What type of cables are they? e.g. are they armoured?

   - Andy.

This is armoured cables.

Is it definitely not earthed via the steelwork or some other natural connection? Perhaps even between the rebar and the strut embedded in the concrete?

Indeed, is there rebar in the concrete floor and is that adequately earthed?

Completely floating is unlikely to meet the needs of ENA TS 41-24 or BS EN 50522, unless there's a specific reason for it. I can't think what the advantage would be to having the tray floating and looks like bonding would be very easy to achieve, but I would be inclined to contact the designer, or at least their specification in case there's something we're not aware of.

Of course conformity to a standard and risk assessment aren't the same thing. I'd not want to do the latter on the basis of this much information.

are the armours of the cables earthed, either at one end or both ?

How are the genset frames earthed?

Regardless,  it seems a bit odd if not at least tied to the genset earthing arrangement. As you say how would you know if it went floating off.- you do not need a conventional fault to create a nasty sting in the sort of situation,  just stray coupling.

It would be sensible to enquire why - In your shoes I'd llike and expect to see the frames of the genset, and both cable trays ,and any other "electric plumbing" that might be touched at the same time to be incapable of being at different voltages.

Mike.

This is armoured cables.

HV might be a bit different from LV, but in broad principles, as long as the armour is adequately Earthed, then the tray won't be an exposed-conductive-part, so won't need Earthing on that score. If they tray supports are fixed into the ground in such a way that they could introduce an potential (Earth potential) that could be different from the Generator's Earthing, then it probably should be bonded (as distinct from Earthed) as an extraneous-conductive-part.

Just out of curiosity, what's that green(?)/yellow looking cable going up from the top left corner of the tray doing?

   -  Andy.

Dear All Thans for your valuable comments. 

Sorry for late reply,

There are two cable trays, one is Horizontal laid across the Generator Frame (Marked in Red), this cable tray has earthed with Generator frame at two yellow marked locations. Other second Cable tray marked in black is not grounded anywhere to earthed and MV cables are laid over it. 

At generator end the cable Armour is not grounded to body (Pl refer the image attached) i think only at MV breaker end the cables are entering in cubicle through cable glands, where the Armour is earthed with gland.

The yellow cable entering in generator body is the frame earthed which is connected to the earthing grid via nearest earth point. 

So, Generator Fram/Body is connected with earth, Horizontal cable tray is connected with Generator frame which is earthed. 

Only Black marked cable tray (Vertical across the Generator frame) which carrying MV cables is not connected to earth. So, this what I'm worrying about. I think this cable tray also connect in the same earthing network where other cable tray and generator Earth is connected. 

MV cable details is Armoured MV Power Cables cat. C,Type : 2XSYR(AL)Y Uo/U 8,7/15 kV.

Kindly share your valuable comments. 

The cable tray should be earthed in one position only if it is steel/iron .  The problem is that the high amperage LV currents will induce a voltage into the iron tray which must be balanced out by the other 2 phases assuming you have 3 phases which should ideally be bundled.. 

Thanks for your valuable reply,

Just want to add here that our system is MV 11KV, so amperage is not that much. But anyhow the good way is to earth the cable tray. 

Hi Andy, 

Are you saying that for an LV installation the traywork would be an exposed or extraneous conductive part if the armouring of a SWA wasn't earthed?

Are you saying that for an LV installation the traywork would be an exposed or extraneous conductive part if the armouring of a SWA wasn't earthed?

I'm suggesting that for something to be an exposed-conductive-part the tray would have to be liable to become and remain live if there was a fault in the basic insulation - interposing an earthed armour (with ADS operational) is one way to to prevent that - but I'm not saying that's the only way - another, for example, would be the use of insulated and sheathed cables (if the installation conditions were suitable). Using an armoured cable with the armour unearthed opens several cans of worms - neither the bedding nor the outer sheath are normally required to have the properties of an insulating sheath of an unarmoured cable, so you comply with neither the requirements for ADS nor the requirements for double or reinforced insulation (using a sheathed insulated cable) - so the cable itself would usually have to be considered a shock hazard even before you get to thinking about contact with the traywork. I suppose you could try and construct some kind of enclosure using tray, but that's really not what tray should be used for (use trunking instead).

Extraneous-conductive-parts are a different (if related) kettle of fish - If the tray could introduce a potential into the installation (or sometimes the location) - e.g. by some independent connection to the general mass of the earth - then it would be extraneous, and the cable mostly wouldn't affect that. If you had an armoured cable with the armour in contact with the tray (perhaps like the old lead covered cables) and the cable was earthed from a different installation, then they tray might in that  case be an extraneous-conductive-part as far as your installation was concerned (but then so would the armour). So there might be the odd corner case where a cable without a plastic sheath from another installation, carried on a tray, would make the tray an extraneous-conductive-part, but not that common I would have thought.

  - Andy.