LV Singles from transformer

[MESS]

Hi Guys, Looking for a bit of assurance really. I have been asked to install 2 x 400mm single conductor, parrallel feeds from suppliers transformer with 1250 amp protection, probably installed on ladder rack in trefoil formation. The cable is likely to be AWA non magnetic armour, what is recommended distances between the two sets and the respective neutral conductor to avoid eddy currents and hots spots, I assume they are ok installed on steel unistrut & ladder rack ?
Grateful for any comments.

 

[benji]

how long is the run ? if your using trefoil cleats make sure you fit them so that you can open them fully (if you put them to close together it can restrict the opening of the cleats )doubt if there is a specific distance but the cleats should give enough clearence between cables

 

[johnboy6083]

Lenny had a similar setup on a job recently if I remember. He was enquiring about similar things. Maybe he will of found out?

 

[Engineer54]

If the cable run is of any distance, ...Always run in bunched/trefoil formation for each parallel cable run. Simple rule of thumb, use the width of one bunched cable group between the cable runs...

Don't forget to use non-conductive cable gland plates such as ''Paxoline'' or the like. S/steel and Aluminium gland plates tend to allow circulating currents, at high cable current carrying levels....

 

[Guest123]

Having scoured various publications and all of the WWW a little while ago for info on this subject to back up a theory of mine, this is all the info I found which I knocked together into a word document.

 

[MESS]

how long is the run ? if your using trefoil cleats make sure you fit them so that you can open them fully (if you put them to close together it can restrict the opening of the cleats )doubt if there is a specific distance but the cleats should give enough clearence between cables

Run is around 10 - 12 mtrs. Thanks

 

[MESS]

Thanks, we do possibly have the option of installing cables direct in ground, I have seen this method before where cables are in phase pairs and kept 200mm - 300mm apart. Not sure which is best for current carrying capacity / size of cable.

 

[Engineer54]

Thanks, we do possibly have the option of installing cables direct in ground, I have seen this method before where cables are in phase pairs and kept 200mm - 300mm apart. Not sure which is best for current carrying capacity / size of cable.

Why on earth would you want to run in phased pairs direct buried for just 15 metres?? Any idea how wide the trench would need to be??

Getting back to reality, ...you can make use of 4 core cleats, to carry the neutral as well as the trefoil conductors, which is what we tend to use for the majority of our parallel cable runs...

 

[MESS]

I have now managed to have a closer look on site. The transformer is located in a separate cabin, the 2 x 400mm parallel supply cables are to be run direct in the ground surrounded by sand for around 10 mtrs, the total run is around 15 mtrs. What would be the best way to install them in trench, using purpose made four core cleats to keep them in formation or just tie wrap them in this formation, or just lay them in with cable space between ?
I did intend to use an alluminium gland plate at one end in order to earth the AWA.
Grateful for any comments.