running other cables alongside electrics

[jaysta]

Hi guys,

Need some more advice.

I'm replacing an alarm cable from a PIR to the control panel.

I thought it would be prudent to pass the alarm cable through the holes in the joists alongside the electric cabling twin and earths rather than through the notches that have been chiselled out at the top of the joist.

Sometime ago I mentioned to my electrician friend that I was going to put some network cabling alongside some twin and earth in the dining area and he said no it's against regs so I didn't... hence the query about the alarm cable in the joists as perhaps the regs are different for running through joists than down a wall.

What's everyone else's opinion?

Thanks,

Jay

 

[ColJack]

it's all to do with interferance.
a coms cable run with a mains cable will pick up a mains "hum" from it..
with network cables it's a problem, and possibly for alarm cables too..

if there are already notches in the joists then why not use them?..

 

[oharaf]

Band I and Band II circuits should be segregated from electrical circuits.

However, depending on who you speak to the opinion varies.

I recently re-wired my cousind house, he is an IT boffin for a LARGE local news paper up here.

When I said to him that the regulations state that these circuits should be segregated he told me that this is the case, but in small installations such as his home network the chance of there being any effect was negligable.

Anyway, I segregated them, spaced 50cm away from the electrical circuits.

So take your pick is my answer, you are doing it yourself so you do not have to worry about compliance as such.

 

[ericmark]

528.2 Proximity of communications cables
In the event of crossing or proximity of underground telecommunication cables and underground power cables, a minimum clearance of 100 mm shall be maintained, or the requirements according to (i) or (ii) shall be fulfilled:
(i) A fire-retardant partition shall be provided between the cables. e.g. bricks, cable protecting caps (clay, concrete), shaped blocks (concrete), protective cable conduit or troughs made of fire-retardant materials
(ii) For crossings, mechanical protection between the cables shall be provided, e.g. cable conduit, concrete cable protecting caps or shaped blocks.
NOTE 1: Special considerations of electrical interference. both electromagnetic and electrostatic, may apply to telecommunication circuits, data transfer circuits and the like.
NOTE 2: Segregation requirements for communications services are given in BS 6701 and BS EN 50174 series.

Although this refers to underground cables normally the same rules are also used above ground. Also you must consider:-

528.1 Proximity to electrical services
Except where one of the following methods is adopted, neither a voltage Band I nor a voltage Band II circuit shall be contained in the same wiring system as a circuit of nominal voltage exceeding that of low voltage, and a Band I circuit shall not be contained in the same wiring system as a Band II circuit:
(i) Every cable or conductor is insulated for the highest voltage present
(ii) Each conductor of a multicore cable is insulated for the highest voltage present in the cable
(iii) The cables are insulated for their system voltage and installed in a separate compartment of a cable ducting or cable trunking system
(iv) The cables are installed on a cable tray system where physical separation is provided by a partition
(v) A separate conduit, trunking or ducting system is employed
(vi) For a multicore cable or cord, the cores of the Band I circuit are separated from the cores of the Band II circuit by an earthed metal screen of equivalent current-carrying, capacity to that of the largest core of a Band II circuit.
For SELV and PELV systems the requirements of Regulation 414.4 shall apply.
NOTE 1: In the case of proximity of wiring, systems and lightning protection systems. BS EN 62305 should be considered.
NOTE 2: Requirements for separation and segregation in relation to safety services are given in BS 5266 and BS 5839.

Because of the voltage rating of alarm cables you can't normally use same holes.

 

[davelx]

Not convinced - the reg you quoted says:

"Except where one of the following methods is adopted, neither a voltage Band I nor a voltage Band II circuit shall be contained in the same wiring system as a circuit of nominal voltage exceeding that of low voltage,"

The normal UK mains supply is low voltage as defined in the regs. So running VBI or VBII circuits in the same wiring system does not violate this.

 

[chapeau]

No, the alarm cable is going to be in voltage band I. The house electrics are voltage band II. So an electrician who is required to work to BS7671 would need to comply. However it appears the OP is not an electrician working to BS7671 so doesn't need to comply. He needs to consider whether it's 'safe' and probably also whether there is going to be any interference.

 

[davelx]

Ah - forgot that the alarm cable is only rated to 60V. But that reg can be interpreted in a couple of ways, ie, is the requirement not to run BI and BII together only applicable when running alongside cables which exceed LV, or is it a seperate condition.

 

[rebuke]

No, the alarm cable is going to be in voltage band I. The house electrics are voltage band II.

As davelx says the reg you quoted doesn't say band I and band II can't be in the same system, it says neither of them can be in the same system as a circuit of nominal voltage exceeding that of low voltage. I'm happy to accept there might be another reg which says they have to be separated from each other, but it's not the reg you've quoted...

 

[chapeau]

I never mentioned systems. I said that alarms are in Band I (this is specifically stated in the BS7671 definitions), house electrics are in Band II (also specifically stated in the BS7671 definitions). Ericmark quoted the reg. The reg quoted lays out the circumstances when you can 'mix' the two systems, if working to BS7671.

 

[rebuke]

Doh, lack of coffee moment I think - I read the bit davelx quoted, and not the full reg that has the "and a Band I circuit shall not be contained in the same wiring system as a Band II circuit", and then managed to get confused over who quoted and said what etc

 

[chapeau]

Ah yes, lack of coffee, been there, done that

 

[jaysta]

Sweet Jesus! I can see that was a fair bit of a discussion and I thank each one of your for your input.

I think I understand it all which brings up an old idea that I had.

Each of the notches in the joists run pretty much in a straight line and also in the notches that have been chiseled out there should be enough room for 16 x 25mm trunking or perhaps something smaller. If I can put some trunking in for most of the way then this should make it safe to run the alarm cable. It still won't be 100mm away from the lighting circuit but imo it's better than running directly alongside.

What do you guys reckon?

Thanks again

J

 

[rebuke]

Personally I wouldn't worry about it - I put in the alarm in my house, and although where possible I tried to keep the alarm cables away from the mains, I'm fairly sure they run right next to each other in a few places, and the alarm works just fine...

 

[JohnD]

ugh, notches

why not drill the centre of the joist?

 

[jaysta]

ugh, notches

why not drill the centre of the joist?

There's already two holes drilled in each of the joists John. The set of holes that I wanted to pass the alarm cable through has just got lighting circuit and smokes circuit running through it. The other holes have got kitchen circuit, boiler radial and fridge radial.

I don't really fancy drilling another hole just for an alarm cable unless absolutely necessary.