Fault

[Martinwigan]

Hi guys I attended a call out today to a some alarm fault. It was a mains voltage fire alarm there was a twin coming from consumer unit to 1st smoke head then 3core out to rest of heads. Brown was used for live grey neutral and black was the interlink hence volt free. On testing I had 240v to live n earth and live n neutral. When testing interlink to earth I found 90v and this was causing heads to activate. I traced circuit bk to second point and disconnect out goin leg and fly leads. And tested again and was getting same results. I went to consumer unit and carried out ze and results were megger high so I re terminated all earths n carried out test again and got a good reading of .20 so put this down to bad earth so went and test again and got at second point and got 30volts on the interlink cable even tho the black cable was connected to nothing at any ends. So we put a head back onto the circuit to c if head went of but never and when we tested the voltage again on black cable and it was clear. But I'm still thinking its a bad earth coming into the building. Has anybody come across this befor or anything similar and am I right in thinking it is a bad earth 

 

[Andy™]

inductance

 

[Evans Electric]

I thought the interlink  worked on around 9volts   for some reason .  Not sure where I got that from .   

Have these detectors   been working OK    previously  ?  

Is Grey definitely  used as Neutral  throughout .?  

Could the first smoke alarm be faulty  and constantly triggering .?  

What make are the alarms?  

Doubt its an earth problem  TBH

 

[Sharpend]

The battery back up interlink are 9v aren't they? 

 

[Murdoch]

I was fault finding something very similar yesterday:

8 Aico alarms, 5 RF bases, 3 hard wired - going off

After consulting Aico support, I disconnected the hardwired links from the RF bases, then reset the RF bases ........... added the smokes and its all OK now.

Aico couldn't offer an explanation of why it happened, but this course of action fixed them.

Very odd

 

[Martinwigan]

Yes interlink is 9volts when triggered. The brand is hi spec. They have been in over 12 months and been working fine. We checked all heads 1 at a time to make sure they were fine befor re fitting them. I no u can get emf but I thort that would have to be a big load to cause that problem but from consumer unit to second point is tops 10 meters and wat baffled me more was when u put head back onto circuit the voltage disappeared 

 

[Evans Electric]

If , as Andy suggests, its inductance  , refitting a head  probably  nulls the induced current within it's circuitry .  Pure guesswork.      I've been fitting Aico's for years  & never experienced any problems with induced voltages  on the trigger wire  TBH  .     

 

[Martinwigan]

Yes 9v dc when triggered 

 

[Doc Hudson]

Bad or poor earth should have no relevance to the operation of the smoke detectors as they are double insulated devices, plus they can work of 9v DC batteries. So their operation has no reference to any earth potential. You say they are 12months old, did you check the voltage of all the batteries? As a general rule if strange things start happening the first point of testing is double check all batteries.

Doc H.

 

[kerching]

Hi Spec, eh?

i have nothing but trouble with anything by HiSpec

i was only talking to their Rep about this the other day in the wholesalers....apparently there is only me who,returns at least one M3 conversion a month and PIRs on a regular basis

 

[Martinwigan]

Everything possible was checked. It was when all smoke heads was removed we had 30-90v on the interlink cable what worried me as it shud b volt and when the voltage was at its highest it was causing the heads to trigger but when we got the voltage down they was not triggering and once we started putting heads on the voltage diapered completely 

 

[Doc Hudson]

Everything possible was checked. It was when all smoke heads was removed we had 30-90v on the interlink cable what worried me as it shud b volt and when the voltage was at its highest it was causing the heads to trigger but when we got the voltage down they was not triggering and once we started putting heads on the voltage diapered completely 

Your 30v - 90v on the interlink wire with all heads removed is almost certainly an induced voltage. i.e. a conductor that is open circuit at both ends with no devices connected is basically an aerial. Plus the type of meter you were using to measure with phantom voltage would not be putting any load across the wires to read the true voltage. We see it time and time again people reporting 50v, 60v, 70v, 80v+ on a lighting circuit they are fault finding on with wires disconnected at the CU. An aerial will pick up all sorts of induced voltages depending upon the environment it is installed in. If you put a load on this interlink wire your induced voltage would disappear. I think you have been chasing a red herring with the interlink wire voltage. If there genuinely was a 90v potential there you would be able to get a standard filament lamp to glow if you connected it up.

Doc H.