Need some guidance

Unless you have an open/disconnected neutral, shouldn't the neutral in any situation always be at 0 volts (since it is after the load)? Well, maybe not exactly zero volts due to resistance in the wire, but always under a volt or two. If you were sharing a neutral between two circuit breakers, wouldn't the neutral have to be upsized to handle the max current of both breakers at once? In other words, if you had 2 20A breakers, the neutral would have to be sized for 40A.

And how did you drain enough power through your body to make the lights dim and be conscious enough to notice them dimming?

I suspect you have a weak neutral connection someplace. I know in an old office I worked in (a converted house) we had a bad neutral connection at the main meter (or someplace under the power companies control), you got a nice tingle when you touched any faucets.
 
The problem is if during the course of your wiring work on the circuits, you disconnect the neutral. On the load side of that neutral, you are now connected through the load to the "other" live phase that's still powered on. In other words, the power is going like this:

other phase---load---WayneW---ground :D

The voltage will divide up between the resistance of the load and your body's resistance...

The real issue is that when you're working on a circuit that you thought was completely powered off, that shared neutral is just waiting to bite! By having mechanically linked breakers on each side of that circuit, they both turn off together.

With a shared neurtral, the neutral current will be 0 amps if the loads on each phase are the same, because the two phases are 180 degrees out of phase. It is in fact a center tapped transformer (where the neutral is the center tap). Thus current flows in trough one phase, through both loads, and then out the other phase. If the current draw is not the same on both phases, then the neutral will conduct the difference. So the worst case for the neutral is when one phase is drawing 20 amps and the other phase none, in which case the neutral will handle the full 20 amps too.
 
I agree, linked breakers should be required. What if somebody rearranged the breakers without realizing there was a shared neutral involved? Both breakers could end up on the same phase and the neutral wire could could end up carrying twice it's rated load!
 
Yeah, thats what I was thinking. I thought somebody mentioned 110V circuits with a shared neutral, which certainly could be on the same phase. I didn't think that sharing a neutral was a good idea unless it was a 220V circuit with linked breakers, but I am not a real electrician.
 
I'm going to have a chat with my electrician friend and tell him what happened and see what he says. It sounds like what Guy said - 1 circuit off, other on, so the neutral on off circuit carried full load. I did not have to keep holding the wire while it dimmed :) , once the short happened and I got bit (and let go right away), it caused the UPB switches on that line to dim all the way down and then back up. I would think though that was a short and should have tripped the breaker? Either way, the switches are fine and I'm fine. There was only one fatality later on - my nippy cutters. :D
 
Neutral always shares the same reference voltage with ground unless the neutral has a high resistance in its path (bad connection) or the current passing thru it from another circuit is extremely high (or a combination of these factors). When I mean high it is that the line resistance raises the voltage above 42 volts. I understand that 42v are safe yet for most people, but 48 is not. Have you touched the telephone line when it rings? Cool, isnt it? :D

Any of those conditions are enough for assuming that you have an electrical fault. Its a good idea to consult with your electrician friend.

About being conscious, there's a specific current amount that is really dangerous (fall unconscious, heart stops). I dont remember the number , but I believe that it is about 0.1 Amps. Anything higher might burn you to death, but will not cause you to stop your heart/brain. Its impossible to tell which voltage is gonna cause it since each person conducts differently.
 
Time to geek out here...

The danger of an electric shock depends on the current (in milliamperes), duration and the current's path in the body:

* 1 mA causes a tingle
* 5 mA causes a slight shock
* 50 to 150 mA may result in death, e.g. through rhabdomyolysis (muscle breakdown) and resultant acute renal failure
* 1-4 A causes ventricular fibrillation
* 10 A causes cardiac arrest (only at this current will a typical home fuse break the circuit)

Currents through the heart and the nervous system are the most dangerous. As most dangerous sources are voltage sources, the current present depends on the resistance of the body between the points of contact and any current limiting built into the source.
 
It is not a good idea to connect a UPB switch to ground. It has been done and it works but I would not recommend it... for many of the reasons previously stated.

In a switch J-box with no neutral it is likely that the two wires running to the switch are connected between Line at the load and and the load. Line and Neutral are at the load. There are a couple of options:

1) Use a fixture module at the load and a Dedicated Remote (USR) at the switch location. The two wires from load to switch would be connected at the fixture module to the brown/white wire and the white wire... same connection at the USR. Unfortunately there is no source for the LED on the USR in this configuration.

2) Use a fixture module at the load and rewire the Line and Neutral at the load so the two wires running to the switch J-box are Line and Neutral. Install a UPB switch and configure as a virtual remote to control the fixture module. This is a more costly option but more versatile.

Brad
 
TonyNo said:
Currents through the heart and the nervous system are the most dangerous. As most dangerous sources are voltage sources, the current present depends on the resistance of the body between the points of contact and any current limiting built into the source.
Skin resistance is usually 30-40 KOhms, depending on how thick skinned you are :D. Very small currents can be deadly if skin is punctured.
 
It is not a good idea to connect a UPB switch to ground. It has been done and it works but I would not recommend it... for many of the reasons previously stated.

In a switch J-box with no neutral it is likely that the two wires running to the switch are connected between Line at the load and and the load. Line and Neutral are at the load. There are a couple of options:

1) Use a fixture module at the load and a Dedicated Remote (USR) at the switch location. The two wires from load to switch would be connected at the fixture module to the brown/white wire and the white wire... same connection at the USR. Unfortunately there is no source for the LED on the USR in this configuration.

2) Use a fixture module at the load and rewire the Line and Neutral at the load so the two wires running to the switch J-box are Line and Neutral. Install a UPB switch and configure as a virtual remote to control the fixture module. This is a more costly option but more versatile.

Reviving an old thread here...

I found a switch in my house that does not have neutral in it (I have ~30+ UPB switches installed, this is my first). Are the two options above still the best options? With the new products available, is there a better way to do this?

Thanks
 
I believe this is still the option for this kind of installation.

Have you seen the PCS fixture modual, FDM2-4 seen here
FDM2_4.jpg
This is much smaller than the wired in fixture moduals of SA, about an inch wide and only about 2 inches long. Designed to snap into a knockout. The picture doesn't show it but the dimmer version can operate 2 loads. (totaling 400w)
I have not used one but with a 5 year warrenty it must be pretty solid.

Dave
 
I like the PCS inline better than SAI. SAI is only rated to 12A (and mine burned up at 11.5A). I replace it with a PCS that is rated at 20A.
 
I have installed several of the PCS fixture modules. Just be aware of the type of load you are switching. I had to install 120V relays on some RAB metal halide lighting. The ballasts on the RAB MH lights would kick out if only controlled by the fixture module. With the addition of the relay it has been quite reliable. I wouldn't have believed it until I was under a RAB MH light one night and I saw it turn on then immediately turn off.
 
I am sure this is going to raise eyebrows but here is a question: Can you use the ground for the neutral? If you opened up your panel you would see that the ground and neutral are really one in the same. I am sure this isn't up to code but the alternative to re-feeding those switches seems overly complicated.

Just a thought and I am not suggesting you do it. I just through I would toss out that idea. Also if there isn't a neutral in the box what type of wire is in there? If there isn't a neutral maybe there isn't a ground either...

Neil
 
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