jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Lobster tank GFCI protection?
- Thread starter kp542
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jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
2 ohms is to high for a realistic real world loop impedance... for one voltage drop would be noticeable on such a branch circuit- and that would mean 60amps short circuit at a 120 volt outlet. Not likely in the real world- more like 175+ amps or 0.6 maximum fault loop impedance.
Even when UL was conducting testing on AFCIs they found the absolute lowest worse case (really theorized and ultra conservative approach to justify AFCIs) short circuit current one might find at a receptacle to be 75amps:
http://combinationafci.com/resources/doc_ieee_combination_afci.pdf
Page 4:
Many in the industry are doubtful of this low number btw. I know it doesn't prove my point all that well, but even under ultra worst case UL assumptions its still above your 60amps.
Is a 600 volt rated power pact B frame breaker likely to be feeding a 120 volt outlet in a restaurant? Again- no concept of realism. More likely a QO breaker will be feeding said outlet:
https://download.schneider-electric...2.1080103655.1532924957-1088240790.1532924957
Notice the instant unlatching function (magnetic trip) starts around 6x the handle rating or 120amps, below the minimum 175 or more realistically 250amps of short circuits.
In other words that fault won't take a 1/2 second to clear, more likely 1/60th to 2/60ths of a second.
Honestly- you are using unrealistic numbers in a legitimate science to prove 250.122 wrong. Real world loop is way lower and breakers open much faster.
Also- you don't know of my authority or influence, which is a good thing.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Definitely crazy talk.
Ok- so something double insulted somehow starts to leak water to the earth. You really want to go down that rabbit hole?
(yes I know apples to oranges- fresh water to salt- but food for thought)https://www.youtube.com/watch?v=MF9DCNkaE8I
Now on 230 volts AC:
https://www.youtube.com/watch?v=3-3M3r69pOQ
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
2 ohms is to high for a realistic real world loop impedance... for one voltage drop would be noticeable on such a branch circuit- and that would mean 60amps short circuit at a 120 volt outlet. Not likely in the real world- more like 175+ amps or 0.6 maximum fault loop impedance.
Even when UL was conducting testing on AFCIs they found the absolute lowest worse case (really theorized and ultra conservative approach to justify AFCIs) short circuit current one might find at a receptacle to be 75amps:
http://combinationafci.com/resources/doc_ieee_combination_afci.pdf
Page 4:
Many in the industry are doubtful of this low number btw. I know it doesn't prove my point all that well, but even under ultra worst case UL assumptions its still above your 60amps.
Is a 600 volt rated power pact B frame breaker likely to be feeding a 120 volt outlet in a restaurant? Again- no concept of realism. More likely a QO breaker will be feeding said outlet:
https://download.schneider-electric...2.1080103655.1532924957-1088240790.1532924957
Notice the instant unlatching function (magnetic trip) starts around 6x the handle rating or 120amps, below the minimum 175 or more realistically 250amps of short circuits.
In other words that fault won't take a 1/2 second to clear, more likely 1/60th to 2/60ths of a second.
Honestly- you are using unrealistic numbers in a legitimate science to prove 250.122 wrong. Real world loop is way lower and breakers open much faster.
Also- you don't know of my authority or influence, which is a good thing.
Good luck. I is outta this thread.
Watching you get into a grounding/safety fight with a dude who knows this crap down is too painful. The cranky ole train driver does this stuff for MINES for a living.
He may be ornery and terse at times but tangling with him in GF, HRG, and similar issues?
Again, good luck.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Ok- so something double insulted somehow starts to leak water to the earth. You really want to go down that rabbit hole?
https://www.youtube.com/watch?v=MF9DCNkaE8I
Now on 230 volts AC:
https://www.youtube.com/watch?v=3-3M3r69pOQ
I do not watch videoes, I have told you that repeatedly....
As far as rabbit holes....You dove in Alice.......I choose not to follow.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
He knows mines, and knows the science of loop impedance which I do not dispute- but in this case he is choosing numbers which do not reflect the real world outside of mines. As such I will counter those arguments. Will I do so regarding mines? No, because I know zero about mines and as such I won't even make an effort to try. However I do know a little about building wiring and will challenge what I know to be incorrect.
And honestly- you are falling for it- letting him make you believe that 250.122 and modern MCBs are putting lives in danger.
I would stick around, this is very interesting theory being discussed.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
I know, I know- this was a bit beside the conversation. :ashamed1:
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
In directly he is saying that table 250.122 is undersized and breakers trip to slow by using unrealistic numbers. I mean he is technically correct as I can run 1,500 feet of #14 to a shed- but outside of some rare extremes where the installer clearly was not thinking there is no issue. In fact that could be fixed by mandating a max distance like 1000 feet for #14, 1,200 for #12 ect.
