Grounded Conductor required?

[wwhitney]

Hey, I never read (2017) 250.30 closely before yesterday. But for the case of a grounded SDS with wye secondary that serves only line-to-line loads, it is clear to me that there are a few different ways to provide a fault clearing path between the transformer and the disconnect:

A) Use an SBJ at the transformer only. In which case there must be an SSBJ from the transformer to the disconnect. No grounded conductor is required between the transformer and the disconnect. If one were run, it would not connect to anything in the disconnect, it would just sit isolated from the metal enclosure and any other conductors.

B) If the transformer is in the same building as the disconnect, use an SBJ at the disconnect only. In which case there must be both an SSBJ and a grounded conductor from the transformer to the disconnect.

C) If the transformer is not in the same building as the disconnect, use SBJs at both the transformer and the disconnect. In which case there must be no SSBJ run between the transformer and the disconnect, but there must be a grounded conductor.

The difference between (A) and (C) in this case seems primarily semantic. E.g. for an existing installation under (A) with the transformer outdoors, no continuous metallic conduit, and an SSBJ of the wire type, I could cut the SSBJ in the disconnect and splice the two ends back together. Then the portion of the former SSBJ coming from the transformer I could recolor white and call the grounded conductor, and the other portion I could call the SBJ, and now the installation fits (C).

Cheers, Wayne

 

[packersparky]

Hey, I never read (2017) 250.30 closely before yesterday. But for the case of a grounded SDS with wye secondary that serves only line-to-line loads, it is clear to me that there are a few different ways to provide a fault clearing path between the transformer and the disconnect:

A) Use an SBJ at the transformer only. In which case there must be an SSBJ from the transformer to the disconnect. No grounded conductor is required between the transformer and the disconnect. If one were run, it would not connect to anything in the disconnect, it would just sit isolated from the metal enclosure and any other conductors.

B) If the transformer is in the same building as the disconnect, use an SBJ at the disconnect only. In which case there must be both an SSBJ and a grounded conductor from the transformer to the disconnect.

C) If the transformer is not in the same building as the disconnect, use SBJs at both the transformer and the disconnect. In which case there must be no SSBJ run between the transformer and the disconnect, but there must be a grounded conductor.

The difference between (A) and (C) in this case seems primarily semantic. E.g. for an existing installation under (A) with the transformer outdoors, no continuous metallic conduit, and an SSBJ of the wire type, I could cut the SSBJ in the disconnect and splice the two ends back together. Then the portion of the former SSBJ coming from the transformer I could recolor white and call the grounded conductor, and the other portion I could call the SBJ, and now the installation fits (C).

Cheers, Wayne

:thumbsup:

 

[jaggedben]

This thread does not seem like it will be helpful to the OP. We don't even know if the OP's transformer has an XO, or why exactly he's asking the question, except that presumably he's not connecting a grounded conductor to any loads.

 

[Dale001289]

Hey, I never read (2017) 250.30 closely before yesterday. But for the case of a grounded SDS with wye secondary that serves only line-to-line loads, it is clear to me that there are a few different ways to provide a fault clearing path between the transformer and the disconnect:

A) Use an SBJ at the transformer only. In which case there must be an SSBJ from the transformer to the disconnect. No grounded conductor is required between the transformer and the disconnect. If one were run, it would not connect to anything in the disconnect, it would just sit isolated from the metal enclosure and any other conductors.

B) If the transformer is in the same building as the disconnect, use an SBJ at the disconnect only. In which case there must be both an SSBJ and a grounded conductor from the transformer to the disconnect.

C) If the transformer is not in the same building as the disconnect, use SBJs at both the transformer and the disconnect. In which case there must be no SSBJ run between the transformer and the disconnect, but there must be a grounded conductor.

The difference between (A) and (C) in this case seems primarily semantic. E.g. for an existing installation under (A) with the transformer outdoors, no continuous metallic conduit, and an SSBJ of the wire type, I could cut the SSBJ in the disconnect and splice the two ends back together. Then the portion of the former SSBJ coming from the transformer I could recolor white and call the grounded conductor, and the other portion I could call the SBJ, and now the installation fits (C).

