parallel conductors and neutral switching of through contactors in lighting circuits

[Cyril Molony]

Re: parallel conductors and neutral switching of through contactors in lighting circu

I was just wondering if Cyril works for NICEIC?? lol!!

No not NICEIC I am a retired JIB electrician.

 

[Engineer54]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Dear engineer you need to read the reg I quoted again apart from some exemption when you reduce conductor sizes eg from 6 mm to 5 mm (2 x 2.5 mm) you should fit protective device, in the original question a 20A DP switch was used, so would 6 mm comply, if you fitted some form of protective device. I have no problem with non standard circuits, that the general point I was expressing

My question to you, was will a 6mm/2.5mm lollipop ring conform sitting on a 32A MCB/RCBO protective device??....

Providing all other critera conforms, then the 32A protective device will be good to to protect both the 6mm radial section and the ring 2.5mm section, so will therefore comply... The lollipop ring has been used and generally accepted as a non-standard circuit for as far back as i care remember. There is no need to fit a protective device at the point of cable size reduction.

 

[HandySparks]

Re: parallel conductors and neutral switching of through contactors in lighting circu

My question to you, was will a 6mm/2.5mm lollipop ring conform sitting on a 32A MCB/RCBO protective device??....

Providing all other critera conforms, then the 32A protective device will be good to to protect both the 6mm radial section and the ring 2.5mm section, so will therefore comply... The lollipop ring has been used and generally accepted as a non-standard circuit for as far back as i care remember. There is no need to fit a protective device at the point of cable size reduction.

Totally agree with you here E54 (there's a first!).

BS 7671 2008 Amdt 1, para 433.2.1 requires a device for protection against overload to be installed at the point where a reduction occurs in the value of current-carrying capacity of the conductors of the installation.

I was going to say that this reg appears to be nonsensical and should be ignored. Then I spotted 433.3.1 (i):

"A device for protection against overload need not be provided for a conductor situated on the load side of a point where a reduction occurs in the value of current-carrying capacity, where the conductor is effectively protected against overload by a protective device installed on the supply side of that point."

Following on from the lollipop example, if I chose to use 2.5mm² for the first leg of a 6A lighting circuit to reduce voltage drop, and then 1mm² for the final legs to ease termination to accessories, the 6A breaker at the origin would be entirely adequate to protect the whole run.

If 433.3.1 didn't exist, you'd have to fit an overload protective device wherever a cable ran through an insulated wall!

 

[Engineer54]

Re: parallel conductors and neutral switching of through contactors in lighting circu

There's always a first for everything HandySparks!! lol!!

With regards to the subject in hand, your example is yet another good example where a reduction in cable size does not automatically call for a protective device to be installed.

Not interested that much in 433.3.1 i don't take BS7671 as the Be All and End All of electrical installations, i treat it as an informed guide only, but then most of my alternatives will tend to be over and above anything that BS7671 and it's GN's will call for!!