You have a point- and its good that you know how LE and frame potentials work. Though if I may take a swipe at electricians not all of them know what earth fault loop impedance is. Its not something mentioned in the NEC.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
How likely is the lobster tank going to be inside a mine? If it is, then GFCI protection seems even more important. If it is in a place with primarily non conductive surfaces it seems more redundant then a necessity. Isn't that part of why 210.8 lists the places it does for GFCI protection requirements? The ones mentioned typically have greater risk of conductive surfaces. Ignore the dishwasher, that wasn't even added for shock protection reasons:happysad:
GFCI as you have mentioned isn't about water, though presence of water does increase conductivity in many instances and therefore it appears to some it is all about the water.
That lobster tank could just be a steel case with electric components inside and the risk of shock is similar.
MasterTheNEC
CEO and President of Electrical Code Academy, Inc.
- Location
- McKinney, Texas
- Occupation
- CEO
Greetings Gents,
I found this a very interesting thread. I guess from my perspective both the "safety ground" and the "GFCI" serve a specific role in saving lives and I tend to focus on that versus the "theory" of which is better or which can save a life. Interesting enough, we on CMP 5 actually focus on the aspects of the "safety circuit" concept of ensuing a properly sized EGC is provided in order to give a properly installed OCP the change of operation, which in turn will remove a shock hazard that would potentially exist if it didn't open the circuit as it pertains to ground faults.
We spend a lot of time in system designs to make sure we do provide that "intentionally" constructed low-impedance, electrically conductive path from the point of a ground-fault back to the OCP to ensure that it trips reliably within the instantaneous range (~ 5-7 times it's handle rating). Sure currents less than that "range" are in reality time-delayed and in cases where GFCI's are installed it simply enhances that level of safety over the systems designed safety. I guess from my perspective the two serve different roles; the EGC is to remove a condition that creates a hazard while the GFCI removes conditions of lower levels of current where the EGC may lack the low-impedance aspects needed to ensure quick and reliable operation of the OCP. Both of which are very important to a safety, with regards to the installation of a "safety circuit" as given in Part VI of article 250 for all installations where an EGC is required and where the elevated hazards existing where a breakdown in Part VI, in areas deemed critical by the NEC® [such as Pools, Kitchen Counters, Etc. as in 210.8(A) and (B)] GFCI's are mandated and serve their lower current detection enhancement.
As for the numbers - You guys are too smart for me as i like to keep it simply. The NEC® tells me where I have to put the GFCI's so I put them, the NEC® tells me I have to provide a EGC so I provide one. I will take the high road and say they both are equally important and leave it at that. As for the Lobster Tank, well we can always exceed the NEC® and if the condition warrants then providing a EGC to the circuit (as required) and offering a GFCI would never harm the situation. Do I think the GFCI is required, well if the location is not determined by the AHJ to be one covered in 210.8(A) or (B) or other areas of the NEC® then no it would not be required.
About all I have on the subject.... Happy Monday!
I found this a very interesting thread. I guess from my perspective both the "safety ground" and the "GFCI" serve a specific role in saving lives and I tend to focus on that versus the "theory" of which is better or which can save a life. Interesting enough, we on CMP 5 actually focus on the aspects of the "safety circuit" concept of ensuing a properly sized EGC is provided in order to give a properly installed OCP the change of operation, which in turn will remove a shock hazard that would potentially exist if it didn't open the circuit as it pertains to ground faults.
We spend a lot of time in system designs to make sure we do provide that "intentionally" constructed low-impedance, electrically conductive path from the point of a ground-fault back to the OCP to ensure that it trips reliably within the instantaneous range (~ 5-7 times it's handle rating). Sure currents less than that "range" are in reality time-delayed and in cases where GFCI's are installed it simply enhances that level of safety over the systems designed safety. I guess from my perspective the two serve different roles; the EGC is to remove a condition that creates a hazard while the GFCI removes conditions of lower levels of current where the EGC may lack the low-impedance aspects needed to ensure quick and reliable operation of the OCP. Both of which are very important to a safety, with regards to the installation of a "safety circuit" as given in Part VI of article 250 for all installations where an EGC is required and where the elevated hazards existing where a breakdown in Part VI, in areas deemed critical by the NEC® [such as Pools, Kitchen Counters, Etc. as in 210.8(A) and (B)] GFCI's are mandated and serve their lower current detection enhancement.
As for the numbers - You guys are too smart for me as i like to keep it simply. The NEC® tells me where I have to put the GFCI's so I put them, the NEC® tells me I have to provide a EGC so I provide one. I will take the high road and say they both are equally important and leave it at that. As for the Lobster Tank, well we can always exceed the NEC® and if the condition warrants then providing a EGC to the circuit (as required) and offering a GFCI would never harm the situation. Do I think the GFCI is required, well if the location is not determined by the AHJ to be one covered in 210.8(A) or (B) or other areas of the NEC® then no it would not be required.
