An electrician hoping to do our next house was showing us a sample of his work a while ago. It was a real work of art at the panel, with bundles of wire coming down to the panel and then splitting off at regular intervals to go into the panel.

I was just reading my simplified (Canadian) code book and read about derating cables that are bundled together. If conductors are in contact with each other for more than 24", then they have to be derated. The derating depends on the number of conductors. For example, 7-24 conductors derate the current carrying capatiy to 70% of original.

I understand the major circuits should be installed on their own, but if we install more than 6 conducts of plugs/ lights circuits (say two 14/2 and one 14/3) in a single run could the inspector say that the cable sizes are not big enough? I've never heard of that... but the rules are written that way.

Really depends on the amp rating of the insulation and conductors.

If NM cable is used, usually the conductors are rated 190 Deg C, and the amp rating in that column can be used. For example, #14 is rated 25 amps at 190 Deg C.

With a 15 amp breaker on #14 wire, the derating will not be an issue,as 70 % of 25 amps is 17.5 amps.

Whenever possible, try not to bundle cables.

Homes are not usually an issue, as it is unlikely that all conducotrs will be loaded 100%.

Consult with your inspector to see what he will require.

Thanks - those de-rating calculations help a lot in understanding this.