Questions (correction)

[Josesaucedo]

Thanks for taking the time to answer my questions.
These are homework questions, and for question 1 a had to make a correction. It is branch circuit.

1) How is branch circuit mechanical grounding accomplished with EMT?

2) How is grounding of the receptacles accomplished with METAL SURFACE RACEWAY?

3) I have some lights and some receptacles. Couple of lights with couple of receptacles connected from circuit breaker 1, couple more lights & receptacles connected from circuit breaker 2 and couple more lights & receptacles connected from circuit breaker 3. Circuit breaker 1 & 2 are connected fro phase line 1, and circuit breaker 3 from phase line 2. Circuit breaker 1 & 2 have their own neutral conductor, and circuit breaker 3 has its own neutral conductor as well. The question is:

What would happen to the grounded (neutral) conductor if only one grounded conductor were used for this project?
Thank you very much.[/b]

 

[charlie b]

1. The phrase "circuit mechanical grounding" does not make any sense. The word "mechanical" has no business being in that phrase. If you are asking how EMT can serve as an equipment grounding conductor, all that is needed is that there be a continuous metal-to-metal connection of the EMT and its fittings and wiring devices from the load (e.g., from the grounding pin of a receptacle) to the source (i.e., to the ground bus of the main panel).

2. In the same way described above.

3. The first thing is that you would be in violation of 210.4. That section allows multi-wire circuits. However, Article 100 defines multi-wire branch circuits in such a way as to require there to be a voltage between any two ungrounded conductors. Your wires coming from circuits 1 and 2 do not meet that definition. So you cannot have a multi-wire branch circuit that uses the same neutral for circuits 1 and 2.

The next thing is that you would have to put all four wires (actually, you would need 5, as I mention above) in the same conduit, because of 300.3(B). Therefore, you would have to derate the ampacity of all conductors, because of 310.15(B)(2)(a).

Finally, the neutral that you use to serve circuits 1 and 2 (which as I said, is a violation) could become overloaded, and no overcurrent protection would be available to prevent it from being damaged. You could run 20 amps through circuit breaker 1 and 20 amps through circuit breaker 2, and no load on circuit breaker 3, with the result that 40 amps will flow through the neutral, and no breaker would trip.

 

[George Stolz]

Jose,

A key to Charlie's answer that may not immediately leap out to you is that panels are labelled "odds left" and "evens right."

This means that 1 and 2 share the same bus, so they are not a multiwire circuit. They are side by side, horizontally.

1 & 3 would be, because they use two different phases (busses). They are side by side, vertically.

 

[don_resqcapt19]

George,
While you are correct that the majority of panels are labeled that way, some are not. There are no rules that require that numbering method. Some panels number starting at 1 at the top left and number down consecutively to the bottom and then jump to the upper right. Many panel directories provided with panels are printed on both sides letting you use either method.
Don