insulation resistance tested ring veritas 8 still connected

Discussion in 'Alarms, CCTV & Telephones' started by dingodeano, 26 Jan 2009.

  1. dingodeano

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    Hello i recently did an insulation resistance test on a ring main. the customer 'forgot to mention the alarm was connected on a fused spur!!!
    the alarm was last seen with a light flashing ( prob to indicate supply faliure ?)
    And as far as im aware(ACCORDING TO CUSTOMER) the main 3a fuse on spur is still intact.
    What damage might have been done and how do i go about rectifying it?
    Thx in advance .
     
  2. rebuke

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    Most alarms are powered off a transformer inside. Presumably your insulation resistance test failed, since it should have picked up a low resistance across the transformer.

    You are likely to have either damaged the transformer (at which point just find an appropriate equivalent and swap it in), or, if the transformer happily carried the 500V, then it will basically have put double the volts across the alarm (e.g. if it normally uses 12 then it would have got 24) - the alarm may have some protection against this, so it might just have blown a fuse in the alarm box, or, it could have blown up some component on the board, which would be much more tedious to fix...

    How long ago did this happen, most alarms have an internal battery that will keep them running about 24 hours or so, so if it's still working now and it was quite a while ago, then it might just be a fault light complaining about the fact that there was a power failure that needs to be acknowledged, rather than a permanent fault. Note however I don't know this particular alarm, so can't really help further than this...
     
  3. Spark123

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    I can't see it doing much in the way of damage, afaik a veritas 8 has a wire wound transformer, the earth terminating at the terminal rail in the unit so IR testing L-E shouldn't make any odds to the panel.
    I take it the customer has pressed reset on the panel? Think they need to enter the user code then press reset.
     
  4. rebuke

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    I was assuming he did a L-N IR test, as agreed a L-E/N-E test is unlikely to cause any problems in this situation...
     
  5. Spark123

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    A normal IR tester only delivers a few mA DC at 500v, if there is an inductor in the way like a transformer it will normally show it as a short, the tester not delivering enough power to drive the voltage up to 500v. The IR tester is also DC hence only the initial charge can pass through a transformer.
     
  6. securityinstaller

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    Erm is maybe DC but it is pulsed DC otherwise it could not keep the volts at 500V this is what caused the damage.

    The transformer would have hence put 24volts into the panel at low current. Which knowing this panel may have damaged it.

    But depending on what version it would need a reset after the power was restored in any case.

    Sparks did an IR test once on a job I was on and he blew the PCB.

    Easy way over this and to be cautious is to do the IR CPC(Earth) to BOTH live and neutral at the same time half the result and you have the IR of each current carrying conductor.

    In other words one probe on the earth (cpc) the other on BOTH Live and nuetral NAPIT are okay with this in fact they pointed it out to me. The only thing is to make sure that washings machines etc are unplugged as the capacitors in these can affect the reading.

    It can also stop the damage done if the customer has not told you he has an alarm, but all due respect you should have at least seen signs of the alarm as you would have had to carry out a visual inspection first.

    don't forget there is guidance with regards to what you should do first. Visual is important as if the installation is really old etc then on visual it is not worth doing tests. IE Rubber cables, no CPC(Earth) no bonding etc.
     
  7. Spark123

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    No - an insulation resistance tester delivers DC, not pulsed DC. If it was pulsed DC then it would end up measuring the capacitance of the cables as well, similar to why they don't use AC for this measurement.
    Not entirely convinced there would have ever been 500v there to allow enough current to flow to produce enough magnetic flux to eventually give a momentary 24v after smoothing on the DC side of things.
    More likely something like this imho, sometimes I have known a fuse to pop in the panel when messing about with the supply side of things, might be the battery fuse when the panel was powered back on has popped.
    Doesn't it do the opposite i.e. wouldn't you would need to double the result as they are in parallel to ensure you have a near correct reading but as this is impractical owing to you not being guarenteed to have equal lengths of phase and neutral conductors recording just the reading which is obtained for L+N to E is afaik fine.
     
  8. dingodeano

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    there was a light on the panel which flashed for 'a while' after the test. but now the panel is dead. i have got five replacement fuses listed in the engineers manual [url]http://www.mas-uk.co.uk/v8c8r8installtion.pdf [/url] which i will try first then i will check the transformer. i will keep you posted :0). thx for all your replys.
     
  9. dingodeano

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    no i dont think he has tried this yet however the pannel is reported as 'dead'.
     
  10. Spark123

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    If it is now dead then likelyhood is that it has lost its mains supply, could be a fuse inside the panel or something else. The backup battery has now run down and the panel has died. I don't think the veritas 8 loses its memory on power off so you shouldn't need to re-program it. It is recommended after deep discharge that the backup battery is replaced.
    I take it they didn't have a battery backed bell box as that usually goes into alarm for 20mins when the panel dies.
     
  11. RF Lighting

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    The green light flashes when mains is lost, and will stop altogether when the battery in the panel goes flat.

    You should not be carrying out IR tests between L&N>E as standard. You should test each conductor to each other.

    A simple continuity test will usually show up a hidden load without damaging it.
     
  12. dingodeano

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    No there was no sound from the bell box when power stopped. i did conduct the insulation tests between live conductors and then live conductors to cpc so i have probably increased the chance of damage!! as i had no reason to believe and any loads were still connected
    However as rightly pointed out i should have took more time visually inspecting first.
    The consumer unit was poorly labled ( red insulation tape " upstairs ,living room , dining room) the alarm was in the utillity room. (still my fault though)
    I have sent the customer all the fuses for the panel which he will try then get back to me to see if i need to replace the panel , c.e.f. do them for 38.00 plus vat.
    thx again for all your help guys a lesson has been learned ;0)[/b]
     
  13. securityinstaller

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    Okay it is "inverted" to 500V you still get the voltage through the transformer though otherwise when I was at skool I would not have been able to use a 9 volt battery a buzzer and a hornby transformer to make a rather nasty shock machine!

    12 volt coil battery buzzer 240 coil couple of long wires bare at the end press into someones hand. Did even more damage with a capacitor Mum slapped me around the face though if I realsied what I was onto would have got to the tazer .......
     
  14. Spark123

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    Never taken a modern megger to bits, dunno if they use transformers or voltage doublers to make up the 500v.
    You can use something like a square wave to run a transformer, as long as the current is constantly changing. With DC only the initial pulse will give a voltage on the output.
     
  15. dingodeano

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    Went back to customer today sure enough his panel was dead...but no voltage TO fused spur either... further investigation revealed the alarm was not even on the ring. it just so happened that the protek 6 amp mcb which supplied alarm had failed to 'close' when switched back on.
     

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