Ground Wire From 3 Phase Pad Mounted Utility Transformer

[mbrooke]

I don't believe 250.6 can ever be cited or rules as it is not defined in anyway at all.

It may not be defined because the term is so broad/encompassing, but its up to the installer to make the judgment call. I liken it to the 80% rule for continuous loads. The code doesn't list everything (electric heat is explicitly) as a continuous load, rather anything the installer deems that will run over 3 hours. In the case of a customer owned, customer maintained pad, its now their worry.

 

[mbrooke]

Beyond that it is the service point that will be the deciding factor, not the ownership of the equipment.

I think your right, but I was think of this. Starts at 5:00:

http://www.youtube.com/watch?v=tNVoJbhH764&list=PLD41B83BDFD524A0C&index=3

 

[iceworm]

Ive always wondered, why do we have 2 codes?

...I guess what I am saying is don't confuse me with a ton of rules I will never have to know about....

I wouldn't mind three versions of the NEC
Residential (up to three families)
Commerical (public access and residential - quads and up)
Industrial (limited public access)

That way the NEC code panels wouldn't get confused between Grandpa's cottage and a steel foundary.

Before y'all get out your slings and arrows. I want each to be 1/3 the size of the existing - maybe even one boilerplate and three addendums.

ice

 

[mbrooke]

I wouldn't mind three versions of the NEC
Residential (up to three families)
Commerical (public access and residential - quads and up)
Industrial (limited public access)

That way the NEC code panels wouldn't get confused between Grandpa's cottage and a steel foundary.

Before y'all get out your slings and arrows. I want each to be 1/3 the size of the existing - maybe even one boilerplate and three addendums.

ice

IMO you have the best idea:thumbsup::thumbsup: The resi version can keep the handle ties for MWBC, neutral to switch legs, GFCIs everywhere, ect while the 2 others remove the dumb proofing.

 

[GoldDigger]

IMO you have the best idea:thumbsup::thumbsup: The resi version can keep the handle ties for MWBC, neutral to switch legs, GFCIs everywhere, ect while the 2 others remove the dumb proofing.

The neutral to switch legs is mostly motivated at this point by occupancy sensors required by energy codes than by dimmers in the commercial sphere. For that reason I can see it as more than just dumb proofing, especially for new construction where more strict energy codes are pretty certain to be adopted in the near future.
At a minimum the commercial plans would have to show the locations of all occupancy sensors so that neutrals can be provided at those boxes (from the correct circuits).

 

[iwire]

It may not be defined because the term is so broad/encompassing, but its up to the installer to make the judgment call.

I disagree that there is any judgement call allowed by 250.6.

If I judge there is 'objectionable current' can I start ignoring other NEC sections to aliviate it?

I liken it to the 80% rule for continuous loads. The code doesn't list everything (electric heat is explicitly) as a continuous load, rather anything the installer deems that will run over 3 hours.

There is a huge difference with continuos loads.

1) A Continuos load is clearly defined in article 100.

2) We are directed to a specific course of action by various code sections when we have a continuos load.

 

[mbrooke]

I disagree that there is any judgement call allowed by 250.6.

If I judge there is 'objectionable current' can I start ignoring other NEC sections to aliviate it?

I don't think you would be violating the NEC treating this pad as separately derived even if the customer does own it completely (no poco involvement at all). Yes the section is vague in that it doesn't 'specifically' tell you what to do, but a competent EE would know what to do without jeopardizing the rest of the code.


There is a huge difference with continuos loads.

1) A Continuos load is clearly defined in article 100.

2) We are directed to a specific course of action by various code sections when we have a continuos load.

Explain what you mean on #2. Yes articles tell you what to do based on continuous or not, but often its the installer who makes that determination based on what is known to be installed along with its application.

 

[iwire]

I don't think you would be violating the NEC treating this pad as separately derived even if the customer does own it completely (no poco involvement at all). Yes the section is vague in that it doesn't 'specifically' tell you what to do, but a competent EE would know what to do without jeopardizing the rest of the code.

Unless there is a service disconnecting means on the supply side of it I do not believe it can be treated as a separately derived system. The customers we have that own and maintain their own pad mount transformer have to install a service disconnect ahead of it.


No one, regardless of their skill can determine what an undefined condition is.

Explain what you mean on #2. Yes articles tell you what to do based on continuous or not, but often its the installer who makes that determination based on what is known to be installed along with its application.

