I was directed to the archive for this forum and found one recent post worth commenting on. I will cut an paste some points then comment. I hope this is OK.
Pat Naughtin said: "I noticed the closeness of 2.52 inches and 64 mm and then I wondered whether they were trying to fit a metric cable into an old- pre-metric space or vice-versa." "On another issue from the same article, I wondered about where in Italy you could buy a 2 inch cable. This would be a most unusual size in Italy and would have to be a special order as I don't think any Italian cable maker would routinely make products to inch sizes." John F-L said: " I believe (any electrical experts here that could confirm this?) that cables are all based on a rational progression of their (metric) cross sectional areas. Even the cable to my electric kettle is shown in terms of its mm2 value. I would imagine that the 2 inch value is a (rough) approximation of its actual metric diameter, for the benefit of the US public." It doesn't appear they were trying to fit a metric cable into a pre-metric (do you mean existing?) space. More then likely they designed the space to be in inches and possibly used inch parts obtained locally. Someone didn't check to see what the total diameter of the cable would be compared to the channel it was being put into. Yes, 2.52 inches would be unheard of when using inches unless it was intended based on a conversion from 64 mm. If the diameter was truly 64 mm, and is converted to inches the value would be 2.519 685.... and simply rounded to 2.52. The rounding is what makes the two values differ when converted back and forth. I can see where the contractor used 2.5 inches (63.5 mm) as that is a common size in US operations. 2.52 inches is unheard of except as an exact conversion of 64 mm. But as others have noted 0.5 mm of difference should not have been a problem. But of course we would all have to be there to know for sure if it was and how it could be. It could also be a coincidence that Mr. Bill Bryant's comments about the 2.52 inches worked out to be a whole number of millimeters. The contractor, Berger ABAM is an American company and would have done the entire design in American measurements. If they did obtain a cable from Italy it would be made in accordance with the IEC 60228 series, unless it was made as a special. 50 mm² is a common size in the IEC series. The reporter may have incorrectly assumed that since 50 mm is about 2 inches, that 50 square millimeters is about 2 square inches. However, the diameter of the 50 mm² cable would only be about 8 mm which should easily fit into a 64 mm channel. The article doesn't go into the details as to whether the total diameter of the cable was to be 2 inches or just the conductor diameter. There is no exact two inch cable in the AWG system. AWG wires use either gauge numbers for smaller sizes or cmil/kcmil for large diameters. A 50 mm cable would have a cross sectional area of under 2000 mm². This would be about a 4000 kcmil conductor if that was what was originally sized using AWG cable. That would be a very large cable. I can't imagine how much current it was intended to carry. It could be that the kcmil conductor plus insulation was slightly too big or tight for the channel and the closest metric size down fit. Simon
