300a supply

[flyingsparks]

Can someone please tell me what size 6181y I need for a 300a supply, 3 phase 3 wire on tray. I have no regs book to hand! Think 120mm is too small? Going to have to be 240mm I think?! Thanks.

 

[ricicle]

Trefoil ? Free air ? 150mm² is the next up from 120mm²

 

[flyingsparks]

Trefoil ? Free air ? 150mm² is the next up from 120mm²

Free air, oh yeah forgot 150mm! thanks.

 

[RF Lighting]

120mm² is ok for CCC assuming no correction factors apply. You'll still need to verify VD etc.

 

[flyingsparks]

Ok thanks rf.

 

[Lectrician]

Concur, 120mm for 6181y on tray.

I would prefer to opt for tri rated personally, assuming a short distance from main panel to CT chamber. Easier to install, neater, and you could then use 95mm.

Consider cable basket too, rather than tray.

 

[flyingsparks]

Concur, 120mm for 6181y on tray.

I would prefer to opt for tri rated personally, assuming a short distance from main panel to CT chamber. Easier to install, neater, and you could then use 95mm.

Consider cable basket too, rather than tray.

Tri rated is ok but then how do you get about having singly insulated cables on tray/basket?

 

[ban-all-sheds]

And could you run it that hot?

 

[Lectrician]

Concur, 120mm for 6181y on tray.

I would prefer to opt for tri rated personally, assuming a short distance from main panel to CT chamber. Easier to install, neater, and you could then use 95mm.

Consider cable basket too, rather than tray.

Tri rated is ok but then how do you get about having singly insulated cables on tray/basket?

You get tri-rated DI cables. Very common to see this these days on installs.

You can always up the size to prevent higher operating temps, and still retain the flexibility. This is why I said *could* use 95mm. I would hope that the cables on the tray/basket where in a controlled plant room though, otherwise I would be looking to use galv trunk instead.

 

[flyingsparks]

In a plant room yes. Ah right cOol I didn't realise you could get DI tri. That may be the way to go then, thanks.

 

[flyingsparks]

And could you run it that hot?

Why do you say that? Correct me if I'm wrong but according to table 4e1a 95mm tri rated on tray 3phase will carry 341A. So it's a fair bit over the 300A supply, right?

 

[plugwash]

Trirated cable is rated to a continuous operating temperature of 90C compared to the 75C limit for normal british cable. This means it can safely carry more current for a given size.

However this is only true if the devices you are connecting to are also rated to operate safely at a cable temperature of 90C. Furthermore I could see hot cables posing a hazard in some situations.

 

[Lectrician]

This is true, but as said, it wont be run to it's limit, and a larger size could be used (using the 6181y figures for example), meaning it will not be hotter. You can set most cable calc software to use 70deg temp rather than 90deg.

Eaton panel boards have be confirmed suitable for 90deg, I have that in writing. Most others I am sure will be fine too, but should be confirmed.

 

[flyingsparks]

Oh and at the bottom of the volt drop tables for the larger cables there is 3 numbers either r, x, or z. It's been a while since i used these, what are the three letters referring to?! thanks.

 

[ricicle]

They are the resistive and reactive components of voltage drop. (If you know the power factor of a load you can work it out from there).
Generally for one off calculations use the impedance (Z) figure.