Cheers, Wayne

Very nice thought process -


Sent from my iPhone using Tapatalk

 

[kwired]

Joining this party a little late - will make some general statements as I see things here - many likely already been mentioned.

First thing - a "grounded conductor" isn't always a neutral conductor. Most common applications when it isn't is with two wire sources, or three phase three wire sources. The rules for bonding/grounding don't change because the grounded conductor is or isn't a neutral conductor. Whether or not the grounded conductor is intended to carry current in normal operation does have some impact on where it may be grounded/bonded. Once you get past the main/system bonding jumper you split into two directions - the (current carrying) grounded conductor, and (non current carrying) equipment grounding conductor, and with some SDS's a SSBJ between first overcurrent device and the source.

With a service we must always run the grounded conductor, even if it isn't intended to carry any current. It is the only low resistance path back to the source that we can rely on to assure a ground fault will carry high enough current level to help make the overcurrent protection trip.

With a SDS things are different. We must install system bonding jumper either at the source or at the first disconnect - and as mentioned we have EGC's beyond that point. A ground fault is returning to the system bonding jumper, then to the source via the grounded conductor. Grounded conductor is required to the first disconnecting means if the bonding jumper is to be installed at the first disconnecting means. A SSBJ in such application isn't for carrying fault current back to the transformer, it is for carrying a fault on the supply side of the bonding jumper back to the bonding jumper - so it can get back to the source via the grounded conductor. Have a secondary conductor fault to transformer housing in such an installation - the fault current has to travel via the SSBJ to the first disconnecting means, through the system bonding jumper, then it can return to the source via the grounded conductor. You can't bond at both the source and the first disconnect because if you did then any normal operating current on the grounded conductor becomes paralleled on the SSBJ.

If you have an SDS application where there is never going to be current on the secondary grounded conductor and your system bonding jumper is at the source - there is no reason to bring a grounded conductor to the first disconnect or extend it to any additional feeders or branch circuits. First it will never carry any "normal current" because there isn't any. Second only time it will carry any "fault current" is if the fault is to the grounded conductor itself. Other ground faults will bypass this conductor as it is suppoese to be isolated from the EGC everywhere beyond the system bonding jumper.

I still believe a dedicated white grounded conductor is required to be run with circuit conductors from all transformer LV secondaries to panels, disconnects etc even if no phase to neutral loads exist.


Sent from my iPhone using Tapatalk

Not all grounded conductors are also neutral conductors. If no load is to be connected to the grounded conductor you do not need to run it, for anything other then service conductors, for service conductors it is also your return path for ground fault current. For other then service conductors we always have either an EGC or a SSBJ filling any missing pathways back to the source and they eventually meet up with the grounded conductor somewhere if a grounded system.

Where line to neutral loads are present, for example a delta-wye XFMR, the grounded conductor (must be white) carries unbalanced current from the panelboard to the XO whereas the SSBJ does not -its for bonding between Ground and Neutral busses (sometimes at the panel board or may go directly back to XFMR from the ground bus)
If no neutral loads are present (all 3 phase loads for example) the white conductor is still required - even if the XFMR is corner or center grounded from one winding.
The SSJB may in effect do the same thing as the grounded conductor but the code still wants to see a dedicated white conductor from the XFMR to service or panelboard neutral bar (Ref250.24.)

For branch circuits, containing current carrying neutral conductors such as lighting, receptacles etc, the EGC becomes the primary fault path since it contains the lowest path of impedance as explained in 250.134 Handbook.


Sent from my iPhone using Tapatalk

What function is it going to perform? Nothing connects to it except on it's source end. As I mentioned above, a fault to the grounded conductor would be the only way this conductor ever carries any current, other typical ground faults are taking paths via EGC and SSBJ and back to the grounded conductor - but at the point of the system bonding jumper. Anything beyond the SBJ is just isolated conductor that never carries any current if left as is.

Would you rely on the SSBJ to handle unbalanced loads including harmonics...answer is “No” - the grounded conductor does that but it has to be present in order to function


Sent from my iPhone using Tapatalk

How are there harmonics in a grounded conductor in a corner grounded delta system?

