Fire rated bus cable?

[MDAR]

Hello everyone

I’m looking for opinions or thoughts.

Last night I saw a post on LinkedIn about a National Trust property LINK (UK Old Buildings etc), where the specification clearly demanded fire rated cabling.

This got me think about how to bring digital controls into that market.

Clearly a centrally wired solution for lighting / fans etc has to be better in the event of a fire as only ONE power supply cable has to survive for the light / fixture to remain on (as opposed to power feed AND the switch cable)

Draka FT Data Cable

Specifically ------ 2 pair (2 x 2 x AWG22)

387FTD203.pdf

Then I thought, that’s okay, what if the Velbus control points (assuming they’d ask for a combination of glass panels, brass switchgear or gang plates) data cable did get damaged and the bus voltage was compromised?

That’s an easy one, just put the cabinet modules on a seperate PSU
and if you want to be super protected, pop a DPST relay on the bus Data cable external of the cabinet, so that if the control point PSU is compromised, the relay will drop out and the cabinet data will continue to work.

I’ve created a wiring plan to show what I am thinking.

BasicWiring_Protected_FireSafe.pdf

What are all your thoughts?

• Is this an edge case that should be ignored?
• Could we use fire rated (With or without armour) in historical buildings to get digital controls in there without causing too much damage to delicate plasterwork etc.
• Should we look at theorising a fail safe where power to light fittings / fans / electrical devices is switched off in the event of a fire? - Or just a “Fire Marshall - Press here to switch OFF all circuits” button?

[PrzemoF]

My 2 euro cents…
Interesting… What are the benefits of keeping the power on during fire? Before the fire crew can start extinguishing the fire they have to cut off the power anyway? In industrial applications only the Fire Alarm system is wired with fire rated cable. And possibly some really critical stuff, but that´s rare. The exception might be for industrial HVAC installation - a fireman switch at the gate to remove smoke from the premises.
Switching all stuff off with velbus makes no difference if you cut off the main power. A UPS with 230V output might make things worse - you don´t want to hold a water hose pointed at that UPS.

P.S. As a fireman - would you trust “Fire Officer - Press here to switch OFF all circuits” button? The life of your team might depend on it…

[MDAR]

@PrzemoF

What are the benefits of keeping the power on during fire?

I was thinking more for safe well illuminated evacuation.

@PrzemoF

you don´t want to hold a water hose pointed at that UPS.

yeah, that’s “never a good idea”

@PrzemoF

In industrial applications only the Fire Alarm system is wired with fire rated cable

Which is what I thought, but looking at that post on LinkedIn, it seems the light switch is in the same cable type.

• is it to keep it looking the same?
• Is it because the cable is exposed and they want the robust cable, rather than the fire protection?
• Is there a need for it to not expose live wires in the event of a fire?
  (before the system is powered down etc)

I’m just trying to find a way that designers and specifiers CAN have a digital solution and keep to the fire protection regs that they appear to be referring to.

@PrzemoF

P.S. As a fireman - would you trust “Fire Officer - Press here to switch OFF all circuits” button?
The life of your team might depend on it…

Excellent point.

Maybe that should be “Fire Marshall - Press here to switch OFF all circuits” ?

[nagisa]

Hm, but what benefit does a fire-rated (resistant?) cable bring if the panels and most modules themselves aren’t? Does the spec in question not mandate that the entire system is “fire-proof” for whatever definition of “proof”?

After all, most systems are as good as the weakest link (and fire is well outside of operating spec for indoors velbus modules,) so with my spec author hat on I would definitely put in a provision for buttons and whatever else may be attached to said cables too. So I would start by checking what that spec really says and see if there’s anything digital (velbus or not) that would be to spec in the first place.

That said I know of at least one reason why one might want to mandate at least fire retardant cables (IIRC they all are by default nowadays.) Poor cable will contribute to fire spreading (kind of like a fuse) and with them being hidden away from plain sight they quite likely than not be missed during efforts to extinguish fire.

[MDAR]

@nagisa

so with my spec author hat on I would definitely put in a provision for buttons and whatever else may be attached to said cables too

That is 100% what I assumed would be the requirements.

Certainly in a cabinet or end point.

re fire alarm points, if they melt without being triggered (or indeed trigger because they are melting) I guess that’s okay.
( I don’t recall ever seeing a metal fire alarm point, metal back box, but the front has always been plastic )

But for light switches, the digital solution wins, because there is no dangerous mains voltage at the switch and in reality it has nothing to do with the actual mains voltage switching.

If it melts… who cares?

My drawing even accounts for the data and power to the switch point being compromised .

As Przemo suggests, any attending fire crew will want the whole building powered down anyway.
(what better that a single point of isolation?)

All of that said… and agreed with.
(Especially your point about melting cables and “travelling ignition”)

There is the glaringly obvious (and some would say humorous) detail that the “light switch” featured in the original photo, encased in a metal box… is…

Plastic (or at least ceramic)
and mounted to a wooden post.

