Increasing the Size of the Ungrounded Conductors But Reduce the ECG per the NEC 250.122(B) Exception

[jar546]

What happens when you need to increase the size of your ungrounded conductors due to voltage drop but then consider reducing the size of the equipment grounding conductor (EGC)? To comply with the NEC, it's essential to understand who is qualified to make these decisions and the rules that govern such changes.

The National Electrical Code (NEC) defines a "qualified person" as one who possesses the skills and knowledge related to the construction and operation of electrical equipment and installations and who has received safety training to recognize and avoid the hazards involved. This definition underscores the importance of both expertise and safety awareness in the field of electrical work. The NEC further clarifies the requirements for a qualified person, emphasizing the need for comprehensive training as detailed in NFPA 70E-2021, Standard for Electrical Safety in the Workplace.

According to NFPA 70E-2021, Section 110.6(A), electrical safety training is mandatory for employees exposed to electrical hazards when the associated risks are not reduced to a safe level by existing electrical installation requirements. Such employees must be trained to understand the specific hazards associated with electrical energy, and in safety-related work practices and procedural requirements necessary to provide protection from these hazards. This training must enable employees to identify electrical hazards and understand the relationship between these hazards and potential injuries.

A qualified person must be knowledgeable about the construction and operation of equipment or specific work methods and trained to identify and avoid the electrical hazards that might be present. They must also be familiar with special precautionary techniques, applicable electrical policies and procedures, personal protective equipment (PPE), insulating and shielding materials, and insulated tools and test equipment. Importantly, a person can be considered qualified for certain equipment and tasks but may still be unqualified for others. Additional training is required for those permitted to work within the limited approach boundary, covering skills to distinguish exposed energized electrical conductors and circuit parts, determine nominal voltage, understand approach distances and corresponding voltages, and make informed decisions regarding job safety planning, hazard identification, risk assessment, and selection of appropriate risk control methods, including PPE.

An example of the application of a qualified person's expertise can be found in NEC 250.122(B), which requires equipment grounding conductors (EGCs) to be increased proportionately in size when ungrounded conductors are increased for reasons other than those specified in NEC 310.15(B) or 310.15(C). However, an exception to this rule permits a qualified person to determine an alternative EGC size, provided it ensures an effective ground-fault current path in accordance with NEC 250.4(A)(5) or (B)(4).

Consider a scenario where an electrical system requires the ungrounded conductors to be increased from 250 kcmil to 350 kcmil. Normally, the EGC would need to be increased proportionately, resulting in a size of 4 AWG. A qualified person, leveraging their training and knowledge, might assess the system and determine that a 6 AWG EGC would suffice. This decision would be based on a thorough evaluation of fault current levels, distance, and impedance, ensuring the EGC provides a low-impedance path and supports the proper operation of the overcurrent protective device (OCPD). The qualified person would document this decision, including the rationale and calculations supporting the alternative sizing, ensuring compliance with NEC 250.4(A)(5) or (B)(4).

The flexibility provided by this exception allows for cost-effective and practical solutions while maintaining safety. By permitting qualified persons to use their expertise to determine appropriate EGC sizes, the NEC acknowledges the complexity of electrical systems and the need for informed, safety-focused decision-making. Ultimately, the rigorous training and qualification requirements outlined in both the NEC and NFPA 70E ensure that only those with adequate expertise can make these critical decisions, thus safeguarding both the electrical infrastructure and personnel.

In summary, a qualified person per the NEC is not only defined by their knowledge and skills related to electrical systems but also by their extensive safety training. This training, as detailed in NFPA 70E, equips them to handle complex scenarios, such as determining appropriate EGC sizes when ungrounded conductors are increased, ensuring safety and compliance with NEC requirements.

 

[wwhitney]

Consider a scenario where an electrical system requires the ungrounded conductors to be increased from 250 kcmil to 350 kcmil. Normally, the EGC would need to be increased proportionately, resulting in a size of 4 AWG. A qualified person, leveraging their training and knowledge, might assess the system and determine that a 6 AWG EGC would suffice.

Your numbers are off here. You haven't specified the conductor material (copper or aluminum) or the OCPD size.

