Bonding XO when not using a neutral conductor

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infinity said:
I agree that is the reason, I would just use the bar as is from the manufacturer why bother with the extra work?
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i think it is a much more robust installation and it doesn't take much to do it, i keep a little wire wheel for drills in my toolbag
 
Kinexis said:
i think it is a much more robust installation and it doesn't take much to do it, i keep a little wire wheel for drills in my toolbag
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pretty easy to determine if it iscan issue (imo not)
meter from case/frame to bar

and is it an issue?
assume 208 ph-g fault
assume a bad 0.1 ohm across frame/bar joint
i fault = 1200 A, should pose no primary tripping issue
 
If the bolts or machine screws attaching the bar to the enclosure are threaded through the enclosure material itself there's no need to remove paint. That sort of thing is for locknuts without teeth, perhaps especially when using an outdoor fitting with a gasket on one side. My opinion for what it's worth.

I had an inspector gripe about paint the other day on a 3/4" offset nipple between two bonded enclosures. The locknuts were totally the type that scrape the paint away on their own, so I just ended up adding a grounding bushing cause I really didn't understand how I could improve contact by removing more paint. DMM measured .01 ohms between the nipple and the ground bar in the enclosures before I added the bushing. I was fairly ticked off about it.
 
jaggedben said:
If the bolts or machine screws attaching the bar to the enclosure are threaded through the enclosure material itself there's no need to remove paint. That sort of thing is for locknuts without teeth, perhaps especially when using an outdoor fitting with a gasket on one side. My opinion for what it's worth.

I had an inspector gripe about paint the other day on a 3/4" offset nipple between two bonded enclosures. The locknuts were totally the type that scrape the paint away on their own, so I just ended up adding a grounding bushing cause I really didn't understand how I could improve contact by removing more paint. DMM measured .01 ohms between the nipple and the ground bar in the enclosures before I added the bushing. I was fairly ticked off about it.
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I agree with you, but also don't see that being universally accepted - especially by inspectors. I will argue with them if attaching said item to a factory provided mounting hole, that is it listed to go there, in fact with loadcenters and grounding bars same thing is sometimes installed in same manner at the factory.

Will remove paint if mounting it in my own location, though I question whether it is really necessary in many cases, Bigger question may be if enclosure thickness is enough to engage enough threads for reliable continuity. Factory designated mounting holes - often it is.
 
Ingenieur said:
pretty easy to determine if it iscan issue (imo not)
meter from case/frame to bar

and is it an issue?
assume 208 ph-g fault
assume a bad 0.1 ohm across frame/bar joint
i fault = 1200 A, should pose no primary tripping issue
Click to expand...



use a dlro on both types of connections, there will likely be a significant difference, under fault conditions i want as low impedance on the ground fault return path as possible, the overrcurrent protection device is 1. more likely to open and 2. will open quicker and even if it is a millisecond quicker that with high current faults can prevent a lot of damage to equipment and people.

also you have to consider the possibility of corrosion for the life of the system, the more contact area originally the more corrosion the system can withstand, tha'ts also why i suggested the conductive grease


to myself i justify it easily with simple cost benefit, it takes me relatively little time to do it and i think it makes the installation much more robust
 
the bar is likely serated for good engagement
likely attached with boths/washers, unlikely to count only on tapping screws
I would like to believe the guys designing the gear have minimum competency

the enclosure is not considered intentionally as part of the egc/gnd fault path, although effective bonding is important

multiple parallel ground paths (conduit systems out to other enclos where a bond is present to the egc BACK to the gnd bar in question)

a little impedance may result in a marginally longer trip time but magnitude is reduced, so a wash

going the extra mile won't hurt, but imo yeilds little (if any) benefit
I'll need to look at some in the field, never really thought about it
just measured enclosure to lug R and usually in the few 100'ths range
the egc itself is much higher
 
The terminal bar in the transformer bolted to the enclosure is only bonding the enclosure. The transformer with the terminal bar is listed equipment so for me I won't waste a second removing it and scraping off the paint.
 
i know the bar is only for enclosure for code purposes but good parallel paths lower circuit impedance, i'm not saying it's required or should be just saying that's what i do and why.





