In kitchens, it’s often desirable to be able to control a hidden 13A socket outlet remotely. For example when the socket is behind a washing machine or dishwasher.

With reference to BS7671 can you use a 20Amp switch to control a socket connected to the spur off a ring final circuit?

What happens when you use an impact driver to install a consumer unit? We know it’s a terrible way to carry out an electrical installation but we went ahead anyway.

Manufacturers of circuit breakers and consumer units receive lots of warranty returns caused by electricians using impact drivers. So we decided to see exactly what happens to the terminals inside a consumer unit, Lewden RCBO and an expensive Wylex AFDD.

With BS7671 amendment 2 just around the corner, the use of AFDD’s in consumer units is expected to increase. Is it worth the risk of damage using an impact driver on an expensive device?

An mcb will trip if the current exceeds it’s limit whichever way around you connect it. However they have an exhaust type mechanism on one end of them that will expel heat and whatnot should they have to deal with a massive short circuit. This is the reason that when connected into a board they need to be connected the right way round.

A simple thermal-overload type circuit breaker is bi-directional. That is, the LINE and LOAD terminals can be arbitrarily assigned Up, Down, Left or Right. It merely depends on where the LOAD is, relative the circuit breaker.

A simple thermal-overload type circuit breaker is bi-directional. That is, the LINE and LOAD terminals can be arbitrarily assigned Up, Down, Left or Right. It merely depends on where the LOAD is, relative the circuit breaker.

Examples;

1) If a main circuit breaker, MCB, is located above the distribution breakers, then the MCB load terminals are on the bottom and connected to the distribution bus bars.

2) If a main circuit breaker, MCB, is located below the distribution breakers, then the MCB load terminals are on the top and connected to the bus bars.

The above applies only to low Voltage miniature circuit breakers which are unit mounted or mounted in a distribution panel-board. The typical Medium Voltage, or rack mounted, circuit breaker has the LOAD terminals at the bottom of the breaker.

Here is a catalogue page, showing busbars at the bottom, and therefore the load terminals at the top

I lectured for many years on this stuff.

I always said it was logical that you push the switch into the direction of the load.

Therefore, because you push the switch up to close the circuit,

the load is at the top.

Incidentally switches go up to be ON because it was said

that it was more likely that something would push a switch accidentally down,

and therefore shut it off.

What is the difference between a single pole and a double pole MCB?
Single Pole MCB is used to break ‘single phase’ and Double pole is used to break ‘phase and neutral’.

In other words, single pole controls 1 live wire and it trips the respective line when the fault current exceeds the pickup setting and double pole can control 2 live wires/ one live & one neutral.

Should I use a single or double pole circuit breaker?
Assuming this is a single phase system, you use a single pole breaker for a 120 volt circuit and a double pole breaker for a 240 volt circuit. You are only attaching the hot leads to the breakers not the neutral wires. If you do not know this, it is probably advisable to hire an electrician.

Can single phase load connected to 3 pole MCB run normally? What will be the consequences?
You can connect to any of the 3 poles and can act as a single phase breaker

Or if you are goin to use it permanently you can do as shown in d attached picture so that you can use 3 poles of breaker even we are using single phase

Can we use 2 double pole MCBs instead of one 4 pole MCB?
I would say “ NO”

Simply because a 2 pole MCB & a 4pole MCB are designed for different purposes.

While a 2 pole MCB is designed for switching action of 1-phase circuit consisting of phase-neutral, the 4 pole MCB is designed for 3-phase systems with higher voltage levels ( approximately 1.7 times the single phase voltage).

What is the operating current of MCB?
MCB=Miniature Circuit Breaker.

Operating current;-

Actually there is no operating current (negligible). It is just a very low resistance conductor once the load consumes more power than rated power of CB it heats which results in tripping the breaker mechanically.

So we could say there is no operating current in normal working and during overloaded condition a small amount of power will be consumed to heat the conductor which operates the tripping mechanism mechanically.

If your question is the current during tripping action, then the answer is it depends on the load if the load is very high it ta

Great answers here to your question.

Totally agree going up is ON where the live side is and down is OFF to isolate the load.

ABB make AC circuit breakers from 110Volt 5Amps to 1 200 000Volts 6300Amps. Wow that is one hell of a range.

You know what in every instance up is on and down is off.

It doesn’t matter which way around you use it but the convention is in at the top and out at the bottom. It’s good to know which side is live when the breaker is tripped!

MCBs are used in more locations than just distribution boards…

Hello Guys ,
thank you for this helpful Forum

my question is related to Circuit breakers position ,and its supplying direction

i mean it is marked as always input or supply side to CB from upper terminals and it connecting to load side from lower terminals
according to NEC ,and according to CB performance
CAN we supply the circuit breaker from the lower terminals ?

2- what is the preferable supplying the main CB or the enclosure from upper and other branch breakers be lower it ,i mean cable entrance the enclosure from the top or the bottom of the enclosure ?

Unless a breaker is marked line and load, it can be fed from either terminals. Most typical is line at the top and load at the bottom.

Another example example is a main lug only panel that is back fed from a breaker. Power is fed from into the lug terminals and fed to the bus from the stab connection.

Whether cables and conductors enter an enclosure/cabinet on top or bottom is a matter of choice, design and ease of install.

No matter what orientation a breaker is installed, it is preferred the line be connected to the end towards which the handle points when in the closed (ON) position. I say preferred because it is not a hard rule. You will find some bottom-feed panels with MCB at the bottom, the line terminals are at the bottom of the MCB and the handle must be flipped up to close the breaker. Some manufacturers avoid this discrepancy with the preferred status by mounting the MCB sideways.

