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can 24AWG wire handle the short circuit till the miniature circuit breaker will open

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rgbbv

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Hi
i change a varistor on ventilated oven hood's PCB(that located inside the hood,above the filter,inside a box)because it was damage.when the varistor burn out,it also burn out one of the conductive pathways of the PCB.the oven hood is powered by 230v through miniature circuit breaker of 16A(C).the PCB itself doesn't has a fuse.i want to solder 24 awg wires in order to pass the disconnected conductive pathway.the current that will pass through this wire is 0.4A(220v),and it will flow through the relay contacts(the relay coil controled by separated 12vdc transformer)and turn-on 2x40w bulbs.
the 24 awg wire can handle the 0.4A,but can it handle the current of a short circuit untill the MCB will operate?
thanks in advance.
 
Yes, but it should be fused. A circuit that draws only 400mA and is only protected by a 16A breaker doesn't seem right.
 
Thanks Sangoma.
The first thing that i did(before i found that the varistor is blow out)was to search for a fuse on the PCB,but there wasn't.so,apparently,this is the way it has been designed.(the MCB,by the way, protect also on other appliance and wall outlets).
so just to be 100% sure,for safety reasons,i would like to clarify the situation.
The wire is awg 24(0.2mm^2,area of the wire)if a short will happen in the circuit and a short circuit current will pass through this wire,can the wire handle the short current untill the MCB will operate?.i would like to mention that the short circuit current that will be developed on the wire refer to the 220v(from the MCB phase to the wire to the bulbs and back to the neutral) and not refer to the 12v(that operate only the relay's coil),because the wire is connected to the power contacts of the relay.
i check twice because i want to prevent a risk of fire in case of a short,so i try to describe the case as clear as i can.
 
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Why don't you simply put a 3A fuse in the place you want to put the wire?

Why did the tracks burn? What caused the short?

What country are you in? If you use fused plugs, then fit a 3A fuse in the plug, if the plug (fused) has been removed to hardwire it, then you need to fit a fuse.

It will also depend on the MCB, 24g wire would normally trip it, but if it does not, it will fuse.....

I can't agree with the idea of wanting to load such a low current circuit to the extent it will trip the MCB, it would be much safer (and prevent loss of power to other circuits) to fuse the appliance, so if there is a short, the fuse simply blows at well under the rated current of the whole circuit, it would be far safer, and much less of a fire risk if that is the concern
 
Why don't you simply put a 3A fuse in the place you want to put the wire?
it is not that i am insist not to put 3A fuse.the oven hood,simply,come like that(the circuit has been planned like that,without the use of fuse),and i think to myself if the engineer decide not to put fuse they probably know what they are doing(though,i think like you,they should) .and i don't want to complicate the circuit,there isn't a place to solder a fuse,and it is very difficult to close the box with all the wires,and addind more component to the circuit will be a problem with closing the box.
Why did the tracks burn? What caused the short?
the tracks burn because there was a large voltage surge(after electrical blackout) that blow up the MOV(varistor),the area around it burn out and the tracks burn.
It will also depend on the MCB
the MCB is 16A type C.
I can't agree with the idea of wanting to load such a low current circuit to the extent it will trip the MCB,
like i said the MCB(that located in the electrical board with all the other) protect on several appliance,and the oven ventilated hood is one of them,it came from the factory like that(it is not that the fuse is missing,it,just,planned without fuse)i didn't make something on purpose.
i agree with you on 100% that adding a fuse will make it safer but i don't want to make it complicate(from the reason i mention above),so if you say that the MCB would normally trip it before the 24g wire will damage,it is good enough for me.

by the way,for general education,what is the minimum area size of copper wire that can handle short circuit current untill the MCB will operate without be damaged?
 
From memory, I think the 24g wire will fue between 25A and 30A. 26g is probably the smallest you could go and still trip the MCB.

But these things don't always work as planned in practice, fuses take time to blow, MCBs take time to trip.

If you can't fit a 5mm fuse in the box, I would say it is all the more reason to fit a fuse, even if it was inline. If there are other components and relays on the board, and the wires are packed so close you can't fit a 5X20 fuse, it sounds as if the design could be unsafe anyway.

Maybe do it the farmers way, and replace the tracks with dome 10g galvanised fence wire :)

Fuses and MCBs don't match exactly in operation, ie a 10A fuse as a short could quite likely trip a 16A MCB.

What country are you in?
 
Sangoma,i am familiar with electric regulation about the minimum allowed size of the wires in the house.and it is min. 1.5mm^2 ,even for connection to low current consumers like bulbs.those regulations refer only untill the appliance but not inside it.because of that i thought that the 0.2mm^2(24g)wire will not handle the short circuit current.so my question:if this size(24g) of wire can handle the continuous current and the short circuit current in the appliance,what is the reason that it is not allowed to use this size around the house(like to low current consumers) but in the appliance it is allowed?:confused:
about your question,i am really sorry,but if it is ok. with you,i would like not to mention personal information.
 
