Extending existing electrical wiring

   / Extending existing electrical wiring #11  
I am not up with the NEC so I cant say weather this is true or not, but it is not a good Idea.

You should always size the wire to the breaker. 110v and 220v are the same guages for the given amps as listed above.

.
LD1, Trust me, what I wrote was right. I'm a Master Electrician in the State of Maryland... I work with motors quite often.. I'LL refrain from Posting on this Topic, but will answer any PM's sent to guide one on motors...
 
   / Extending existing electrical wiring #12  
First off this wiring is not up to code and I'm glad I dont have to live in a home wired by some of the people that claim to be experts on many boards.

the NEC allows for 1.5 to 2.0 times FLA on motor branch circuits on the protection ahead of the rest of the branch circuit. the term branch circuits infers that there are supplementary breakers for short circuit protection (again rating and device determines the ampacity aloud times the type of protection, fuses can be rated up to 300% based on the type of fuse and Time based Breakers are generally 1.5 to 2 times FLA.) and includes fact that there are OVER LOAD PROTECTION included for/with each motor. the motor overload protection stops long term overload condition by opening up the control circuit that is normally between the Breaker and the Overload protection (Motor Starter) Typical 220 home type motors do not have this safety circuit and generally use thermal overloads built in at the motor. this does not provide the added safety factor of industrial equipment so the two should not be compared in a case like this.

BUT under pretty much ALL conditions the breaker in this case HAS to be sized to the LOAD and the wire HAS to then be sized to the BREAKER... In this case the Wire is under sized and is not up to code. 12 awg wire is good for max of 20 amps per code, voltage does not matter it is amperage (under 600 volts)...

Mark
 
   / Extending existing electrical wiring #13  
Keep in mind that it's legal to use a higher amp breaker on motor circuits in the USA when wiring to the NEC!!! Wire can be sized according to a Motor Name Plate and the Breaker sized according to Name Plate Start up amps, using the NEC... I'm not implying in any way that one can do this to a typical 15 or 20 amp branch circuit... Also when doing this a motor needs overload protection as outlined in the NEC...
This is somewhat misleading. while its true you can overfuse motors for startup, Wire size and main fusing MUST be sized accordingly, and overfusing must be rated per the tables/article 430 NEC.
Under no circumstances can a 40 amp fuse be used for number 12 wire.
As far as overfusing motors the amount they can be overfused depends on the motor type and application, but isnt/can not be done in an application where (for example) you have an xx hp motor that requires 120 volts 15 LRA (load running amps) connected with # 12 wire a max 20 amp fusing is all thats allowed though in some limited applications 25 amp fusing is legal on #12 wire.
What can be done is supplied amperage can be increased using appropriate wire size and breakers, and appropriate fusing protection provided at the point wire size changes. (for example) 100 amp feed w/#2 aluminum, or #4 copper feeds a sub panel or motor control center. the branch circuit fuse protection is then applied at that point for the derated wire size. note too, to mix aluminum and copper wire, while not a good idea, must be done with al/cu approved connecters.

You should always size the wire to the breaker. 110v and 220v are the same guages for the given amps as listed above.
Sorry but this isnt true. If anything, you do just the opposite, size the breaker to the wire, this goes back to you cant legally or safely put a #12 wire under a 40 amp breaker.
However, you can use a larger conducter than the minimum required for the breaker size. In long wire runs it may be a necessity due to resistance/voltage drop. VD calculations could well require oversizing the conductor.
NEC article 210.19(A) FPN no. 4
"Conductors/sized to prevent a voltage drop exceeding 3% and the furthest outlet of power"
One can extend a circuit of #12 wire with #10 though the prevention of VD will be limited by the current carrying abilities of the smaller conductor. The entire circuit still MUST be protected @ 20 amps. Conversly, if one were to extend the circuit with a smaller #14 conductor, then the larger #12 wire will need to be derated to 15 amp fuse protection.
 
   / Extending existing electrical wiring #14  
LD1, Trust me, what I wrote was right. I'm a Master Electrician in the State of Maryland... I work with motors quite often.. I'LL refrain from Posting on this Topic, but will answer any PM's sent to guide one on motors...

Yes you are correct. I was reading too fast and I missed the part where where you mentioned if the motor had overload protection.

Wire size is 125% of FLA and branch protection can be up to 250% of FLA.

So...You could run a 10 A motor on 14ga wire on a 25A breaker ONLY as long as the motor has overload protection of its own. But there is no harm in oversizing wire.

So...correct me if I am wrong, but a motor with a FLA of 16A, (16 x 125% =20) could run on 12 ga and be protected by a (16 x 250%=40) 40a breaker AS LONG AS it has overload protection.

Boy that just sounds nuts in my head. I guess I am more used to constant loads, like lights and outlets and such.

