Neutral Conductor Size - Main Switch to Neutral Bar

[vwes59]

Don't come across this very often - but I've had a CU delivered for a caravan job (not static btw), and it's been supplied with a neutral conductor from the main switch to the neutral bar! Definitely an oversight, but I've got plenty of singles cable in stock, so rather than send it back, I thought I could reuse what I have. However I've scoured the regs book, and I can't get a definitive answer as to what size this particular conductor should be. Obviously in a domestic setting it's either 16 or 25.

It's a 25A main switch with RCD and the highest the incoming current will be is 16A, so I can't see it's going to need a huge neutral conductor. I'm guessing a 4mm will do.

If there is something in the regs about this, could someone point it out to me. Cheers.

 

[James]

Make it at least as big as the incoming live cable and all will be good.

 

[brianmoooore]

Incoming cable on a touring 'van will probably be only 2.5mm2, while RCD and neutral bar terminals will be designed for 25mm2 or more.
The cable selected for the link will have to be a bit bigger than 2.5mm2 to get a reliable connection, or have ferrules or lugs crimped onto the ends.

 

[vwes59]

Thanks, I thought that's what it would likely be. Just as a note, I found the neutral cable for it, tucked separately in the packing! But its so big it doesn't fit the neutral bar terminals anyway lol. Looks like they've just bunged in a 16mm and thought "That'll do"

 

[davesparks]

Incoming cable on a touring 'van will probably be only 2.5mm2, while RCD and neutral bar terminals will be designed for 25mm2 or more.
The cable selected for the link will have to be a bit bigger than 2.5mm2 to get a reliable connection, or have ferrules or lugs crimped onto the ends.

Terminals in a CU will be designed for 1mm upwards otherwise they wouldn't be much use in a CU.

 

[brianmoooore]

Terminals in a CU will be designed for 1mm upwards otherwise they wouldn't be much use in a CU.

Those go into the MCB or RCBO terminals, which are generally somewhat smaller than those on the incomer. The terminals on the neutral bar that will accommodate cables down to 1mm2, but the one intended to terminate the link from the incomer is usually much larger.

 

[davesparks]

Those go into the MCB or RCBO terminals, which are generally somewhat smaller than those on the incomer. The terminals on the neutral bar that will accommodate cables down to 1mm2, but the one intended to terminate the link from the incomer is usually much larger.

I can't say I've ever noticed that on the boards I fit, all the terminals are normally the same size.

 

[Dranok]

I can't say I've ever noticed that on the boards I fit, all the terminals are normally the same size.

Very often, even on a domestic CCU, but especially in commercial DBs, one or more neutral and earth terminal in the bars will be larger than the remaining ones. Small domestic boards often have 3x 16mm² holes and the rest 10mm, one for the tri-rated tail and the others to install those pesky ovens and showers...