You lost me.

A continuos load is clearly defined, when we find we have one there are code sections that tell us what we are required to do.

 

[mbrooke]

Unless there is a service disconnecting means on the supply side of it I do not believe it can be treated as a separately derived system. The customers we have that own and maintain their own pad mount transformer have to install a service disconnect ahead of it.


No one, regardless of their skill can determine what an undefined condition is.

Undefined by the code. However, it grants an Engineer to make the judgment call to his own experience. Other wise the NEC would never list it, or give an allowance for action.

A service disconnect is needed in any case after the pad mount. Do you have a specific code section in the NEC that means a pad mount is not allowed to have a 5 wire output feed?




You lost me.

A continuos load is clearly defined, when we find we have one there are code sections that tell us what we are required to do.

Yes, the code sections tell us what to do if it meets the definition of continuous, but only the installer knows if the load will be 3 hours over or not. Electric heat is automatically assumed regardless of known operation time. But the rest is up to the installer/engineer. My point was sometimes things are relative in a sense.

 

[meternerd]

Wow! Didn't think it was such a hot button. As an "Evil POCO guy", here's the way we do it. Medium voltage is provided to a utility transformer. (usually 7200V or 14,400V). The customer specifies secondary voltage and amperage. The utility then installs an appropriate transformer. If it requires a grounded secondary (usually the case), then the utility will drive a ground rod at the pad mount transformer and ground the secondary neutral at that point. The transformer case is also bonded. Three (single phase) or four (three phase) wires, hots and a grounded neutral, will be run to the service meter equipment. From there, it's customer equipment and Code applies. A ground wire is never run in addition to the grounded neutral conductor.

 

[mbrooke]

Wow! Didn't think it was such a hot button. As an "Evil POCO guy", here's the way we do it. Medium voltage is provided to a utility transformer. (usually 7200V or 14,400V). The customer specifies secondary voltage and amperage. The utility then installs an appropriate transformer. If it requires a grounded secondary (usually the case), then the utility will drive a ground rod at the pad mount transformer and ground the secondary neutral at that point. The transformer case is also bonded. Three (single phase) or four (three phase) wires, hots and a grounded neutral, will be run to the service meter equipment. From there, it's customer equipment and Code applies. A ground wire is never run in addition to the grounded neutral conductor.

Your not evil, we like you!

Question, is there ever a time when poco just supplies the MV to a customer transformer? Wondering how its done.

 

[iwire]

Undefined by the code. However, it grants an Engineer to make the judgment call to his own experience.

I do not see it limited to an engineer, however with objectionable current being undefined how do we know when we have it?

If we were to say that neutral current flowing on raceways is objectionable then there are literally hundreds of thousands of past, present and future installations in violation of 250.6.

Other wise the NEC would never list it, or give an allowance for action.

The intent and reasons for it may be very good, but the execution was poor. They need to define what objectionable current if they expect action to be taken.

A service disconnect is needed in any case after the pad mount. Do you have a specific code section in the NEC that means a pad mount is not allowed to have a 5 wire output feed?

No, but I do have a specific code section that tells me what is allowed on the supply side of a service disconnect and SDS transformers are not on it.



2011 NEC

230.82 Equipment Connected to the Supply Side of Service
Disconnect. Only the following equipment shall be
permitted to be connected to the supply side of the service
disconnecting means:

(1) Cable limiters or other current-limiting devices.

(2) Meters and meter sockets nominally rated not in excess
of 600 volts, provided all metal housings and service
enclosures are grounded in accordance with Part VII
and bonded in accordance with Part V of Article 250.

(3) Meter disconnect switches nominally rated not in excess
of 600 volts that have a short-circuit current rating
equal to or greater than the available short-circuit current,
provided all metal housings and service enclosures
are grounded in accordance with Part VII and
bonded in accordance with Part V of Article 250. A
meter disconnect switch shall be capable of interrupting
the load served.

(4) Instrument transformers (current and voltage), impedance
shunts, load management devices, surge arresters,
and Type 1 surge-protective devices.

(5) Taps used only to supply load management devices,
circuits for standby power systems, fire pump equipment,
and fire and sprinkler alarms, if provided with
service equipment and installed in accordance with requirements
for service-entrance conductors.

(6) Solar photovoltaic systems, fuel cell systems, or interconnected
electric power production sources.

