Absurdly Simple Question

[iwire]

Bob.
Grounded conductors generally are not connected to an overcurrent device. If a branch circuit grounded conductor makes contact with an equipment ground conductor and/or a grounded surface, the circuit breaker/fuse for that circuit will not open. Therefore groundfault current does not flow on the grounded conductor

No ground fault current does not normally flow on the grounded conductor, but short circuit current will.

No the grounded conductor does not directly connect to the OCP in most cases but regardless of that the OCPD is intended too, and does protect the grounded conductor from overload / overcurrent.

 

[Jim W in Tampa]

It was a question posed to him in a class. :roll:


I must have blown through the opening to 240.4 too fast - I thought I saw "ungrounded" in there, but I don't see it now. Thanks!

Its good that the subject came up in class. What needs brought up is that they can mix #12 and #14 but the smaller wire is what we must use to size the max fuse or breaker.
While his load is 10 amps there is no problem unless addition load or a fault enters into the circuit. The neutral must also be protected from over current and we do this by sizing the breaker on the ungrounded circuit so that it will not be higher than what the neutral is.

In the example there would not need be a 20 amp circuit

 

[Pierre C Belarge]

No ground fault current does not normally flow on the grounded conductor, but short circuit current will.

No the grounded conductor does not directly connect to the OCP in most cases but regardless of that the OCPD is intended too, and does protect the grounded conductor from overload / overcurrent.

I do not agree with this comment.
The OCPD is not designed to protect the grounded conductor. It is designed to protect the ungrounded conductor. Due to the fact the ungrounded conductor is part of the circuit, it will be protected by the OCPD opening while protecting the ungrounded conductor.

 

[acrwc10]

Bob.
Grounded conductors generally are not connected to an overcurrent device. If a branch circuit grounded conductor makes contact with an equipment ground conductor and/or a grounded surface, the circuit breaker/fuse for that circuit will not open. Therefore groundfault current does not flow on the grounded conductor.

210.19(A)(1) ex#2 permits the grounded conductor to be sized differently than in the past (before 2008 NEC).
The answer to this question would be yes. I really do not see the issue, we downsize service and feeder grounded conductors.

240.4(D) has no exception for the grounded conductor to be excluded from it's application.
In the OP there was no definition that the "grounded conductor" was a neutral conductor or that it is single phase.("Suppose you have a 10A load on a dedicated 20A circuit. Can you install a 12 ungrounded and a 14 grounded conductor?") It is possible that this could be a corner grounded system and both grounded and ungrounded conductors are "full current" carrying conductors that are connected to the OCPD.
210.19(A)(1)ex#2 is only for sizing the conductor not the OCPD, it does not change the requirements of 240.4

 

[acrwc10]

I do not agree with this comment.
The OCPD is not designed to protect the grounded conductor. It is designed to protect the ungrounded conductor. Due to the fact the ungrounded conductor is part of the circuit, it will be protected by the OCPD opening while protecting the ungrounded conductor.

You mean to tell us that a failure/fault can not occur, before the load, between the grounded and ungrounded conductor? Or that the "utilization equipment" can't fail and run an overload threw the grounded conductor? I have seen such failures occur.

 

[charlie b]

What reference do you have for this?

Take a look at the thread to which he placed a link in post #15.

 

[charlie b]

You mean to tell us that a failure/fault can not occur, before the load, between the grounded and ungrounded conductor?

Yes it can, but that is not relevant to the discussion. That would activate the breaker's instantaneous trip. The impact on the #12 and #14 conductors would be the same, regardless of whether the breaker were 15 amp or 20 amp.

Or that the "utilization equipment" can't fail and run an overload through the grounded conductor?

That is the relevant failure mechanism. If the "current due to equipment failure (i.e., not to be confused with 'current due to ground fault')" were more than 15 amps, but lower than 20 amps, the breaker would not trip, and the wire would be passing more than we are allowed to give it. Would that cause a fire or cause the #14 wire's insulation to melt? No. Would it be a situation that violates 240.4(D)? Yes.

 

[Pierre C Belarge]

Take a look at the thread to which he placed a link in post #15.

Charlie
I started reading the thread, it is too long for me to focus on it now, I will try to read it later.

