Bonding XO when not using a neutral conductor

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Kinexis said:
it depends on what impedance and time your talking about. if the difference is the ocpd opening in 1 or 1/2 cycle instead of 30 it has a negative effect
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obviously
but we talking on the order of xx%, not xxxx%

and even then i is reduced by the same factor
30^2 x 1 = 900
1^2 x 30 = 30
1/30th the energy
 
Ingenieur said:
obviously
but we talking on the order of
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we are not talking about the same thing, your just talking about the ratio's of time and current compared to energy. if you play with formulas what you are saying is true but those ratios are relative. what matters is the real world affect of fault impedance
 
and by real world i mean where it is required by nec for ocpd to be rated for available fault current, when you have ocpd rated for the available fault current, why wouldn't you want your fault circuit impedance outside of the transformer to be 0? you would and the ocpd would open safely because it is rated for the available fault current



does anyone know of the videos that show short cycle time faults? i'm not finding them right now
 
Kinexis said:
we are not talking about the same thing, your just talking about the ratio's of time and current compared to energy. if you play with formulas what you are saying is true but those ratios are relative. what matters is the real world affect of fault impedance
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here's an extreme example
480/3, 80 A load, 100 cb, line-line fault
1% total v drop 4.8 v, z = 4.8/80 = 0.06 Ohm
5% total v drop 24 v, z = 24/80 = 0.30 Ohm
1% isc = 480/0.06 = 8000 A (80 x ir)
5% isc = 480/0.3 = 1600 A (16 x ir)

what is the trip time for each?
what is the i^2 r energy?

if you want a reference on faults(transients) imho a good one
 
Ingenieur said:
here's an extreme example
480/3, 80 A load, 100 cb, line-line fault
1% total v drop 4.8 v, z = 4.8/80 = 0.06 Ohm
5% total v drop 24 v, z = 24/80 = 0.30 Ohm
1% isc = 480/0.06 = 8000 A (80 x ir)
5% isc = 480/0.3 = 1600 A (16 x ir)

what is the trip time for each?
what is the i^2 r energy?
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trip time is dependent on the ocpd your using, there all different


what i mean by your ratios are only relative is the 1 and 5% seam like small difference and 8k and 1.6 k seam a lot larger and they are, they are bigger ratios but that does not directly translate in the real world to mean less current is safer
 
Kinexis said:
trip time is dependent on the ocpd your using, there all different
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most meet standard approval agency guidelines, ul, iec, etc
they have to in order to protect standard conductor sizing/ampacity ratings
it's why you can't use a 100 cb with a #12 lol
just pick any off the shelf eaton cb
 
Ingenieur said:
most meet standard approval agency guidelines, ul, iec, etc
they have to in order to protect standard conductor sizing/ampacity ratings
it's why you can't use a 100 cb with a #12 lol
just pick any off the shelf eaton cb
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we are honestly talking about 2 different things. 1% and 5% impedance in real world is very big difference compared to 8ka and 1.5ka fault current which is not in terms of what we are talking about
 
Kinexis said:
we are honestly talking about 2 different things. 1% and 5% impedance in real world is very big difference while 8ka and 1.5ka fault current is not
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my example is real world
for the same 100 A 480/3 1.6 ka vs 8 ka is a huge difference

1000 A ckt
1% z = 4.8/800 = 0.006 Ohm, isc = 80 ka (80 x ir)
5% z = 24/800 = 0.03 Ohm, isc = 16 ka (16 x ir)
both ~ instantaneous (>13/15 x ir)
is a factor of 5 or 64 ka a big difference?
go ahead, pick ANY cb
 
Ingenieur said:
my example is real world
for the same 100 A 480/3 1.6 ka vs 8 ka is a huge difference

1000 A ckt
1% z = 4.8/800 = 0.006 Ohm, isc = 80 ka (80 x ir)
5% z = 24/800 = 0.03 Ohm, isc = 16 ka (16 x ir)
both ~ instantaneous (>13/15 x ir)
is a factor of 5 or 64 ka a big difference?
go ahead, pick ANY cb
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a 22kaic breaker

the system would already be properly designed the breaker would never see 80ka


REAL WORLD


do you commonly use breakers that go that high?


no system has infinite ampacity
 
Kinexis said:
a 22kaic breaker

the system would already be properly designed the breaker would never see 80ka


REAL WORLD
Click to expand...

if total system v drop is 1% and with a stiff util it would
I'll be back when you pick a cb
very simple to do
but it sinks your 'point'
both would trip within a few cycles
but i^2 is 25 times higher

the nec guidelines are not random guesses
they protect one from theirself if followed
 
Square D MAL361000


once again i will say we are talking about 2 different things, i'm saying 1 cycle is a lot safer than 30 cycles, 15 cycles.

you cannot accurately adjust your impedance of bad bonding connections throughout a ground fault return path, zero is the ideal z to shoot for in this subject matter
 
Kinexis said:
a 22kaic breaker

the system would already be properly designed the breaker would never see 80ka


REAL WORLD


do you commonly use breakers that go that high?


no system has infinite ampacity
Click to expand...

yes: 600,800,1000 are used often

a 2 mva 4.5% 53ka with a stiff supply
easily see >40ka on on short hi amp feeders
 
once again i will say we are talking about 2 different things, i'm saying 1 cycle is a lot safer than 30 cycles, 15 cycles.

you cannot accurately adjust your impedance of bad bonding connections throughout a ground fault return path, zero is the ideal z to shoot for in this subject matter. i am not disputing the numbers you are coming up with i assume they are correct, those numbers are related to what i am talking about but they do not look at the real world scenario i'm talking about
 
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