Fan Connection wire size

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  #1  
Old 11-16-05, 08:31 AM
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Fan Connection wire size

When connecting a Bath Fan or Light Fixture to a junction box (20a circuit) can I use #14 wire?
Typically, the flex conduit connectors are prewired with #14 wire as are the fixture connectors, so it would seem that #14 wire from a J-box to an individual fixture would be OK.

Thanks, Joe
 
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  #2  
Old 11-16-05, 08:56 AM
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No. Not okay. Use #12.
 
  #3  
Old 11-16-05, 09:19 AM
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No, you cannot do this.

What you are describing is known as a 'tap'; a set of conductors that is smaller than would ordinarily be permitted by the upstream overcurrent protection, which is protected by the 'downstream' load or overcurrent protection. Taps _are_ permitted, but there are very complex and strict rules regarding tap installation and use. For example, there may be length limits, minimum ampacity limits, occupancy limits, or other 'fine print' for the proper use of taps.

The 'undersized' conductors that are a supplied part of a 'listed assembly' are essentially taps that have been tested and certified by some testing lab (eg Underwriters Laboratories). You can't take the use of these conductors as some sort of permission to use them for the entire circuit feeding the assembly. The rest of the circuit must still be sized using standard sizing rules, which require at least #12 conductors for 20A circuits.

-Jon
 
  #4  
Old 11-16-05, 09:59 AM
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Taps

Originally Posted by winnie
No, you cannot do this.

What you are describing is known as a 'tap'; a set of conductors that is smaller than would ordinarily be permitted by the upstream overcurrent protection, which is protected by the 'downstream' load or overcurrent protection. Taps _are_ permitted, but there are very complex and strict rules regarding tap installation and use. For example, there may be length limits, minimum ampacity limits, occupancy limits, or other 'fine print' for the proper use of taps.

The 'undersized' conductors that are a supplied part of a 'listed assembly' are essentially taps that have been tested and certified by some testing lab (eg Underwriters Laboratories). You can't take the use of these conductors as some sort of permission to use them for the entire circuit feeding the assembly. The rest of the circuit must still be sized using standard sizing rules, which require at least #12 conductors for 20A circuits.

-Jon
Hi Jon,

At this point, I will make this discussion an academic one. It's not that difficult to do it with #12 wire, but I'd like to know the reasoning for the rule and under what conditions a "Tap" is allowed.

The circuit is all #12 wire. The instructions with the fan and also with the recessed light fixtures indicate that there should be a flex conduit connection from a J-Box to the connection box of the fixture itself. These are typically sold at HD, etc. (3' & 6' lengths factory assembled) with #14 wires in them and 3/8" clamp connectors preattached. I have a grounded metal J-Box with NM 12/2 w/g coming in to this box which is to provide power to 1 light fixture and a fan. Another NM 12/2 wg exits the box to provide power to a 20a GFCI outlet. Connecting 3 sets of 4 #12 wires in a single J-Box is a pain and it would be easier to deal with 3 sets of 2 #12 wires and 3 sets of 2 #14 wires.

Would it not be a valid "Tap" condition to connect each of the fixtures to the circuit with these cables? Considering the amp rating of each fixture, I can't see how an unsafe condition would result.

-Joe
 

Last edited by Joe.Carrick; 11-16-05 at 10:51 AM.
  #5  
Old 11-16-05, 02:38 PM
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The situation that you described, while a _plausible_ tap design, is, as far as I know, not compliant with the NEC. If you wish to explore, I suggest that you read the section in the NEC on 'tap conductors'.

I do not know enough to explain why, but I can guess that it has something to do with how the system would respond in the event of a failure. There are many aspects of the NEC that are based on keeping things safe when something fails, rather than keeping things working.

The situation that you describe would certainly work fine as long as nothing goes wrong, but I bet that it would not be sufficiently safe, if, for example, the fan were to stall and draw considerable excess current.

If everything always worked fine, we wouldn't even need circuit breakers. Simply connect everything (from a 100W lamp to a 25000W heater) directly up to the transformer using fat enough wires for each load, and perhaps a few switches to control things. Circuit breakers are only necessary if something overloads or shorts.

-Jon
 
  #6  
Old 11-16-05, 03:30 PM
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tap conductors

Hi Jon,

Thanks for your reply. After reading the NEC sections I have come to the conclusion that my scenario does comply. The key elements are:

1. The tap is not over 10' in length
2. The conductors must be enclosed in grounded conduit.
3. The ampacity of the conductors must be equal or greater than the demand of the fixture.
4. The tap must not extend beyond the fixture
5. The tap itself must not be tapped.

In my case, all of the above are complied with. In fact, the exhaust fan (Fantech FR-110) is only an 80 watt fixture drawing about 2/3 amp maximum. Since the ampacity of #14 wire is 15 amps, I'm totally within those requirements. The NEC indicates that the tap conductors are in fact protected by the limited possible draw of the device.

In theory, this would allow branch circuits to be sized based on branch demand _however_ items 1,2,4 & 5 above make that illegal.

In any event, tap conductors are analogous to a plug in lamp. ie: You can plug in a lamp to a 20 amp circuit even though it's cord is only 16 gauge. The fact that the circuit is 20 amp does not place the cord at risk because the fixture itself will not cause the ampacity of the cord to be exceeded. A short in the cord or fixture is almost always going to cause the 20a breaker to blow before the cord fails.

Of course, extension cords with multiple taps would violate item #5 but since the NEC is only dealing with "hard-wired" cases it's a moot point.

-Joe
 
  #7  
Old 11-16-05, 03:47 PM
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Wink

Originally Posted by winnie
If everything always worked fine, we wouldn't even need circuit breakers. Simply connect everything (from a 100W lamp to a 25000W heater) directly up to the transformer using fat enough wires for each load, and perhaps a few switches to control things. Circuit breakers are only necessary if something overloads or shorts.

-Jon
Circuit breakers are necessary to prevent conductor overload. The main cause of this is too much demand caused by too many appliances being used simultaneously. Shorts will also cause breakers to trip in most cases. Since wire costs money, most wiring uses the smallest size allowable for the need and circuit breakers are then required to protect the wire. IOW, if you have #12 wire you can use a 15 or 20 amp breaker - but if you use a 20 amp breaker, you can not use #14 wire - except for tap conductors meeting the requirements thereof.

Your hypothesis is correct that we could just use fat enough wires, but the cost would be prohibitive and I really can't imagine connecting a 15 or 20 amp outlet to #6 wires.
 
  #8  
Old 11-16-05, 10:59 PM
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Which section of code are you reading? It appears to me that you are looking at 240.21(B), which does not apply to branch circuit conductors. But perhaps you are looking elsewhere?

I believe that you want to look at 210.19(A)(2) and (A)(4).

I was not suggesting that we _should_ wire things without circuit breakers; just that circuit breakers are required and that taps need to be used very judiciously.

Yes, a skinny cord plugged into a receptacle outlet is a form of a tap (though not called such in the NEC). Cord length and size is restricted in many ways.

-Jon
 
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