I sell access systems and one of my suppliers has a RS485 optical Mux. One in and eight out that are optically isolated. Can you add a link to your units? I will pass it by the manufacture for their consideration. The theory is something is putting voltage on the ground. The entire system uses RS485 two wire with ground. The ground is connected at one spot to earth ground. Bad juju if the ground is feed voltage not dissipating it.
Three Phase site - multiple electrical issues.
- Thread starter Sparty D
- Start date
- Status
I sell access systems and one of my suppliers has a RS485 optical Mux. One in and eight out that are optically isolated. Can you add a link to your units? I will pass it by the manufacture for their consideration. The theory is something is putting voltage on the ground. The entire system uses RS485 two wire with ground. The ground is connected at one spot to earth ground. Bad juju if the ground is feed voltage not dissipating it.
The code did require AFCI in the bedrooms. I think NEC 2008 even though the building was built in 2010-2011. The engineer speced AFCI and required each branch to have a dedicated neutral. The fact the install was not to spec is basically a known fact even though the EC is trying to keep the GC out of hot water and saying they think it meets code. The owner was short changed IMO.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
140327-0007 EDT
Sparty D:
I do not make an RS422 or RS485 isolator. Mine are 232 to 422 and by use of a crossover cable the same unit is used at the other end of the line for 422 to 232.
My comments were to show that with optical isolation and moderately fast data transmission that it is possible to tolerate large common mode voltages. I recommend isolation at both ends to protect the equipment at both ends.
A single isolator might be satisfactory if there is no likelihood of a high voltage short to the communication line.
.
Sparty D:
I do not make an RS422 or RS485 isolator. Mine are 232 to 422 and by use of a crossover cable the same unit is used at the other end of the line for 422 to 232.
My comments were to show that with optical isolation and moderately fast data transmission that it is possible to tolerate large common mode voltages. I recommend isolation at both ends to protect the equipment at both ends.
A single isolator might be satisfactory if there is no likelihood of a high voltage short to the communication line.
.
NEC 250 Question
NEC 250 Question
I know this tread is getting long. Earlier I noted that we discovered that some feeder panels did not have the same number of hots as neutrals. The EC hired by the GC has basically confirmed our one hour investigation and in deed the site does NOT meet spec. The EE designed it with no shared neutrals and that did not happen. I also learned that they found 12 branch circuits that they can not identify where they lead to. I am assuming they flipped breakers and nothing went off, but did not tone out where they lead. Plan is not to meet spec as they feel it meets code. Customer was short changed IMO.
Also, as I mentioned this is three separate buildings and classified as residential for building code even though it is a three phase wye service. The service enters building two, because it is in the center, but one and three are feed from 400amp disconnects in building two (after the 1600amp main panel). Buildings one and three also have around five sub panels with 42 breakers average. There are no ground rods or grounding system in building one or three and they get earth ground from building two only*. This was built in 2010/2011 and NEC code 2008 was the city's standard. There is one bond at the service panel, but as I read NEC 250.32 buildings one and three should have ground rods themselves. Remember, these are wood frame structures and no metal water pipes, building steel or ufer was available so that is why I say rods.
*If what I am told is correct, would buildings one and three not having their own grounding system be a code violation? It appears they are grounded, but in another building.
I know here in the Midwest, I would not want a lightning strike to have to go any further than necessary to find home. Through one building then underground and through a second building and out the side wall to the bonded ground rods seems dangerous.
250.32. Grounding Separate Buildings and Structures
(A) Grounding - To the Earth. Metal parts of the electrical system in separate buildings or structures supplied by a feeder, building or structure must be grounded to the earth to prevent the destruction of electrical components from superimposed voltage from line surges, unintentional contact with higher voltage lines, and voltage transients and to help prevent the build-up of static charges on equipment and material [250.4(A)(2).
Exception. A grounding electrode at a separate building or structure is not required where only one branch circuit (with an equipment bonding conductor) supplies the building or structure. Slide 209
DANGER - Failure to ground the metal parts of the electrical system to the earth can result in electric shock, fires and the destruction of expensive electronic equipment from lightning or high voltage line surges.
(B) Grounding - Effective Fault Current Path. To protect against electric shock from a ground-fault (line-to-case fault), dangerous voltage on metal parts of the electrical system must be removed in less than 1 second by opening the circuit overcurrent protection device. To accomplish this, the impedance of the fault current path must allow the ground-fault (line-to-case fault) current to raise to a value of at least 5 times and preferably 10 times the rating of the overcurrent protection device.
