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.

 

[UKMeterman]

Would suggest a ferrule at the very least, did the conductor get clamped correctly?

 

[uksparks]

Yes I'll ferrule it, I always do with fine stranded.

its just a job I'm doing tomorrow, not badly thought out but more a case of that's the easiest option!

 

[uksparks]

its hot today isn't it.

 

[davesparks]

Why not use 1mm flex? Then you will be complying with the minimum size of 1mm for cables in lighting circuits.

 

[Richard Burns]

The minimum size conductors that can be used for lighting circuits is 1.0mm² according to table 52.3.

 

[Dave OCD]

1mm would be the better option really, if using flex it should still be easy to interconnect.

 

[Andy78]

As much as I'd like to disagree with this, table 52.3 says flex is OK at 0.75mm. News to me though, and I certainly wouldn't do it.
Where In = It I'd always rather step it up a size.

 

[uksparks]

let me look at that...

 

[HappyHippyDad]

Table 52.3 is very clear Tom, 1mm for lighting circuits.

I cant understand your reason for using 0.75mm, why not 1mm as Dave said?

 

[uksparks]

I must admit I often use 0.75 for flood lights etc, but always through a FCU to 3A with appropriate label on FCU.

Ill just do it in 1.00mm three core and earth grey instead then, its all inside the garage anyway, just thinking about it I can, I was thinking it was going on the outer wall.

 

[uksparks]

Table 52.3 is very clear Tom, 1mm for lighting circuits.

I cant understand your reason for using 0.75mm, why not 1mm as Dave said?

Its just that I have a lot of 0.75mm 4 core flex that I use for "specific applications" such as a couple of outside lights strung together off a FCU from a ring maybe... Im not trying to bend the rules, but its quite adequately protected and only has a very small load on it usually.

 

[uksparks]

The minimum size conductors that can be used for lighting circuits is 1.0mm² according to table 52.3.

Yes you are quite right, the only time I would ever use 0.75 is on a single light if I have no 1mm, I have had this conversation with the NICEIC and they have always said so long as its protected adequately its fine, I appreciate they do not make the rules up, well not all of them, only the ones you cant find in the book!

 

[uksparks]

I think ill buy myself some 1mm 4 core flex for next time.

 

[HappyHippyDad]

Its just that I have a lot of 0.75mm 4 core flex that I use for "specific applications" such as a couple of outside lights strung together off a FCU from a ring maybe... Im not trying to bend the rules, but its quite adequately protected and only has a very small load on it usually.

I thought that was more likely to be the reason :smile5:

 

[davesparks]

Its just that I have a lot of 0.75mm 4 core flex that I use for "specific applications" such as a couple of outside lights strung together off a FCU from a ring maybe... Im not trying to bend the rules, but its quite adequately protected and only has a very small load on it usually.

Is it of the heavy duty type or were you planning to install mechanical protection for it or otherwise prevent mechanical damage etc?

 

[HappyHippyDad]

Yes you are quite right, the only time I would ever use 0.75 is on a single light if I have no 1mm, I have had this conversation with the NICEIC and they have always said so long as its protected adequately its fine, I appreciate they do not make the rules up, well not all of them, only the ones you cant find in the book!

I suppose you could argue that it may not be protected adequately. The 0.75 can take 6A, the 6A MCB will take 30 mins to trip with 9A running through it and wont trip at all with 8A going through it, so it's not great to design a circuit this way. In reality it's probably going to be fine, at least for now, and then someone may start adding to your circuit at a later date. I cant see anything wrong with using it for a single appliance, which will have a fixed load, but not straight from the MCB.

 

[uksparks]

Yes it's good chunky stuff, it's not think cheapo stuff.

this is why I queried it really, I'll just use grey TC&E, I can get 1mm 4 core flex quite cheap, think I'll get myself a drum.

 

[uksparks]

I suppose you could argue that it may not be protected adequately. The 0.75 can take 6A, the 6A MCB will take 30 mins to trip with 9A running through it and wont trip at all with 8A going through it, so it's not great to design a circuit this way. In reality it's probably going to be fine, at least for now, and then someone may start adding to your circuit at a later date. I cant see anything wrong with using it for a single appliance, which will have a fixed load, but not straight from the MCB.

Yes, totally agree, it's a bit sailing close to the wind!

 

[davesparks]

I suppose you could argue that it may not be protected adequately. The 0.75 can take 6A, the 6A MCB will take 30 mins to trip with 9A running through it and wont trip at all with 8A going through it, so it's not great to design a circuit this way. In reality it's probably going to be fine, at least for now, and then someone may start adding to your circuit at a later date. I cant see anything wrong with using it for a single appliance, which will have a fixed load, but not straight from the MCB.

Wtf? The problem is not with the flex's current rating, it's tabulated at 6A and after factors being applied that may well be adequate. The tabulated current ratings have been arrived at after taking in to account of short duration overloads etc, they aren't the maximum steady current the cable could handle safely or anywhere near the current required to harm the cable.

The problem is that the minimum size cable for a lighting circuit is 1mm, and there are specific requirements about the type of flex or other protection to be used if flex is to be used as an installed cable.