Grouping Factors

[uksparks]

Hi,

I have just finished off a kitchen and swapped the CU out at the same time...

Part of the run of the cable goes under the kitchen floor in a duct...

Its 2m long the duct.

When applying rating factors, is there a min and max length in comparison to the overall length of the run?

I have 5 lots of twin and earth running in a duct, strictly speaking I should apply a factor of 0.60 to them but if it was only 2m long does it really need it applying?

 

[alanl]

Yes, you do have to de-rate, and also make sure the ducting/trunking is large enough for the cables. If the tables do not show the cables you are using, a 45% 'empty' should suffice - that means the trunking / conduit should not be more than 55% full by volume - or it could be only 45% full, cant remember properly now without going out to get the book out.

It's all in easily readable form in the on-site guide Appendix E.

 

[Plonker 3]

So you know where to look for grouping factors, why not a bit more and see if it says anything about the length of ducting?

 

[D Skelton]

Hi,

I have just finished off a kitchen and swapped the CU out at the same time...

Part of the run of the cable goes under the kitchen floor in a duct...

Its 2m long the duct.

When applying rating factors, is there a min and max length in comparison to the overall length of the run?

I have 5 lots of twin and earth running in a duct, strictly speaking I should apply a factor of 0.60 to them but if it was only 2m long does it really need it applying?

Yes, you do have to de-rate, and also make sure the ducting/trunking is large enough for the cables. If the tables do not show the cables you are using, a 45% 'empty' should suffice - that means the trunking / conduit should not be more than 55% full by volume - or it could be only 45% full, cant remember properly now without going out to get the book out.

It's all in easily readable form in the on-site guide Appendix E.

This isn't a dig, but both of you need to familiarise yourself with the whole of appendix 4. Remember also, out of all the appendices, only 1 is normative.

The chances of someone having to apply a grouping factor in your average domestic installation is slim to none.

 

[guest119]

Yes, you do have to de-rate, and also make sure the ducting/trunking is large enough for the cables. If the tables do not show the cables you are using, a 45% 'empty' should suffice - that means the trunking / conduit should not be more than 55% full by volume - or it could be only 45% full, cant remember properly now without going out to get the book out.

It's all in easily readable form in the on-site guide Appendix E.

And applies to single core cables, not double skinned as t+e.

 

[davesparks]

Hi,

I have just finished off a kitchen and swapped the CU out at the same time...

Part of the run of the cable goes under the kitchen floor in a duct...

Its 2m long the duct.

When applying rating factors, is there a min and max length in comparison to the overall length of the run?

I have 5 lots of twin and earth running in a duct, strictly speaking I should apply a factor of 0.60 to them but if it was only 2m long does it really need it applying?

0.60? what are these 5 twins which are going to be running at full load 24hours a day in a domestic installation??