Fire alarm switch????

[nicsin02]

Hi guys, I am out testing a building 2day and have come across a fire alarm switch/isolator fed directly from the mains side of the isolator that's feeding a d/b, so basically that means a 2.5mm cable is protected by the 80a cut out fuses, surely a C2 guys?? But my boss is telling me this is the correct wae it's done so that the fire alarm is on all the time :-S, any advice would be great thanks

 

[snowhead]

Correct that it's fed from the live side.

What's potentially more dangerous, a cable that might overload or a building Not protected by a fire alarm.

I see sprinkler systems done this way on commercial buildings and the only protection is a 2000amp air circuit breaker at the incomer.

 

[Clive P]

Hi,
Just googled this,

Installation/Wiring
The Fireman Switch is used for the breaking of the low voltage circuit of exterior and interior
signs and luminaries installations e.g. neon signs for AC.
The Fireman Switch can also be used to operate the Under Voltage Release or Shunt Trip in
the Main Incoming Breaker. If there is a fire in the building, the Fireman uses an insulated rod
(Firemans Axe) to pull the handle to O position which isolates the utility supply to the building.
• The Under Voltage Release is fed through one of the Main Contacts of the Fireman Switch. .
When the voltage is removed, the Breaker Trips.
• The Shunt Trip is fed through N/C Auxiliary Contact. When the Fireman Switch closes, the
Auxiliary Contact opens, giving power to the Shunt Trip which trips the Breaker.

I would guess then that in this situation the Firemans switch would be part of a control circuit rather than a straight on/off. No doubt there are more experienced sparks on the forum who deal with this on a regular basis and have more relevant information.

Regards.

 

[Engineer54]

Correct that it's fed from the live side.

What's potentially more dangerous, a cable that might overload or a building Not protected by a fire alarm.

I see sprinkler systems done this way on commercial buildings and the only protection is a 2000amp air circuit breaker at the incomer.

Not sure how or why the fire pump would be supplied from a 2000A incomer breaker, but it pretty standard for designated fire pumps to be able to run till destruction. Normally fed from a breaker that is 10X it's rated running load, and no starter overload protection. The idea behind this set-up is that the fire pump will continue to pump water into fire water dry risers and the like. There is always a remote fireman's override switch, located in a safe location... A lot more to this type of installation but that's the rough basics... lol!!

 

[snowhead]

Not sure how or why the fire pump would be supplied from a 2000A incomer breaker,lol!!

It's the Distribution board supplying the Fire equipment that's only protected by 2000amp (straight off the incomer) the equipment is fed and protected from the Fire distribution board.

Re Firemans Switch, that's for specific circuits, like Fuel pumps on forecourts or neon or other external signs that could not be isolated by the Fire brigade if the premises were unattended.

It could turn out in the future that all houses with P.V panels on the roof will have to have an external Firemans switch, as the Fire Brigade are quite rightly concerned over throwing water onto roofs with live panels on .

 

[Brightspark2]

How far in 2.5mm I'd the run?...

Overload protection can be placed within 3m of the change in cable diameter...

 

[MDJ]

How far in 2.5mm I'd the run?...

...

You started on the Guiness already fella? :earmuffs:

 

[Engineer54]

It's the Distribution board supplying the Fire equipment that's only protected by 2000amp (straight off the incomer) the equipment is fed and protected from the Fire distribution board.

Re Fireman's Switch, that's for specific circuits, like Fuel pumps on forecourts or neon or other external signs that could not be isolated by the Fire brigade if the premises were unattended.

It could turn out in the future that all houses with P.V panels on the roof will have to have an external Fireman's switch, as the Fire Brigade are quite rightly concerned over throwing water onto roofs with live panels on .

As i stated, what i posted above is literary scratching the surface, and i'm only talking about the Fire Pump!! Very often the fire pumps are diesel engine driven, rather than electric motor driven...

 

[tazz]

This was the old way of suppying essential fire opperated equipment pre 2002. Most new builds now have essential db boards alongside normal db boards, all relevent bs standards now comply with each other on protection. Fire alarm, sprinklers and other equipment are now a days are capable of being supplied off generators, or the their own battery systems. Main different now is supply cables must be enhanced fire proof.

 

[Engineer54]

This was the old way of suppying essential fire opperated equipment pre 2002. Most new builds now have essential db boards alongside normal db boards, all relevent bs standards now comply with each other on protection. Fire alarm, sprinklers and other equipment are now a days are capable of being supplied off generators, or the their own battery systems. Main different now is supply cables must be enhanced fire proof.

What do you mean by the Old Way?? I did state there is a lot more involved in such a system, and Essential/Non Essential boards are just another small part of it. Are you saying that diesel engined fire pumps are no longer used?? Never seen or heard of a battery system supplying a fire pump, you'd need an awful lot of batteries, and a fair sized room to house them all too. ...lol!!

 

[tazz]

What do you mean by the Old Way?? I did state there is a lot more involved in such a system, and Essential/Non Essential boards are just another small part of it. Are you saying that diesel engined fire pumps are no longer used?? Never seen or heard of a battery system supplying a fire pump, you'd need an awful lot of batteries, and a fair sized room to house them all too. ...lol!!

Essential supplys are no longer taken direct from the incoming bus bar. Fire alarms will be from the essential db protected by an mcb, supplys to sprinklers the same, with as stated genorators, which would include using a diesel pump, most housed in a seperate isolated building, not because of the size of batteries, but the size of tank required, which is buried underground.

 

[Engineer54]

Essential supplys are no longer taken direct from the incoming bus bar. Fire alarms will be from the essential db protected by an mcb, supplys to sprinklers the same, with as stated genorators, which would include using a diesel pump, most housed in a seperate isolated building, not because of the size of batteries, but the size of tank required, which is buried underground.

I have no idea what your talking about here, basically because it's total rubbish!! Incoming supply will be split at the main switchboard bus sections, (and/or essential supply fed from a designated TX from the MV switchboard), One side being designated essential the other non-essential. Fire fighting installations do NOT rely on a generator installation, though the essential side of the incoming supply would be supplemented by an auto start and change over to stand-by generator on loss of primary power. As i said, never seen or heard of a battery powered Fire Pump, probably because of the astronomical initial cost, and the ongoing intensive maintenance of the batteries (which will require a specialist hazardous rated storage room) along with the battery charging system!!!

 

[Robert Turnbull]

It could turn out in the future that all houses with P.V panels on the roof will have to have an external Firemans switch, as the Fire Brigade are quite rightly concerned over throwing water onto roofs with live panels on .

What's that going to turn off?

The SUN!

 

[tazz]

I have no idea what your talking about here, basically because it's total rubbish!! Incoming supply will be split at the main switchboard bus sections, (and/or essential supply fed from a designated TX from the MV switchboard), One side being designated essential the other non-essential. Fire fighting installations do NOT rely on a generator installation, though the essential side of the incoming supply would be supplemented by an auto start and change over to stand-by generator on loss of primary power. As i said, never seen or heard of a battery powered Fire Pump, probably because of the astronomical initial cost, and the ongoing intensive maintenance of the batteries (which will require a specialist hazardous rated storage room) along with the battery charging system!!!

You have just answered your own question all equipment not taken off bus bars, supplied from dbs, what switches on the deisel pumps and control gear, battery ups control

 

[Engineer54]

oh Dear!!....