Addressable fire alarm system and interference to data network. 2

[wayne079]

Hi,

Wondered if anyone can share an opinion on the following:-

My employers have recently had an alarm company install an addressable system inside a hotel.

We are having difficulty with the interference from the FP200 rated, screened cable that they have used to install their circuits.

I can hear pulsing coming through both voice and data networks in certain places the interference is enough to totally block data signals on the data side and bleed into both analog and digital voice circuits.

The alarm company have had to install in some hard to access places and have had to use some entry points through walls in the same place as the voice/data circuits.

We've confirmed that they have used the correct cabling for the install and personally I have never come across a problem such as this? Even toning a cable going through certain routes is near impossible.

This installation is not ran in separate data baskets, there appears to be no thought for impact on surrounding cabling and in most places is not clipped up, just laid on joists in the roofspaces.

As a result we are in dispute with the company financially and need to come up with a solution.

Thoughts? Opinions?

In the UK.

TIA

 

[sbcsu]

Hi,
If possible turn off the mains electricity and see if the pulsing is still active.
If the building is in a rural area it could be local pulsing from an electric fence for example.

 

[wayne079]

We are talking about an 80 bed hotel here.

It is coming from the fire system and this has been proved.

 

[sbcsu]

Sure - I understand,
That was not clear in the original post.
If it was me I would prove that to the fire alarm company by showing them what you have found.
Document your findings...
I suspect the cables are not correctly earthed or shielded.
Test again using CAT6 or better on your own LAN to see if the CAT6 screens out the interference.
They must have come across this before on other sites ?
There may be a way to reduce the power output on the offending cables ?
Possibly try ferrite cores.
Get opinions from other alarm companies
Find out what standards the alarm cabling is installed to

 

[wayne079]

Current network is cat6.

They are aware and have installed to the correct British standard. As such they are unwilling....They are using screened cable but I've never seen interference of this magnitude.

They say the screening on the cable is there to prevent induction into their circuit. In my eyes it should stop it or reduce both ways.

 

[edfair]

One thing you might want to check is the grounding on the screening. If no grounding then it might be acting as an antenna.

There are also differences in the shields. It might help to know if it is a woven wire shield or foil wrapped.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[misseditbythatmuch]

I believe edfair is on the right track. If the grounding tests as present, I would also test to see if there are any shielding was grounded in more than just the origin point. If one or more of your remote stations has the shielding grounded there at the remote end and if it is also grounded at the central panel (which is the one point it typically would be), you have all the makings for a ground loop current in one or more shields. An 80 room hotel will most likely have multi phase feeds from more than one transformer, so that is just prime setting for a ground loop. Not all grounds are truly equi-potential, so a good meter is needed to check impedance at each grounding point. One test would be at the central point to find where the bonding strap is between the shield connections and the earth ground. Hopefully you have a fastener that is field removable and you can interrupt the ground path, then put you meter in series and see if you find any current passing from shields to ground. If so, you have a ground loop with at least one remote point and you need to remedy it (or have the alarm company remedy it). Even if it is the right cable, if it is improperly installed, it will give you huge amounts of noise.

 

[wayne079]

Cable used is Vencroft low burn, with 1mm conductors a foiled screen and tinned annealed copper CPC (Earth).

In the places where the most interference is caused, there appears to be 4 cables running parelell.

So we should be asking if ground tests have been done? The manafacturer (different to the installer) has signed off the install and warrantied, however, suggested that they do not inspect the wiring?

 

[edfair]

In a similar situation many years ago I reran the data cable to avoid the pinch point conduit. Nothing I did would eliminate the interference picked up from other cables.

I suspect that the cabling specs for the alarm company have minimum spacing requirements to other conductors but that would be for protection for their circuits, not others. The parallel cables are the problem and separating them would be the solution.

The ideal way to have prevented the issue was metal conduit but any ferro bases metal that you can get between the alarm cables and your data cables should help.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[LoPath]

RF Interference? Maybe?
RF Filters

LoPath
Maintain HiPath 4000 V5 & V6, OpenScape Xpert V4, Xpressions, Contact Center

 

[BTBZ]

have then shut their system down to see if the problem is still there.