No equipment ground pulled to sub-panel

[kwired]

We're talking about a simple detached outbuilding with a sub panel. Lets not make this more difficult than it is.

-Hal

Well simple is NEC doesn't allow it anymore on new installs and has conditions for allowing existing installs.

If you want to ask why they changed the rules, in 2005 I believe, or ask why it was allowed to be different before, it won't necessarily be simple.

 

[romex jockey]

We're talking about a simple detached outbuilding with a sub panel. Lets not make this more difficult than it is.

-Hal

And i'm pointing out a simple fundmental

We are allowed to Bond-system in industry , in fact it's required we do to building steel , what difference in terms of a return paths , is there between that and the existing 250.32(B) detached outbuilding sub panel allowing the same?

Further, some of the sparks that do PV here more than I have tipped me off that this conflict extendes itself to a bit of a dispute betwixt 705 and 230. As in PV's being an SDS, w/ GES's , along with the specter of bond-system pursuant to compliance

~RJ~

 

[jaggedben]

...

We are allowed to Bond-system in industry , in fact it's required we do to building steel , what difference in terms of a return paths , is there between that and the existing 250.32(B) detached outbuilding sub panel allowing the same?

Bonding an SDS neutral to building steel doesn't create an additional return path.

But to the larger point, the code considers acceptable for two neighbors to both ground their services to the water supply, which may create another return path. Not much difference there, except that the NEC has less control over that.

Further, some of the sparks that do PV here more than I have tipped me off that this conflict extendes itself to a bit of a dispute betwixt 705 and 230. As in PV's being an SDS, w/ GES's , along with the specter of bond-system pursuant to compliance

~RJ~

That's a separate issue.

 

[mbrooke]

Bonding an SDS neutral to building steel doesn't create an additional return path.

It does. Picture Y-Y 13.8kv to 480 volts.

But to the larger point, the code considers acceptable for two neighbors to both ground their services to the water supply, which may create another return path. Not much difference there, except that the NEC has less control over that.



That's a separate issue.

And what control does the NEC have over a zig-zag transformer application?

 

[kwired]

Originally Posted by jaggedben
Bonding an SDS neutral to building steel doesn't create an additional return path.

It does. Picture Y-Y 13.8kv to 480 volts.

It does on a MGN system.

Otherwise beyond service equipment we only ground the system once. There are paths that exist via EGC's but we don't intentionally put current on them to avoid stay currents and voltages.

Originally Posted by jaggedben
Bonding an SDS neutral to building steel doesn't create an additional return path.

 

[mbrooke]

Originally Posted by jaggedben
Bonding an SDS neutral to building steel doesn't create an additional return path.







It does on a MGN system.

Otherwise beyond service equipment we only ground the system once. There are paths that exist via EGC's but we don't intentionally put current on them to avoid stay currents and voltages.

Originally Posted by jaggedben
Bonding an SDS neutral to building steel doesn't create an additional return path.

I disagree- there are certain situations like data centers where its unavoidable.

 

[kwired]

I disagree- there are certain situations like data centers where its unavoidable.

Data centers have neutral current on the steel building frame? current associated with service grounded conductor can be an exception because of the MGN network upstream, but all SDS's in the facility should be designed to bond near the source and keep the grounded current carrying conductor separate from EGC's beyond that bond - which should eliminate such stray currents.

 

[mbrooke]

Data centers have neutral current on the steel building frame? current associated with service grounded conductor can be an exception because of the MGN network upstream, but all SDS's in the facility should be designed to bond near the source and keep the grounded current carrying conductor separate from EGC's beyond that bond - which should eliminate such stray currents.

Some very large systems with multiple sources, generators and other setups end up having more then one neutral to ground bond.

 

[kwired]

Some very large systems with multiple sources, generators and other setups end up having more then one neutral to ground bond.

Maybe, but don't they arrange things to prevent objectionable current? Seems NEC would require that.

 

[mbrooke]

Maybe, but don't they arrange things to prevent objectionable current? Seems NEC would require that.

The NEC is silent on many aspects of stray current.

 

[kwired]

The NEC is silent on many aspects of stray current.

Bonding at separately derived system or at the first disconnecting means only still limits where there may be stray current during normal operation.

