A little help with a discussion elsewhere about plc switching neutrals

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macmikeman

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At another Q+A electrical place the question about a plc that switches the neutrals instead of the hot side of the circuits is going on.
I'm retired from grabbing a code book. We know you cant do that stuff in chapter three wiring, is it allowed for controls work?
I think not, but as always I understand I could easily be wrong about this. What say ye? P.S. I come from relay and contactor days and was taught that it was a no no to switch neutrals in controls back then.
 
As long as you think of it as switching a dedicated return for that circuit and not a common or neutral wire, the logic works out just fine.
It only calls for some different thinking when wiring the logic up.
I would not hesitate to do it for sensor or actuator wiring, but might have second thoughts about using the plc outputs to control power relays that are in the return line from the device they are powering, even it that device were Class 2 limited power.

It can also make troubleshooting more difficult if the person doing the work is not used to switched returns.

And if someone is <shudder> used to jumpering devices to hot to test them and cannot be broken of that habit, then all bets are off.
 
iwire said:
Unless they are also switching the hot it is an NEC violation for controls or not.
Click to expand...

Thank you Robert , I thought so. Anything on each laddder rung before the last resistance was hot as I was taught and after that came the neutral side bus hookups. I understand the .5 volt dc side or 24v ac side of modern controls it makes no diff, I should have elaborated a bit more to mean the 120 or higher control voltages.
 
iwire said:
Unless they are also switching the hot it is an NEC violation for controls or not. .
Click to expand...

I believe this is way outside the scope of the NEC. Look at:

90.1 Purpose.
(A) Practical Safeguarding.
The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. This Code is not intended as a design specification or an instruction manual for untrained persons.
>>> there is no, zero, zilch hazard from opening the "grounded" side of a 0.5V circuit.
>>> Consider the standard and time-honored practice of placing the NC contacts of a motor overload relay between the grounded control power wire and the coil (the coil at ANY voltage). This is done to enhance safety.

(B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of
electrical use.
>>>No safety hazard

90.2 Scope.
(A) Covered. This Code covers the installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for the following:
>>>You could ignore 90.1 and common sense.
 
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fmtjfw said:
I believe this is way outside the scope of the NEC. Look at:

90.1 Purpose.
(A) Practical Safeguarding.
The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. This Code is not intended as a design specification or an instruction manual for untrained persons.
>>> there is no, zero, zilch hazard from opening the "grounded" side of a 0.5V circuit.
>>> Consider the standard and time-honored practice of placing the NC contacts of a motor overload relay between the grounded control power wire and the coil (the coil at ANY voltage). This is done to enhance safety.

(B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of
electrical use.
>>>No safety hazard

90.2 Scope.
(A) Covered. This Code covers the installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for the following:
>>>You could ignore 90.1 and common sense.
Click to expand...

If the conductors in question in this thread are outside of the scope of the NEC, then Article 725 needs to be removed from the code.
 
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