Let me guess:
I don’t know. Can you explain?
I checked this on an open panel this AM and A is correct. The bottom reading was 7 and then went to 0 on the two breakers.
Thank you John!
Kenton,
You are correct, the first graphic is correct. Opposite single pole breakers share the same lug. Every other single pole breaker pair uses the other lug. Never looked at the lug arrangement that close.
I had to look it up myself. A panel board diagram learned me. Now I know what I never thought to know before, thanks Kenton.
Kenton, if black is flowing 10 amps and red is flowing 5 amps the neutral will only carry 5 amps. If both black and red were on the same leg the neutral would carry the sum of both black and red.
Yes. The shared grounded conductor of a properly configured MWBC will only carry the difference in load between the two ungrounded conductors. If it’s misconfigured (i.e., both on the same phase with potential of 0), the grounded conductor will carry the combined load, which may significantly exceed the ampacity of the shared grounded conductor.
I see this with surprising frequency where MWBCs are wired to tandem breakers.
Well…unless we are looking at a RIGGED image. The one I would choose it “A” but again I don’t know Mexico. I do know that they are using the NEC for the most part and our Latin America division of NEMA is pushing to its use. I would say A, use of nominal voltages should always be encouraged. The fact it is labeled as 254/120 is strange (unless its a Mexican thing) but who knows what Kenton is shooting for.
It helps to read the posts you comment on, Paul.
As for what I’m shooting for, you know what I’m shooting for. I wrote you directly asking for help, but didn’t get any.
Thanks Jim!
Firstly, I am very busy Kenton and I answer ALOT of posts here. Also I did respond to your questions and gave you a specific answer. However, if you send more than one I might not have seen it…I do travel a lot Kenton and I do not get to answer all of my emails as quickly as some might want.
Also…emails should be sent to my personal email account and not the office email for the people I work for unless it is related to that work. So if you consider I do not answer questions…NEVER ASK ME ANOTHER ONE!
Hi Paul,
As InterNACHI’s Director of International Development I am in Mexico writing a complete set of home inspection courses to found an inspection industry here. In writing the Electrical course I have to be able to answer questions and I’ve encountered a couple of basic questions to which I cannot find answers. I asked on the InterNACHI message boards but in reply I got so many squabbles that I don’t think that any of them know what they’re talking about. Extensive online research has failed to supply me with an answer. I’m really stuck, and I need to finish this course, and then complete two more, so I’m hoping you can help me.
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What is the actual danger- and level of danger- from having a bonded neutral at a sub-panel? I need to be able to explain this fairly simply to those wanting to become Mexican home inspectors, to those performing electrical work, and to homeowners and clients.
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I don’t know much about fused disconnects. I often see three cartridge fuses in what I assume is a single-phase 120/240v system and I don’t know why. I would expect to see only 2, each a 120v leg. Should I see neutral and grounding bus bars bonded together and bonded to the panel in service panels with fused disconnects? I really need to understand residential systems with fused disconnects, but I can’t find any resources I trust.
Thanks,
[FONT=“Calibri”]Kenton Shepard, CMI[/FONT]
Kenton,
As you can see by the email address I am already working on life after NEMA. I will have my new website up very soon and hope to offer an exclusive deal to NACHI members if Nick is agreeable to it. Anyway, to your questions.
[FONT=Calibri]1. [/FONT]What is the actual danger- and level of danger- from having a bonded neutral at a sub-panel? I need to be able to explain this fairly simply to those wanting to become Mexican home inspectors, to those performing electrical work, and to homeowners and clients.
Answer: The neutral (grounded) conductor provides a return path for imbalanced current and normal return current from the energy source, to the load, and back to the energy source. When the neutral (grounded) conductor is improperly connected to the equipment grounding conductor and bonded metal enclosure downstream from the service disconnection mean, you create multiple paths for potential current to flow back to the energy source. The equipment grounding conductors and associated bonding jumpers will now carry current known as objectionable current. The hazard of this event is that metal components that are bonded to that effective fault current path will carry potential current and if someone comes in contact with the exposed metal parts of the electrical system they could become the unintended path of that current back to the source resulting in possible electrocution. Also in the event of a lose neutral (grounded) conductor connection, if the improper case to neutral connection as described above is located in a remote distribution panel (sub-panel), the equipment grounding conductor would serve as the sole return path resulting in energizing all of the metal parts in the system.
[FONT=Calibri]2. [/FONT]I don’t know much about fused disconnects. I often see three cartridge fuses in what I assume is a single-phase 120/240v system and I don’t know why. I would expect to see only 2, each a 120v leg. Should I see neutral and grounding bus bars bonded together and bonded to the panel in service panels with fused disconnects? I really need to understand residential systems with fused disconnects, but I can’t find any resources I trust.
**Answer: **Typically when you see a 3-pole cutout box or fused disconnect you are looking at a device that is listed for 3-phase application. In order to use a 3-pole cutout box as you described, it would have to also be listed for its intended use by a Nationally Recognized Testing Laboratory like UL or ETL. If the cutout box or fused disconnect is rated for single phase 120/240 then it will say so on the label and inform you of what poles to use in the device. If the device says 3-phase and adds no mention of single phase then it is not intended for use with single phase 120/240 systems. You also ask should you see a neutral (grounded) and grounding bus bar in these cutout boxes. Well, remember that the NEC only permits the connection of the neutral (grounded) conductor and the equipment grounding conductors at the service disconnection means and not downstream. The equipment grounding bus would be present in order to maintain the effective fault current path for the equipment grounding conductors but the neutral would not terminate to this bar…it will be isolated or continued on to the load where applicable.
Lastly, I am a resource you can trust. Use me ! Just remember that NEC 250.24(A)(5) in the 2014 NEC prohibits the connection of the grounded conductor to normally non-current carrying metal parts, including the equipment grounding conductor on the load side of the service disconnection means…period.
Educationally Yours,
Paul Abernathy
SO…YOU LIE!
I am DONE helping ungratefuls !
Excellent suggestion. WTMIL