If you're talking copper, 250 kcmil Cu has a 75C ampacity of 255A, while the next smaller size of 4/0 has an ampacity of 230A. Since you've implied that 250 kcmil would be the smallest size allowed, we can conclude that the minimum ampacity for the circuit is 231A-255A. As far as I'm aware, that implies that the minimum OCPD size would be 250A in all cases. But the OCPD size could be 350A or even 450A in the case of a motor load.

So depending on the OCPD size, the starting size for a copper EGC would be #4 Cu (201-300A), #3 Cu (301A-400A), or #2 Cu (401A-500A). In all cases, larger than the #6 EGC you mentioned. Only once you've determined that starting size can you determine what size 250.122(B) would require due to the upsized ungrounded conductors.

In the case of a motor load protected at 350A, say, there is a good argument that a #3 Cu EGC would suffice without upsizing when the ungrounded conductors are upsized from 250 kcmil to 350 kcmil. Namely, that 350 kcmil copper has an ampacity of 310A, and therefore for typical loads outside of those specified in 240.4(G) (like motors) would generally be protected at 350A or less. For which a #3 Cu EGC would be par for the course. Since the fault clearing capability of the circuit does not depend on the nature of the load, by comparison to this non-motor case we can conclude that the #3 Cu GEC would provide an effective ground fault current path.

Cheers, Wayne

 

[ICE]

Wayne beat me to it.

 

[jar546]

Your numbers are off here. You haven't specified the conductor material (copper or aluminum) or the OCPD size.

If you're talking copper, 250 kcmil Cu has a 75C ampacity of 255A, while the next smaller size of 4/0 has an ampacity of 230A. Since you've implied that 250 kcmil would be the smallest size allowed, we can conclude that the minimum ampacity for the circuit is 231A-255A. As far as I'm aware, that implies that the minimum OCPD size would be 250A in all cases. But the OCPD size could be 350A or even 450A in the case of a motor load.

So depending on the OCPD size, the starting size for a copper EGC would be #4 Cu (201-300A), #3 Cu (301A-400A), or #2 Cu (401A-500A). In all cases, larger than the #6 EGC you mentioned. Only once you've determined that starting size can you determine what size 250.122(B) would require due to the upsized ungrounded conductors.

In the case of a motor load protected at 350A, say, there is a good argument that a #3 Cu EGC would suffice without upsizing when the ungrounded conductors are upsized from 250 kcmil to 350 kcmil. Namely, that 350 kcmil copper has an ampacity of 310A, and therefore for typical loads outside of those specified in 240.4(G) (like motors) would generally be protected at 350A or less. For which a #3 Cu EGC would be par for the course. Since the fault clearing capability of the circuit does not depend on the nature of the load, by comparison to this non-motor case we can conclude that the #3 Cu GEC would provide an effective ground fault current path.

Cheers, Wayne

So what you are saying is that if we were discussing copper, 250kcmil under normal circumstances (75C) has an ampacity of 255A, which would require an ECG of #4cu per Table 250.122, and that if we were to bump that 250 to 350kcmil for, let us say it's the only size we have on the truck. It would cost more to stop working, go get the other side and come back, then that 350kcmil would be rated at 310A if we still use the 75C column, taking us back to Table 250.122 and the ECG would then have to be a 3awg copper, (I love long sentences) unless we could legally take advantage of the exception to 250.122(B) and reduce the ECG back to a smaller #4cu if we could prove it? Is that what you are saying?

 

[ICE]

Jeff beat me to it,

 

[jar546]

So the question is: Is it up to the inspector or plans examiner to determine who is a qualified person?

 

[wwhitney]

So what you are saying is that if we were discussing copper, 250kcmil under normal circumstances (75C) has an ampacity of 255A, which would require an ECG of #4cu per Table 250.122,

No, stop there. Table 250.122 goes by the OCPD used on the circuit, so you've skipped a step. The OCPD could be anywhere from 15A to 500A.

