0.75mm Flex into 6A MCB

[ImpededLoop]

2A and 4A circuit breakers should be obtainable from most manufacturers. They are often used in control applications.

 

[uksparks]

Hager do a 2A type C

Hager NCN102 MCB Type C Single Pole 2A 10kA

 

[uksparks]

Hager actually do a large range in Type C which I suppose is quite acceptable to use on a normal circuit.

MCB 10kA & 15kA Type C MCBs

 

[Richard Burns]

For table 52.3 I would interpret this as meaning that if there is a connection to a mobile piece of equipment such that the connection needs to be flexible then 0.75mm² sheathed or non sheathed cable may be used.

 

[Andy78]

I didn't know one existed, it's s shame you can't get 3A breakers across the different brands, o don't know if I'd have much need for one to be honest, but then there's always that once!

You get all different sized breakers across most decent brands. The lower sized (<6A) breakers are generally produced for panel and control applications as I understand it, they just won't be classed as 60898, or rather just 60898.

 

[NDG Elecs]

You get all different sized breakers across most decent brands. The lower sized (<6A) breakers are generally produced for panel and control applications as I understand it, they just won't be classed as 60898, or rather just 60898.

I did wander if that was the case Andy. But just had a look at the MK tech spec. See the approvals bit just below the table:

 

[Andy78]

I think it's open to interpretation.
I read it as the minimum size for a lighting circuit is 1.0mm and a power circuit is 1.5mm then flexes which are not part of a such general circuits (ie appliance tails etc) are restricted to 0.75mm minimum

For table 52.3 I would interpret this as meaning that if there is a connection to a mobile piece of equipment such that the connection needs to be flexible then 0.75mm² sheathed or non sheathed cable may be used.

Yep I must concur with you guys that the description in table 52.3 "for any other application" listed for flex actually should mean "for any other application than those listed above"
I have always worked to the 1mm for lighting and 1.5mm for power rule myself, just this thread prompted me to look up the table and question it. I also have never considered flex a suitable selection for fixed wiring other than for fused down circuit extensions.
Still an ambiguous table though in it's wording.

 

[davesparks]

Hager actually do a large range in Type C which I suppose is quite acceptable to use on a normal circuit.

MCB 10kA & 15kA Type C MCBs

They should be available from most DB manufacturers, they won't be available for ranges exclusively intended for CUs though.

Can you use them for general/standard circuits? I see no reason why not, but undoubtedly someone will be able to come up with a reason why not.

7.5A was a reasonably common size once upon a time. I've seen a lot of 3871 MCBs in this size.

 

[Richard Burns]

Still an ambiguous table though in it's wording.

BS7671 to a T and we think that the letters refer to British Standard, I don't think so!

 

[NDG Elecs]

Slightly off topic, sorry UK! I never realised there are altitudinal limits on breakers!

View attachment 29429

 

[davesparks]

Slightly off topic, sorry UK! I never realised there are altitudinal limits on breakers!

View attachment 29429

Obvious when you think about it!

 

[NDG Elecs]

Obvious when you think about it!

Nope, not to me! All I can recall about the internals of mcbs is a bi-metal strip and possibly a solenoid.. Not from an engineering background so please enlighten me because it's bugging me now!!

 

[Andy78]

They should be available from most DB manufacturers, they won't be available for ranges exclusively intended for CUs though.

Can you use them for general/standard circuits? I see no reason why not, but undoubtedly someone will be able to come up with a reason why not.

7.5A was a reasonably common size once upon a time. I've seen a lot of 3871 MCBs in this size.

I love a 25A MCB myself. Not very common but so useful.

 

[davesparks]

Nope, not to me! All I can recall about the internals of mcbs is a bi-metal strip and possibly a solenoid.. Not from an engineering background so please enlighten me because it's bugging me now!!

You'll be surprised how many things are rated to work within specified altitudes. I've drink too much to discuss it at the moment
But basically it is due to the change in atmospheric pressure causing it to operate outside of limits

 

[NDG Elecs]

You'll be surprised how many things are rated to work within specified altitudes. I've drink too much to discuss it at the moment
But basically it is due to the change in atmospheric pressure causing it to operate outside of limits

Cheers Dave, I realise many things do have various limitations. Just never read that particular one before! Just been googling it and found nothing specific, but my money is on the coil/solenoid/hammer trip part being the reason. I would imagine a bimetallic strip would perform above 2000M.

 

[Marvo]

The internal heater that operates the bi-metalic strip produces a certain amount of heat at a certain current. The bi-metalic strip is designed to distort according to the heat being absorbed from the internal heater.

At sea level the air is quite dense and it has a certain cooling effect the removes a certain quantity of heat from this internal mechanism but at altitude the thinner air doesn't cool the mechanism as efficiently so more of the heat being produced is retained internally causing inaccuracies to occur.

The higher altitude causes the tripping curve of the mechanism to drift so your C curve MCB starts behaving more like a B curve. Many MCB's would have an altitude derating factor available from the manufacturers on request.

 

[Andy78]

The internal heater that operates the bi-metalic strip produces a certain amount of heat at a certain current. The bi-metalic strip is designed to distort according to the heat being absorbed from the internal heater.

