Author Topic: 230VAC outlet measures 100VAC against grounding contact. WTF?  (Read 1971 times)

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Online Benta

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Re: 230VAC outlet measures 100VAC against grounding contact. WTF?
« Reply #25 on: July 30, 2018, 09:30:45 am »
For an RCD to work, somewhere upstream of the RCD something must be connected to ground. Otherwise a fault will not make a circuit capable of tripping the RCD.
Eg: A RCD on the output of a transformer has no effect. One of the output terminals must be grounded.

I think we can all agree on this?

Yes, of course. This usually happens at the utility transformer and depending on code/country at the building. A fully floating supply would not require an RCD, as no ground fault is possible.

 

Offline Zucca

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Re: 230VAC outlet measures 100VAC against grounding contact. WTF?
« Reply #26 on: July 30, 2018, 10:12:34 am »
To ground, of course, eg, a water pipe or whatever. That's why it's called a ground fault.

That's why a RDC with PE is much better than a RDC without PE because the faulty current will find his way through the PE cable.
On top of that with PE the RCD will trip without you touching the faulty device and carring the current to the ground with your body. Worst case of course.
Nobody will die, because the RDC should be designed properly; still you will feel the 220VAC on your body. Not nice.

This is why I think a RDC must have a PE to work properly at 100%, yes it will work also without but in a safety point of view the two system are not even comparable.
« Last Edit: July 30, 2018, 10:17:42 am by zucca »
Can't know what you don't love. St. Augustine
Can't love what you don't know. Zucca
 

Offline Jeroen3

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Re: 230VAC outlet measures 100VAC against grounding contact. WTF?
« Reply #27 on: July 30, 2018, 10:52:35 am »
Theoretically an RCD can still work without any ground, current just has to run trough some different path around the RCD. Some other live or neutral for example.
But these faults are rare.
 

Offline capt bullshot

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Re: 230VAC outlet measures 100VAC against grounding contact. WTF?
« Reply #28 on: July 30, 2018, 11:40:46 am »
Yes, it is unsafe and shite. Sadly, for buildings erected pre 1974/75, it is absolutely fine* to only have two-strand wiring running in the walls.
For what you are proposing a third strand is needed.
It may be legal to leave the existing two-conductor wiring in place. What is NOT okay is to bond neutral to PE at the outlet, since that puts live electricity on the chassis of connected equipment.

Connecting the PE pin to Neutral is the usual way to deal with 2wire-wiring here. You'll find many homes using this old standard. Of course, one cannot use this wiring for new installations, but there's no obligation to change it.
So if you're working on such old installations, always triple check, don't expect anything to conform to todays conventions.
Safety devices hinder evolution
 

Offline sokoloff

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Re: 230VAC outlet measures 100VAC against grounding contact. WTF?
« Reply #29 on: July 30, 2018, 11:43:05 am »
Outlets with grounding contact have to be grounded all the time. An RCD on that system would mean, that PEN would also be switched, thus breaking the grounding rule.
This is not the case in the US under National Electric Code. In legacy buildings, we are allowed to use a ground fault interrupter to protect circuits which have 3-prong (grounding) outlets downstream. Those outlets need to have a sticker saying “No equipment ground” on/near them. NEC 250.114(3).

It is not permissible to cross-connect ground and neutral in such outlets (or anywhere other than the initial service entrance).

It is true that grounded outlets with connected grounds need a full-time (unswitched) ground, but your exact situation is covered as an exception to that rule under NEC.
 

Online amyk

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Re: 230VAC outlet measures 100VAC against grounding contact. WTF?
« Reply #30 on: July 30, 2018, 11:53:59 am »
https://en.wikipedia.org/wiki/Ground_and_neutral
https://en.wikipedia.org/wiki/Earthing_system

Some good reading for those interested. It's interesting how different it is across countries.
 
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