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Sangoma,i am familiar with electric regulation about the minimum allowed size of the wires in the house.and it is min. 1.5mm^2 ,even for connection to low current consumers like bulbs.those regulations refer only untill the appliance but not inside it.because of that i thought that the 0.2mm^2(24g)wire will not handle the short circuit current.so my question:if this size(24g) of wire can handle the continuous current and the short circuit current in the appliance,why it is not allowed to use this size around the house and in the appliance it is allowed?:confused:

Because it can't carry that current continually - it's all down to how hot the wire would get.

Back to your original 'problem', there is no 'problem' - the low current tracks on the PCB have no relationship to the MCB feeding the device, soldering wires across the damaged board is a standard and perfectly fine technique.
 
Sangoma,i am familiar with electric regulation about the minimum allowed size of the wires in the house.and it is min. 1.5mm^2 ,even for connection to low current consumers like bulbs.those regulations refer only untill the appliance but not inside it.because of that i thought that the 0.2mm^2(24g)wire will not handle the short circuit current.so my question:if this size(24g) of wire can handle the continuous current and the short circuit current in the appliance,what is the reason that it is not allowed to use this size around the house(like to low current consumers) but in the appliance it is allowed?:confused:
about your question,i am really sorry,but if it is ok. with you,i would like not to mention personal information.



Your question has been answered.

No problem on the "personal" info, though unless you are the president, or the country only has ten residents, I don't understand how the country is personal. However, it does make a big difference to the answers you may get, as different countries have different practices and regulations, ie of the 3 I am familiar with, 2 have quite tight regulations and good practices, and the third, if it has any, doesn't have any that are followed! So my reason for asking was certainly not personal.
 
Hi Nigel goodwin.
.. the low current tracks on the PCB have no relationship to the MCB feeding the device, soldering wires across the damaged board is a standard and perfectly fine technique.
can you explain why the tracks on the PCB have no relationship to the MCB?
because i track the way of the current and it flow from the MCB phase to the PCB track to the power contacts of the relay(after the coil is trigger)and continue to the neutral track of the PCB and out of the appliance back to the electric board.so if it will be a short circuit on this line while i soldered 24g wire across the damage track,shouldn't i take into consideration if the 24g wire will handle the short circuit current untill the MCB will trip?after all this high current will flow through it.
.. soldering wires across the damaged board is a standard and perfectly fine technique.
and from your experiance,what is,usually,the recommended size of wire to solder across the damaged PCB?

Sangoma,i understand the reason for your question.
you are right,it is totaly relevant question,and i appreciate your help.
 
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Hi Nigel goodwin.

can you explain why the tracks on the PCB have no relationship to the MCB?
because i track the way of the current and it flow from the MCB phase to the PCB track to the power contacts of the relay(after the coil is trigger)and continue to the neutral track of the PCB and out of the appliance back to the electric board.so if it will be a short circuit on this line while i soldered 24g wire across the damage track,shouldn't i take into consideration if the 24g wire will handle the short circuit current untill the MCB will trip?after all this high current will flow through it.

and from your experiance,what is,usually,the recommended size of wire to solder across the damaged PCB?

You're over thinking this, what would it matter if the wire wouldn't take the S/C?, the PCB track didn't.

If the track carries high current I would use thicker wire (or multiple wires) to repair the damaged track, at no time would I ever give the slightest thought to the possibility of anything to do with an MCB, it's not relevant.
 
You're over thinking this, what would it matter if the wire wouldn't take the S/C?, the PCB track didn't.

If the track carries high current I would use thicker wire (or multiple wires) to repair the damaged track, at no time would I ever give the slightest thought to the possibility of anything to do with an MCB, it's not relevant.

Agreed.

Why do people make simple things complicated :confused:

Bugs me no end.

Regards,
tvtech
 
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thanks for your replies.
Nigel goodwin:what would it matter if the wire wouldn't take the S/C?, the PCB track didn't.
i thought maybe the isolated wire will behave different and maybe could be burn and make a fire.
i,really,don't care if the wire won't take the short circuit current(if will happen,at all) and will be cut into two pieces.i,always,can solder new wire.the,only,thing that i was concern is the safety issue.i,simply,don't want that the wire will burn and make fire in the box or worse.
but if you say that the only thing that can happen is that the isolated wire will be cut like the track did,without any risk of fire,i can be more peacful.
i am sorry that it seems like i make simple things complicated but when it's belong to safety i try to be sure that everything is fine,and i happy that this site is exist and there is someone to consult with.:)
 
thanks for your replies.
i thought maybe the isolated wire will behave different and maybe could be burn and make a fire.
i,really,don't care if the wire won't take the short circuit current(if will happen,at all) and will be cut into two pieces.i,always,can solder new wire.the,only,thing that i was concern is the safety issue.i,simply,don't want that the wire will burn and make fire in the box or worse.
but if you say that the only thing that can happen is that the isolated wire will be cut like the track did,without any risk of fire,i can be more peacful.
i am sorry that it seems like i make simple things complicated but when it's belong to safety i try to be sure that everything is fine,and i happy that this site is exist and there is someone to consult with.:)

Hi rgbbv

Sorry if I sounded harsh. It was not directed at you

It was directed at people that try to help and them make simple things complicated. Pet peeve of mine.

I think Nigel gave you the correct, simple advise. And because you are such a Polite and humble person, I would like you to stick around here and learn more. We need more like you :D

+1

Regards,
tvtech
 
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