Electrics, Smoke Alarms and Building Control

[S1llyB1lly]

Hello folks, I am trying to project manage a house refurb and just wanted to double check as to what's required when it comes to smoke alarms in order that I don't fall foul of anything.

Am I right in thinking that I would need a smoke alarm in the kitchen and also one in any hallway leading to bedrooms? Do I need smoke alarms in bedrooms as well?

 

[bernardgreen]

In the kitchen a heat alarm is better than a smoke alarm.

Alarms in bedrooms are more likely to wake sleepers while an alarm on the landing may not wake them due to the door reducing the sound..

If it is a house for multiple occupancy then Building Control advice and rules must be followed

 

[S1llyB1lly]

It's my own flat, all on one level, 2 bedrooms and an open plan kitchen / living room area.
I am guessing they need to be mains powered and on a separate circuit?

 

[bernardgreen]

I am guessing they need to be mains powered and on a separate circuit?

with battery back ups.

It used to be considered sensible to have them on a lighting circuit so that loss of mains supply to the circuit would be obvious when lights did not work. But some modern energy saving lights create a lot of electrical noise on the mains circuit and there is a school of thought that in extreme cases thise noise on the circuit could affect the operation of the alarms.

 

[S1llyB1lly]

Thank you for your help.

I just ordered some Aico Ei2110e units, priced at about £35 a piece shipped.

 

[SimonH2]

... some modern energy saving lights create a lot of electrical noise on the mains circuit and there is a school of thought that in extreme cases thise noise on the circuit could affect the operation of the alarms.

With this noise magically stopping at the MCB in the CU ? I find it hard to believe that there would be enough noise to cause problems in a shared circuit, but that this would stop at the CU and not affect the alarms if on a separate MCB. In any case, I would have expected a current model from a reputable brand like Aico or Kidde to have been designed with this in mind.

 

[Iggifer]

I would have expected a current model from a reputable brand like Aico or Kidde to have been designed with this in mind.

My Megger MFT is from a reputable brand, and it can't cope with noise from CFLs on circuits. It pops up with a little symbol and then gives me a Zs of something insane like 89.6Ω when I know it should be under 1Ω. Just don't give me a reading!!

 

[EFLImpudence]

Flukes just give an 'Err 5'.

Handy for buying cheap ones on ebay when people haven't read the instructions.

 

[Iggifer]

Not sure if that's more or less useful than the Megger display.

Having just checked what it is in the manual, it makes sense now - but I know what it means. On site the first time I saw it, meant nothing to me. Had to look it up

It's a sine wave with a spike in the peak and a spike in the trough. Battery symbol is next to useless (two sideways T's facing each other) and the fuse blown one is inexplicable, a rectangle with a straight line all the way through the middle. To me, that would indicate the fuse is good. A line broken in the middle would make much more sense

 

[endecotp]

My Megger MFT is from a reputable brand, and it can't cope with noise from CFLs on circuits.

But your Megger MFT isn't a smoke alarm! This is about Bernard Green's allegation that a smoke alarm might be influenced by electrical noise from other devices on the circuit. It is far more plausible that a test instrument might be influenced in that way.

 

[bernardgreen]

This is about Bernard Green's allegation that a smoke alarm might be influenced by electrical noise

Have a read of

Cenelec EN 50130-4:2011 13/05/2016

Alarm systems - Part 4: Electromagnetic compatibility - Product family standard: Immunity requirements for components of fire, intruder, hold up, CCTV, access control and social alarm systems


While the risk is small it is not insigificant and hence alarms are required to be type tested to show they are immune to EMC

 

[JohnW2]

It used to be considered sensible to have them on a lighting circuit so that loss of mains supply to the circuit would be obvious when lights did not work.

For what it's worth. I personally still consider than sensible.

For the same reason, I'm no fan of freezers being on dedicated circuits - OK, so there is a greater (but still incredibly small) risk of a fault in some other appliance/whatever taking out the freezer whilst one is away from the house, but one is much more likely to become aware of the problem whilst one is in the house (which is most of the time) if it is on a 'shared' circuit.

But some modern energy saving lights create a lot of electrical noise on the mains circuit and there is a school of thought that in extreme cases thise noise on the circuit could affect the operation of the alarms.

A you have subsequently written, the alarms are required to be "immune" to such problems. In any event, as SimonH2 has said, even if it were not immune to high levels of EMC, I don't see that the problem would necessarily be alleviated by using a different final circuit from the one in which the EMC originated.

Kind Regards, John

 

[bernardgreen]

I don't see that the problem would necessarily be alleviated by using a different final circuit from the one in which the EMC originated.

The coil in the solenoid of an MCB is an inductor with a significant impedance at high frequency.

 

[JohnW2]

The coil in the solenoid of an MCB is an inductor with a significant impedance at high frequency.

True, but what's the relevance of that? ... the currents normally flowing in the circuit surely do not go through that solenoid coil. When the MCB is closed, there is just a straight-through path to the L bus, and thence through other closed MCBs to other final circuits.

... and what about the high frequency components in the neutral?

Kind Regards, John

 

[bernardgreen]

the currents normally flowing in the circuit surely do not go through that solenoid coil.

They have to go via the coil, otherwise there could be no magnetic trip action