0.75mm2 flex for fixed equipment - reality check.

[Selfmade]

Hi Folks

I've never thought twice about using 0.75mm2 flex for connecting fixed equipment (e.g. extractor fan in window) to a fused connection unit with 3A fuse where this is sufficient for the load of the equipment. But table 52.3 of BS7671 states minimum csa for copper cable in lighting circuits as 1.0mm2 and power circuits as 1.5mm2. The 18th edition even adds 'Note 4', which states "For lighting circuits and associated small items of current-using equipment, such as a bathroom extractor fan".

So am I wrong to use 0.75mm2? Or does the FCU take the place of a plug and mean I can use this? This has come up as I have bought an RF remote switch for a customer's outside lighting and this has 16mm glands that will not accept 1.5mm2 flex. I don't have any 1.0mm2 to try, but pretty confident that wouldn't fit either. The remote switch is obviously intended for permanent installation. I'm interested in the answer generally, as well as for this specific piece of equipment - essentially, does the presence of a fused connection unit negate table 52.3?

 

[Ian1981]

Hi Folks

I've never thought twice about using 0.75mm2 flex for connecting fixed equipment (e.g. extractor fan in window) to a fused connection unit with 3A fuse where this is sufficient for the load of the equipment. But table 52.3 of BS7671 states minimum csa for copper cable in lighting circuits as 1.0mm2 and power circuits as 1.5mm2. The 18th edition even adds 'Note 4', which states "For lighting circuits and associated small items of current-using equipment, such as a bathroom extractor fan".

So am I wrong to use 0.75mm2? Or does the FCU take the place of a plug and mean I can use this? This has come up as I have bought an RF remote switch for a customer's outside lighting and this has 16mm glands that will not accept 1.5mm2 flex. I don't have any 1.0mm2 to try, but pretty confident that wouldn't fit either. The remote switch is obviously intended for permanent installation. I'm interested in the answer generally, as well as for this specific piece of equipment - essentially, does the presence of a fused connection unit negate table 52.3?

Table 52.3 also makes allowances for non sheathed and sheathed flexible cables as specified in the product standard,for any other applications and for extra low voltage circuits all with a minimum CSA of 0.75mm

 

[Deleted member 9648]

The regulation refers to the circuit cable protected by the OCPD in the DB, not a flex from a local point of connection serving a load. Think of a pendant flex, often 0.5mm or 0,75mm

 

[Selfmade]

Table 52.3 also makes allowances for non sheathed and sheathed flexible cables as specified in the product standard,for any other applications and for extra low voltage circuits all with a minimum CSA of 0.75mm

Thanks Ian. How did I miss that? Momentary brain malfunction!

 

[Selfmade]

The regulation refers to the circuit cable protected by the OCPD in the DB, not a flex from a local point of connection serving a load. Think of a pendant flex, often 0.5mm or 0,75mm

Thanks Wirepuller, makes sense. And the pendant doesn't even have its own OCPD like an FCU. But don't you mean downstream? Or is my brain still malfunctioning?

 

[Deleted member 9648]

Thanks Wirepuller, makes sense. And the pendant doesn't even have its own OCPD like an FCU. But don't you mean downstream? Or is my brain still malfunctioning?

Indeed it should have been downstream (Beers to blame)......edited to something else!