It is permissible to branch a Smaller gauge wire off Larger gauge wire?

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TheColonel26

TheColonel26

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It is permissible to branch a smaller gauge wire off larger gauge wire as long as it is fused at the splice point?

Example: If I have a 200A circuit with 1/0 wire can I branch off 10AWG from and fuse it at 30A?

I've always been under the impression that I can but I can't find anything in the code that really covers this.

Here is a quick diagram

20141119_163929-scaled.jpg
 
Just make sure that the fuses and holders are appropriate for branch/feeder protection.
If the OCPD is upstream of the small wires it is not even a tap.
 
Per the image, he has a branch circuit tap which would have to comply with 210.19 and 210.20. It doesn't appear to comply to me.
 
To me it looks like the large conductors are both feeder and branch wires at the same time. And the smaller conductors are protected at their source of supply, so why a tap?
The OP did not specify whether both loads were motors, which could change the applicable sections.
But it seems to me that not all tees are taps.
 
infinity said:
Take look at the tap rules in 240.21.
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ah hah I missed that.

GoldDigger said:
Just make sure that the fuses and holders are appropriate for branch/feeder protection.
If the OCPD is upstream of the small wires it is not even a tap.
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Yes after infinity pointed me to 240.21, it seems 240.21(B) does not apply here since the OCPD is at the point of supply for the smaller wire.

what I got from 240.21(b) was...

If this was less than 25ft and I wished to have the OCPD down stream from the tape I could could use 24.21(B)2. Which is tap circuits under 25 feet, however that is only allowed when the tap circuit is rated for atleast 1/3 of the feeding circuit. Which which is this case my tap circuit would need to be rated at 70A.

If this was out side this would be permissible at any length if the entrance to the load device has a fused disconnect or a circuit breaker.

david luchini said:
Per the image, he has a branch circuit tap which would have to comply with 210.19 and 210.20. It doesn't appear to comply to me.
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I don't see my example doesn't comply with 210.19 and 210.20. would you elaborate?

GoldDigger said:
To me it looks like the large conductors are both feeder and branch wires at the same time. And the smaller conductors are protected at their source of supply, so why a tap?
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GoldDigger said:
The OP did not specify whether both loads were motors, which could change the applicable sections.
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]But it seems to me that not all tees are taps.
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The load on the 200A would most likely be to a device that has motors and other loads on it it is actually a conductor bar system with collectors. The 30A circuit is a mostly resistive load. [/FONT]
 
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I don't see an issue with 210.19 or 210.20. The 1/0 wires are sized for the load that they will serve. The #10 wires are sized for the load they will serve. In both cases, the wires are protected against overcurrent at their ampacity. What are you seeing that I am not seeing?

I will say that you raise an interesting question. What do you call the (red) 1/0 conductors between the 200 amp breaker and the point at which the fuses and the #10 conductors attach to the 1/0 conductors? Is it a branch circuit? Perhaps not, as there is another overcurrent device further downstream. Is it a feeder? Perhaps not, as there are conductors that lead from the breaker to a load without passing through another overcurrent device.
 
charlie b said:
I don't see an issue with 210.19 or 210.20. The 1/0 wires are sized for the load that they will serve. The #10 wires are sized for the load they will serve. In both cases, the wires are protected against overcurrent at their ampacity. What are you seeing that I am not seeing?

I will say that you raise an interesting question. What do you call the (red) 1/0 conductors between the 200 amp breaker and the point at which the fuses and the #10 conductors attach to the 1/0 conductors? Is it a branch circuit? Perhaps not, as there is another overcurrent device further downstream. Is it a feeder? Perhaps not, as there are conductors that lead from the breaker to a load without passing through another overcurrent device.
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The red conductors shown are a branch circuit (the conductors between the OCPD and the outlet.) If you are going to tap that branch circuit, you must do so in accordance with the rules in 210.19 (via 240.21(A)). The original branch circuit doesn't appear to fall under 210.19(A)(3) so 210.19(A)(4) would apply. How does the tap shown meet the requirements of 210.19(A)(4) Ex. No. 1?

One could make the existing branch circuit a feeder by adding another OCPD and then tap the feeder in accordance with 240.21(B).
 
charlie b said:
I don't see an issue with 210.19 or 210.20. The 1/0 wires are sized for the load that they will serve. The #10 wires are sized for the load they will serve. In both cases, the wires are protected against overcurrent at their ampacity. What are you seeing that I am not seeing?

