To Andy

You said "one easy way of achieving that is to use the 70-degree tables"

It's very helpful for me to understand what you mean.

Thank you.

Almost pinching Mike's example, think of a 4mm² conductor in a simple multicore cable, installation method B.

According to table 4D2A it's got a rating of 30A single phase - or in other words pushing 30A through two of the cores under standard conditions will raise the conductor temperature to 70 degrees.

Table 4E4A however says 40A - or in other words pushing 40A through it under standard conditions will raise the conductor temperature to 90 degrees.

So one approach to keeping the conductor temperature at 70 degrees or below (in standard conditions) is just to keep the design current below 30A. Nice and simple and easy to demonstrate compliance.

That's not the only approach though. Thermosetting plastics (e.g.XLPE) have somewhat better thermal conductivity than typical thermosetting (PVC) so if you did shove 30A through a XLPE insulated cable the conductor temperature would actually be a little lower than 70 degrees - so you could actually shove a little extra current through and still be within the 70-degree limit. I'd have to dig out the formula, but from memory if table the 4E4A figure and de-rate to 70 degrees it actually comes out at 32A rather than 30A. It's only a small difference, but can be quite handy where you want to demonstrate that 4mm² BS 8436 cable is actually adequate for a 32A radial! (larger sized of that particular cable type being almost unavailable in the UK).

   - Andy.

To Andy

You said "one easy way of achieving that is to use the 70-degree tables"

It's very helpful for me to understand what you mean.

Thank you.

Almost pinching Mike's example, think of a 4mm² conductor in a simple multicore cable, installation method B.

According to table 4D2A it's got a rating of 30A single phase - or in other words pushing 30A through two of the cores under standard conditions will raise the conductor temperature to 70 degrees.

Table 4E4A however says 40A - or in other words pushing 40A through it under standard conditions will raise the conductor temperature to 90 degrees.

So one approach to keeping the conductor temperature at 70 degrees or below (in standard conditions) is just to keep the design current below 30A. Nice and simple and easy to demonstrate compliance.

That's not the only approach though. Thermosetting plastics (e.g.XLPE) have somewhat better thermal conductivity than typical thermosetting (PVC) so if you did shove 30A through a XLPE insulated cable the conductor temperature would actually be a little lower than 70 degrees - so you could actually shove a little extra current through and still be within the 70-degree limit. I'd have to dig out the formula, but from memory if table the 4E4A figure and de-rate to 70 degrees it actually comes out at 32A rather than 30A. It's only a small difference, but can be quite handy where you want to demonstrate that 4mm² BS 8436 cable is actually adequate for a 32A radial! (larger sized of that particular cable type being almost unavailable in the UK).

   - Andy.

Greteful to your additional explanation.

Last part of your explanation gave me impression that you have deep knowlege on those tables.

Thank you again.