At sea level the air is quite dense and it has a certain cooling effect the removes a certain quantity of heat from this internal mechanism but at altitude the thinner air doesn't cool the mechanism as efficiently so more of the heat being produced is retained internally causing inaccuracies to occur.

The higher altitude causes the tripping curve of the mechanism to drift so your C curve MCB starts behaving more like a B curve. Many MCB's would have an altitude derating factor available from the manufacturers on request.

The same effect that causes water to reach boiling point at lower temperatures at higher altitudes ?

 

[NDG Elecs]

Cheers Marv, good job I aint a betting man eh!!

I always thought that overcurrent flowing through the bimetallic strip caused the bend and break. Did not realise there was another mechanism at play ie the heater. Is that the arc chutes?

Am I correct in thinking the bimetallic protects better for gradually overloaded ccts and the solenoid for more instantaneous overcurrent.

 

[Marvo]

The water boiling point thing is more about the reduced atmospheric pressure than the actual cooling effect reduction by the air being thinner but it's all kinda linked in a roundabout sort of way.

 

[Andy78]

The water boiling point thing is more about the reduced atmospheric pressure than the actual cooling effect reduction by the air being thinner but it's all kinda linked in a roundabout sort of way.

Well my physics thinking may be dulled by a bottle or two of shiraz. I was just hoping it would be that simple. Just say yes

 

[NDG Elecs]

Part of my degree course covered atmospheric science...but I was mainly in the pub all the time so I remember diddly squat of it!!

 

[NDG Elecs]

Well my physics thinking may be dulled by a bottle or two of shiraz. I was just hoping it would be that simple. Just say yes

In a nutshell bubbles have less opposition!!!

pressure - Explanation for different boiling points of water on different altitudes - Physics Stack Exchange

 

[Marvo]

Cheers Marv, good job I aint a betting man eh!!

I always thought that overcurrent flowing through the bimetallic strip caused the bend and break. Did not realise there was another mechanism at play ie the heater. Is that the arc chutes?

Am I correct in thinking the bimetallic protects better for gradually overloaded ccts and the solenoid for more instantaneous overcurrent.

Yep, there's two separate tripping mechanisms in an MCB, I was discussing the thermal mechanism which caters for partial overload scenarios, the magnetic mechanism caters for overloads of 5 times the rated current or more and this operates in a completely different way.

The weakness in the thermal system is because the mechanism isn't operated directly by current, there's a couple of steps in between where the discrepancies creep in. The load current firstly causes a small heater to produce heat, this heat is then transferred to a bi-metalic strip, the strip deflects and this deflection is what causes the mechanism to trip. Each of these steps in the chain provides scope for inaccuracies to creep in and altitude is an external factor that takes the inaccuracies beyond the point where they can be ignored. Ambient temperature would be another external factor that could require compensation being applied by using a derating factor as well, in extreme cold conditions a C curve MCB starts behaving more like a D curve. This isn't just an MCB issue, same applies for thermal overloads in DOL starters for example.

Arc shutes just contain the flash that occurs when contacts are separated whilst they're under load.

 

[Andy78]

In a nutshell bubbles have less opposition!!!

pressure - Explanation for different boiling points of water on different altitudes - Physics Stack Exchange

Ah now that makes more sense. I was thinking there was a general relationship between temperature within matter and atmospheric pressure.
But then, I haven't ever studied physics past school level and I have had much wines

 

[NDG Elecs]

Yep, there's two separate tripping mechanisms in an MCB, I was discussing the thermal mechanism which caters for partial overload scenarios, the magnetic mechanism caters for overloads of 5 times the rated current or more and this operates in a completely different way.

The weakness in the thermal system is because the mechanism isn't operated directly by current, there's a couple of steps in between where the discrepancies creep in. The load current firstly causes a small heater to produce heat, this heat is then transferred to a bi-metalic strip, the strip deflects and this deflection is what causes the mechanism to trip. Each of these steps in the chain provides scope for inaccuracies to creep in and altitude is an external factor that takes the inaccuracies beyond the point where they can be ignored. Ambient temperature would be another external factor that could require compensation being applied by using a derating factor as well, in extreme cold conditions a C curve MCB starts behaving more like a D curve. This isn't just an MCB issue, same applies for thermal overloads in DOL starters for example.

Arc shutes just contain the flash that occurs when contacts are separated whilst they're under load.

Now if there is no plagiarism in the above I applaud you!! When I looked at an mcbs internals I saw the arc chutes, and like the name implies I thought they were for what you said. Then you threw a heater into the equation and I went off at a tangent!

Where is the heater, presumably adjacent to the bimetal strip... Cheers fella.

 

[uksparks]

They should be available from most DB manufacturers, they won't be available for ranges exclusively intended for CUs though.

Can you use them for general/standard circuits? I see no reason why not, but undoubtedly someone will be able to come up with a reason why not.

7.5A was a reasonably common size once upon a time. I've seen a lot of 3871 MCBs in this size.

I love a 25A MCB myself. Not very common but so useful.

yes it gives just that bit more in a 2.5mm radial instead of a 20A, I think I should get myself a few!

