Singles and Data in the same Dado trunking compartment

The risk of mains giving someone on a phone or using data network a shock is pretty much nil, unless the trunking also includes choc block or wagos or other un boxed mains joints., or perhaps there is a mouse problem.

However there is a very real risk of interference with data/ comms wiring that runs very close to mains cable, and that may give effects that are hard to trace. Back in the last century phones that had background hum and crackles whenever some specific piece of machinery was in operation stood some chance of being understood and traced. These effects are replaced by data links that magically crash or stop loading but only at certain times and such things can be very hard to debug. especially when interferer and victim may be hundreds of metres apart.

How short is the so called  'short' distance - a few 10s of cm will be negligible, the full length of a wall probably not. In general, I share your unease - its probably OK, but its not good practice, and we are told not to,  for a reason.

Also, if they are breaking that guidance, what else is happening where you cannot see ? Fire stopping, grouping factors and many other details usually don't matter but should not be omitted willy nilly. 

Mike.

Stuart Urban said:

What are peoples thoughts on mixing 230V 6491B singles and standard structured wiring data cables in the same compartment of Dado trunking.

Not to be done for indoor ICT (telephone, data, PoE and other digital controls) cabling, according to BS 6701.

Being in the same compartment is notionally fine according to Parts 4 and 5 of BS 7671, BUT it's unlikely to conform to BS 6701, Clause 5.4.4.2, which requires at least 50 mm physical separation (but in some circumstances can be > 150 mm), even if there is a metal separator:

5.4.4.2 Protection of telecommunications cabling and attached equipment

NOTE: The following requirements represent the “Local regulations for safety” referred to in BS EN 50174-2:2009+A2:2014, 6.1.

Telecommunications cabling shall not be installed in any compartment of a cable management system that contains LV electricity supply cabling with unenclosed live terminals.

Telecommunications cabling and LV power supply cabling shall be separated by a distance:

a)≥150 mm;

b)≥50 mm, where the separation is provided and maintained by a partition as specified in BS 7671; or

c)50 mm where one or more of the following conditions are met:

1)the LV electricity supply cables are enclosed in a separate conduit or trunking which, if metallic, is bonded in accordance with BS 7671;

2)the LV electricity supply cables are of a mineral-insulated type;

3)the LV electricity supply cables are of an earthed armoured construction;

4)the LV electricity supply cables are of a flexible, insulated and sheathed type (e.g. “kettle leads” supplying LV mains power to telecommunications equipment in cabinets)

Where telecommunications cables and the electricity supply cables cross and there is a risk of damage, mechanical protection shall be provided at the crossing point.

As the Clause notes, this is for safety.

Is there a problem with conformity to BS 7671 because of this? Well, potentially. Regulation 110.1.3 tells you that you need to supplement BS 7671 with other standards, and in particular, Regulation 110.1.3 (f) tells you to use BS 6701 for telecommunication systems.

Stuart Urban said:

I have a contractor that isn't concerned by this, however even if the client agrees with a departure from BS7671 I'm still concerned from a health and safety perspective as many of the instances of this are in a medical location.

Even if it's not a medical location, CDM Regulations Designers Duties still apply, i.e. the Designer is still responsible for considering the safety of anyone repairing or maintaining the electrical installation, or the telcomms installation, in the future ... regardless of whether this is a notifiable project.

Not conforming to Clause 5.4.4.2 of BS 6701 when it specifically has the NOTE that the distances are provided for reasons of safety isn't really a good place to be in if something were to go wrong later.

Thanks for the replies. I also note the following from 120.3

"Any intended departure from these Parts requires special consideration by the designer of the installation and shall be recorded on the appropriate electrical certification specified in Part 6. The resulting degree of safety of the installation shall be not less than that obtained by compliance with the Regulations."

What is the concern here? BS 7671 and BS 6701 (thank you, Graham) appear to be concerned with the risk of LV cables raising the voltage in the Band 1 cables. If I have understood that correctly, can the minimum 50 mm separation be achieved in the dado trunking? Could one (or both) of the sets of cables be enclosed in some sort of flexible trunking, mini-trunking, etc?

Surely, part of the concept of dado trunking is that different types of cable go in different compartments, but perhaps one or more of the circuits are new to existing trunking?

If the risk is interference with data, then I doubt that a couple of mm of PVC (or other polymer) will make a lot of difference, but I am no electronic engineer.

mapj1 said:

The risk of mains giving someone on a phone or using data network a shock is pretty much nil, unless the trunking also includes choc block or wagos or other un boxed mains joints., or perhaps there is a mouse problem.

Although from a BS 7671 point of view we "don't trust" basic insulation alone for shock protection (and perhaps with some reason - overheating conductors aren't unknown to creep through insulation on sharp bends for instance) - exposed basic insulation is a C2 and although this is within trunking unless the data cables are OK to be exposed directly to sustained mains voltage (and mains surges) we really should consider that the data cable could be energised by a fault ... and an exposed RJ45 somewhere then makes that touchable.

Had the singles been sheathed though, BS 7671 would have been a lot happier from a shock perspective.

  - Andy.