During training sessions, if anyone comments on the plastic back boxes, I do draw their attention to the markings that state the melting point of 830ºc with the rye comment of…

If… someone is in the building and they are worried about the box melting at that point, I would suggest that there is something much more urgent that needs considering…

[pdhoogh]

For home use, I’m not sure what that means. Cables are in the walls or the floors, so fire protection is right there. I guess the installation cabinets and the equipment inside aren’t, so if the fire gets there, everything is gone anyway. Also, I guess if there is a fire, you WANT to cut out electricity, wouldn’t you?

[MDAR]

@pdhoogh

For home use, I’m not sure what that means. Cables are in the walls or the floors, so fire protection is right there

I mean in more commercial environments, where there is a design requirement for fire rated cables etc.

[MDAR]

Better photos to follow and maybe a video

[pdhoogh]

OK… I have a background in electrical circuits / process control in petrochemical plants. Fire hazards don’t get much worse… so what do we do there?

Well… fireproofing wires does not make too much sense if your Velbus stuff is rated to 50 degC. And not only the power can be compromised, the molten circuit will short the data bus too.

We will only fire proof wires to critical stuff we cannot put away from fire hazard, like motor controlled emergency block valves to shut off what is feeding the fire. We use electric motors with fireproofed wires because we know everything will die anyway, but a motor will last longer than anything else we know. And for that, we will remove the torque or overcurrent protection on the motor, so it still has a chance to move the deformed valve closed before burning out anyway. The controls to the motor will be put as far from the fire hazard as necessary. Putting a switch in the middle of a fire means you need to go into the fire to switch it, not something we’d recommend.

The above is practice based on decades and decades of fires, analyzing what happened and what we could have done better. It is etched in our “Design Practices”.

I’m sure you can extrapolate these principles to your specific situation.

[MDAR]

As it happens.

I totally agree.

But what we have in the industry are two different thought processes.

Those that really understand what’s going on and those that simply do as they are told.

I’ve had people tell me, " we can’t use digital kit because it can’t be installed with fire safe / fire survival cable"

The fact that my mind is doing summersaults and my eyes are crossed, has nothing to do with it.

[pdhoogh]

Depends on who you have I guess. I worked for ExxonMobil 33 years, have designed and executed about 10 projects, some of which half a billion dollar projects, I was global process control #1 (Lead Specialist) for High Pressure PolyEthylene and Aromatics, headquarterd in Houston and working out of Antwerp: global support works better if you are on UTC. Supported US, Europe, Saudi Arabia, Singapore and Thailand. Was #1 process control in HPPE Licensing, made the design packages for process control for over 10 Licensees, gave them training, helped with start-up issues, provided counseling once they were running… helped write the ExxonMobil Process Control Practices, our rulebook for design… you get the picture, I guess. My expertise goes from field wiring all the way up to safety systems, process control and also advanced process control: last 10 years of my career I roamed the world with our #1 DMC specialist building multivariable model based control, some of which were 40 manipulated variables and 80 controlled variables large… to make these work you need to understand everything, from the process to the equipment, the wiring, the instrumentation, the control systems and (sufficiently) advanced math. I’ve been around a bit. I’ve done more than that, also did fault insertion testing on digital equipment for process control, examining the failure modes of instrument transmitters, control and safety systems… certifying for use in our company and when not good enough, advising the manufacturers how to improve their stuff to improve reliability and safety of their digital systems…I’m electronics by background.

That is why I chose Velbus. It uses CANbus, probably the most used protocol in the world or certainly up there with TCP/IP. It is a real distributed control system for the home and therefore superior to any competing home automation in the world in terms of reliability and compatibility over the years. The native application features are somewhat limited, but that is what you get with the choice and that is fine. The only thing it lacks is a VARPR, a VARiable PRocessor or Applications Module to make the more complex stuff. But that may not be a thing that would have massive commercial success. The Signum falls terribly short, it is merely a gateway to the hackers and I don´t like that. I wish for a native VARPR. No connection to the hackers.

There is not going to be an issue with producing the VELBUS chips, the world is invested heavily in these. It is “open” in terms of hardware, very rare. But … programing native VELBUS and getting it to do what I want still proved to be a challenge sometimes, even for me :-). I’ve forgotten a lot of the intricate stuff by now, everything runs fine since 2016 and I’m rarely touching it these days. I should write documentation for my system, I fear with my passing people might find it a challenge to maintain…

Anyway, you decide what to do with fire proofed installation of Velbus. I wouldn´t bother. Digital Emergency back-up systems located in a fire don´t make any sense to me. If having light is the issue, even LEDs will prove to be inferior to incandescent bulbs. LEDs are silicon based semiconductors or similar, they cannot stand the heat of a fire. The wiring to the fixtures should be fire proofed for the run in fire hazardous area, then cabling should be run to a safe location where a mechanical switch can be used to turn it on or off. Then test the system every quarter.