 

[Leesparkykent]

yes it gives just that bit more in a 2.5mm radial instead of a 20A, I think I should get myself a few!

Just about if it's clipped direct.

 

[Pete999]

Hi,

As per title, how would you feel about connecting a few garage lights onto some 0.75mm flex straight into the 6A MCB, ignore switching, just that its 0.75mm.

I have to say I normally go via a FCU but in this occasion I don't feel I need to as its in the garage with a 6A MCB I can come off.

referring to table 4F3A on page 378 it states 0.75 can take 6A.

id say I'm good to go, I k ow I'm probably stating the obvious but it's not something I usually do, hooking such a small co doctor up to an MCB.

reason for it being small is due to the fact I'm using 3 core and earth flex so I can use the switched output on the lights so they Interconnect on PIR.

Old school I know, but flex for fixed wiring? tut tut

 

[cprfenom]

I cant see why using 1.0 or 1.5mm flex to wire downlights in would be an issue. Most of the clamps seem to be designed for round cable also. You also seem to see lots of companies doing full rewires in flex.

 

[Pete999]

I cant see why using 1.0 or 1.5mm flex to wire downlights in would be an issue. Most of the clamps seem to be designed for round cable also. You also seem to see lots of companies doing full rewires in flex.

D oes the customer have to provide feed for their horses, rewires in flex, what is this trade coming to? I for one am out of this conversation.

 

[cprfenom]

I cant really see the advantage of doing that. I cant see a valid trade off between time and cost. Also terminating flex is harder than solid core.

Sorry for taking the thread off topic.

 

[Sintra]

Old school I know, but flex for fixed wiring? tut tut

D oes the customer have to provide feed for their horses, rewires in flex, what is this trade coming to? I for one am out of this conversation.

Pete, you might find this hard to believe but as you know I have been involved in rewires of the prestigious overseas buildings you used to frequent. These as you know are designed in the UK and installed to UK spec. Within the last 5 years the trend has changed and we have been forced to used flex for all of the fixed wiring in some of these properties. I think it's down to the individual designer as it's not a blanket thing across all properties.

 

[Leesparkykent]

I've never seen a full rewire in flex lol.

 

[Darkwood]

Old school I know, but flex for fixed wiring? tut tut

It certainly is an old school thinking, flex holds similar electrical properties as T&E but the issue has always been termination, when screw terminals were really the norm with no alternative many simply terminated without ferrule and this has over the years been a big factor in building fires, now the call to ensure correct termination is greater and people are more aware due to sites like this and it been discussed more about correct crimping and/or suitable connections for fine wire. There is no reason flex cannot be used, as we all know it has its advantages and disadvantages against standard methods of wiring but we should no longer condone it as long as the cable calcs are fine.

 

[Pete999]

Pete, you might find this hard to believe but as you know I have been involved in rewires of the prestigious overseas buildings you used to frequent. These as you know are designed in the UK and installed to UK spec. Within the last 5 years the trend has changed and we have been forced to used flex for all of the fixed wiring in some of these properties. I think it's down to the individual designer as it's not a blanket thing across all properties.

Thanks mate, still riles me does that, best I'm out of it now. rewires that is.

 

[uksparks]

And here is the finished article... I like these lights, they look nice and work well. I did it in three core and earth 1mm in the end, fitted an IP66 switch to override on the outside too just the other side of the drain pipe.

 

[Dave OCD]

Looking good, I use loads of those too, nice how you connect to the base [very easy] then the main fitting just plugs in and secures with 2 small screws.

 

[Dave OCD]

Thinking about it assuming all 3 come on when any of the PIR's are activated- couldn't the 'middle' one have been a slave unit without P.I.R ? That would have saved a few quid.:smiley2:

 

[uksparks]

It's the ASD light as you probably guessed, I really enjoy fitting them as they are so easy, plus you have the switched live terminal to hook them together.

fit the difference in price I just fitted three with PIRs... It's only a few quid more.

 

[Dave OCD]

Yeah they're great, and totally made from polycarbonate so no falling to bits within a couple of years like the horrible cheap painted metal lanterns.

 

[uksparks]

I couldn't agree more!

 

[HappyHippyDad]

And here is the finished article... I like these lights, they look nice and work well. I did it in three core and earth 1mm in the end, fitted an IP66 switch to override on the outside too just the other side of the drain pipe.
View attachment 29436

I need to see pictures Tom... WE NEED PROOF.... I reckon you just used up some of your 0.75mm!

 

[Dave OCD]

I need to see pictures Tom... WE NEED PROOF.... I reckon you just used up some of your 0.75mm!

Yeah I want to see how neat his clipping is :smiley2:
And in all honesty what harm would there be in 0.75 with a maximum load there of 300w, that should get a few going .:smilielol5:

 

[Marvo]

Now if there is no plagiarism in the above.....

Nope, not plagiarized.

Where is the heater, presumably adjacent to the bimetal strip... Cheers fella.

The old MCB's that were around when I was an apprentice used to have a separate heating coil that ran in proximity to the bi-metal bar, nowadays they use a bi-metal strip that self heats according to the current flow through it.