Cable Installation - Bringing Cables Above Ground

[biglee82]

Gents

Folowing a 240mm2 3c 3.3kV cable failure i have been taksed with replacing the cabling of the circuit that experienced the fault. The cables (3 parallel 3c 240mm2 XLPE) run from an incoming 3.5MVA transformer to our 3.3kV Motor Control Centre for a run of approx 50m, with around 30 direct buried and the last 20 in buried single way ducts. Other cables run along the same path but budget will not be approved for the replacement of these.
I have been tasked with looking at installing the new cables on ladder racking, which will allow only the damaged cicuit to be replaced with the existing healthy cables left in situ, but have been advised not to bring the cables above ground by colleagues.
They haven't given any tangible arguments that I can go back to the site owners with so I was hoping someone on here may be able to provide some assistance and guidance on the risks, as seen by the industry, that are posed by above ground MV cabling.
Co-incidentally I believe ladder racking will be fine on this site and due to the available route will cause no access issues.
Any thoughts?

 

[ScottyUK]

Ladder rack is used in many locations. Are there any hazards from either vehicles or from fire which you need to consider? De-rating due to solar radiation if you are a warm location - not something we in the UK need to be worried about, ha-ha - and the long-term effects of UV on the cable sheathing need to be considered.

Leave enough room on the ladder to add future cables and size the supportwork to carry an LV ladder too even if you don't install it right now.


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If we learn from our mistakes I'm getting a great education!

 

[biglee82]

Thanks for the reply.

Thankfully no risks from vehicles or fire and should be no other works along the route. The main comment against ladder racking has been with regards to the effects of a possible future incident as this is the second time that a cable has gone on this circuit.

The previous was a pinhole fault to earth but this time a fist sized chunk of the cable was blown off and the duct, which surfaces in the switch room, acted like a shotgun cannon for the over pressure. We believe the latest incident is down to damage caused during installation as it was pulled through the duct.
Does anyone know of any incidents of above ground installations where the measures included in the post above were not considered, de rating, UV covers etc?

 

[trosepe]

You may want to use something like the product attached. I have been using it for over 15 years on systems upto 21KV.