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Strong Eagle
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Postby Strong Eagle » Wed, 23 Jan 2013 7:51 am

x9200 wrote:It has the door bell wiring running 400VAC.


No way a door bell runs on 400VAC, unless the guy that wired it is a total idiot. Always a step down transformer, usually to 16 to 24 volts to run the dinger.

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Postby offshoreoildude » Wed, 23 Jan 2013 8:01 am

Strong Eagle wrote:
x9200 wrote:It has the door bell wiring running 400VAC.


No way a door bell runs on 400VAC, unless the guy that wired it is a total idiot. Always a step down transformer, usually to 16 to 24 volts to run the dinger.


If he's using a DMM parasitic coupling can do very weird things with high input impedance devices. Perhaps he was measuring live to earth as well.
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Postby x9200 » Wed, 23 Jan 2013 9:38 am

He was measuring L-N and there was no bell installed nor any description but the cables appeared too thick so he checked them out.
Actually the bells running on 220-240VAC are not that uncommon (at least outside Singapore) but not on 400. And something like this happens if some shit*ty developers try to do some things quickly engaging similar class contractors. There are dozens of development from the said period like this. The list of defects in this brand new flat was pretty long with probably the most troublesome the tiles in the bathrooms, half of them cracked.

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Postby x9200 » Wed, 23 Jan 2013 9:47 am

offshoreoildude wrote:
x9200 wrote:Partly on this subject: have you actually ever checked what do you have in your power sockets or some different related places at home? In the first condo we lived it was 250-260V average most of the time and up to 300V occasionally. Even better surprise we had in the next one, brand new, built at the boom condo devel. time few years ago. It has the door bell wiring running 400VAC.


Are you using a true RMS meter? If not divide those readings by square root of 2 for a start.

At this point I can not tell as it was like 5-6y ago (the 250-260V) but I believe it was true as what made me to check the voltage was epidemic failure of a number of power adapters. Some time later it got back to more standard range. Not sure where the problem was.

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Postby offshoreoildude » Wed, 23 Jan 2013 10:49 am

x9200 wrote:He was measuring L-N and there was no bell installed nor any description but the cables appeared too thick so he checked them out.
Actually the bells running on 220-240VAC are not that uncommon (at least outside Singapore) but not on 400. And something like this happens if some shit*ty developers try to do some things quickly engaging similar class contractors. There are dozens of development from the said period like this. The list of defects in this brand new flat was pretty long with probably the most troublesome the tiles in the bathrooms, half of them cracked.

I bet the bell transformer was wired incorrectly. If done incorrectly it could actually act as a step up transformer.
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Postby x9200 » Wed, 23 Jan 2013 11:32 am

It did not look like there was any bell transformer over there. There was just a small box in the wall, that supposed to go underneath the bell, with a number of wires dangling lose. 3 of them were L-N-G with the mentioned voltage; another two connected to the door bell switch. A bit unusual combination for me.

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Postby offshoreoildude » Wed, 23 Jan 2013 12:00 pm

x9200 wrote:It did not look like there was any bell transformer over there. There was just a small box in the wall, that supposed to go underneath the bell, with a number of wires dangling lose. 3 of them were L-N-G with the mentioned voltage; another two connected to the door bell switch. A bit unusual combination for me.



Ok - I've seen those type (maybe). They use a coil to pull the chime in.

Line - coil - NO contact - Neutral.

What happens (I think - no analysis) is the coil appears to step up the AC to a DMM (by acting as an inductor and storing and releasing charge). In actuality under load it doesn't. Hence an AVO is a better meter to use in these cases.
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Postby Strong Eagle » Wed, 23 Jan 2013 2:14 pm

offshoreoildude wrote:What happens (I think - no analysis) is the coil appears to step up the AC to a DMM (by acting as an inductor and storing and releasing charge). In actuality under load it doesn't. Hence an AVO is a better meter to use in these cases.


The coil couldn't step up anything... if that were the case... unless the button was pushed and the coil energized. But I read that x9200 simply pulled the voltage off a couple of leads.

Besides... and I could be wrong... it's been a long while... I can't figure out how a coil could increase voltage (apparent or otherwise) to a high resistance DMM.

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Postby offshoreoildude » Wed, 23 Jan 2013 5:05 pm

Strong Eagle wrote:
offshoreoildude wrote:What happens (I think - no analysis) is the coil appears to step up the AC to a DMM (by acting as an inductor and storing and releasing charge). In actuality under load it doesn't. Hence an AVO is a better meter to use in these cases.


The coil couldn't step up anything... if that were the case... unless the button was pushed and the coil energized. But I read that x9200 simply pulled the voltage off a couple of leads.

Besides... and I could be wrong... it's been a long while... I can't figure out how a coil could increase voltage (apparent or otherwise) to a high resistance DMM.


It's a coil ... on AC... magnetic field charges and collapses... It's too long ago for me but I really don't like high Z DMM's for this type of work. False readings are too common.
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