Specifically, what part of 250.30 says that the grounded conductor has to be brought to the disconnect?

Harmonics have nothing to do with fault clearing. Harmonics exist in any/all current carrying conductors supplying non linear loads. They become conductor issues in the neutral of wye systems - but that is a topic outside this discussion.

It would be a violation to mark the SSBJ with white tape.

There is no requirements for color identification of SSBJ or grounding electrode conductors. They can be any color you want.

 

[infinity]

There is no requirements for color identification of SSBJ or grounding electrode conductors. They can be any color you want.

Although you are correct for other colors according to 200.7(A) they cannot be white or gray.

 

[kwired]

Although you are correct for other colors according to 200.7(A) they cannot be white or gray.

Only white or gray can be used for grounded conductors, doesn't restrict white or gray to be used only for grounded conductors.

Now there is limitations in (C), but that also only applies to circuits of 50V or more. Is a GEC or a SSBJ a circuit - maybe, but is it also one that has nominal voltage of 50 v or more? I don't think it fits in there, no color designations apply to GEC or SSBJ.

I have had inspectors that want them marked green -I always tell them there is no requirement and point out sections that don't require such, and even ask them to produce a section that does. Nobody ever has, occasionally I still mark them green just to be able to move on, but do need to at least make them think about it first. If it were something that was going to cost a lot or be a big hassle, I won't give up so easily.

 

[roger]

doesn't restrict white or gray to be used only for grounded conductors.

Yes it does unless allowed by 200.7(B) or (C) which doesn't apply to this conversation.

(A) General. The following shall be used only for thegrounded circuit conductor, unless otherwise permitted in
200.7(B) and (C):

Roger

 

[kwired]

Yes it does unless allowed by 200.7(B) or (C) which doesn't apply to this conversation.



Roger

OK, I read that before but your emphasis on "only" kind of changes the meaning. Too bad it isn't in boldface in the NEC.

White and gray are restricted to grounded conductors as a general rule.

GEC's and SSBJ's still have no color designations though, and can be any color except white or gray which are restricted to grounded conductors only.

 

[don_resqcapt19]

Although you are correct for other colors according to 200.7(A) they cannot be white or gray.

Actually what ever color you use as a grounding conductor cannot also be used as an ungrounded conductor. 310.110(C).

 

[thomaslopez]

Re:

Re:

Thanks for the question! As a general rule, white and gray are restricted to grounded conductors.

 

[Adamjamma]

It could be a metallic raceway. Also how does that impact the need to bring in the grounded conductor?

Perhaps this is why the UK code has onelook at placing a ground within the metallic raceway in some instances, and requires bonding of all conduits and raceways at both ends with the circuit ground so that if any ground fails, the rest of the grounding circuit still carries the ground and trips the breaker? Or am I reading the textbooks wrong?
Since a student, even with ARRL Advanced background, know I may be wrong but hoping I understand what I am reading.

 

[Dale001289]

Perhaps this is why the UK code has onelook at placing a ground within the metallic raceway in some instances, and requires bonding of all conduits and raceways at both ends with the circuit ground so that if any ground fails, the rest of the grounding circuit still carries the ground and trips the breaker? Or am I reading the textbooks wrong?
Since a student, even with ARRL Advanced background, know I may be wrong but hoping I understand what I am reading.

Are you referring to BS 7671? As I recall this is a derivative of IEC 60364? What you've just described is closer to the equipment grounding conductor, 'EGC' than grounded conductor in NEC. The British counterpart would be a TNS system, if I remember correctly.

 

[StvRamnd48!]

Single phase residential transformer

Single phase residential transformer

I just recently read that the H2 connection of a residential distribution transformers primary winding is fed by one hot wire (on H1) and the other end of the primary winding (H2) is connected to the transformers case ground. If that’s correct then what do they use for a neutral ?

 

[kwired]

I just recently read that the H2 connection of a residential distribution transformers primary winding is fed by one hot wire (on H1) and the other end of the primary winding (H2) is connected to the transformers case ground. If that’s correct then what do they use for a neutral ?

On a multi grounded neutral system this normal. Neutral/ground are the same thing on such a system.