Using Ground as Neutral

[Chiba]

Ok - points are very well taken. It's either a no-neutral switch or I rewire to bring in a neutral.

Thanks for the feedback!

- Jared

[kepartin]

You can only (by code) share the neutral with two hot wires if the two hot circuits are on different phases. I had an inspector out and he caught me on this. Fortunately that was not what he was there to inspect, so he just mentioned it to me and let it go (after I promised to fix it).

This is actually not an uncommon situation. In my situation I was running 12/3 with ground - a red hot, a black hot, a shared white return, and ground. I had both hot wires terminating into 20 amp breakers on the same phase -- potentially subjecting the return to 40 amps of current. I guess derating the breakers would reduce the risk, but it would still violate the code.

[gcyeaw]

Michael,
You are correct in the fact that it will work. The issue is the safety of anyone working on the electrical system and potential hazards. If you ignore the electrical code you introduce conditions that may put people at risk of shock or even death. The person responsable for the situation may have passed on, and the new person (maybe your wifes new boyfriend?) could be seriously injured by the unpredictable design. (maybe you would approve of that) However, The main concern is that the built in safety of GFI circuits, etc could be compromised. I would hate to hear that one of your children was injured due to a failure of a GFI circuit, say in the bathroom.
The final lesson here is, don't fool around with the safety of your family for something as unimportant as home automation.

I know, I sound like I am preaching here, but i am fully aware of the consequences of ignoring published safety standards, and it isn't worth the consequences.

Gardner

[General Patton]

I know that a lot of older construction does not have a neutral in the switchbox but how common is this in new construction? Is it common practice now to have a neutral in the switchbox.

We are going to be moving this year and will probably be going the new construction route.


Thanks,

[chrkov]

Well, it all depends. Most electricians only run what need to be run. So a basic switch doesnt require a Neutral so to a switchbox that is not a junction point, you very well might not get a neutral. My brother had a house built last year and wants to do the automation stuff. So I told him to tell his electrician to run neutrals to every box in the house. They did do this and it was really pennies to do.

[jcc]

First off, 2 10 Amp breakers do not make a 20 Amp. circuit unless they are in parallel. Secondly 10Amp breakers for a distribution panel are a myth.

When supplying a load with 230/115 voltage comprised of a double pole breaker feeding 2 live wires, and a neutral, the important thing is to have as close to equal current (Amps) flowing in both circuits to minimise neutral current.

Standard home lighting circuits have 2 methods (not including 3 way) of wiring.

1) Power comes into the fixture box with a loomex 2/14 (black & white), a second loomex 2/14 (black & red) for new homes or (black & white) for old homes, goes from the fixture box to the switch box.

2) Power comes into the switchbox with loomex 2/14, and a second loomex 2/14 goes to the fixture box.


Three way circuits have 3 methods of wiring:

1) Power comes into the fixture box with a loomex 2/14. A second loomex 3/14 goes to the first switch box. a third loomex 3/14 goes from the first switchbox to the second switchbox. In this case, the white & the black are travellers and the red is the return back to the fixture box. The neutral is not used in the first switchbox. The 3/14 from fixture to switchbox may be replaced with a 2/14 (red & black).

2) Power comes into the first switchbox with a loomex 2/14. A second loomex 2/14 goes from switchbox to fixture box. A third loomex 3/14 goes from switchbox 1 to switchbox 2. Wiring is similar to (2) except the returning red wire is spliced to the black wire going to the fixture.

3) Power comes into switchbox 1 with a loomex 2/14. A second loomex 3/14 goes from switchbox 1 to switchbox 2. A third loomex 2/14 goes from switchbox 2 to the fixture box. In this instance, the neutrals are all tied together. The red & black wires in the 3/14 are the travellers.

If drawings would help, let me know and I will post some.