Ingenieur said:
a little impedance may result in a marginally longer trip time but magnitude is reduced, so a wash
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higher magnitude is better, it will trip even quicker (less energy will be released in fault, arc flash/blast, it can be lowered to an insignificant little spark instead of a second long big incident with lower current)
 
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Kinexis said:
higher magnitude is better, it will trip even quicker (less energy will be released in fault, arc flash/blast, it can be lowered to an insignificant little spark instead of a second long big incident with lower current)
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Until a certain point is reached that equipment can't take the forces imposed on components, which is what SCC and AIC ratings are about.
 
kwired said:
Until a certain point is reached that equipment can't take the forces imposed on components, which is what SCC and AIC ratings are about.
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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
 
Kinexis said:
i know the bar is only for enclosure for code purposes but good parallel paths lower circuit impedance, i'm not saying it's required or should be just saying that's what i do and why.


higher magnitude is better, it will trip even quicker (less energy will be released in fault, arc flash/blast, it can be lowered to an insignificant little spark instead of a second long big incident with lower current)
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no it isn't
impedance may dampen the rate of rise so you trip at a lower magnitude
which is better?
15ka at 2 cycles
7ka at 6 cycles

a 10% increase in Z will reduce i fault inversely proportionally
there is a reason Z is artificially introduced into the gnd fault path
 
Kinexis said:
besides high impedance grounded neutral system where is this allowed?
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you are missing the point
ALL ckts have Z
it imposes a damping factor, which lowers fault mag AND rate of rise
eqip is rated for an upper sc current, not lower
too much is a problem, less is not

using your logic 0 Z is best, giving infinite i sc
the energy i^2 x t is proportional to time but the square of i
 
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Input Data
Voltage = 0.4 kV
Three Phase Fault = 15 kA
Arcing Time = 0.033 s
Grounding = Grounded
Equipment Type = Open Air
Conductor Gap = 32 mm
Distance to Person = 910 mm
Protection Boundary Incident Energy = 5 J/cm2

Calculation Results
Distance factor, x = 2.000
Arcing Current = 6.75 kA
Incident Energy = 0.5J/cm2 [= 0.12 cal/cm2 ]
Flash Protection Boundary = 286 mmInput Data


​Input Data
Voltage = 0.4 kV
Three Phase Fault = 7 kA
Arcing Time = 0.1 s
Grounding = Grounded
Equipment Type = Open Air
Conductor Gap = 32 mm
Distance to Person = 910 mm
Protection Boundary Incident Energy = 5 J/cm2

Calculation Results
Distance factor, x = 2.000
Arcing Current = 3.7 kA
Incident Energy = 0.78J/cm2 [= 0.19 cal/cm2 ]
Flash Protection Boundary = 360 mm
 
Ingenieur said:
you are missing the point
ALL ckts have Z
it imposes a damping factor, which lowers fault mag AND rate of rise
eqip is rated for an upper sc current, not lower
too much is a problem, less is not
Click to expand...


yes it raises z and lowers magnitude, i'm saying the lower magnitude is worse because all of your ocpd has to be rated for the available short circuit current rating already, a fault on a system with zero impedance downstream of the transformer will never be above the sccr of the equipment downstream if correct equipment is installed to begin with
 
Kinexis said:
yes it raises z and lowers magnitude, i'm saying the lower magnitude is worse because all of your ocpd has to be rated for the available short circuit current rating already, a fault on a system with zero impedance downstream of the transformer will never be above the sccr of the equipment downstream if correct equipment is installed to begin with
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exactly
so lowering i and increasing trip time per the cb curve has no negative effect
 
15^2 x 0.033 = 7.4
7^2 x 0.1 = 4.9
50% more energy

this is the energy the cb must handle

arc flash is the radiant energy the human absorbs
big difference

you have reduced current 7/15 and increased time 0.1/0.033 ~ 1.4 times (40%) more exposure time per unit i
yet energy only increases 55%
 
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