Author Topic: Oscilloscope and no proper grounding  (Read 8991 times)

0 Members and 1 Guest are viewing this topic.

Offline c4757p

  • Super Contributor
  • ***
  • Posts: 7805
  • Country: us
  • adieu
Re: Oscilloscope and no proper grounding
« Reply #25 on: July 03, 2013, 04:54:07 pm »
In the US, The neutral is tied to ground at the breaker panel in the house. So, They are at the "same potential".

This assumes that you live in an inductance-free world with wires that never fail.

I just measured almost half a volt here, and the only things running on this circuit are my laptop, the multimeter, and a small fan. You'll get some nice, big spikes when motors stop and start.
« Last Edit: July 03, 2013, 04:58:07 pm by c4757p »
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline richcj10

  • Supporter
  • ****
  • Posts: 201
  • Country: us
Re: Oscilloscope and no proper grounding
« Reply #26 on: July 03, 2013, 05:55:45 pm »

I just measured almost half a volt here, and the only things running on this circuit are my laptop, the multimeter, and a small fan. You'll get some nice, big spikes when motors stop and start.

 Across what?
 

Offline c4757p

  • Super Contributor
  • ***
  • Posts: 7805
  • Country: us
  • adieu
Re: Oscilloscope and no proper grounding
« Reply #27 on: July 03, 2013, 05:58:42 pm »
Neutral to ground.
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15379
  • Country: za
Re: Oscilloscope and no proper grounding
« Reply #28 on: July 03, 2013, 06:26:09 pm »
Many people do a lot of things out of necessity that are not ideal.  Just this afternoon, I was driving to the surplus place, and someone in a white car was dodging through traffic, tailgating, hitting their brakes repeatedly, weaving around, and finally cut across two lanes of traffic.  He did so without incident and no one got hurt.  The alternative of driving safely would have been much safer, but one could say that many people drive stupidly without incident.  That doesn't mean you want to tell people that it's OK to drive stupidly because everybody does it.

It's a bad example because driving stupidly is a choice, and proper grounding isn't always, but that's how I see it.  Ground if you can, and have a good reason for not doing it.  Don't just do it because you think you can get away with it.... because that's when you won't.

You mean like half the drivers and all the taxi drivers do here........

I have measured 10V between neutral and earth, and this is often the case when there are large loads on the home line.
 

Offline c4757p

  • Super Contributor
  • ***
  • Posts: 7805
  • Country: us
  • adieu
Re: Oscilloscope and no proper grounding
« Reply #29 on: July 03, 2013, 06:30:31 pm »
In before "but 10V won't shock you!!!!"

|O
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15379
  • Country: za
Re: Oscilloscope and no proper grounding
« Reply #30 on: July 03, 2013, 06:43:17 pm »
No, but it can deliver around 100A or more into a short circuit, and the current is NOT limited by anything other than wire resistance, as there are no protective devices in the neutral or earth conductors, other than a double pole disconnector on the main supply.
 

Offline c4757p

  • Super Contributor
  • ***
  • Posts: 7805
  • Country: us
  • adieu
Re: Oscilloscope and no proper grounding
« Reply #31 on: July 03, 2013, 07:08:16 pm »
I'm not sure I follow you. Wouldn't it ultimately come from the live conductor anyway, where it can trip the breaker?
« Last Edit: July 03, 2013, 07:21:12 pm by c4757p »
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15379
  • Country: za
Re: Oscilloscope and no proper grounding
« Reply #32 on: July 03, 2013, 07:15:37 pm »
Comes from the sum of all the live feeders fed from the substation transformer, so while it theoretically is fused it would be a 400A fuse typically.
 

Offline c4757p

  • Super Contributor
  • ***
  • Posts: 7805
  • Country: us
  • adieu
Re: Oscilloscope and no proper grounding
« Reply #33 on: July 03, 2013, 07:20:54 pm »
...  |O yes, the rest of the world isn't wired like the U.S., one transformer per 1-4 houses...
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15379
  • Country: za
Re: Oscilloscope and no proper grounding
« Reply #34 on: July 03, 2013, 07:28:48 pm »
Here it is more like one minisub for around 100 houses, or more for the older suburbs. At work I share a 250kVA minisub with another 5 businesses, about 30 flats and a hotel.
 

Offline madires

  • Super Contributor
  • ***
  • Posts: 5123
  • Country: de
  • A qualified hobbyist ;)
Re: Oscilloscope and no proper grounding
« Reply #35 on: July 03, 2013, 08:31:32 pm »
In the US, The neutral is tied to ground at the breaker panel in the house. So, They are at the "same potential".

But only at the point where they are connected together. Since neutral is the return path for hot the current flowing through neutral causes a voltage drop. That voltage drop increases with the wire length and the load attached to it. 
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf