kwired
Electron manager
- Location
- NE Nebraska
Bathroom fan/light/heater - I almost always run power to switch box than 2 - 12-2's to the unit.
2 romex cables 12/2, why they do this?
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
Or a 12-2 and a 12-3 for a fan/light/heater/night-light combo.
brother
Senior Member
Interesting responses.
This scenario I have seen here is the main feed hot and neutral was ran to the light box first then the (hot only) to the switch box. So basically if they have the hot and neutral in one cable and the switch legs in the other cable, the switch leg cable wont have the counter emf to reduce the inductance/heat. I thought this was a code violation . If they use both cables as just a hot and switch legs , one for fan and one for light, then there is no neutral at the both, which is also a code violation.
Am I still missing something here?
This scenario I have seen here is the main feed hot and neutral was ran to the light box first then the (hot only) to the switch box. So basically if they have the hot and neutral in one cable and the switch legs in the other cable, the switch leg cable wont have the counter emf to reduce the inductance/heat. I thought this was a code violation . If they use both cables as just a hot and switch legs , one for fan and one for light, then there is no neutral at the both, which is also a code violation.
Am I still missing something here?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Yes. For balanced current to flow in a pair of conductors, it is not necessary for one of them to be a neutral (grounded). A hot to a switch and the return to the light will also carry the identical current.
Having a neutral to a switch has nothing to do with the above comment; it's for electronic switching.
brother
Senior Member
I understand that about the balance current flow, i was looking at how they they may have this going without it technically being a code violation. I still see a code violation on a technicality. Like i said, if they use each cable as a hot and switch leg for the 2 switches they will have balance current flow, but then the there is a code violation because there is no neutral at the 2 switch box per the new requirements of the nec because the source feed is at the ceiling fan light box.
If they use one cable as a hot and neutral (just to get the neutral at the box per nec) then the other cable will have the 2 switchlegs but then its a code violation because the 2 switchlegs cable will not have the counter emf to cancel out. That neutral requirement for switches at their location (just the possibility of future automatic switches) makes things a little more challenging .
and yes I do believe that 12/2 cable is probably all they had on the truck at the time, but its still a code violation from the way the install is done.
Seven-Delta-FortyOne
Goin’ Down In Flames........
- Location
- Humboldt
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- EC and GC
End-of-line-3-way and no 12-4 on the truck is the other possibility.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The simple solution is to use one re-colored white to feed both switches, and the other white for the neutral.
As long as the two cables are run together, especially through KOs in metal, there is no induction problem.
winnie
Senior Member
- Location
- Springfield, MA, USA
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- Electric motor research
The key to the fields around the wires balancing is their proximity and the materials between them.
Take the situation you are concerned about. It would be a code violation to run the conductors in separate emt raceways.
It would be a code violation to run the conductors in separate MC cables.
In fact in general what you describe is a code violation.
But in the specific case of NM cables and NM boxes, or NM cables all passing through the same openings in metal boxes, the inductive effects are small enough that code permits the installation.
Additionally if the two cables are run side by side the magnetic cancellation is effectively the same as a single cable enclosing all the conductors.
You are exactly right about the voltage and current balancing effects. It is simply that for NM cables the effects are small enough that code permits the installation.
Jon
Take the situation you are concerned about. It would be a code violation to run the conductors in separate emt raceways.
It would be a code violation to run the conductors in separate MC cables.
In fact in general what you describe is a code violation.
But in the specific case of NM cables and NM boxes, or NM cables all passing through the same openings in metal boxes, the inductive effects are small enough that code permits the installation.
Additionally if the two cables are run side by side the magnetic cancellation is effectively the same as a single cable enclosing all the conductors.
You are exactly right about the voltage and current balancing effects. It is simply that for NM cables the effects are small enough that code permits the installation.
Jon
kwired
Electron manager
- Location
- NE Nebraska
done that as well.
Also have run two 2 wire cables between switch boxes when needing both L1/L2 as well as a set of three way traveler conductors between those two boxes. Using a 3 wire cable as one of them uses 1 more conductor than you actually need.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Especially when done a lot, like I described here:
Wiring Scheme
Very basic here but would like input So if a neutral is required at the switch because your not using a raceway or can't access the switch to pull a neutral in the future would you run wiring like this? See pic( bad drawing). My main question is getting power/neutral to each switch. So you...
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