# Phase block acceptable voltage difference



## just the cowboy (Sep 4, 2013)

When did you see volts on secondary side? Your post reads as it was there before racking in main.


If I am reading this correct the 17-20 volts was on the same phase but across the reactor, and that went away after power up. I would say ghost voltage, use a low Z meter and I think that would go away.


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## Apelectric (Dec 6, 2017)

just the cowboy said:


> When did you see volts on secondary side? Your post reads as it was there before racking in main.
> 
> 
> If I am reading this correct the 17-20 volts was on the same phase but across the reactor, and that went away after power up. I would say ghost voltage, use a low Z meter and I think that would go away.


Yes voltage on the secondary side of both the main and the reactor pts. 

The voltage was on the same phase(for example a phase main to reactor a phase).


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## paulengr (Oct 8, 2017)

There is a problem especially with vacuum switchgear. The very small gaps in the vacuum bottles are basically capacitors. So measuring on the secondary side is effectively like seeing a capacitive tap. It's harmless and you won't even get an arc when you are installing or removing a personal protective ground, but it's very spooky.


If you want to call it that, the limit for shock purposes is always 50 V or less, except in one province in Eastern Canada where they made the limit 30 V, which is a real problem because even telecommunication equipment exceeds that. Nobody has ever died at under 50 V, except some rare (and questionable) exceptions like a Canadian researcher that was reading several Chinese safety reports where even he admitted that the credibility was suspect.


If you use bracket grounding, you can unintentionally induce voltage into the line because it forms a loop through the Earth (line to first ground cluster to Earth to second ground cluster and back to line) which then acts as a transformer and induction from nearby lines can energize the one being worked on. That's one scenario. Wind can also induce voltage as well as a second parallel line run closely together for several miles. Never mind 60 Hz inductive pickup from almost anywhere.


Best thing to do is to use equipotential grounding. Then it doesn't matter because the voltage is ZERO where you stand regardless of what else is going on. That's why OSHA switched a few years ago and now mandates it. Granted there are cases where it doesn't work that well but there are many more proving that it works.


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## B-Nabs (Jun 4, 2014)

paulengr said:


> There is a problem especially with vacuum switchgear. The very small gaps in the vacuum bottles are basically capacitors. So measuring on the secondary side is effectively like seeing a capacitive tap. It's harmless and you won't even get an arc when you are installing or removing a personal protective ground, but it's very spooky.
> 
> 
> If you want to call it that, the limit for shock purposes is always 50 V or less, except in one province in Eastern Canada where they made the limit 30 V, which is a real problem because even telecommunication equipment exceeds that. Nobody has ever died at under 50 V, except some rare (and questionable) exceptions like a Canadian researcher that was reading several Chinese safety reports where even he admitted that the credibility was suspect.
> ...


Canadian volts are stronger

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