0.75mm Flex into 6A MCB

[uksparks]

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.

 

[uksparks]

It's under 521.9

 

[uksparks]

It points you to BSEN 50565-1, for grades of cable, then to 422.3.201 and 521.9.1

 

[Andy78]

So with reference to my post #8, Am I wrong in my interpretation of table 52.3 ?

I understand that 521.9 applies which is what Davesparks is referring to, and I would never personally consider flex for fixed wiring, or less than 1mm live conductors for any fixed circuit, but the table does seem to support the OP's ideas.

 

[uksparks]

Well it's not "heavy duty" as its not good for 450v i wouldn't think...

 

[uksparks]

It's a confusing grey area I say, I suppose, the bottom line to this is if the cable is suitably protected or not, I will reevaluate my usage of 0.75mm cable and use 1mm from now on.

as said, this is only to feed an outside light, I am not a silly billy wiring an entire light circuit up with it.

 

[hotfingers]

I'll just go and get the book...

521.9.1

 

[uksparks]

It's a strange one actually, Reg 422.3.201 says suitably protected against mechanical damage, but it's strange how it doesn't say a word about suitable protection if it's twin and earth which is just a different shape...

why should flex need any more protection than any other cable irrespective of the CSA of the conductors.

 

[Andy78]

It's a strange one actually, Reg 422.3.201 says suitably protected against mechanical damage, but it's strange how it doesn't say a word about suitable protection if it's twin and earth which is just a different shape...

And different conductor construction, and insulation construction, and sheath construction.......

 

[davesparks]

It's a strange one actually, Reg 422.3.201 says suitably protected against mechanical damage, but it's strange how it doesn't say a word about suitable protection if it's twin and earth which is just a different shape...

It's a fairly recent change in the regs which allowed flex to be installed at all, it was previously limited to 2 metres max length for appliance tails.
Every cable has to be suitably selected with regards to protection suitable for the environment it is in, regardless of what type it is.

 

[uksparks]

Andy, you have a point.

Dave, well I shod think myself lucky that I live in such a modern world with updated regs!

 

[davesparks]

Have you considered the max conductor operating temperature of the flex? A lot of it is rated to only 60degrees when fixed wiring and accessories are all rated for 70degrees. Will this make any difference? I don't know, but you need to consider it

 

[uksparks]

This is quite an interesting thread which I don't recall being touched upon before!

 

[davesparks]

This is quite an interesting thread which I don't recall being touched upon before!

It certainly beats a thread about stiff cutters!

 

[Andy78]

Any takers about my post #8 and the regs stating a minimum csa of 0.75mm for the use of flex ?

 

[davesparks]

Here's a bit of relevant history
14th edition

13th edition

 

[davesparks]

Any takers about my post #8 and the regs stating a minimum csa of 0.75mm for the use of flex ?

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

 

[uksparks]

I would say you are quite possibly right

 

[NDG Elecs]

Is there any reason this can't be used: https://www.tlc-direct.co.uk/Images/Products/size_3/MK5903.JPG

Though I have never seen one, never mind fitted one.

 

[uksparks]

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!

 

[davesparks]

If I remember correctly the smallest mcb I've fitted was a 0.5A but may have been 1A, it was just doing a contactor coil

 

[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!

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