Metal cable tray regulations

Hi Tomas,

My opinion would be that you have identified separate containment for LV and ELV cables. This straight away meets compliance in relation to cable sharing same containment and not factoring insulation of the lowest to highest voltage range.

I would probably suggest 50-300mm seperation. 

Sorry I haven't been able to give you further references just saw this question on my lunch break. 

I'm not sure I'd think of tray as "containment" as such - more just cable support. Unlike say conduit or trunking cables on tray should be sheathed, so voltage-wise they should be safe to touch (or be touched by sheathed cables of other circuits). There are other considerations though - e.g. preventing interference. I can't think of any specific separation distances for above ground situations in BS 7671 (but there may be some in related standards, depending on quite what the ELV circuits are - e.g. data/comms cables and the type of cables). In any case the required separation would typically be between cables themselves, rather than the trays they're on. 528.1 (iv) does seem to permit Band I and Band II cables to share the same tray provided they're physically separated by a partition (but again other standards may ask for more).

   - Andy.

Thank you, John, for your valuable information. As you mentioned, providing separate containment (metal perforated cable trays) for LV and ELV should meet compliance, as they are considered two separate “services.” The main issue is that I cannot find any regulation or requirement specifying the minimum separation distance between LV and ELV cable trays. BS 7671 refers to grouping of cables and separation within trunking, but it is difficult to find guidance specifically related to cable trays.

Your suggestion is appreciated, and a separation of 50 mm or more seems reasonable for installation; however, I still need to support this with a specific regulation or standard for my project.

Thank you, AJJewsbury, for your valuable input as well. You make a valid point that cable trays could be regarded more as a means of cable support rather than full containment. However, I would still tend to classify them as a form of containment unless regulations explicitly state otherwise.
My understanding is that when cables are installed in separate trays, this provides a degree of mechanical segregation that also helps to reduce electromagnetic interference. This follows the same principle as using a divider within a single tray to separate LV and ELV circuits.
I have also reviewed BS 6701 and could not find any specific references to cable trays in this context.

Hi Tomas,

Check out this discussion on relation to cable distances. It may provide further guidance there is a section from a fellow member gkenyon.

engx.theiet.org/.../minimum-separation-distance-between-lv-power-230v-400v-and-unscreened-utp

As others have said, cable trays and ladder would be more cable support than containment.

In IEC60079 series of standards for explosive atmosphere electrical installations, so part 14 for the design, and construction and installation and initial verification of those installations. Again it mentions separation distances Min per cable function. Not containment or cable tray separation. It speaks about separation of basically cables whose circuit conductors are ignition capable and those that are not i.e. Intrinsically safe circuits. So as an absolute Min separation distance is 50mm between non-is and is circuits. Unless they are on a tray with an earthed metal partition or cables are armoured and screened.

So separation of trays and you had cables right on the edge of each? I would be saying Min 50mm between trays, that way in the future and an installer put a cable on edge of a tray, then should be covered.

Cheers GTB