Code Violation?

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mbrooke said:
Ok, this is delta. Sorry about the scattered reply, just opened the thread haven't read it all.


Its not a violation, however on most delta services bond wires aren't run from the switchgear to the transformer... at least this is how utilities do it. Most utility owned delta secondary PAD and pole pig banks only have 3 wires coming from the customer and nothing else. In fact some POCOs even discourage it, I will give an example.


However, as far as I know tying the secondary EGC to the HV EGC is not a violation. Whether its desirable or not is based on engineering requirements.
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If it is not POCO equipment and NEC applies - it is not service equipment - it is a separately derived system just like a 480 to 208/120 transformer is. Should the primary circuit of that transformer require a neutral conductor for proper operation then NEC would require a separate neutral and separate EGC on the supply side, all the way back to wherever the service is or to the next upstream separately derived system originates if still NEC application at that point.

Any particular POCO standards or practices are meaningless if it is an NEC application.
 
mbrooke said:
From Duke Energy's service booklet:
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Is that image supposed to represent an ungrounded secondary? It is showing a wye secondary but seems to be indicating leaving the X0 floating and no grounding of anything else on secondary either. Not exactly an ungrounded delta system, but to the user is still effectively about the same thing.

Still don't get their "fault current flow" shown there either, if ungrounded there is no fault current unless you have fault on more then one line.
 
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kwired said:
Is that image supposed to represent an ungrounded secondary? It is showing a wye secondary but seems to be indicating leaving the X0 floating and no grounding of anything else on secondary either. Not exactly an ungrounded delta system, but to the user is still effectively about the same thing.

Still don't get their "fault current flow" shown there either, if ungrounded there is no fault current unless you have fault on more then one line.
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Look at the title of the drawing. It is intended to be an ungrounded system. Since the secondary is not subject to NEC, POCO is under no obligation to ground the neutral of its wye transformer. And since the center point is not brought to the customer, they have no obligation to bond it either.
I am more uneasy about the situation where POCO grounds the center point but does not provide a neutral to the customer, although I think that is equally legal.
 
GoldDigger said:
Look at the title of the drawing. It is intended to be an ungrounded system. Since the secondary is not subject to NEC, POCO is under no obligation to ground the neutral of its wye transformer. And since the center point is not brought to the customer, they have no obligation to bond it either.
I am more uneasy about the situation where POCO grounds the center point but does not provide a neutral to the customer, although I think that is equally legal.
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Where do you find a title of the drawing? I don't find one, nor do I find any information specifically stating this is intended to be ungrounded, I kind of deciphered that after looking carefully at it.

If POCO grounds anything whether it be the center point or not it is a grounded system IMO. Would create too much hazard to not run a conductor to service from that grounded point. If POCO refuses to furnish a grounded conductor to the service point when they do have a grounded point - they are asking for lawsuits when an accident happens on that system.

But this is kind of veering off topic - OP is about non utility controlled/operated transformer that happens to have over 1000 volts for the primary circuit. The rules of grounding/bonding and separation of grounded/grounding conductors are the same for over 1000 volts as for less then 1000 volts (600 volts before 2014 NEC)
 
kwired said:
Where do you find a title of the drawing? I don't find one, nor do I find any information specifically stating this is intended to be ungrounded, I kind of deciphered that after looking carefully at it.
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When I first saw the thread on my phone, I thought that the image was linked rather than attached and the ULR mentioned "ungrounded" in the file name. But I guess either I misremembered or the post was changed to use an attachment instead.
That information is not within the image itself.
 
kwired said:
If it is not POCO equipment and NEC applies - it is not service equipment - it is a separately derived system just like a 480 to 208/120 transformer is. Should the primary circuit of that transformer require a neutral conductor for proper operation then NEC would require a separate neutral and separate EGC on the supply side, all the way back to wherever the service is or to the next upstream separately derived system originates if still NEC application at that point.

Any particular POCO standards or practices are meaningless if it is an NEC application.
Click to expand...

From another thread my understanding was the NEC doesn't necessarily consider this separately derived?






kwired said:
Is that image supposed to represent an ungrounded secondary? It is showing a wye secondary but seems to be indicating leaving the X0 floating and no grounding of anything else on secondary either. Not exactly an ungrounded delta system, but to the user is still effectively about the same thing.