There should be a limit of 5 responses to a thread...they are too long for late comers to come in and read them.....



Real quick. I do not see where the NEC restricts the size of the branch circuit grounded conductor to 250.122 or where it states the branch circuit grounded conductor is to be the same size as the ungrounded conductor.

In regards to a "SHORT CIRCUIT', and current flow for safety. Think of motor circuits where the overcurrent protection is sized much larger than we do for other typical branch circuits. The OCPD will still operate as designed.

 

[charlie b]

Think of motor circuits where the overcurrent protection is sized much larger than we do for other typical branch circuits. The OCPD will still operate as designed.

The OCPD will trip in its instantaneous range, to protect against a high current fault. What protects the wire against overload is the motor's overload device. The situation is different enough that it does not help clear up this question.

 

[acrwc10]

The OCPD will trip in its instantaneous range, to protect against a high current fault. What protects the wire against overload is the motor's overload device. The situation is different enough that it does not help clear up this question.

Seems clear to most of us, it's not allowed.:grin:

 

[Dennis Alwon]

What reference do you have for this?

Pierre, I didn't think an expert like you needed a reference. 215.2(A)(1) after the exception

 

[charlie b]

Seems clear to most of us, it's not allowed.:grin:

Perhaps so, but the process for designing motor branch circuits does not involve the same rules, and therefore does not help clear up the situation.

 

[Dennis Alwon]

Real quick. I do not see where the NEC restricts the size of the branch circuit grounded conductor to 250.122 or where it states the branch circuit grounded conductor is to be the same size as the ungrounded conductor.

It does not for branch circuits but it does for feeders that is why I made a proposal. I think it makes sense that the grounded counductor be no smaller than 250.122

 

[charlie b]

I must have blown through the opening to 240.4 too fast - I thought I saw "ungrounded" in there, but I don't see it now.

You still missed the part of 240.4 that contains your answer. :grin: It is indeed within the opening sentence. The key words are "protected against overcurrent in accordance with their ampacities. . . ." It does not go on to say, "depending on the role they play within the circuit."

It does go on to say, ". . .unless otherwise permitted or required. . . ." The "or required" is what brings the notion of 15 amp breakers for #14 wire into play.

 

[iwire]

I do not agree with this comment.
The OCPD is not designed to protect the grounded conductor. It is designed to protect the ungrounded conductor. Due to the fact the ungrounded conductor is part of the circuit, it will be protected by the OCPD opening while protecting the ungrounded conductor.

In that case I will start running two wire 30 amp circuits using a 10 AWG ungrounded conductor and a 16 AWG grounded conductor.:grin:



Just to be clear I disagree with your disagreement.

 

[LarryFine]

In my opinion, a 2-wire circuit should have all conductors sized for the OCP. In a 3-wire, it usually is anyway.

Would a dryer circuit be permitted to have a smaller neutral than the line conductors? Methinks not.

 

[Dennis Alwon]

In my opinion, a 2-wire circuit should have all conductors sized for the OCP. In a 3-wire, it usually is anyway.

Would a dryer circuit be permitted to have a smaller neutral than the line conductors? Methinks not.

How do you explain 210.19(A)(1) except. 2

It is pretty clear that if I can have a noncontinuous load of 14 amps to a parking lot light, for instance I could then size my neutral to 15 amps while the ungrounded conductor would need to be 20 amps- 14 *1.25= 17.5

 

[LarryFine]

How do you explain 210.19(A)(1) except. 2

My NEC doesn't have one.

 

[Dennis Alwon]

My NEC doesn't have one.

I forgot you were in the dark ages still.

Exception No. 2: Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100 percent of the continuous and noncontinuous load.

 

[Jim W in Tampa]

How do you explain 210.19(A)(1) except. 2

It is pretty clear that if I can have a noncontinuous load of 14 amps to a parking lot light, for instance I could then size my neutral to 15 amps while the ungrounded conductor would need to be 20 amps- 14 *1.25= 17.5

Yes it would work but no not legal. What happens if the other circuit for what ever reason is not on ? Thats why its a no go. All conductors must be protected. Usually the neutral is protected by the ungrounded conductor being fused