Max rating for 2.5mm T&E

[MES]

Can anyone tell which is correct. Is the max rating for 2.5mm T&E 7200 watts at 30amps or 4800 watts at 20 amps.
I have be working from a DIY manual approx 10 years old which states 30 amps 7.2 kw, yet it seems that this is now 20 amps 4.8 kw.
I take it that this has been a regulation change, but can anyone tell me why?
I take it that the change is not retospective as my ring mains are 2.5mm with 32 amp MCBs. Is this now a problem???

 

[securespark]

No, your ring is fine, providing it is complete across all three conductors.

2.5 cable is rated around 27A (6.21kW @ 230V).

Not sure where you get your figures from - the rating of 2.5 is neither of these!

If you have a 2.5 ring, you can use a 30/32A CPD.

If you have a 2.5 radial, the maximum CPD is 20A.

Maybe these are the figures you refer to.

Edit: Sorry. As Dingbat said, I forgot to quote an installation method.

If there are no other factors involved & the installation method is 1, the above figures are correct.

 

[dingbat]

The rating of a cable is the steady current which will cause the cable to heat up to its nominal operating temperature, which is 70 deg C for twin & earth. If you insulate the cable, or group it closely with others, or enclose it in conduit a lower current will cause this amount of heating, as heat generated cannot be so easily dissipated.

For that reason no set current-carrying capacity can be quoted without knowing the installation method. Generally, cable that is plastered in and is not enclosed in insulation is considered to have the same rating as if it were simply clipped to a surface. For most socket circuits in traditionally constructed houses this will be the case and Securespark's figures reflect this.

 

[MES]

Thanks fellas.

Thought that might be the case. My wirering has been retro fit to a Geoergian cottage with a 1970's extention on it, about 16 years ago, so the cableing has either been wooden 'boxed' in, clipped or had the routings chased out of the solid walls. With the occasional drop behind plaster board. Certainly nothing fancy.

As for the figures

240 volts x 30amps (old ring rating, I know modern MCB are 32 amps) = 7200 watts

240 volts x 20amps = 4800 watts, taken from the advisory lables from all the new 2.5mm T&E cable I have seen.

Thanks