CharlieS: You are correct. I said it backwards. Size the breaker to the wire. Except under some special circumstances like these electric motors.
 
   / Extending existing electrical wiring #15  
So...correct me if I am wrong, but a motor with a FLA of 16A, (16 x 125% =20) could run on 12 ga and be protected by a (16 x 250%=40) 40a breaker AS LONG AS it has overload protection.

Boy that just sounds nuts in my head. I guess I am more used to constant loads, like lights and outlets and such.

CharlieS: You are correct. I said it backwards. Size the breaker to the wire. Except under some special circumstances like these electric motors.

LD1
somewhat correct but code doesnt allow for, and no inspector i know, (myself included) will allow an overfusing scenerio where you overfuse a conductor in a main or sub panel. The proper and safe way is supply amperage through a larger amp circuit and fuse it accordingly at an approved connection point. An SSU on a furnace blower for example by code is required to have fuse protection in accordance with motor overfusing guidelines. so a hypothetical moter with an LRA of 2 amps could legally have a 3 amp fuse fed by a 15 or 20 amp circuit. In the furnace case because of the motor type and application is rated at 150% for start up purposes.
An industrial motor, fed through a contactor with heater coils, or dedicated fuse block, in cases where contactor startup isnt needed, can indeed be over fused sometimes as high as 400% when fed off a properly sized main feeder.
there are a couple of code regs that apply here depending on the application. 25 foot tap rule, and 10 foot tap rule are the most commonly applied.
Though overcurrent protection by code may be rounded up to the next standard fuse (or breaker) size in some cases a slightly higher % overfuse rating may be used. Many inspectors though will not allow this and require the smaller standard size based on application tables.

you are right in your example calculations with the 125% multiplier but that's actually a derate factor. amp draw of any electrical load must be derated to 80 percent, so a load of 16 amps x 125% =20 meaning you can supply a 16 amp load on a 20 amp circuit. Another way to calculate is whats the max load an xx amp circuit can carry. 20 amps x 80% = 16.

the way a breaker or fuse works is pretty basic. they are nothing more than a thermostat that senses overheating in the conductor and opens up when the conductor becomes to warm. larger conducters carry more heat thus larger breakers have a higher temp. rating. (its more complex than that but this is the simple way to explain it) Thus in the 40 amp breaker/#12 wire example the wire doesnt get hot enough, soon enough to trip a breaker or blow a fuse to prevent a melt down.
Wire insulation type as well has a bearing on fusiblity.
THWN rated insulation for example has a lower temp rating than THHN.
physical containment is also an issue. free air power lines for example can be rated at a much higher fused load, than the same conducter/load in conduit.

The number of conductors or "conduit fill" also play's a key part in how circuits must be derated, because of overall heat generation in the raceway.
A conduit at max fill capacity can result in Current carrying conductors having to be derated by as much as 50% over maximum allowable load based on conductor size alone.

Bottom line is there are may variations/combinations allowed by code depending on the application/equipment/working conditions.
Code has many different exceptions that allow for variations depending on specific application and conditions, but in no cases are main feeders allowed to be overfused under conditions discribed in the origional post.
 
   / Extending existing electrical wiring #16  
If Captain is talking about the "LRA" rule then sure if not than by wire size only should the breaker be sized..
 
   / Extending existing electrical wiring #17  
3 horsepower is 2237.1 watts. At 220 volts that gives 10.17 amps load. This is theoretical and doesn't take into account any inefficiencies. Actual running amperage is probably going to be very close to 5 amps per horsepower @ 220 or 240 volts.

I used a voltage drop calculator found at Voltage Drop Calculator to give some values. If I haven't made an error, this is what I found.

With 15 amps load current @ 220 volts at the panel with 12 gauge copper wire in steel conduit and 100 foot run, you should have an estimated voltage drop of 2.7 % giving 214V at the motors. If you actually have 240 volts at the panel, you should have an estimated voltage drop of 2.5 % giving 234V at the motors.

60 feet of 12 gauge @ 220V has 1.6% voltage drop.
40 feet of 10 gauge @ 220V has 0.7% voltage drop.
60 feet of 12 gauge@ 240V has 1.5% voltage drop.
40 feet of 10 gauge@ 240V has 0.6% voltage drop.

60 feet of 12 gauge plus 40 feet of 10 gauge with 220V at the panel should give you 215V at the motors.
60 feet of 12 gauge plus 40 feet of 10 gauge with 240V at the panel should give you 235V at the motors.

Going up to 10 gauge for the last 40 feet only lessens the voltage drop by one volt.