About all I have on the subject....
Happy Monday!wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I think your narrative omits your assumed "body z", and I think you are taking it to be 600 ohms? Is that correct? Just want to be sure I'm following your calculations.
Cheers, Wayne
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Ok- so something double insulted somehow starts to leak water to the earth. You really want to go down that rabbit hole?
Freudian slip?
correct, the range is 500 to 1250, mean 900 or so
as far as 'he only knows mines'
35 year career
29 in industry: data centers, comm, oil/gas, mil facilities, pharma/biotech, water/wasrewater, commercial
no residential other than large apts and public housing
mining 6 years, as complex, or more so, than almost anything else I've done
2 ohms is to high for a realistic real world loop impedance... for one voltage drop would be noticeable on such a branch circuit- and that would mean 60amps short circuit at a 120 volt outlet. Not likely in the real world- more like 175+ amps or 0.6 maximum fault loop impedance.
Even when UL was conducting testing on AFCIs they found the absolute lowest worse case (really theorized and ultra conservative approach to justify AFCIs) short circuit current one might find at a receptacle to be 75amps:
http://combinationafci.com/resources/doc_ieee_combination_afci.pdf
Page 4:
Many in the industry are doubtful of this low number btw. I know it doesn't prove my point all that well, but even under ultra worst case UL assumptions its still above your 60amps.
Is a 600 volt rated power pact B frame breaker likely to be feeding a 120 volt outlet in a restaurant? Again- no concept of realism. More likely a QO breaker will be feeding said outlet:
https://download.schneider-electric...2.1080103655.1532924957-1088240790.1532924957
Notice the instant unlatching function (magnetic trip) starts around 6x the handle rating or 120amps, below the minimum 175 or more realistically 250amps of short circuits.
In other words that fault won't take a 1/2 second to clear, more likely 1/60th to 2/60ths of a second.
Honestly- you are using unrealistic numbers in a legitimate science to prove 250.122 wrong. Real world loop is way lower and breakers open much faster.
Also- you don't know of my authority or influence, which is a good thing.
faults are seldom bolted, usually arcing
wag that is one reason for 1/t cb's
btw I posted the cb curve if you know how to read it
ask any real electrician; most fires are hi Z faults, say 30 A on a 20, 10-20 min
175 x 0.6/600 = 175 ma
Dalziel 0.33 sec
your chart 0.75 sec
cb trip at 175, 8 x Ir or 800% 1 sec = dead
you have less authority or influence than you do understanding
garage
2 pole plug, cracked/compromised insul and wet
wet floor
wet hands
20/1 or egc will do nothing
guess that is why the nec requires it
many industries use sgf and ngr
iirc gfci started out in order
bathrooms
kitchens
outdoors
garages
pools
all have decreased gf paths and increased shorting hazard, ie, water
never said mccb's are dangerous
they are primarily fire/equip/elec sys protections
they do afford some personnel protection (deenergise faulted ckts before they become a shock hazard)
they offer minimal protection to personnel DURING a fault
hence gfci = personnel protection
in a perfect 'cost no object' world you would have both set to appropriate levels
iirc gfci started out in order
bathrooms
kitchens
outdoors
garages
pools
all have decreased gf paths and increased shorting hazard, ie, water
never said mccb's are dangerous
they are primarily fire/equip/elec sys protections
they do afford some personnel protection (deenergise faulted ckts before they become a shock hazard)
they offer minimal protection to personnel DURING a fault
hence gfci = personnel protection
in a perfect 'cost no object' world you would have both set to appropriate levels
Last edited:
hey!!! I represent that! lol
I may be old, and terse (you try posting on an iphone
)but ornery and cranky?!? lol, frustrated for wasting time trying to explain it
ok, I come across as such at times, but really, no emotional content, no ill will
just being a smart @$$
not a fight
trying to show him a gfci provides protection solid grounding/bonding does not
NOT saying: eliminate egc's, mccb's are dangerous, etc
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
hey!!! I represent that! lol
I may be old, and terse (you try posting on an iphone
but ornery and cranky?!? lol, frustrated for wasting time trying to explain it
ok, I come across as such at times, but really, no emotional content, no ill will
just being a smart @$$
not a fight
trying to show him a gfci provides protection solid grounding/bonding does not
NOT saying: eliminate egc's, mccb's are dangerous, etc
Okay, you be old and terse, I will be ornery and cranky.
I was just having a bit of fun, we all got personalities around here for sure.
I hate using phone.
I agree about GFCI and EGC. Both serve their purposes.
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