ELECTRICIANS Q&A - BS7671 TRUNKING FACTORS IET ON SITE GUIDE

Trunking factors are often a source of confusion when calculating how many cables you can install within electrical trunking.

Joe Robins explores how the trunking factors within the IET on-site guide are calculated.

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📹 Presented by

Joe Robinson - Technical Editor eFIXX

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#efixx #electriciansQ&A #bs7671

[SparksPlumbers]

This is so timely as I recently watched a video by Residual Current where he had to install new larger tails and the adjacent trunking was rammed and I mean rammed! ... So whilst a nice idea in universe far, far away, in real world scenarios the 45% factor get slung out the window for the 'cram it all in and then some' option. 🤔

[orielzob]

How would you code an EICR where the trunking is stuffed with cable and the lid just about fits?

[guffermeister]

Several of the YouTube sparks dont take in to account trunking factoring and de-rating as appropriate. When I've raised it, it gets shot down. Much the same with grouping single cores together in a consumer unit with cable ties - in theory that should be de-rated as well....

[AndrewCook]

How are the cable factors worked out, ie. 8.0 for 1.5 and 11.9 for 2.5

[ericcsonluy]

Do you have a link of the PDF file of the Cable trunking factors table shown on your video? I would like to request a copy for reference in containment sizing. Thank you.

[MatSmithLondon]

I installed 100mm steel trunking in my home plant room (walk in cupboard under stairs) and didn’t even know of this requirement! Argh! Thanks.

[Ressy]

Hrmmm, I thought cross sectional area is derived from " pi x 50 x 50 / 4 " which would be 1962.5.
Or is that calculation only applicable for round material like conduit?

[busman]

Joe, how do you work out 45% of the inner area?

[gbelectricks]

Great video Joe, could we reverse the setup of calculating maximum amounts of cables that can be installed?
As for example, twin and earth cable factors are not in the osg, so could we measure the diameter of a te, then use this new information to calculate how many t&e’s would fit inside a given trunking?

This could also be applied to double insulated tails in trunking, as double insulated tails are not in osg either 🤷‍♂️

[ryanjones]

And how many of us have seen trunking so rammed, the lid won’t fit ?