BS 7671 - Firefighting lift question

[Donkey Kong]

Hi all. I'm hoping you guys can answer a question for us. I work in a multi tenant/phased evac building built in 1992. The building is 9 storeys with 2 sub basements. There are two firefighting lifts in two separate risers. During a recent inspection of an electrical distribution panel it was found that one of the the 120mm MICC supply cables to the panel (which serves 4 passenger lifts and one of the two fire lifts) has been damaged. Our client seems happy for us to replace the short section of damaged cable with an ordinary armoured cable. I however have my reservations about this as the rest of the installation is in MICC.

The newest copy of the I.E.E regs (17th Ed) states:

Reg 560.5.2 For safety services to operate in fire conditions, the following two coditions shall be fulfilled

(i) A safety source of supply shall be selected which will maintain a supply of adequate duration.
(ii) Equipment shall be provided, either by selection or by erection, with protection ensuring fire resistance of adquate duration.

What I need to know is what would be classed as 'adequate duration'? Would this be enough time to ground the lift, or enough time to carry out a full evac of the building? I have read elsewhere on this site that for phased evac buildings that this time should be increased.

Any ideas?

Many thanks for you responses!

[Galeon]

I would stay with spec for spec and give him the best option 1st , and you don't forget that you cant go size for size on cable , as mineral always has more capability ie amperage for size . You can always joint this size mineral off , you also need to take into account whether this circuit is generator backed. Cabling has moved on since 92 and if you are quoting SWA you have to check the spec carefully.

[Donkey Kong]

Thanks for that - The unit is generator backed and I have taken this into consideration. The extra sizing on the SWA over the MICC I had not.

The jury is still out on what 'adequate duration' is though!

[Galeon]

That's why I would stay with the mineral , you cant beat it in this application , and dont have to worry about its integrity.

[Donkey Kong]

True - But if you could see the tight area we have to work in and the difficulty in forming nice bends on 120mm MICC, you'd be wanting to install SWA too...

I think MICC is the way forward still but our engineering manger thinks otherwise.

Oh and of course they want the works carried out when the passenger lifts are quiet, so Sunday night between 5 pm and 06:00 the following morning. Great!

[kurnal]

BS5588 part 5 gives the spec for firefighting lifts and section 16 covers electrical services.

Firefighting lifts are required for use in firefighting as well as evacuation so an extended duration of safe operation is required.
There are several clauses that talk about duration, eg diesel generators if providing supplies to the lift must have sufficient capacity to run for 3hrs without replenishing the fuel.

The main clause of interest is 16.2.d.. In summary it advises that all electrical services should be
1- located in a protected shaft - where possible in the lift well
2- Adequately protected against fire for not less a period than that of the elements of structure forming the shaft or it should be classified as CWZ in accordance with BS6387.

Fire fighting shafts will have 2 hours fire resistance.

16.2.g goes on to include all other equipment eg  dist boards etc  again referring to the same period of fire resistance as the protected shaft.

Personally I have no idea what CWZ refers to- would be interested to hear from someone who does!

[Galeon]

Have a look at www.batt.co.uk good website for all the info  on CWZ

[kurnal]

Thanks Galeon.

So where a cable is CWZ can it just have been tested to any one of the following tests or all of them? Because on the Batt website there is a huge range of cables that are listed as CWZ and the range of tests is very different.

It may be that there is inadequate guidance in BS5588 part 5 to be of use  to an installation engineer?

BS6387:1994 CWZ
Fire Resistance, with and without water and mechanical shock
Specification for performance requirement for cables required to maintain circuit integrity under fire conditions
Cat.C Exposed to Fire @ 950 Deg. C. for 3 Hours

Cat.W 1, Exposed to Fire @ 650 Deg C. for 15 Minutes, Then
2, Exposed to Fire @ 650 Deg C. with water for 15 Minutes  

Cat.Z 1, Exposed to Fire @ 650 Deg C. for 15 Minutes, Then
2, Exposed to Fire @ 650 Deg C. with Mechanical Shock  for 15 Minutes.

[Donkey Kong]

Many thanks for your replies - interesting stuff, as it happens I just sat the C&G 2382-10 (BS7671 17th Ed I.E.E. regs) and there are new regs on eddy currents and so on which preclude the use of any other type of cable in this particular case.

Time to get the MICC tools out. Feel the joy