Providing that breaker is not marked LINE and LOAD, which it does not appear to be, the NEC does not prohibit any of those cases.

Is that third breaker upside down?

If so, it cannot be installed like that.

240.81 Indicating. Circuit breakers shall clearly indicate
whether they are in the open “off” or closed “on” position.
Where circuit breaker handles are operated vertically
rather than rotationally or horizontally, the “up” position of
the handle shall be the “on” position.

Yes, but some breakers, such as AFCI or GFCI or some electronic trip units which contain circuitry powered from the circuit they protect, or DC breakers with a preferred current direction, will be marked with Line and Load terminals for a good reason.
And under the NEC, even if there is no theoretical justification for it, connecting the source to a marked Load side is a code violation.

INSIDE THE LAB THAT PUSHES SUPERGRID CIRCUIT BREAKERS TO THE LIMIT
https://spectrum.ieee.org/inside-the-lab-that-pushes-supergrid-circuit-breakers-to-the-limit

Tomorrow’s megavolt transmission lines need breakers that can withstand titanic forces

The Guardian: KEMA Laboratories tests a circuit breaker under extreme conditions to ensure it won’t fail when it really matters.

A BLAZINGLY HOT DAY IN CENTRAL CHINA, when all the air conditioners in every megacity are running at full blast. Through the remote mountains of Shanxi province, the major transmission lines that carry ultrahigh-voltage electricity to the cities are operating at close to maximum capacity. Heated by the sunshine and the flowing current, the transmission lines sag dangerously close to the treetops. Suddenly the current jumps from line to tree branch, finding the path of least resistance and pouring through the tree into the ground. There’s a bright flash as the current ionizes the air.

During this short circuit, the abruptly unleashed current reaches 10 to 20 times its normal level within a blink of an eye. Now the power grid’s protection system must act fast. Within milliseconds, protection relays must recognize the fault and command the circuit breakers at both ends of the line to switch off the current, isolating the faulted line. The stakes are high: A sustained short-circuit current can trigger a chain reaction of failures throughout the grid and cause widespread blackouts, severely damaging expensive equipment in the process.

just separating the contacts doesn’t stop the current. Instead, the current creates an electrical arc inside the breaker. That small space, which has a volume of just a few liters, now contains a roiling plasma that may reach temperatures of many thousands of degrees Celsius. The breaker can’t contain that plasma for long; if it’s not cleared away quickly, there will be a terrible explosion.

Now the alternating nature of the AC current comes into play: Each time it changes direction (every 10 milliseconds in China’s 50-hertz system), the current temporarily becomes zero, and the energy supply to the arc plasma momentarily halts. It’s at one of these “current zero” moments that the fault current must be interrupted. At that crucial moment, a cooling system inside the circuit breaker injects a high-pressure jet of gas into the gap, blasting away any residue of the hot arc plasma.

Immediately after the arc disappears and the fault is cleared, the power system ramps up again. In this recovery process, the voltage across the gap steeply rises to over 1 million volts before settling to its normal operational level.

So in the microseconds before and after current zero, the contacts need to change over from channeling approximately 50 kiloamperes of current through the arc plasma to withstanding 1 megavolt of voltage. This rapid change puts enormous strain on the breakers’ components.

Yet the circuit breakers must perform flawlessly, because the transmission line needs to go back into operation. They must work even though they may have been inactive for long stretches of time and through all kinds of weather.

Tomorrow’s power grid will likely rely on large-scale renewable energy facilities such as hydropower plants, solar parks, and offshore wind farms, located far from power-hungry cities. To transport that energy across long distances, system operators are planning and constructing massive transmission lines. These lines must be high voltage, so they’ll lose only a small fraction of energy through resistance in the lines. Building these cutting-edge high-voltage systems is quite expensive. But many power companies are deciding that the ability to move huge amounts of energy across vast distances justifies the costs.

Choosing to construct a high-voltage transmission system is the first step. The next step is to decide: DC or AC? High-voltage DC transmission systems are an increasingly attractive option, as DC overhead transmission lines require less space and lose less power than do AC lines. But AC technology is more mature, and the world’s most powerful transmission systems are still designed for AC. The latest AC supergrids use ultrahigh voltage (UHV) of at least 1,000 kilovolts, a staggering level not yet realized in DC.

In UHV transmission systems, the most crucial piece of technology is the circuit breaker. The breaker is the system’s guardian: It must be eternally vigilant and prepared to act instantly. And it must function in all environmental conditions and despite great systemwide stress. At the KEMA test facility, in Arnhem, Netherlands, we put these breakers under extraordinary strain to provide an independent assessment of their performance. There’s a clear need for this service: About a quarter of the circuit breakers brought to our labs fail to pass their tests.

Why not rely on simulations to study the stresses at work? Unfortunately, computer models aren’t yet up to the task of simulating microsecond-scale interactions between electrical circuits and extremely hot and chemically complex plasmas. A study carried out by CIGRÉ, the International Council on Large Electric Systems, evaluated the simulation tools used by seven major manufacturers. First, the good news: These different tools did model the electrical fields at critical locations inside a circuit breaker with great accuracy and agreement. But when the tools modeled a breaker’s failure—the point at which it succumbed to electric stress—they produced values quite different from each other and from the true tested value.

The table below gives the watts loss per pole at rated current.
MTN Electrical Characteristics.
MCB Rated current (A) 0.5 1 2 3 4 6 10 13 16 20 25 32 40 50 63
Watts loss per pole 1.2 1.3 1.5 2.0 1.8 1.4 1.9 2.1 2.5 2.8 3.2 3.8 4.0 4.5 5.1