JC

[Michael McSharry]

jcc, go to your local Home Depot electrical section and look next to the Cuttler Hammer 7.5 amp breakers and you should find the 10 amp ones. Don't get confused between the 10 amp ones and those skinny 20 amp ones where you can fit two in a standard width slot. Alternately if you cannot wait for your next trip to HD and are mechanically handy then something like http://shop.sailnet.com/product_info...oducts_id/6017 should suit the purpose.

As I indicated before I'm not a certified electrician and I do concur about the safety issues associated with not following code. I actually tried to illustrate thte unsafe nature of non-standard wiring in my original input about the implications to the new owner. I also hope nobody reads any seriousness into my first paragraph of this posting.

What I'm not understanding from Garnder is the relationship between the GFCI and the shared neutral. My understanding of the GFCI is that is senses the current between between neutral and ground and when it exceeds a small threshold it will trip its internal breaker. How does sharing a neutral reduce the abiltiy of the GFCI to monitor the neutral vs. ground?

[gcyeaw]

Michael,
I believe the GFCI unit actually senses the current in the supply (hot) and return (Neutral). If there is a difference then there is another path to ground, which is a problem, so it trips.


Gardner

[BraveSirRobbin]

http://www.codecheck.com/gfci_principal.htm

[Michael McSharry]

Thanks for the reference. I learned a little. It makes sense that if GFCI are on the bastard circuits that they will constantly trip which makes the circuits useless, but never the less still safe. If they are on normal circuits then I do not see how they are affected by those with dual hots.

[gcyeaw]

Michael
You are correct. If the GFCI devices are on different circuits they should not be effected.

Gardner

[stanb17]

Another Neutral question

Hi,

Since we are on the subject... (don't mean to hijack), I have started loading up my Leviton Structured Media Enclosure with what used to be my hair-ball of CAT5 hell. It looks real nice and is a work of hi-tech art.
My question is what do I ground the enclosure to? It has AC power going into it through a UPS currently only powering the switch. It also has net patch bay, telecom and cable. I have the cable splitter grounded to the enclosure, but need to ground the enclosure box iteself to something. Would grounding it to a copper cold water pipe work here?

Thanks.

Stan

[unibits]

Gfci

A Ground Fault Current Interrupter works by measuring the difference or imbalance between the supply and the neutral .

The physical connection to ground is just that, a connection to ground for any device that may be plugged into it.

A GFI, senses that it has 4 A draw on it, The neutral will have that same current value on it. If there were a leak to ground on either wire that EXCEEDED 5 milli amps, it would trip out and prevent a shock or possible electrocution.

It should be noted that on a two wire circuit with no ground, a GFCI can be installed at the beginning of a circuit, preferably at the service panel, to protect all devices in that circuit that require 3 prong devices.

Unibits

[Gogs]

Hi JC,

First off, 2 10 Amp breakers do not make a 20 Amp. circuit unless they are in parallel.

I am curios.

Being UK, I am not accustomed to the US system of phases, except when we use 3 phase over here, and then we are talking 440+ volts and 10 Amp breakers don't come into the equation.

So, a question.

How do two 10 Amp breakers or fuses in parallel make a 20 Amp breaker in the US, when over her all you have is two 10 Amp breakers/fuses? When the first blows it stops the current, the second in parallel has nothing to do.

Or did you mean in series, in which case the same thing would happen.

Sorry, just throwing balls in the air. I am imagining that your Low voltage and phases system still goes by the basic rules.

just curios as to does your basic electrical system work so different.

[Michael McSharry]

All neutrals are connected to the same bus at the circuit panel. Each hot is connect through a breaker. If two hots are returned to the panel via a single neutral, then the desire is to protect the neutral from carrying current beyond its capacity. If each hot is sourcing 20 Amps then the return neutral must carry 40 amps. This capacity is something like an 8 gauge wire. If only a 12 gauge is used and one needs to protect against the potential worst case situation, then it cannot allow more than 10 amps to be sourced from each hot.