use conduit as neutral in low-voltage system?

Hi, I'm planning a remote control lighting system. There are two parts of this system: 1) the low-voltage 24VAC signalling side and 2) the 120VAC power side. Each side runs in its own separate thickwall conduit.
I understand that conduit can be used as the grounding (green) conductor in many cases, but my question concerns NEUTRAL (white) in a low voltage system.
Can I use the conduit as NEUTRAL (white) on my 24VAC low-voltage side? If not why not?
--zeb
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thing? No idea what code says, but it seems a pretty silly way to save ten bucks worth of wire. And if that conduit is bonded to the house ground and therefore the other conduit, I forsee lotsa problems with GFCIs and misc. electronics in the house.
But I'm no EE or licensed electrician, so I'll step aside now and let them weigh in.
aem sends...
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ameijers wrote:

I would also worry what might happen if a fault put 120V on that conduit.
--
Joseph Meehan

Dia duit
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You need local help.
A neutral is a grounded conductor. How long do you think your transformer will work with one side grounded?
If your running conduit is one more wire that big of a deal?
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This is a good question. If the transformer secondary and its load is a closed circuit, why would having it connected to ground cause a problem?
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wrote:

Grounding the transformer or the conduit is not the problem. The problem is using the conduit as a current carrying conductor. There are many more currents flowing through conductive surfaces than just the circuits that are intentionally made. Electrical currents happens from chemistry, thermopile, magnetics, RF, and transient voltages that are induced when AC current flows through wires enclosed or passing over ferrous metal pipes, conduits and metal sheets.
When these currents are induced they either build up as in a capacitor.......or they flow to ground where the free electrons can do whatever free electrons do. Anyway there are thousands of these little circuits that come an go. With electronic devices everywhere, transient voltages often work against the purposes of the intentional electronics. Sometimes they cause momentary failure..........sometimes blowouts. Everybody knows blowouts happen........they just don't know why.
So we understand enough about electricity and electronics to make things work, but we really don't understand everything that is happening. We adopt certain rules and standards as we discover problems. Our standards change as we learn or think we learn more. One of the standards we have adopted is that we don't intentionally use conduits as current carrying conductors. Yes, it will work........but it can cause some of the other problems that I have written about and some that I have not.....and most likely many that we don't even know exist.
Randy R. Cox
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Randy Cox ( snipped-for-privacy@airmail.net) said...

I agree with this, however Randy's text goes into a pretty complicated line of reasoning. I don't disagree with it, but let me offer a simpler reason...
It is the same reason why the neutrals and grounds are only tied (bonded) together at the service entrance. Neutrals are groundED conductors and grounds are groundING conductors.
Grounded conductors (neutrals) are bonded to ground but are designed to carry current. Grounding conductors (grounds) are not designed to carry currents under normal load conditions, only in exception cases for safety purposes. Think of a grounding conductor as a reserved lane for emergency vehicles only on a highway! ;-)
Under normal load conditions, neutrals carry current and since we don't live in the theoretical world of high school electricity in science class where conductors have ZERO resistance, the tiny resistance in the neutral causes a voltage drop to occur (voltage = current * resistance). This means that other than the spot where the neutral is bonded to ground, all other neutral points are not truly ground.
If you used a conduit to carry a neutral current, it would not be at true ground potential, depending on the actual load current. If you touched such a conduit at the same time as touching a nearby metal water pipe, you could be alerted to the fact pretty quickly! :-O
In the case of a LOW voltage system, the problem is actuall worse since higher currents are needed for the same power! A 50 watt lamp only draws about 0.42 amps if it is designed for 120 volts, but a 50 watt lamp for a 24 volt system draws 2.1 amps! Any voltage drop on the conduit would be FIVE times worse.
Now, the original poster did say that the 24 VAC wiring was for signalling, so there is less likely a problem with voltage drops, but a signalling system may be very susceptable to noise if the conduit were to be used for a neutral conductor.
--
Calvin Henry-Cotnam
"I really think Canada should get over to Iraq as quickly as possible"
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On 05 Mar 2006 19:10:36 GMT, snipped-for-privacy@remove.daxack.ca.invalid (Calvin Henry-Cotnam) wrote:

Thanks, and thanks to Randy too.
Randy's helped but I did follow this one better.

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snipped-for-privacy@hotmail.com wrote:

This is probably a matter of local code. For instance, some low voltage systems have lights that hang from 2 exposed wires. Sometimes those wires have to be insulated, sometimes they do not.
Im going to bet though that the answer is NO since no electrician would expect the conduit itself to be energized. It could be dangerous for folks doing work. Plus other reasons I can think of.
--
Thank you,



"Then said I, Wisdom [is] better than strength: nevertheless the poor
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