Still don't get their "fault current flow" shown there either, if ungrounded there is no fault current unless you have fault on more then one line.
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Ungrounded secondary. The reason for the wye over a delta is that both requirements can be met without stoking 2 different transformers. In fact Id say half of unground service fed by POCOs are ungrounded wye, however delta and floating wye are identical operation wise.



The graphic is confusing but its basically is there to show a breaker will trip after 2 phases are grounded.
 
GoldDigger said:
Look at the title of the drawing. It is intended to be an ungrounded system. Since the secondary is not subject to NEC, POCO is under no obligation to ground the neutral of its wye transformer. And since the center point is not brought to the customer, they have no obligation to bond it either.
I am more uneasy about the situation where POCO grounds the center point but does not provide a neutral to the customer, although I think that is equally legal.
Click to expand...


My understanding is that is you want an ungrounded system even in the NEC you can leave the center floating as long as all other bonding and grounding is met along with an approved ground detector.

As for grounding the wye but not brining in a neutral that is against code. Perhaps some pocos might do it but all the ones I know have a specific policy that if the wye is grounded, or the center is grounded at any transformer a neutral MUST be brought to the customer.





kwired said:
Where do you find a title of the drawing? I don't find one, nor do I find any information specifically stating this is intended to be ungrounded, I kind of deciphered that after looking carefully at it.

If POCO grounds anything whether it be the center point or not it is a grounded system IMO. Would create too much hazard to not run a conductor to service from that grounded point. If POCO refuses to furnish a grounded conductor to the service point when they do have a grounded point - they are asking for lawsuits when an accident happens on that system.

But this is kind of veering off topic - OP is about non utility controlled/operated transformer that happens to have over 1000 volts for the primary circuit. The rules of grounding/bonding and separation of grounded/grounding conductors are the same for over 1000 volts as for less then 1000 volts (600 volts before 2014 NEC)
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My apologies here is the link along with a picture at the bottom of the post. Page 87 for a floating wye, page 86 grounded wye: https://www.progress-energy.com/assets/www/docs/business/service_requirements_manual.pdf



Poco may not ground down a center or a wye if the customer is looking for an ungrounded service or a high resistance grounded service where an isolated neutral is brought over. However, if the center is grounded, even to something as simple as a ground rod it is policy for utilities that I know of to give a neutral to the customer. Just my 2 cents.







GoldDigger said:
When I first saw the thread on my phone, I thought that the image was linked rather than attached and the ULR mentioned "ungrounded" in the file name. But I guess either I misremembered or the post was changed to use an attachment instead.
That information is not within the image itself.
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Sorry:ashamed1: Here is the link and picture, page 87: https://www.progress-energy.com/assets/www/docs/business/service_requirements_manual.pdf
 
mbrooke said:
From another thread my understanding was the NEC doesn't necessarily consider this separately derived?









Ungrounded secondary. The reason for the wye over a delta is that both requirements can be met without stoking 2 different transformers. In fact Id say half of unground service fed by POCOs are ungrounded wye, however delta and floating wye are identical operation wise.



The graphic is confusing but its basically is there to show a breaker will trip after 2 phases are grounded.
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Art 100 defintion (2014):
Separately Derived System.
An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.

Was completely rewritten for simplicity but basically has same intended meaning as it did in 2011.

With that definition, only way this is not a NEC recognized SDS is if it is POCO transformer supplying a service, grounded conductors from both primary and secondary of a SDS are incidentally connected together because they are grounded, but we do not intentionally use the primary grounded conductor to carry secondary grounded conductor current or vice versa. If we did we are a step closer to calling it an autotransformer instead of a SDS.

BTW I have stoked up a wood burning stove before but never a transformer, doesn't seem like it would really be very good for the transformer:)
 
mbrooke said:
My understanding is that is you want an ungrounded system even in the NEC you can leave the center floating as long as all other bonding and grounding is met along with an approved ground detector.
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250.20(B)(1) provides at least one circumstance (208Y/120 secondary) in which the center point, if it exists, must be grounded, whether the neutral is used in a circuit or not. Actually, a 240Y/132 secondary would also fall under the provisions of (1) even if there are no 132V loads.
Other mandatory grounding rules, (2) and (3) are conditioned on the wye or high leg delta neutral being a current carrying conductor.
 
kwired said:
Art 100 defintion (2014):
Separately Derived System.
An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.

