Cable Size Calcs..... too much !!!

[plugwash]

or where it squeezes through a 16mm hole i drilled for it to get through a RSG (for all of 5-10 mm)??

Another point is, Any steel girder which has cables running through it, Or very close to it, Should be bonded to the main earth terminal using a minimum 10mm2 earth cable,

surely its the cuircuit earth that it should be connected to (just like metal conduit)

 

[Albert]

Should it? why?

Am not in the habit of drilling through RSJ as they are difficult. But the principle of drilling through the centre should be exactly the same as with a timber beam. The centre of the beam is under neither compresion or tension forces, so nothing terrible will happen if you remove it. it just serves to hold the top and bottom apart. The tope of the beam is being force together by the weight above, the bottom is being pulled apart. In the middle all should be calm. Have you seen those exciting cut away beams they put on bridges or fancy victorian railway stations?

As a principle you are right, concerning the bridges etc. but the beams csa is not drilled but the whole structure is built to consider the '0' tension/stress points. Another thing is that this is correct in a perfect world, if you consider forces upwards and/or downwards only, it might be ok, but you will have side forces and twisting forces that decreasing the beams csa will weaken it. In general I think that this beams are overedesigned, but only a person who is competent in this matter (structural engineer?) can tell you what is safe to do.