7,300 Watts supplied on a 2.5mm2 T&E.

gkenyon: 
 

whjohnson: 
 

Go on Dave, tell us what current a 2.5mm cable can carry at -273K. I'm intrigued.

Since 2.5mm at 70' will carry something like 21A in a best case clipped direct scenario, and given that -273K is absolute zero in degrees C terms, I would imagine that the current carrying capacity would be much much higher. However, we would need length of run and duration of load to get a bit nearer.

very very roughly, with ambient temp 30 degrees, with a 32 A load after a few minutes use (up to 5 mins but may be less):

• Ref method C (clipped direct) get to about 80 deg C
• Ref method 102# gets to about 90 deg C
• Ref method 103# gets to well over 100 degrees C

 

I think in this particular case, the installation may have been lucky based on duration of use and ambient temperature, and I'd guess Ref method C ???

If for any reason the cable is accidentally further thermally insulated, or the ambient temp gets above 25 degrees, things could change quite quickly.

Indeed.  The exact run is unknown, but the chalet is like an old  wooden shed. If the cable runs in the roof void with the sun beating down on the roof outside, and the cable is covered by thermal insulation I suspect a danger of fire.

Z.

gkenyon: 
 

whjohnson: 
 

Go on Dave, tell us what current a 2.5mm cable can carry at -273K. I'm intrigued.

Since 2.5mm at 70' will carry something like 21A in a best case clipped direct scenario, and given that -273K is absolute zero in degrees C terms, I would imagine that the current carrying capacity would be much much higher. However, we would need length of run and duration of load to get a bit nearer.

very very roughly, with ambient temp 30 degrees, with a 32 A load after a few minutes use (up to 5 mins but may be less):

• Ref method C (clipped direct) get to about 80 deg C
• Ref method 102# gets to about 90 deg C
• Ref method 103# gets to well over 100 degrees C

 

I think in this particular case, the installation may have been lucky based on duration of use and ambient temperature, and I'd guess Ref method C ???

If for any reason the cable is accidentally further thermally insulated, or the ambient temp gets above 25 degrees, things could change quite quickly.

Indeed.  The exact run is unknown, but the chalet is like an old  wooden shed. If the cable runs in the roof void with the sun beating down on the roof outside, and the cable is covered by thermal insulation I suspect a danger of fire.

Z.