Was completely rewritten for simplicity but basically has same intended meaning as it did in 2011.

With that definition, only way this is not a NEC recognized SDS is if it is POCO transformer supplying a service, grounded conductors from both primary and secondary of a SDS are incidentally connected together because they are grounded, but we do not intentionally use the primary grounded conductor to carry secondary grounded conductor current or vice versa. If we did we are a step closer to calling it an autotransformer instead of a SDS.

BTW I have stoked up a wood burning stove before but never a transformer, doesn't seem like it would really be very good for the transformer:)
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Makes sense.





GoldDigger said:
250.20(B)(1) provides at least one circumstance (208Y/120 secondary) in which the center point, if it exists, must be grounded, whether the neutral is used in a circuit or not. Actually, a 240Y/132 secondary would also fall under the provisions of (1) even if there are no 132V loads.
Other mandatory grounding rules, (2) and (3) are conditioned on the wye or high leg delta neutral being a current carrying conductor.
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But how is an ungrounded service legal then? I know of countless ungrounded 240 and 480 volt services.
 
mbrooke said:
...
But how is an ungrounded service legal then? I know of countless ungrounded 240 and 480 volt services.
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Simple. The service does not meet (1), (2), or (3).
If there is no wye center point or high leg neutral, and the voltage from conductor to conductor is not less than 150 volts, then the service or SDS can be ungrounded, subject to the restrictions in other sections.
Or if there is a neutral but it is not used in the circuit (carries no current).
 
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GoldDigger said:
Simple. The service does not meet (1), (2), or (3).
If there is no wye center point or high leg neutral, and the voltage from conductor to conductor is not less than 150 volts, then the service or SDS can be ungrounded, subject to the restrictions in other sections.
Or if there is a neutral but it is not used in the circuit (carries no current).
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Got it! :)
 
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.
 
GoldDigger said:
Simple. The service does not meet (1), (2), or (3).
If there is no wye center point or high leg neutral, and the voltage from conductor to conductor is not less than 150 volts, then the service or SDS can be ungrounded, subject to the restrictions in other sections.
Or if there is a neutral but it is not used in the circuit (carries no current).
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Ok reading it over Im confused again:( If the system voltage to ground could exceed 150 volts it must be grounded... but this has me confused. That would mean no ungrounded system would be allowed in this case. It does use a soft verb "can", so that means if provisions exist for a sold ground it must be done but if not then its ok?:?
 
mbrooke said:
Ok reading it over Im confused again:( If the system voltage to ground could exceed 150 volts it must be grounded... but this has me confused. That would mean no ungrounded system would be allowed in this case. It does use a soft verb "can", so that means if provisions exist for a sold ground it must be done but if not then its ok?:?
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You have it backwards.
You are required to ground the service or supply if you can keep the maximum voltage between conductor and ground below 150V.
In a 240Y/132 for example, grounding any leg of the wye would produce a voltage greater than 150V between every conductor except the wye point and ground (no good) or you could ground the wye point and have only 132V from all the other conductors to ground.
Since there are several choices of what to ground and for one of them the condition is met, the "can" in the rule is satisfied. So the circuit must be grounded.
For the picky or litigious among us, note that it does not say that you must ground it that way. :angel: So a "corner grounded" wye would be OK, unless prohibited by other code sections.
 
GoldDigger said:
You have it backwards.
You are required to ground the service or supply if you can keep the maximum voltage between conductor and ground below 150V.
In a 240Y/132 for example, grounding any leg of the wye would produce a voltage greater than 150V between every conductor except the wye point and ground (no good) or you could ground the wye point and have only 132V from all the other conductors to ground.
Since there are several choices of what to ground and for one of them the condition is met, the "can" in the rule is satisfied. So the circuit must be grounded.
For the picky or litigious among us, note that it does not say that you must ground it that way. :angel: So a "corner grounded" wye would be OK, unless prohibited by other code sections.
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But this would still make a delta illegal then? Or is it legal for a delta but not for wye?
 
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