Grouping factor

[Grunt]

Hi,

Would you apply a grouping factor if running a new cable with these? Cables run for about 5m under flooring.

Thanks in advance for any help.

Untitled

• Grunt
• 29 Dec 2009
• 3

Untitled

• Grunt
• 29 Dec 2009
• 2

 

[ban-all-sheds]

Probably not. This is a normal domestic dwelling, yes?

How many circuits do those cables represent, and how
lightly/simultaneously loaded are they?

I tell you what I would definitely apply though - some mechanical protection over them.

 

[Cremeegg]

What do the cables serve? Are they all on together or likely to be for any length of time? What size/loading the new cable?

In the real world - probably not - seems plenty of spare space where it is notched across the joist, only loosely together between the joists, plenty of air circulation - not as if its contained in PVC trunking.

 

[ericmark]

In theory yes but in practice it would depend on what they all feed.
If in a house the total amount of power is 100A and where there is a bunch of cables leaving a consumer unit they will not all be fully loaded and are likely to conduct as much heat away as they heat and where I have found a cable which has been grossly overloaded it is normally melted where it is a single cable and where in the group it is OK.

However your picture does not tell us what those cables carry and it is an impossible question to answer with information given. Also since some are white one must ask at what temperature the cables are rated? The idea of mixing 70 deg and 90 deg rated cables seems wrong and I think on personal basis I would look for another route as I would not want to get blamed for mixing cables of different temperatures together. That's assuming the white cables are rated 90 degs?

 

[ban-all-sheds]

I'd assume they were just white.

 

[holmslaw]

..

 

[bloxy]

I tell you what I would definitely apply though - some mechanical protection over them.

Yep.

Some of these http://www.tlc-direct.co.uk/Main_In...Index/Necessities~Cable_Protection/index.html would do nicely.

 

[GaryMo]

Assuming a domestic situation, you don't have a problem, the grouping factors are based on the cables being simultaneously fully loaded.

And of equal size.

 

[Grunt]

Hi,

Thanks for your replies.

Domestic dwelling. It's just three 32A rings, two 6A lighting and one 40A cooker circuit.

Cables have been there (apart from the white ones which were an addition to the upstairs lighting) since the property was built circa '73. I'm doing some calcs to determine if the existing 6mm will suffice for new cooking appliances. It's a long time since I did cable calcs and I guessed that for practical purposes the grouping would not apply but wanted some other opinions. Cables sit a bit tighter in other cutouts along the route but they're never tight.

As for mechanical protection I suppose in theory they should be in conduit so close to the floor but they'll have to go without. Routes are marked on the chipboard flooring and everything is RCD protected.

Thanks again.

 

[ban-all-sheds]

As for mechanical protection I suppose in theory they should be in conduit so close to the floor but they'll have to go without. Routes are marked on the chipboard flooring and everything is RCD protected.

522.6.5.

 

[Grunt]

Hi bas,

Yes, but one isn't expected to do that retrospectively? Even if a single new cable is run one can't be expected to rip up every flooboard along the route to comply? If cable route is clearly marked that should be ok. Being practical and reasonable.

 

[GaryMo]

If you're installing a new cable to run along the same route then the above regulation applies.

Afterall, you'll be certifying the addition or alteration to BS7671:2008.

 

[securespark]

I agree. Plus, if you're running a new cable, you need to pull up the boards anyhow, so you can fit mech. prot. at the same time.