse Blows in a 12 Miliseconds Peak of 6A, in a 220v Circuit?

Thinking here in using a 5A fuse in a certain circuit, but it may reach 6A sometimes for a mather of 10 or 12 miliseconds only. That way, would this fuse blow or it would sustain and blow only in ...
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1answer
69 views

Flash in MCCB when switched off

Recently I switched off several molded case circuit breaker (MCCB) and saw a flash at the back of the breaker for an instant. This happened to all the MCCB on-site (around 14). The MCCB are all rated ...
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75 views

What do the white and green colours on the earth leakage CB denote?

I've come across two 4 pole earth leakage circuit breakers, one with the all green lever and another with white levers for phases and green for neutral. Is there any special meaning to this? I've ...
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2answers
231 views

Why arc only happens when circuit on load?

I'm preparing research about high voltage electric distribution for my university but I don't understand why the arc only happen when current is flowing. I made my internship in an electric ...
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0answers
40 views

Circuit breaker wiring: put source current on side marked with X or side with switch? [duplicate]

I am trying to wire an electrical panel in a standard manner. I have several automation devices that take 120 Vac power. In order to protect them, I have purchased a 2-pole circuit breaker, Phoenix ...
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0answers
76 views

Protection Devices in DC ciruits

I am putting together a design for a custom Electrical panel. The panel consists of mainly DC powered components (Sensors, Controllers). Components are to be mechanically positioned using a DIN rail. ...
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1answer
747 views

Switching Power Supply - Type of MCB for Inrush Current

it's regarding this PSU from Mean Well: https://www.meanwell.com/Upload/PDF/LRS-350/LRS-350-SPEC.PDF It has a 60A inrush current. My lighting circuit (1.5mm2 wiring) is tied to this PSU supplying ...
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1answer
228 views

Switching Power Supply - Inrush Current, Input Current, MCB

I am getting several PSUs (LRS-350-24) from Mean Well. Here's the specs: https://www.meanwell.com/Upload/PDF/LRS-350/LRS-350-SPEC.PDF 1) The input current is stated to be 3.4A/230VAC at 88%. 350W ...
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2answers
195 views

24V LED Strip Circuit - Switch, Breaker & Wiring Size Requirement

I am running a long LED strip (24V, 21 meter, 0.6A per meter, so technically 13A). The 24V PSU supplying power to the strips is to be connected to a switch that is rated 240V, 10A & 2400W. ...
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1answer
66 views

Tripping a circuit breaker when using a half wave rectifier

How does a half wave rectifier or phase control dimmer affect the triggering of a circuit breaker? For example, if a 20A resistive load was on a 15A breaker with a half wave rectifier. Now average RMS ...
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2answers
47 views

Both fuse and circuit breaker operated

Is there a reason that both a fuse and a circuit breaker would operate? From my understanding, the fuse should blow first and kill any current flowing through it leaving the breaker intact. So why ...
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0answers
46 views

Modeling the thermal part of the Time-current curve

G’ day, I am working on designing protection devices for my research work and I am struggling to model the thermal part for the low voltage circuit breakers based on IEC standards. Based on the ...
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1answer
118 views

MCB with electronic trigger-off [closed]

How can I design a system that gives the functionality of an MCB (overload protection, operates in an AC circuit) with an electronic trigger-off. So that once the device is in ON state, it should be ...
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1answer
506 views

Floating DC power supply (solar panels) - do I need double-pole breakers and why?

I am in the process of building a small off-grid solar setup. There will be 4 parallel strings of panels in this setup, and I understand that for 3 or more strings, you need some sort of over-current ...
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2answers
335 views

What sort of protection does a 2 pole circuit breaker offer?

I am trying to understand the advantages of using a 2 pole circuit breaker. I mean when the 2nd pole is used in the Neutral line in a single phase 230VAC system. Normally they cost more so they must ...
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1answer
73 views

Device for preventing 12V battery from dying

I am looking for a device which cuts off the connection between batteries and the system just like a circuit breaker when my 12V battery goes below 9V(for example) for preventing it from dying ...
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3answers
393 views

Rounding up or down with Motor Overcurrent Protection

When sizing motor over-current protection, CSA 22.1 28-200 3a states that a circuit breaker can be sized up to 250% of the rated full load amperage (FLA) of the motor. E.g. 100hp, 575VAC motor ...
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3answers
5k views

How can I check if two outlets are connected to the same electrical circuit?

I have some internet problems, and I was thinking to buy a PowerLine, that will help me extend the WiFi range. The thing is, to get this PowerLine working, both need to be conected to the same ...
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3answers
3k views

Can double-pole breakers trip each side separately?

How many of you have used double pole breakers? Are double-pole breakers just two single pole breakers physically joined? Someone stated that only one side of the double pole breaker provided short ...
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2answers
1k views

Help identify this breaker

I salvaged this breaker unit from the scrape yard. Compared to every other breakers i have seen before, this is very different. It has 5 terminals. The labels are very clear but there is no ...
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4answers
8k views

Why cut both live and neutral wires?

It is a common practice, for high power loads such as boilers, furnaces, etc., to install a circuit breaker that "cuts" both live and neutral wires - at least in Europe. In my search for EVSE, I saw ...
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1answer
528 views

240v AC Circuit Breaker for 24v AC

I am essentially intending to use this Schneider Electric A9F44120 MCB as an automatic brake for my wind turbine, which has an output of 25A @ 24Vac. Can I use the normal 240Vac MCB for 24Vac? Will it ...
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1answer
58 views

Can you bridge off of a 240 V Breaker Box that connects to an Intermatic Timer?

I have an Intermatic T104 Timer drawing power from a Homeline Breaker Box for a home swimming pool. I'm wondering whether it would be considered safe to use the knockout in the timer enclosure to ...
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1answer
309 views

amp rating a circuit breaker

My application has a max Amp draw of 56@24Vdc, if I use a Circuit Breaker that is rated 60A@48Vdc, will it "trip" 60A@24Vdc? If not, what do you suggest? The Minn Kota MKR-19 Circuit breaker is rated ...
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1answer
3k views

When to use a 2 pole circuit breaker over 1 pole

We are currently designing a product that connects to 230VAC mains power (single phase) (South Africa). It has a simple 12v switch mode power supply that runs the electronics. We want to put a Circuit ...