 

[romex jockey]

Bonding N/G anywhere means the return is divided according to the impedance of it's paths

Building steel is a better path than earth , so one would image a detatched garage less a path than our <NEC allowed> industrial Y/Y installs

ergo ,why i question the old 250.32(B) change rationale, which 'in theory' should have been all or nothing....

~RJ~

 

[jaggedben]

It does. Picture Y-Y 13.8kv to 480 volts.

I meant a return path for normal circuit current, not fault current. As in, it.does not create a path for 'objectionable current'. Services are different from SDSs in this respect.

I hope that clears things up. This thread has drifted to where I'm not sure it's still useful.

 

[jaggedben]

Bonding N/G anywhere means the return is divided according to the impedance of it's paths.

No, a parallel path is only created if the neutral is grounded in more than one place. This is not the case for an SDS, for example.

The code doesn't consider a small amount of current through the earth itself to be objectionable. It allows what it would otherwise consider objectionable current to flow between services on water service lines, I think. because it can't really tell electricians to go investigate their customer's neighbors properties. The 'premises' are a limiting line for code requirements (in a society where private property is of great importance).

The code does consider neutral current flowing on metal other than neutral conductors, all within the same premises on the load side of the service, to be objectionable. I'm pretty sure the code change discussed above was put in to prevent that.

 

[mbrooke]

I meant a return path for normal circuit current, not fault current. As in, it.does not create a path for 'objectionable current'. Services are different from SDSs in this respect.

I hope that clears things up. This thread has drifted to where I'm not sure it's still useful.

A Y-Y SDS is an SDS by code, but not by electrical theory.

 

[kwired]

No, a parallel path is only created if the neutral is grounded in more than one place. This is not the case for an SDS, for example.

The code doesn't consider a small amount of current through the earth itself to be objectionable. It allows what it would otherwise consider objectionable current to flow between services on water service lines, I think. because it can't really tell electricians to go investigate their customer's neighbors properties. The 'premises' are a limiting line for code requirements (in a society where private property is of great importance).

The code does consider neutral current flowing on metal other than neutral conductors, all within the same premises on the load side of the service, to be objectionable. I'm pretty sure the code change discussed above was put in to prevent that.

With services we have more than one point of a large network of grounded conductors that are bonded and grounded. They are even bonded to the secondary grounded conductor of SDS's. But if the SDS only bonds the grounded conductor at one point and keeps it isolated everywhere else there is no parallel path for grounded conductor to take without introducing fault conditions.

A Y-Y SDS is an SDS by code, but not by electrical theory.

Y you say that?

If the secondary side is only grounded in one place, the SDS itself is no different than a delta-wye.

If your primary utilizes a neutral, shouldn't you be bringing a separate neutral from the supply and keeping it isolated from the EGC so you don't have parallel paths for the neutral?

 

[mbrooke]

With services we have more than one point of a large network of grounded conductors that are bonded and grounded. They are even bonded to the secondary grounded conductor of SDS's. But if the SDS only bonds the grounded conductor at one point and keeps it isolated everywhere else there is no parallel path for grounded conductor to take without introducing fault conditions.

Y you say that?

If the secondary side is only grounded in one place, the SDS itself is no different than a delta-wye.

If your primary utilizes a neutral, shouldn't you be bringing a separate neutral from the supply and keeping it isolated from the EGC so you don't have parallel paths for the neutral?

Not when you have multiple transformers- the primary neutral acts like a bonding conductor.

 

[GoldDigger]

...
...
ergo ,why i question the old 250.32(B) change rationale, which 'in theory' should have been all or nothing....

~RJ~

"In theory there is no difference between theory and practice. In practice, however...."

Sent from my XT1585 using Tapatalk

 

[kwired]

Not when you have multiple transformers- the primary neutral acts like a bonding conductor.

Why are you bonding the primary neutral other than at the service or at the upstream secondary?

If transformer is permanently bonded it isn't suitable for the application.

 

[mbrooke]

Why are you bonding the primary neutral other than at the service or at the upstream secondary?

If transformer is permanently bonded it isn't suitable for the application.

You aren't, but picture a property with multiple MV-LV rooms through out.


What code section forbids this?