Can I get benefit's from use MCB with Fuse ?

Thread Starter

meowsoft

Joined Feb 27, 2021
494
Can I get benefit's from use MCB with Fuse ?
if I used MCB with fuse, I can have circuit cutted faster when shorted (with Fuse), and cutted faster when overload (with MCB), and I can replace Fuse more safely, because I wire MCB before Fuse, also MCB have greater breaking capacity, 6kA (MCB) vs 150kA (Fuse), so.. in case MCB is faulted and can't cut circuit, fuse is cutted the circuit
Disadvantages : More expensive, need enough space in panel, also need lots of wiring, with MCB or Fuse only, I just use comb busbar, with this system I use comb busbar and wire
Is that a good idea ?
What do you think ?
and Is really Fuse can cut circuit faster than MCB in case of short circuit ?
 

Deleted member 115935

Joined Dec 31, 1969
0
IMHO, abs no real advantage
MCB and a fuse both switch faster the more the over load is
Fuses have a VERY wide range of operation, much harder to tie down than a MCB that is tightly specified.

If you want to spend more on safety

consider multiple RCD's, and multiple MCB , such as

lights on one RCD , multiple MCD
House power on another RCD muliple MCB
Kitchen on another RCD , multiple MCD

Allows you to have very low leekage RCD on the lights,
medium on the kitchen
high on the house power ( depending upon local regulations )
 

MisterBill2

Joined Jan 23, 2018
9,549
Think about it: How often have you seen this done?
I have never seen it done with a single fuse in series with a single circuit breaker. I have seen a circuit with one breaker feeding a bank of much lower rated fuses, AND I have seen a single high rated fuse (60 amps) feeding a panel of lower rated breakers.
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
Think about it: How often have you seen this done?
Yes it's very uncommon... and do you think why ?, but in my case, I don't want MCB tripped to late and burnt relay, because that's circuit is connected in series with relay, also there is big range choice for fuse in my local area, from 1a to 63a, also same size with MCB
Note : Relay is arduino relay for smart home system, I think that's not industrial grade, currently I use MCB and fuse in series for each circuit with same amps, in my local area fuse is common for things that need's small amps size and need's faster short circuit disconnection, usually panel components like pilot lamp, CT, kwh meter, volt meter, bla bla bla
 

MisterBill2

Joined Jan 23, 2018
9,549
OK, certainly there are very fast fuses available, and the fast ones will protect quite a bit. BUT for a load switched by a relay, consider that the relay must operate and close the circuit first, before any circuit protection device could possibly operate. So if the current is enough to operate a protective device then it is already flowing through the relay contacts.
In that case it will make the most sense to use only a fuse, because a miniature circuit breaker will cost quite a bit more but not provide as good of protection.
It is also possible to design and use current limited circuits in which an over-current is not possible.
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
OK, certainly there are very fast fuses available, and the fast ones will protect quite a bit. BUT for a load switched by a relay, consider that the relay must operate and close the circuit first, before any circuit protection device could possibly operate. So if the current is enough to operate a protective device then it is already flowing through the relay contacts.
In that case it will make the most sense to use only a fuse, because a miniature circuit breaker will cost quite a bit more but not provide as good of protection.
It is also possible to design and use current limited circuits in which an over-current is not possible.
If I don't care about cost, is fuse with MCB a good idea ?
 

Deleted member 115935

Joined Dec 31, 1969
0
If I don't care about cost, is fuse with MCB a good idea ?
I think I'd sum it up as

Its not a bad idea,
in that it will do "no harm"

but its also not likely to do "any good" either.

it just costs money and space to achieve at best , not a lot
 

MisterBill2

Joined Jan 23, 2018
9,549
The only possible benefit that I can see is the convenience of being able to switch off the MCB when you need to switch off the power. But if the location is not convenient then there is no benefit.
And certainly there is no benefit in circuit protection if the ratings on both devices are correct.
The correct selection of the device characteristics is important with both fuses and MCB devices. A motor-starting time-lag fuse will not protect semiconductor diodes or transistors because it is made to withstand short overloads. This means that both the current rating and the response times must be selected correctly for the specific application.
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
The only possible benefit that I can see is the convenience of being able to switch off the MCB when you need to switch off the power. But if the location is not convenient then there is no benefit.
And certainly there is no benefit in circuit protection if the ratings on both devices are correct.
The correct selection of the device characteristics is important with both fuses and MCB devices. A motor-starting time-lag fuse will not protect semiconductor diodes or transistors because it is made to withstand short overloads. This means that both the current rating and the response times must be selected correctly for the specific application.
It is good to install 25a MCB per each branch, and specified fuse ?, all circuit branch maximum wire capacity is 34a, and then use fuse for specific load (10a, 6a, ...) ?, MCB is just for switching on/off and for short circuit protection ?, I can safe money if I want upgrade amps I just replace fuse, no needs to replace MCB
 

MisterBill2

Joined Jan 23, 2018
9,549
Now the condition is different. If each branch would have 34 amp wires and a 25 amp circuit breaker, and the intention is to protect a load device, then a lower rated fuse may be of some benefit for protecting the load device.
But normally device protection is provided by a fuse or circuit breaker that is part of the device assembly, not a part of the distribution system. That is because the power distribution system usually feeds several loads, and the distribution circuit breakers are rated to protect the wires feeding the outlets and lighting fixtures. Thus there are two different applications entirely. They have different purposes and different locations. It would not be reasonable to put the fuses to protect each device at the main distribution panel if the wires were all that very large size, adequate to carry 34 amps.
 

shortbus

Joined Sep 30, 2009
8,888
MCB is just for switching on/off
Using a circuit breaker of any type as a switch is kind of a no-no. Many even large breakers have a life time, the number of times they can be blown/turned off and still keep their rating. Then doing it on DC where there is a much bigger chance of an arc between the contacts? If you need a switch use a switch.
 

Thread Starter

meowsoft

Joined Feb 27, 2021
494
Now the condition is different. If each branch would have 34 amp wires and a 25 amp circuit breaker, and the intention is to protect a load device, then a lower rated fuse may be of some benefit for protecting the load device.
But normally device protection is provided by a fuse or circuit breaker that is part of the device assembly, not a part of the distribution system. That is because the power distribution system usually feeds several loads, and the distribution circuit breakers are rated to protect the wires feeding the outlets and lighting fixtures. Thus there are two different applications entirely. They have different purposes and different locations. It would not be reasonable to put the fuses to protect each device at the main distribution panel if the wires were all that very large size, adequate to carry 34 amps.
No... 34 amps is only 4 square millimeters in my case... It's not very big... Schneider MCB is supported about single 10-16 Square meter solid copper wire
 

MisterBill2

Joined Jan 23, 2018
9,549
Shortbus is correct in that using a circuit breaker for a switch will certainly lead to the mechanical failure of the circuit breaker.
So now i must ask just what sort of application is this for? It would offer no benefit t all for residence that people live in, but it may be useful in the electrical repair area of a large factory. It could be of a small benefit in a castle for rulers with very large amounts of money.
There would be no benefit of improved safety from electrical overloads as compared with a correctly designed breakers, or fuses, only electrical system. So for a correctly designed system it would be a poor use of resources, (money).
 
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