OMS:
You've not got any circuits in there from different supply sources by any chance - eg, some stuff operating from say a UPS that wouldn't necessarily have it's output synchronised with other systems ?
Regards
OMS
Hi OMS,
I'll have to check once I'm back on site, but there may be some new FPs in the trunking that are fed from static invertor, - new emergency lighting install. If not in the trunking then in the vicinity on basket.
Wouldn't that level of movement imply quite a substantial fault current such that the OCPD should have tripped, and hence there shouldn't have been many vibrations to hear?
Sparkingchip:
Voice pipes could be used over distances as long as 300 feet (90 m).
Wikipedia- Speaking tube.
Interesting as a resident of the borough to read of the "Gosport Tube", but I would still say that if you stuff the tube full of cables, it will not transmit sound. Nonetheless, a chum of mine who is a professor in Nottingham, once made the very valid point that if you do not know the answer, you have to do an experiment; which is exactly why I suggested the buzzer.
Please don't over-think this one.
MHRestorations:
I'm definitely with Andy Jewsbury here... the fault has to be substantial to physically throw cables around, but to simply make an audible noise, especially as arcing tends to be high frequency.. steel trunking tends to sound tinny (pun not intended), inasmuch it accentuates higher frequency noises.
I can imagine that a significant series arc could cause current fluctuations enough to cause a crackling or arcing noise a long way away from the actual fault.
Morning,
Where's the high frequency coming from? A 230V arc might be caused twice every cycle, i.e. once per half cycle, and that's about it (the arc current itself will follow the sine wave, where there is current flowing). So the crackling or buzzing should have a 50Hz sound to it.
Also, a series arc will limit the current drawn as it is inline with the load and as far as impedance goes, it is additive. I.e. if the cable doesn't move under load, I don't see why it would be moving (due to magnetic effects) under series arc conditions.
A parallel arc would be different and could cause higher currents (low impedance from phase/phase, phase/earth) but that would imply cable damage, which has not been shown up by the IR testing.
Dutch of the Elm:
Where's the high frequency coming from? A 230V arc might be caused twice every cycle, i.e. once per half cycle, and that's about it (the arc current itself will follow the sine wave, where there is current flowing). So the crackling or buzzing should have a 50Hz sound to it.
No, I don't think that is correct. The frequency is much higher than a mains hum, which is two and a bit octaves below middle C. It is more like little shots firing off so you hear the frequency generated by each arc.
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