I will say that you raise an interesting question. What do you call the (red) 1/0 conductors between the 200 amp breaker and the point at which the fuses and the #10 conductors attach to the 1/0 conductors? Is it a branch circuit? Perhaps not, as there is another overcurrent device further downstream. Is it a feeder? Perhaps not, as there are conductors that lead from the breaker to a load without passing through another overcurrent device.
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The typical issue is that a set of conductors cannot be both a branch circuit and a feeder circuit. Such a circuit does not agree with their definitions explicitly. That and branch circuit tap rules are very specific about what can be tapped... but FWIW, they do not have any OCP protecting the tap conductors.

We can throw that out the window if there is even one motor involved. I assumed that from the get go because 1/0 is not rated for 200A on a regular branch circuit. Somewhat confirmed by OPer's second post to thread. When a motor is involved, 210.2 sends us to Article 430. Motor circuits seem to be the only type that nobody questions whether conductors are both branch and feeder.
 
I dispute the assertion that one set of conductors cannot be both feeder and branch.
The NEC definition does not explicitly or implicitly state that the two are mutually exclusive, we just act as if it does. Given the example of a circuit that meets both definitions, we have proof that they are not mutually exclusive. QED.
Now a problem will arise if the rules for feeders and the rules for branches cannot both be satisfied at the same time, but all that means is that that particular circuit arrangement is not allowed!
 
OOOOH I need 3/0 for 200A, now I understand why it doesn't comply with 210.19,210.20. You could have just said that. The example is only a hypothetical one. I just glance at the ampacity tables and must have read the wrong line. lets call it 3/0 from now on. I don't think it changes anything.
 
david luchini said:
Per the image, he has a branch circuit tap which would have to comply with 210.19 and 210.20. It doesn't appear to comply to me.
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As drawn it looks to me like a feeder supplying a set of 30A OCPD's....based on where the connection (tap) is located I would say it was a feeder to the 30A OCPD and a branch circuit from the final OCPD to the load in this example. It is with nearly 100% certainty the EI would assume this as a feeder tap application.

I wont argue the "it can be both concept"...as this image clearly in my mind (the way it is actually drawn) is a feeder that terminates into an enclosure with 30A OCPD's that feed some LOAD which is not specified. If it did not have the OCPD's located where they are I would have no problem calling it a branch circuit...but at this stage I call it a feeder and those are feeder taps.

To each his own I guess.....I will substitute your logic with my logic and make it happen !:angel:

Definition of Branch Circuit - The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s). Seems to me based purely on this drawing...I have final overcurrent devices (30A) between there and the outlet(s)....now if that was simply a disconnection means only then I would call it the entire thing a branch circuit....but based on how it is drawn I would not...convince me otherwise please as I always like to learn something new.

I might add....if that 30A fuses are "supplemental" then I might buy the branch circuit argument....if these 30A OCPD's are required in the circuit to protect the smaller AWG conductors from the 30A to the load then they are not supplemental.
 
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deee said:
The Mai fuses should be rated for the 1/0 feeder which is 125 to 150 amps
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I think we actually left the sizing portion of the show...lol...we are now discussing what constitutes a feeder versus branch circuit in this drawing...i think anyway....lol:angel:

Edit....but don't get me wrong...your point is well taken.

I think what is being said by smart and david is that the part in BLUE is taping off of a branch circuit that is depicted in RED.....so it would be a branch circuit tap now that I believe i see what they are drawing.....now it makes more sense....lol....I think we looked (or at least I did ) as the straight portion as being the circuit...and the small part being tapped off the middle as the "tap" conductors....

But when you reconfigure a circuit as shown....do you actually make trouble for yourself as now it can be looked at as a feeder supplying the 30A OCPD enclosure and then feeder taps are the connections before it.....I see both points now...lol...:sick:
 
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Are you saying that a feeder cannot feed two different branch OCPDs without there being a tap involved? Once again, does a T always imply a tap? It does not in a branch circuit.
 
GoldDigger said:
Are you saying that a feeder cannot feed two different branch OCPDs without there being a tap involved? Once again, does a T always imply a tap? It does not in a branch circuit.
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No I am saying I looked at the original drawing and ignored the "colors" as the intent....I looked at it as the circuit being a straight line (my bad) and it being a feeder...and the conductors tapped ahead of the last 30A OCPD as feeder taps....And to answer your question....no I am not saying that as it happens all the time in motor applications....just saying I think I viewed the image wrong and trying to express that....lol....
 
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