(7) Control circuits for power-operable service disconnecting
means, if suitable overcurrent protection and disconnecting
means are provided.

(8) Ground-fault protection systems or Type 2 surgeprotective
devices, where installed as part of listed
equipment, if suitable overcurrent protection and disconnecting
means are provided.

(9) Connections used only to supply listed communications
equipment under the exclusive control of the serving
electric utility, if suitable overcurrent protection and
disconnecting means are provided. For installations of
equipment by the serving electric utility, a disconnecting
means is not required if the supply is installed as
part of a meter socket, such that access can only be
gained with the meter removed.

Yes, the code sections tell us what to do if it meets the definition of continuous, but only the installer knows if the load will be 3 hours over or not. Electric heat is automatically assumed regardless of known operation time. But the rest is up to the installer/engineer. My point was sometimes things are relative in a sense.

I guess we will remain in disagreement. I see a large difference between following a definition and just guessing what something means based on our own beliefs and thoughts.

 

[meternerd]

Your not evil, we like you!

Question, is there ever a time when poco just supplies the MV to a customer transformer? Wondering how its done.

Yes, we will provide available primary voltage service to a customer who requires it, but we do our metering out at the nearest overhead point where the underground MV riser goes to the customer equipment. That way we are not involved in the customer's equipment at all. Our service point ends at the metering transformers and meter enclosures. The service disconnect and associated switchgear belong to the customer. They are free to do what they want with the MV from there. We do assist in the installation if it requires specialized tools or expertise, but it's pretty rare here since we have very little large industrial load. Other larger utilities do it all the time. There are many manufacturers of MV metering equipment (usually owned by the customer) for underground services (CT's, PT's, fuses and meters) that supply customer switchgear. The utility terminates their UG cables there, and jurisdiction stops at the metering sections.

 

[mbrooke]

I do not see it limited to an engineer, however with objectionable current being undefined how do we know when we have it?

Correct, but 9 out of 10 times its an engineer who makes the call.



If we were to say that neutral current flowing on raceways is objectionable then there are literally hundreds of thousands of past, present and future installations in violation of 250.6.

In a properly wired system you will never have neutral current anywhere on metallic parts or EGCs. Any current means a standing ground fault, usually a neutral connecting to ground beyond the main bonding jumper.

And yes in a few cases you may have a code compliant cause such as a 3 wire range or dryers... but that can always be corrected when following the new code rules. And yes a service may have some current one metal conduits. But if it bothers an EE enough plastic conduit exists.

Yes this doesn't force the mandatory correction of what is or was code allowed to start with, but the engineer can make changes without the code saying "no, you can not" Id think if that was not the intent this code blurb wouldn't exist?



The intent and reasons for it may be very good, but the execution was poor. They need to define what objectionable current if they expect action to be taken.


Perhaps, I do agree with you. But IMO defining something so relative that encompasses millions of unique scenarios under complex conditions is impossible in just a few code blurbs. The NEC would become volumes in such a case. Rather responsibility of judgment is granted to the EE or electrician. And yes I am aware no where on black and white it says who is qualified and who isn't to define objectionable current.




No, but I do have a specific code section that tells me what is allowed on the supply side of a service disconnect and SDS transformers are not on it.

Yes, but something must feed it to start with. And its self obvious this section assumes a utility supply where the transformer is beyond the control or ownership of the user in addition to being under 1000 volts. If my supply is a metered 13.8 or 23kv URD feeder to the building, where do I go from there? Id imagine this article isn't the best for that?

2011 NEC







I guess we will remain in disagreement. I see a large difference between following a definition and just guessing what something means based on our own beliefs and thoughts.

Certainly no definition is in existence, but some can always call out "oh, this is objectionable" and switch to another code complaint method, in addition to the code requirement that if the supply point (metering and utility end point of ownership) is before the transformer the NEC then takes hold.

Lets push 250.6 aside, your correct, it relative. The part that still gets me is the Mike Holt video. Why does he have the graphic of the 4 wire feed when the transformer is customer owned?