In order for the circuit overcurrent device to open and prevent dangerous voltage from remaining on metal parts of electrical equipment, noncurrent-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment must be bonded together and to the grounded (neutral) terminal at the electrical supply source in a manner that establishes an effective ground-fault current path.
(1) Equipment Grounding Conductor. An equipment grounding conductor [250.118], sized in accordance with 250.122, shall be installed with the feeder conductors to the separate building or structure to bonding equipment, structures, or frames .
Author?s Comment: The feeder equipment grounding conductor provided the low impedance path for fault current to ultimately return to the electrical supply source as required by 250.2(A)(3).
CAUTION: To prevent dangerous neutral current from flowing on the metal parts of the electrical system, in violation of 250.6(A), the grounded (neutral) conductor at the separate building or structure must not be bonded to either the equipment grounding conductor or to the grounding electrode system.
(2) Grounded (neutral) Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, and (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded (neutral) conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s). The size of the grounded conductor shall not be smaller than the larger of:
(1) That required by 220.22 (maximum unbalanced neutral load), or
(2) That required by 250.122 (equipment grounding conductor size).
NEC 250 Question
I know this tread is getting long. Earlier I noted that we discovered that some feeder panels did not have the same number of hots as neutrals. The EC hired by the GC has basically confirmed our one hour investigation and in deed the site does NOT meet spec. The EE designed it with no shared neutrals and that did not happen. I also learned that they found 12 branch circuits that they can not identify where they lead to. I am assuming they flipped breakers and nothing went off, but did not tone out where they lead. Plan is not to meet spec as they feel it meets code. Customer was short changed IMO.
Also, as I mentioned this is three separate buildings and classified as residential for building code even though it is a three phase wye service. The service enters building two, because it is in the center, but one and three are feed from 400amp disconnects in building two (after the 1600amp main panel). Buildings one and three also have around five sub panels with 42 breakers average. There are no ground rods or grounding system in building one or three and they get earth ground from building two only*. This was built in 2010/2011 and NEC code 2008 was the city's standard. There is one bond at the service panel, but as I read NEC 250.32 buildings one and three should have ground rods themselves. Remember, these are wood frame structures and no metal water pipes, building steel or ufer was available so that is why I say rods.
*If what I am told is correct, would buildings one and three not having their own grounding system be a code violation? It appears they are grounded, but in another building.
I know here in the Midwest, I would not want a lightning strike to have to go any further than necessary to find home. Through one building then underground and through a second building and out the side wall to the bonded ground rods seems dangerous.
250.32. Grounding Separate Buildings and Structures
(A) Grounding - To the Earth. Metal parts of the electrical system in separate buildings or structures supplied by a feeder, building or structure must be grounded to the earth to prevent the destruction of electrical components from superimposed voltage from line surges, unintentional contact with higher voltage lines, and voltage transients and to help prevent the build-up of static charges on equipment and material [250.4(A)(2).
Exception. A grounding electrode at a separate building or structure is not required where only one branch circuit (with an equipment bonding conductor) supplies the building or structure. Slide 209
DANGER - Failure to ground the metal parts of the electrical system to the earth can result in electric shock, fires and the destruction of expensive electronic equipment from lightning or high voltage line surges.
(B) Grounding - Effective Fault Current Path. To protect against electric shock from a ground-fault (line-to-case fault), dangerous voltage on metal parts of the electrical system must be removed in less than 1 second by opening the circuit overcurrent protection device. To accomplish this, the impedance of the fault current path must allow the ground-fault (line-to-case fault) current to raise to a value of at least 5 times and preferably 10 times the rating of the overcurrent protection device.
In order for the circuit overcurrent device to open and prevent dangerous voltage from remaining on metal parts of electrical equipment, noncurrent-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment must be bonded together and to the grounded (neutral) terminal at the electrical supply source in a manner that establishes an effective ground-fault current path.
(1) Equipment Grounding Conductor. An equipment grounding conductor [250.118], sized in accordance with 250.122, shall be installed with the feeder conductors to the separate building or structure to bonding equipment, structures, or frames .
Author?s Comment: The feeder equipment grounding conductor provided the low impedance path for fault current to ultimately return to the electrical supply source as required by 250.2(A)(3).
