6mm TW+ for a 26 metre run ,32amp RCBO .Max load 4.5KW

[LukeD]

Method B enclosed . sounds ok ?

 

[Pretty Mouth]

Chapter 7 of the OSG has a list of standard circuits, most of the time I can select one from there without having to get the calculator out.

 

[LukeD]

Chapter 7 of the OSG has a list of standard circuits, most of the time I can select one from there without having to get the calculator out.

I get 2.5mm .But thinking of throwing in 6mm

 

[Pretty Mouth]

I get 2.5mm .But thinking of throwing in 6mm

Why?

 

[LukeD]

Why?

I have it left over !! . So its kinda extra money in my pocket And use more 2.5mm . Also if they change printer (Photographic) at alter date to a higher spec .This could be a 7kw load . Banging in a 6mm now might save time

 

[timhoward]

At end of day it comes down to cable loading/capacity, volt drop and ‘will it turn off quickly enough’.
Looks like a tick for first two. Need Ze to tick last one.

I’d add that depending on Ze I get anything between 4mm to 10mm out of the cable sizing calculator, so if it’s at the limit of a TNS Ze it can really change things.

 

[Pretty Mouth]

I have it left over !! . So its kinda extra money in my pocket And use more 2.5mm . Also if they change printer (Photographic) at alter date to a higher spec .This could be a 7kw load . Banging in a 6mm now might save time

Fair do's

 

[Pretty Mouth]

At end of day it comes down to cable loading/capacity, volt drop and ‘will it turn off quickly enough’.
Looks like a tick for first two. Need Ze to tick last one.

I’d add that depending on Ze I get anything between 4mm to 10mm out of the cable sizing calculator, so if it’s at the limit of a TNS Ze it can really change things.

The RCBO will ensure disconnection times are met, assuming an otherwise healthy circuit.

 

[timhoward]

The RCBO will ensure disconnection times are met, assuming an otherwise healthy circuit.

Sure but wouldn’t you agree it’s better if PFC is also high enough, two cracks at the whip then!
My point was really that a circuit design should take into account Ze, and I’ve doubts that Zs with 2.5 would be less than 1.1 ohms.

 

[LukeD]

Sure but wouldn’t you agree it’s better if PFC is also high enough, two cracks at the whip then!
My point was really that a circuit design should take into account Ze, and I’ve doubts that Zs with 2.5 would be less than 1.1 ohms.

good point

 

[timhoward]

good point

It might not be actually! I can’t immediately see why the pro certs calculator is rejecting 2.5. When I’m home later I’m going to need to satisfy my curiosity as at first glance Zs and volt drop are ok….

 

[Pretty Mouth]

Sure but wouldn’t you agree it’s better if PFC is also high enough, two cracks at the whip then!
My point was really that a circuit design should take into account Ze, and I’ve doubts that Zs with 2.5 would be less than 1.1 ohms.

It'd be nice, but I personally wouldn't go out of my way using thicker cable to achieve that. Odds are that the overcurrent part will disconnect instantly anyway.

We would presumably be dropping the breaker to 20A if going 2.5mm, so it should max Zs for that.

 

[timhoward]

It might not be actually! I can’t immediately see why the pro certs calculator is rejecting 2.5. When I’m home later I’m going to need to satisfy my curiosity as at first glance Zs and volt drop are ok….

It was a classic case of garbage in, garbage out. As above, with a 25 or 20 amp OCPD it jumps straight to 2.5mm.
I just couldn't see it for looking earlier.