Electrical Daisy-chained, parallel or series? (failed outlets in home)

[dlgoff]

... but their stories can be read here.

Here'a a story for you. I was helping a lady install an outlet in her small house. She pointed out where she wanted it. Sounded simple enough, just had to cut a hole in some dry-wall, install a box and feed some romex wire down to the box between the wall studs. Well while cutting the hole for the box, fire flew. Turned out the lady had done some electrical work on her own. She had added a circuit to somewhere and buried her wire on the surface of the dry-wall with dry-wall mud. She did have it pretty smooth.

 

[fog37]

Reflecting back on this thread, I was thinking about the following:

In an oversimplified view, devices, appliances, etc. all electrical loads in the house are connected to the panel (which is connected to the electric grid) in a parallel fashion. There are, I believe, sub-circuits in the house. Each sub-circuit is connected to the panel and each sub-circuit comprises several outlets all inter-connected in parallel so the loads connected to those outlets are also all in parallel. A parallel connection is such that if one outlet and/or device connected to it fails, all the other devices continue to operate undisturbed.

In the case of a GFCI outlet, the situation is slightly different: the GFCI outlet is connected in parallel and so are the devices connected in parallel (daisy chained) to the GFCI itself. When a GFCI outlet fails, all the outlets downstream fail too even if they are in connected parallel. My interpretation: when the GFCI fails is it is as if it was disconnected from the panel and so are all the outlets parallel-connected downstream to the GFCI.

Any error in my thinking?

Also, the non contact pen that I used to see if which wire was HOT can only work with AC voltage. The pen would not be able to detect a DC voltage since DC voltage can only be measured considering two points (2 wires). AC potential difference $\Delta V_{AC}= V_2 - V_1$, on the other hand, is a time-varying difference that can be detected even using a single wire. However, since there must two potentials $V$ to take a difference $\Delta V$, The other "wire" can be any other objects with some finite conductivity in the environment.

Thanks as always.

 

[sophiecentaur]

Any error in my thinking?

It's fine if you restrict the description of a GFCI outlet in terms of the practice where you happen to live. Most 'Protected Sockets' in UK will only protect the appliances that are plugged into them. In UK, AFAIK, if you want a protected circuit, then the GFCI will be part of the distribution unit (the 'fuse box'). It worries me that, with the arrangement you describe, there could be one outlet to the right of a GFCI outlet and one on the left of it and you would have no idea which one was protected for a ground fault, without using the test button (or opening up the wiring to look at it).
But, of course, there is no 'downstream' in a ring main circuit and the GFCI would not actually protect any of the other appliances on the ring because the 'other path' would always be connected.
Different strokes.

 

[pbuk]

I have been thinking: the GFCI outlet has two hot connections (top hot is for the hot line, bottom is hot load) and two neutral connections (top is return line, bottom is return load). I connected the black wires and white wires the way they were connected on the GFCI that I replaced...

However, is it possible that the new GFCI outlet is not working because of line-load reversal: the black line hot wire may be connected to the GFCI hot load connection instead of to the GFCI line hot connection?
Same for the load lines: maybe the load return is connected to the the GFCI line return connection and the line return is connected to the GFCI load return...

Is the line cable always on the left and the load cable always on the right on the inside of the receptacle like in the figure below? MY receptacle looks like that with a cable on lower left and a cable on the lower right...

View attachment 276335

How can I verify that line-load reversal is not happening using a voltmeter? I guess I can check the voltage between the hot and neutral for each cable with the breaker on and no GFCI outlet connected to identify the load and line cables...

If you are this uncertain about what you are doing you should not be touching any wiring, call in a professional.

 

[pbuk]

It's fine if you restrict the description of a GFCI outlet in terms of the practice where you happen to live. Most 'Protected Sockets' in UK will only protect the appliances that are plugged into them. In UK, AFAIK, if you want a protected circuit, then the GFCI will be part of the distribution unit (the 'fuse box'). It worries me that, with the arrangement you describe, there could be one outlet to the right of a GFCI outlet and one on the left of it and you would have no idea which one was protected for a ground fault, without using the test button (or opening up the wiring to look at it).
But, of course, there is no 'downstream' in a ring main circuit and the GFCI would not actually protect any of the other appliances on the ring because the 'other path' would always be connected.
Different strokes.

In the UK we use the term Residual Current Device (RCD), not GFCI. The current standard for domestic electrical installation requires that all circuits are protected by an RCD in the consumer unit (distribution board); sockets with RCDs built in are available and can be fitted in a house with older wiring.

It worries me that, with the arrangement you describe, there could be one outlet to the right of a GFCI outlet and one on the left of it and you would have no idea which one was protected for a ground fault, without using the test button (or opening up the wiring to look at it).

Yes, this seems a very bad idea to me. The protected live and neutral on a UK RCD are only accessible through the appliance socket so daisy chaining is not possible.

Discussing wiring on an international forum is not a good idea: what is common practice in one country could be potentially lethal in another.

 

[hutchphd]

Any error in my thinking?

First let me reiterate the "always consult a professional" if you have any doubt. I think there are some US jurisdictions that require professional inspection of your work. This is certainly true if it is a rental property. And the killer issues for me are fire related. Shocks are unpleasant but seldom directly fatal.

That being said I believe your understanding is correct. And the existence of the "ring circuit" was unknown to me until a few years ago. I think it is virtually unused in US. Good luck.

 

[sophiecentaur]

Discussing wiring on an international forum is not a good idea: what is common practice in one country could be potentially lethal in another.

It has its downside but knowing something of what goes on 'over the pond' allows one to make sense of some of the comments that 'they' often make. (This applies in both direction!)
You will always find caveats inside these discussions and the 'compare and contrast' theme runs through most of these threads.
I have a feeling that the 110V system is regarded as much safer than the 240V system and, consequently, people are much easier about regulations and practices. US members always deny this strongly but I can only react to the images of US installations that are often posted on PF. Terrible bodges exist on both sides, of course, but I refer to postings from reputable US engineering types. I'm sure my reactions are based on my automatic assumption that "there's 240V about". Of course, there is a fair amount of 'double Volts' on domestic US. I wonder if there's a European-style worry about that, when they've had generations of 110V built into their instinct.