CAUTION: To prevent dangerous neutral current from flowing on the metal parts of the electrical system, in violation of 250.6(A), the grounded (neutral) conductor at the separate building or structure must not be bonded to either the equipment grounding conductor or to the grounding electrode system.
(2) Grounded (neutral) Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, and (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded (neutral) conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s). The size of the grounded conductor shall not be smaller than the larger of:
(1) That required by 220.22 (maximum unbalanced neutral load), or
(2) That required by 250.122 (equipment grounding conductor size).
zach_zachary1@yahoo.com
Member
- Location
- Apex,NC
I thought Romex was only rated for residential use.
The prints from the EE said the neutral was to be uninterrupted through the ATS and the Gen Set was not to have a ground. I will have to ask if anyone has truly check that. We all are spit balling and we all know what it means to assume. Did you see my 3/31/2014 post?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If it were that simple the uses permitted/uses not permitted would only be one short sentence, but they take up most of a page in the code book.
Even though this is a nursing home it was built under residential codes in most regards.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If the area where the NM is installed meets the uses permitted then it is ok to use it.
Next thing you could run into in a nursing home is some areas are health care areas and it would not be allowed by art 517 in those areas or you could have some common spaces that are maybe considered places of assembly and would not be allowed by art 518.
Thanks for the input. Each home has maybe 18 bedrooms so less than 100 occupants. 518 I think is out then and this is a memory care home (Alzheimer) and maybe outside a typical health care category. They don't have any treatments areas. It is designed to resemble a house in most regards.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
518 generally wouldn't apply to patient/resident rooms, but would apply to a dining room or activities room if it has an occupancy of 100 or more.
I'm not going to look for it right now but somewhere in 517 it describes that rooms in nursing homes or assisted living facilities or similar that are simply sleeping rooms and no patient care is normally provided that area this is not considered a patient care area.
Many such facilities do have some rooms dedicated to specialized care - maybe only intended for a temporary use until the patient can be transported to a facility that is better equipped to handle the patient, but those areas are subject to all the rules of patient care areas if they have such rooms.
Now health care is still provided in those "sleeping rooms" but you kind of need to get into health care some to further distinguish just what kinds of health care activity need to be done before some of 517 requirements kick in. Most of the care that happens is care that could be done at home, but is more convenient / less cost / other benefits to be provide in a setting like a nursing home, 517 starts to kick in when medical procedures become more invasive to the patient or more electronic diagnostic or life supporting equipment becomes a part of the care, and generally the level of training by the attending caregiver(s) is at a higher level as well.
rlundsrud
Senior Member
- Location
- chicago, il, USA
Originally Posted by rlundsrud
Ok, This was a LOT to read, but I tried to read through all of the threads so I don't post anything redundant. With that said, I am curious about the generator, specifically the bonding of the neutral. I am wondering if the neutral was done incorrectly and it is double bonded. You would have to check to see how the neutral was run through the ATS, and whether it was bonded at the generator. If it was bonded at the generator it needs to disconnect from the main system at the ATS. There are some very nice threads on this forum that show how it should be done. I am just spit balling on this, but it would be easy to check and even if it isn't the fix for this, it may well be wrong anyway given the original EC's issues and should be corrected.
Bob
The prints from the EE said the neutral was to be uninterrupted through the ATS and the Gen Set was not to have a ground. I will have to ask if anyone has truly check that. We all are spit balling and we all know what it means to assume. Did you see my 3/31/2014 post?
If that is the case, the neutral should not be bonded at the ATS and only at the main service. Again, something that is worth checking and should be fairly easy to do. Hope that helps.
Ok, This was a LOT to read, but I tried to read through all of the threads so I don't post anything redundant. With that said, I am curious about the generator, specifically the bonding of the neutral. I am wondering if the neutral was done incorrectly and it is double bonded. You would have to check to see how the neutral was run through the ATS, and whether it was bonded at the generator. If it was bonded at the generator it needs to disconnect from the main system at the ATS. There are some very nice threads on this forum that show how it should be done. I am just spit balling on this, but it would be easy to check and even if it isn't the fix for this, it may well be wrong anyway given the original EC's issues and should be corrected.
Bob
The prints from the EE said the neutral was to be uninterrupted through the ATS and the Gen Set was not to have a ground. I will have to ask if anyone has truly check that. We all are spit balling and we all know what it means to assume. Did you see my 3/31/2014 post?
If that is the case, the neutral should not be bonded at the ATS and only at the main service. Again, something that is worth checking and should be fairly easy to do. Hope that helps.
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