Even if you tell us that 250 kcmil is the smallest size that can be used on the circuit, we still don't know the OCPD size, it could be anywhere from 250A to 500A, depending on what the circuit supplies.

and that if we were to bump that 250 to 350kcmil for, let us say it's the only size we have on the truck. It would cost more to stop working, go get the other side and come back, then that 350kcmil would be rated at 310A if we still use the 75C column, taking us back to Table 250.122 and the ECG would then have to be a 3awg copper

Yes, if the the smallest compliant conductor size is 250 kcmil, and if the OCPD size is 250A, then I agree with the above. 250.122(B) creates a presumption that you have to upsize the EGC in proportion to the upsizing of the ungrounded conductors. The exception provides an out in many cases.

Cheers, Wayne

 

[wwhitney]

So the question is: Is it up to the inspector or plans examiner to determine who is a qualified person?

Seems hard to argue against the idea that the AHJ has the authority to determine who is qualified. I have no opinion on how they may or should delegate that authority to their employees.

I would suggest, however, that depending on the reason given under 250.122(B), different qualifications would be required. If as in your example the conductors where upsized because "it's the only size we had on the truck", and if the circuit length is 50', I think any electrician or inspector is qualified to recognize that the minimum size EGC still provides an effective ground fault current path. Conversely, if the circuit length is 500', it might take an engineer to do the calculations to determine the EGC size.

Cheers, Wayne

 

[jar546]

The OCPD could be anywhere from 15A to 500A

Show me a 15A OCPD that accepts a 250kcmil wire. That is preposterous.

Even if you tell us that 250 kcmil is the smallest size that can be used on the circuit, we still don't know the OCPD size, it could be anywhere from 250A to 500A, depending on what the circuit supplies.

Stop reading into things. Based on the information given is how you determine the answer. I can make assumptions all day long with many variables, but the information given was enough. Now, if more detailed information was provided, it could change the outcome.

 

[wwhitney]

Show me a 15A OCPD that accepts a 250kcmil wire. That is preposterous.

It's extreme but not preposterous. Switching to aluminum to be more realistic, If you have a 120V circuit with an actual 15A load, at a circuit length of 1100 feet you'd need to use 250 kcmil to keep the voltage drop to below 3%.

As to the breaker, that's a non-issue. You can use a short pigtail of smaller conductor at the breaker without significant voltage drop.

the information given was enough.

It simply was not enough. Table 250.122 goes by OCPD, so knowing the OCPD size is mandatory. And specifying copper vs aluminum is also critical.

With a 250 kcmil Cu conductor, the 75C ampacity of 255A means the two most likely OCPD sizes are 250A and 300A. Those two choices already have different minimum EGC sizes.

Cheers, Wayne

 

[jar546]

It simply was not enough.

Try taking some NFPA or ICC exams. Stop reading into things. You will quickly find out you have to make decisions with the information you have. Exams don't let you ask questions.

 

[wwhitney]

Try taking some NFPA or ICC exams. Stop reading into things. You will quickly find out you have to make decisions with the information you have. Exams don't let you ask questions.

This is the "Electrical Codes" forum, not the "Exam Prep" forum.

Why so antagonistic?

Cheers, Wayne

 

[jar546]

Why so antagonistic?

This is the "Electrical Codes" forum, not the "Exam Prep" forum.

Why so antagonistic?

Cheers, Wayne

Wayne,

I certainly do appreciate your intelligence and the depth of your insights, which are incredibly valuable to our discussions. I understand that you often raise questions about the many variables that can affect answers, and that's important for fostering a thorough understanding.

As the owner of The Building Code Forum, my vision is for it to serve multiple purposes. While it is indeed an Electrical Code forum, it is also a learning forum and a platform for people with varying levels of experience to learn and grow. This dual purpose is why I sometimes post information that opens up more questions and discussions. It helps everyone see different perspectives and engage in dialogues that are educational.

I believe that there are times when simplicity is needed for those who are just starting out or looking for straightforward answers. We aim to balance detailed discussions with clear, concise information, however, there are times when paralleling certification questions is warranted.

I appreciate you being here and participating. Your involvement is and has been very beneficial to those that belong and those that just browse. I hope you understan.

 

[wwhitney]

there are times when simplicity is needed for those who are just starting out or looking for straightforward answers.

I agree, so here's my simple version of post
#2:

What's the ocpd size in your example? Table 250.122 references ocpd size, not ungrounded conductor size, so we need that to start picking an EGC size.

Other questions may follow depending on the above.

Cheers, Wayne