Code Violation?

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mbrooke said:
So, my take:

wye: must ground

delta: optional

So the pads that are being set down as floating wye are technically not compliant?
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If the wye terminal is not connected to anything by POCO, especially not carried through to the service point, it is still an ungrounded delta as far as the NEC is concerned when the wires get to the customer.
I do not see any NEC problem with POCO using a floating wye transformer bank to provide delta service. There may be some issues of voltage balance that the customer would have to deal with that would not be present on a "true" delta, but that is not a concern of the NEC.
 
GoldDigger said:
If the wye terminal is not connected to anything by POCO, especially not carried through to the service point, it is still an ungrounded delta as far as the NEC is concerned when the wires get to the customer.
I do not see any NEC problem with POCO using a floating wye transformer bank to provide delta service. There may be some issues of voltage balance that the customer would have to deal with that would not be present on a "true" delta, but that is not a concern of the NEC.
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Good to know then.

Not to hijack, but Im curious about the voltage imbalance. How bad is it?
 
mbrooke said:
Good to know then.

Not to hijack, but Im curious about the voltage imbalance. How bad is it?
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If the POCO keeps their taps and load balancing in order, there will not be any imbalance issues. Or at least no greater than with a delta service from a set of delta windings.
 
GoldDigger said:
If the POCO keeps their taps and load balancing in order, there will not be any imbalance issues. Or at least no greater than with a delta service from a set of delta windings.
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Ok I get where your getting at. Basically imbalance from phase angles circulates in the delta.
 
electricalist said:
This is great learning material and over my head. Im not trying to sidetrack the thread. If anyone chooses to reply . Ty ... from meter to mdp main dist pnl. We put bonding bushings on the mdp side. These grounds are egc? True? For 800 a its 1/0 and the 800 a are created by 3 sets of 400 coper in 3 seperate nipples from meter to mdp. My egc for each set is #3 or 1/0. Where we were working the meterbase must be bonded by a egc made if copper wire not the normal by connection or bonding.
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Those conductors you question above are supply side bonding jumpers. Definition is in 250.2. In earlier versions of NEC would be sized same as a grounding electrode conductor (250.66) but 2014 added a new 250.102(C)(1) for sizing this particular conductor.
 
kwired said:
Those conductors you question above are supply side bonding jumpers. Definition is in 250.2. In earlier versions of NEC would be sized same as a grounding electrode conductor (250.66) but 2014 added a new 250.102(C)(1) for sizing this particular conductor.
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But, the part that makes me itch my noggin is why would you need a bonding jumper in an ungrounded delta pad mount... unless the pad is under the NEC then? Does the NEC allow for a MV pad mount to have no bonding jumper?


I ask because my mind is still stuck on utility practices.
 
mbrooke said:
But, the part that makes me itch my noggin is why would you need a bonding jumper in an ungrounded delta pad mount... unless the pad is under the NEC then? Does the NEC allow for a MV pad mount to have no bonding jumper?


I ask because my mind is still stuck on utility practices.
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Assuming the transformer secondary is ungrounded and it is not a POCO transformer (meaning it is completely NEC covered installation), ungrounded systems still need to follow all the same rules for equipment grounding and bonding and grounding electrode system as one follows for a grounded system. The main difference is you don't have a bond to a secondary conductor of the transformer. You still need to run an EGC with all feeders and circuits and bond all the same metallic components you would ordinarily bond together. This is because when you do have a fault it becomes a grounded system at that point, and you still want to prevent the same "stray voltages" that you want to prevent with a typical grounded system, and provide low resistance paths in all non current carrying metal components. should a second fault occur that low resistance allows for high level fault current and faster response time for overcurrent protection devices.
 
kwired said:
Assuming the transformer secondary is ungrounded and it is not a POCO transformer (meaning it is completely NEC covered installation), ungrounded systems still need to follow all the same rules for equipment grounding and bonding and grounding electrode system as one follows for a grounded system. The main difference is you don't have a bond to a secondary conductor of the transformer. You still need to run an EGC with all feeders and circuits and bond all the same metallic components you would ordinarily bond together. This is because when you do have a fault it becomes a grounded system at that point, and you still want to prevent the same "stray voltages" that you want to prevent with a typical grounded system, and provide low resistance paths in all non current carrying metal components. should a second fault occur that low resistance allows for high level fault current and faster response time for overcurrent protection devices.
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Ok good to know. But imo, I don't see a major issue with not having a bond conductor to a pad mount with a delta secondary. Of course there is one case I can think of where a phase grounded down in the padmount making it a corner ground delta by accident. In a case like this have a bond wire helps tremendously in that the second fault in the building would not be using soil to clear itself.
 
mbrooke said:
Ok good to know. But imo, I don't see a major issue with not having a bond conductor to a pad mount with a delta secondary. Of course there is one case I can think of where a phase grounded down in the padmount making it a corner ground delta by accident. In a case like this have a bond wire helps tremendously in that the second fault in the building would not be using soil to clear itself.
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add to that a second scenario ..supposed a phase in the building went to ground (on the ungrounded system) ,, coincidentally a different phase went to ground at the pad.
Be a pretty decent shock hazard for someone touching the pad if it was not bonded to your building system.
I would think to a lesser degree the same situation would occur thru capacitance
voltages. Bonding of all components associated with the system is prudent requirement.
 
augie47 said:
add to that a second scenario ..supposed a phase in the building went to ground (on the ungrounded system) ,, coincidentally a different phase went to ground at the pad.
Be a pretty decent shock hazard for someone touching the pad if it was not bonded to your building system.
I would think to a lesser degree the same situation would occur thru capacitance
voltages. Bonding of all components associated with the system is prudent requirement.
Click to expand...

That's exactly what happened in that scenario... it looked like a one in million event... but it happened.
 
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