 

[mbrooke]

Yes, we will provide available primary voltage service to a customer who requires it, but we do our metering out at the nearest overhead point where the underground MV riser goes to the customer equipment. That way we are not involved in the customer's equipment at all. Our service point ends at the metering transformers and meter enclosures. The service disconnect and associated switchgear belong to the customer. They are free to do what they want with the MV from there. We do assist in the installation if it requires specialized tools or expertise, but it's pretty rare here since we have very little large industrial load. Other larger utilities do it all the time. There are many manufacturers of MV metering equipment (usually owned by the customer) for underground services (CT's, PT's, fuses and meters) that supply customer switchgear. The utility terminates their UG cables there, and jurisdiction stops at the metering sections.

Thanks! Similar here, good to know that

 

[kwired]

I wouldn't mind three versions of the NEC
Residential (up to three families)
Commerical (public access and residential - quads and up)
Industrial (limited public access)

That way the NEC code panels wouldn't get confused between Grandpa's cottage and a steel foundary.

Before y'all get out your slings and arrows. I want each to be 1/3 the size of the existing - maybe even one boilerplate and three addendums.

ice

Though I think NEC could use some cleaning up, I find myself working in all three of those areas at times and think it is easier to know and understand one code instead of needing to know three codes. NEC was once only 1/3 of what it is now, and long ago maybe even a tenth of what it is now. Some changes were good, quite a few go beyond the purpose stated in 90.1

 

[mbrooke]

Though I think NEC could use some cleaning up, I find myself working in all three of those areas at times and think it is easier to know and understand one code instead of needing to know three codes. NEC was once only 1/3 of what it is now, and long ago maybe even a tenth of what it is now. Some changes were good, quite a few go beyond the purpose stated in 90.1

You can say that again. Ever read the one if a 60 watt range hood is cord and plug connected the circuit me be dedicated?:rant:

 

[don_resqcapt19]

...The part that still gets me is the Mike Holt video. Why does he have the graphic of the 4 wire feed when the transformer is customer owned?

Because that makes the transformer a SDS (assuming that the transformer is on the load side of the service point). The rules for SDSs and utility services are not the same. The code code only permits a single point of connection between the neutral and earth for the SDS, triggering a requirement for a supply side bonding jumper between the transformer and the first OCPD.

With the utility, the neutral is bonded at both the transformer and the service disconnect, and the code also permits the grounded conductor to be used as both the grounded and a grounding conductor for anything on the line side of the service disconnect.

 

[iwire]

Correct, but 9 out of 10 times its an engineer who makes the call.

I have never seen that call made by anyone. Can you give an example, you seem to have number of them.

In a properly wired system you will never have neutral current anywhere on metallic parts or EGCs. Any current means a standing ground fault, usually a neutral connecting to ground beyond the main bonding jumper.

That is false.

Due to the requirements to bond the neutral to the meter socket enclosure (supply side equipment) and the requirement to bond the neutral to the service disconnecting means enclosure virtually every service in the US with a metal raceway has neutral current flowing on the raceways and enclosures.

In neighborhoods with metal water piping there will be neutral current flowing on the GECs and water lines.

Yes, but something must feed it to start with. And its self obvious this section assumes a utility supply where the transformer is beyond the control or ownership of the user in addition to being under 1000 volts. If my supply is a metered 13.8 or 23kv URD feeder to the building, where do I go from there? Id imagine this article isn't the best for that?

You simply cannot install an NEC SDS on the supply side of the service disconnect. It is directly prohibited by the code section I posted. I don't see anyway around that.

 

[mbrooke]

I have never seen that call made by anyone. Can you give an example, you seem to have number of them.






That is false.

Due to the requirements to bond the neutral to the meter socket enclosure (supply side equipment) and the requirement to bond the neutral to the service disconnecting means enclosure virtually every service in the US with a metal raceway has neutral current flowing on the raceways and enclosures.

In neighborhoods with metal water piping there will be neutral current flowing on the GECs and water lines.


Read the second paragraph 4th sentence in red in post #34. I specifically mentioned services may have objectionable current while being code compliant. You are just repeating what I already knew and mentioned prior. And yahh, pipes will pass current outside of the structure. But that's beyond the SDS.





You simply cannot install an NEC SDS on the supply side of the service disconnect. It is directly prohibited by the code section I posted. I don't see anyway around that.

But, again, what if your main service is at the medium voltage level? And you haven't answered why the Mike Holt graphic allows for a 4 wire feeder when the utility is out of the picture.


The code section you posted does not prohibit SDS from a pad mount (only equipment when considered a service). I saw no where 'shall be 3 and 4 wire over 4 and 5 wire or shall not be considered SDC in any case'