Discuss b type or c type in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Farmelectrics

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been doing some domestic testing for a freind of mine who has his own firm now i allways use to use b type breakers in domestic dwellings but ive noticed quite alot of c type recently on theses tests your thoughts
 

darkwood

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As long as it meets Zs requirements then not an issue, type 'd' would be just as good as long as Zs is met.
 
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MarkieSparkie

The usual reason for choosing to use Type C MCB in preference to a Type B would be in situations where switching surges would be likely to operate a Type B MCB. Typical situations occur frequently in commercial and industrial installations where there is a wide spread use of discharge lighting, small motors and pumps. For example the highly inductive nature of fluorescent lighting banks are a particularly common source of switching surges requiring a less sensitive MCB. In domestic situations they are required occasionally for home workshop machine tool motors, welder supplies, and shower pumps etc.
Type B MCBs typically operate in the conventional time (0.1 to 5s) at a trip current between 3 and 5 times the nominal current rating (In) of the device. Whereas Type C MCBs are less sensitive and typically operate at a trip current between 5 to 10 In.

 
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Amp David

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Used Type C's on a rewire sometime ago. Loads of halogens installed, so instead of going for the standard of type B MCBs then it tripping everytime a lamp blows, thought i'd fit type C MCBs.

I designed the circuit so knew that my Zs would easily comply with that of a type C.
 

darkwood

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Used Type C's on a rewire sometime ago. Loads of halogens installed, so instead of going for the standard of type B MCBs then it tripping everytime a lamp blows, thought i'd fit type C MCBs.

I designed the circuit so knew that my Zs would easily comply with that of a type C.
If your lamps were selv then the inrush on the transformers would be given extra allowance with a type c, if they are standard 240v GLS or GU10's well any filament lamp then your thinking it reduces tripping when lamps blow is incorrect, as the filament collaspes it leaves an ionized path which has zero resistance and creates a short circuit long enough to trip the mcb irrespective of B,C or D types the time curve is instant on a short with high ampage.
 

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If your lamps were selv then the inrush on the transformers would be given extra allowance with a type c, if they are standard 240v GLS or GU10's well any filament lamp then your thinking it reduces tripping when lamps blow is incorrect, as the filament collaspes it leaves an ionized path which has zero resistance and creates a short circuit long enough to trip the mcb irrespective of B,C or D types the time curve is instant on a short with high ampage.
Oh right, how come the breakers held then. 3 have popped since installation.
 

darkwood

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They dont always blow that way, its random but if the breaker does trip it would have tripped a 'b,c or d'.... it might sound strange but just ask yourself why a mcb would trip just cos the filament broke as its not inductive when it breaks it open circuits and the gas is inert.
 

telectrix

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Oh right, how come the breakers held then. 3 have popped since installation.
you've just been lucky. or could be , however, that the C or D types might withstand the fault current as it's of extremely short duration. nobody can tell the magnitude of said fault current when a lamp blows. it could just be within the capability of the C or D.
 

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halogen lamps trip breaker/fuse if lamp fails... in my expierience..... 9 times out of ten, sure doo..

- - - Updated - - -

not for this sweaty betty
 

darkwood

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The more compact a lamp the higher the chance of a ionized path been created as the filament blows, hence a GLS was an occasional issue but the GU10 were a nuisance, but as i said before it dosn't always do it and nearly always happens when switching the lamp on, the bright flash you sometimes see is the ionized short which is many times brighter than the lamp itself but it only lasts a fraction of a second, if the lamp glows brighter than normal for quite a duration (seconds or minutes) then the tungsten coils have tangled lowering the filament resistance thus increasing the current but as it wasn't designed for this higher current it dosn't last long as it just overheats and pops but this wont a ionized path as it a slow melt.

The type rating of and mcb is the tolerance of inrush associated with inductive loads, and due to an ionized track been a short circuit and not an inductive inrush using the time/current curve charts wont be effective but because the ionized path collapses pretty much as soon as its created you may get the occasional benefit of fitting a type 'C' instead of a 'B' because the current rise can be limited because of the speed of the decay of the short circuit. Its variable as to current flow and time so really not reliable value to afford it in the design stage although if Zs is met it wouldn't do any harm to fit a 'C', they cost the same.
 

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Regardless of all the impressive technical explanations I've found changing type B's for C's where GU10's are fitted has dramatically reduced or even eliminated nuisance tripping when lamps fail.....Good enough for me.
 

telectrix

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Regardless of all the impressive technical explanations I've found changing type B's for C's where GU10's are fitted has dramatically reduced or even eliminated nuisance tripping when lamps fail.....Good enough for me.
quite possibly. just because we 're not sure exactly why something works, doesn't mean it don't work. it could just be that the short duration fault current is below the trip threshold of a type C.
 

darkwood

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Re' GU10 50watts, i stopped using them yrs ago, they are anergy hungry, high temp' running and added to this they have this nuisance tripping issue attached LED equiv's are now getting affordable and ive yet to have a customer refuse them because of the extra cost, its all about sales pitch and showing them the real benefits in the long term....

Although im having difficulty getting inrush details of LED lamps and recommended no's per type 'b' or 'c' as manufacturers haven't fully tested them to their products.
 

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i don't think inrush current, if any , of a 5 or 7 watt LED is going to trip anything. unless you're using milliamp breakers.
 

darkwood

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Its inductive loading, agree with one or two but when you start getting several or more switching on together you'll be supprised at the combined surge it creates, im waiting on mcb manufacturers spec but they already said there will be a limit dependant on type of mcb, im pretty sure others have already posted with this very problem when having a large no' off LED's switching together and we are not talking 'silly large'
 
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