HV 22kV Cable runs 1

[FreddyNurk]

Hello all,
As part of a project for a processing plant we've been asked to assess the legality / other considerations for running a HV cable at around 600mm above ground in a cable tray, part of which is running directly under the floor of the control room. Cable has not yet been run as the installers refused to do it without further direction as they believe its not safe.

We tend to agree on this part, however the site electrical person is adamant that its legal and all ok.

Does anyone have any ideas on legal basis or technical basis for not doing this? Site is in Australia if it helps, though even an IEEE reference on it would be appreciated.

Your responses are appreciated.

 

[davidbeach]

It depends. No where near enough information to begin to answer.

What type of cable?
Is it really HV? MV would be much more likely.
What else is in the cable tray?
What Codes apply?

 

[FreddyNurk]

DavidBeach,
Thanks for the prompt response, I'm aware that some of the items are a bit vague. Distribution is 22kV, so it would probably be termed MV. Nothing that I'm aware of is meant to be run in the same tray, but we've got no concrete reassurance for this. There is no HV distribution layout for the site, which doesn't help.

Site is a mine site, so AS3000, 3008, 3007 would apply, as well as any relevant HV / MV standards, which I've not had much luck in finding quickly.

Cable to be used is XLPE insulated, individually screened PVC sheathed and rated at 12.7k/22kv. Manufacturer suggests use of nylon sheathing when termites are a problem, for underground installations, and this is the crux of the problem. We, along with the senior management, are proposing to underground the cable, but the site guy wants it in the tray above ground. We're basically looking for justification to ditch the cable tray proposal.

 

[dpc]

It could be done with an armored cable such as Okonite C-L-X.

 

[FreddyNurk]

DPC, whats the requirement for the armoured cable? Is this for the mechanical protection, or is there a code requirement somewhere for this?

I appreciate the suggestion, and if I can ascertain the reasoning behind it then I'll be well on my way. Cable is already sitting on site, which is part of the argument for its use, but I don't believe that its armoured.

Thanks again.

 

[dpc]

I have the feeling you are not in the US, so Code references are probably not going to help much. The metal-cladding is for physical protection and essentially gives you an installation equivalent to cable in metal conduit, at least from an NEC perspective. It should solve any termite problems as well.

 

[RalphChristie]

FreddyNurk:

What is the reasoning to mention "it is not safe to run the cable above the ground in a cable tray"?

I work in a mining-environment in South Africa, and we run MV-cables frequently underground (burried), on the ground or in cable trays above the ground without any problems. However, the cable should meet the environmental conditions surrounding it.

Factors such as solar heating, the need for fire retardant sheath, additional mechanical protection, safeguards against chemical attack and corrosion should be considered.

Just a note on termite repellant sheath from Aberdare Power Cables:
Cables are sometimes specified with a termite repellant sheath. It is worth mentioning that no sheath will repel insects since sheath material has to be ingested by the termite to be fatal. Thus the statement "cable with termite repellant sheath" is somewhat erroneous

I will check if I can find anything prohibiting your query in some of the SABS/SANS-standards, (it is based on IEC and BS standards) and although it will not be applicable in Australia, you might find it useful. (if I find anything!)
Another source might be the cable manufacturer.

Regards
Ralph

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[FreddyNurk]

RalphChristie,
the reasoning behind the 'its not safe to run the cable in the cable tray' is primarily the fact that its about 600mm above the ground, right next to a walkway and also run directly under the control room. There are also associated issues on the site with HV distribution elsewhere, as no cable path has yet been designated.

If the HV was lifted above head height, or at least segregated from the control room and the rest of the LV that is running around it, then I don't believe that anyone would have an issue. Theres currently no proposal to cover the cable tray either, and we certainly don't want the personnel onsite trying to walk over it. The cable tray has already been installed.

Thats a very good note from the cable manufacturers as well. Apparently the local supply authority has recognised that termites are a serious issue here and usually specifies cable that has termite protection as a result.

 

[sslobodan]

You can run it but you must require special protection from discharge and accidental touch (cable can energize cable tray if it is malfunctioning, and it can kill everyone, than they need to make sure that in a case of fire the control room will not be affected. That leaves you only one solution To run cables trough metallic pipes. They need to be grounded and connected between them selves so they can be on same potential (accidental touch during a leak) also you need to set up differential protection for that cable.

 

[ePOWEReng]

This may be a useful comparison....in the US MV cables at distribution level voltages (10kV-25kV) are commonly ran down power poles (which may or may not be adjacent to or surrounded by public sidewalks). The MV cables are usually encased in PVC or metalic pipe.