Motors meeting the criteria contained in the NEMA Motors and Generators Standard MG-1-1993 will operate safely within plus or minus 10% of the rated nameplate voltage.
Although NEMA MG1-12.44.1 stipulates that motors must tolerate +-10% voltage variation; the motor should be operated at nameplate voltage for optimum life.

I believe you need to check your voltage at the motors (while they are running) with an accurate volt meter before you decide to do anything about the conductor size.

If the motors start ok, and you don't have any additional load, and the voltage is acceptable, I think you are good to go as is, except for needing to change the 40A breaker to a 20A breaker.
 
   / Extending existing electrical wiring #18  
This is true for 120 volt circuits - but the OP stated that his was a 240V, essentially doubling the amperage capacity of the wire.
Mike

I have to chime back in - this is so wrong, it hurts. Simplified - Wires are rated by the amps they can carry. That is why there is an AMPACITY chart in the NEC for wire gages. Ampacity = Amp Capacity, if you like. Wires and breakers must be sized together. Reference the mini-chart I put up earlier. Within reason the voltage does not matter! It is the current you care about here.

NOTE: we are talking about residential wiring here. Yes, there are exceptions as captaincrab noted for people who know what they are doing, but unless you have a very special circumstance, I can't imagine dealing with those in residential wiring. (Captaincrab - Do you really trust a homeowner to apply the permanently connected motor load exception properly and not change it up down the road?)

With that in mind, the purpose of the breaker is to protect the wires, which in turn protects the structure and it's occupants from a fire. So the breaker and wire must be sized together. You do not want a bigger breaker than the wire can handle for current. That creates a dangerous situation - maybe not now, but somewhere down the road after the house is sold and the new owner does something radically different with the circuit. In many ways, that is the purpose of the code.

Now if you want to go the other way, that is fine - you can put a 6ga wire on a 20A breaker, if you like. Sometimes you need to if the run is exceptionally long and voltage drop is a concern. Or maybe you just want the ability to upsize the breaker down the road if your needs change. But you can't put a smaller than 12ga wire on that 20A breaker as it risks overheating the wire (aka: fire risk) before the breaker would pop.

Residential wiring is fairly simple, and IMHO should be kept that way for good reason.

My $0.02
 
   / Extending existing electrical wiring
  • Thread Starter
#19  
I have to chime back in - this is so wrong, it hurts. Simplified - Wires are rated by the amps they can carry. That is why there is an AMPACITY chart in the NEC for wire gages. Ampacity = Amp Capacity, if you like. Wires and breakers must be sized together. Reference the mini-chart I put up earlier. Within reason the voltage does not matter! It is the current you care about here.

NOTE: we are talking about residential wiring here. Yes, there are exceptions as captaincrab noted for people who know what they are doing, but unless you have a very special circumstance, I can't imagine dealing with those in residential wiring. (Captaincrab - Do you really trust a homeowner to apply the permanently connected motor load exception properly and not change it up down the road?)

With that in mind, the purpose of the breaker is to protect the wires, which in turn protects the structure and it's occupants from a fire. So the breaker and wire must be sized together. You do not want a bigger breaker than the wire can handle for current. That creates a dangerous situation - maybe not now, but somewhere down the road after the house is sold and the new owner does something radically different with the circuit. In many ways, that is the purpose of the code.

Now if you want to go the other way, that is fine - you can put a 6ga wire on a 20A breaker, if you like. Sometimes you need to if the run is exceptionally long and voltage drop is a concern. Or maybe you just want the ability to upsize the breaker down the road if your needs change. But you can't put a smaller than 12ga wire on that 20A breaker as it risks overheating the wire (aka: fire risk) before the breaker would pop.

Residential wiring is fairly simple, and IMHO should be kept that way for good reason.

My $0.02

I often read/hear the term (free-air) in the "electrical world"...I assume this means the wire isn't enclosed in conduit, or is it? Can this be a climate issue too...that helps or hinders the ampacity of the wire?
 
   / Extending existing electrical wiring #20  
I often read/hear the term (free-air) in the "electrical world"...I assume this means the wire isn't enclosed in conduit, or is it? Can this be a climate issue too...that helps or hinders the ampacity of the wire?

Wires that carry current generate heat. Wires are rated for the amps based on how much heat it will generate before the insulation breaks down and fails. Larger guage wires can carry more current cause they dont generate as much heat as a smaller wire if both are carrying the same amps.

There are many different types of insulation and they are rated at different temperaturs, which can have an effect on ampacity.

The term "free air" is just that, it means a wire in the open. This usually has the highest rating. When in conduit/raceways, and multiple wires are ran together in these enclosures, they generate a lot more heat and can cause the insulation to fail sooner. Thus they are de-rated. The more wires, the more they are de-rated. With a search online you could probabally come up with the tables for figuring just this. It is also listed in several pocket guides and the NEC.
 

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