# Thread: Bonding XO when not using a neutral conductor

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Originally Posted by Ingenieur
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

in utility substations?

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Originally Posted by Kinexis
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
and I say that is not plausible if code compliant
and still may not be

it is definitely real world

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Originally Posted by Ingenieur
page 18 http://www.eaton.com/ecm/groups/publ...td012034en.pdf
16x 0.02 sec
80x 0.006

16^2 x 0.02 =5.1, 1.2 cycles
80^2 x 0.006 = 38.4 , 0.36 cycles

over 7 times as much
but a fault rise is a curve, not a straight line
nor is it's mag, transient, subtransient, steady state

whats the incident energy?

and once again we are not talking about the same thing i'm talking about the difference in 1 cycle and 30

both less than
Incident Energy = 1J/cm2 [= 0.24 cal/cm2 ]

so is it more dangerous to scrape off the paint?

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so now factor in real world.

30 years down the road the ground fault current path is rusty, which initial installation is better?

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Originally Posted by Kinexis
in utility substations?
no
industrial and mining

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Originally Posted by Kinexis
whats the incident energy?

and once again we are not talking about the same thing i'm talking about the difference in 1 cycle and 30

both less than
Incident Energy = 1J/cm2 [= 0.24 cal/cm2 ]

so is it more dangerous to scrape off the paint?
ok, let me try another approach
pu values
base: v = 1, i = 1 (ie cb rating), load = 0.8

v drop = 0.05 x 1
z = 0.05/0.8 = 0.0625
i sc = 1/0.0625 = 16 or 1600% of cb rating
inst range
not an issue

if you
comply with code
use listed equipment
install per code, mfgs recommendations, good workman like manner
not an issue

no one said more dangerous, just no advantage, it's not 'less' dangerous

7. Originally Posted by Kinexis
for that you just need to have correct ocpd for the available fault current which is already required by NEC. an impeded ground connection should never be considered adding a safety factor in my opinion
Kind of what I was trying to get at - yes we want higher magnitude to make the device operate as quick as possible, but at same time device is only designed to take a certain level, once you exceed that level, a different device is what is needed or design the supply so that there is enough impedance to keep available fault current below that maximum device rating.

There are more ways to introduce impedance other then via the grounded conductor - longer conductor runs, aluminum vs copper, line reactors, etc.

Only time you should put impedance in the grounded conductor is with intentionally impedance grounded system with ground fault monitoring components. Those systems are somewhat rare but do have places where they have benefits of using them.

8. looks like I missed about 26 posts before that last reply - doesn't change what I had to say much though.

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Originally Posted by Ingenieur
ok, let me try another approach
pu values
base: v = 1, i = 1 (ie cb rating), load = 0.8

v drop = 0.05 x 1
z = 0.05/0.8 = 0.0625
i sc = 1/0.0625 = 16 or 1600% of cb rating
inst range
not an issue

if you
comply with code
use listed equipment
install per code, mfgs recommendations, good workman like manner
not an issue

no one said more dangerous, just no advantage, it's not 'less' dangerous

then i'll say it. impeded bonding connections make an electrical system more dangerous, whether they were initially installed impeded or if they are impeded later in life either by corrosion, vibration loosening or other reason.

i think the big issue where with our disagreement is i look at electrical installations as limited by the transformer for the amount of available fault current, usually a-lot lower than the currents you are considering. also in terms of impedance for bonding connections i am thinking a better connection gets you closer to 1/2 cycle clearing time of short circuit protection and that the system cannot deliver astronomical current's, compared to worse connections that could introduce impedance lowering the short circuit current to levels where the clearing time is increased to something like 15 or 30 cycles.

i think you are looking at this discussion as simply system impedance and fault current where i am looking at the connection impedance and available fault current

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Originally Posted by kwired
Kind of what I was trying to get at - yes we want higher magnitude to make the device operate as quick as possible, but at same time device is only designed to take a certain level, once you exceed that level, a different device is what is needed or design the supply so that there is enough impedance to keep available fault current below that maximum device rating.

your system should be designed for available fault current with 0 impedance at connections, therefore short circuit protection will already have interrupting rating for the max available fault current for the system, making connections with more surface area and using anti oxidants to ensure against corrosion and bad connections for the lifetime of the system would not raise your available current. but if that little terminal bar or whatever other connection your considering hanging on(bonding) by (4) 1/4-20 threads sees some humidity over 40 years along with many other connections in the system the impedance can increase to where the short circuit protection does not open quick enough or at all.

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