250.30 SSBJ

[Isaiah]

We have a 3MVA, 13.8kV-480V 3PH, 3W solidly grounded power transformer that was shipped from the manufacturer with an XO bushing on 480V side - however there are NO neutral loads. The secondary feeds a 480V switchgear with 14, 500kCMIL per phase and a supply side bonding jumper in each conduit, sized per table 250.102(C)(1).
Construction connected ALL 14 of the supply side bonding jumpers to the XO bushing in the transformer and to the ground buss in the switchgear. QA/QC is saying the SSBJ cannot be connected at the transformer XO because the transformer may read “residual voltage” on the XO. I don’t see this as an issue - but they want to see the SSBJ’s removed from the XO bushing. Thoughts?


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[infinity]

QA/QC is saying the SSBJ cannot be connected at the transformer XO because the transformer may read “residual voltage” on the XO. I don’t see this as an issue - but they want to see the SSBJ’s removed from the XO bushing. Thoughts?

So where do they want the SSBJ's connected?

 

[Isaiah]

So where do they want the SSBJ's connected?

They want to see it attached to the secondary air terminal case…however this doesn’t change much since the XO is also tied to the case with the system bonding jumper.


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[Engser18]

Since you call it is SSBJ then it shouldn't connect to XO (feeder). If you call it is reduce Neutral then it should be connected to XO (service). Even though, they are the same as you have bonding jumper (N-G).

 

[Isaiah]

Since you call it is SSBJ then it shouldn't connect to XO (feeder). If you call it is reduce Neutral then it should be connected to XO (service). Even though, they are the same as you have bonding jumper (N-G).

regardless of what you call it shouldn’t matter. Bonding it to the case doesn’t change anything Electrically


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[don_resqcapt19]

Is it the intent to have the 480 volt side a grounded or ungrounded system? With a grounded system the supply side bonding jumper will be connected to XO as it is the fault clearing path.

 

[Isaiah]

Is it the intent to have the 480 volt side a grounded or ungrounded system? With a grounded system the supply side bonding jumper will be connected to XO as it is the fault clearing path.

It’s a grounded system. I agree with you.
QA/QC is incorrect on this.


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[Jpflex]

It’s a grounded system. I agree with you.
QA/QC is incorrect on this.


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What to do when manufacture instructions conflict with NEC codes or procedures?

inter systems instructed installing a grounding rod to their system but isolated from the rest of the building or structure grounding system against NEC code but NEC code also requires following manufacture listed instruction

 

[jim dungar]

What to do when manufacture instructions conflict with NEC codes or procedures?

inter systems instructed installing a grounding rod to their system but isolated from the rest of the building or structure grounding system against NEC code but NEC code also requires following manufacture listed instruction

The NEC grounding requirements must be followed.
If the manufacturer's instructions are in conflict, the equipment cannot be installed/wired.

 

[Engser18]

regardless of what you call it shouldn’t matter. Bonding it to the case doesn’t change anything Electrically


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Even though it is electrically the same. The requirement shall be IAW applicable NEC section. if you are bringing neutral then it shall be connected to XO terminal (grounded conductors). if it is SSBJ then it shall be connected to grounding terminal (grounding conductors).

 

[Isaiah]

Even though it is electrically the same. The requirement shall be IAW applicable NEC section. if you are bringing neutral then it shall be connected to XO terminal (grounded conductors). if it is SSBJ then it shall be connected to grounding terminal (grounding conductors).

In this case not possible to connect to the grounding terminal due to 15 per phase conductors, i.e. 15 grounding conductors. There’s a SBJ - system bonding jumper - bonded to the XFMR case.
The green insulated SSBJ must bond to the XO so it’s a moot point as to where it lands


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[electrofelon]

Even though it is electrically the same. The requirement shall be IAW applicable NEC section. if you are bringing neutral then it shall be connected to XO terminal (grounded conductors). if it is SSBJ then it shall be connected to grounding terminal (grounding conductors).

What is you justification for that? At the service or an SDS grounded conductors and grounding/bonding conductors are common and very frequently tied to the same terminal or buss. In fact the gec is REQUIRED to be connected to the same terminal or bus as the grounded conductor.

 

[Engser18]

In this case not possible to connect to the grounding terminal due to 15 per phase conductors, i.e. 15 grounding conductors. There’s a SBJ - system bonding jumper - bonded to the XFMR case.
The green insulated SSBJ must bond to the XO so it’s a moot point as to where it lands


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If your Xformer outdoor and Xformer/SWG are separated enclosure, then you can connect to XO terminal and call it reducing neutral, SSBJ are not required to bring to SWG IAW NEC 250.30 A(1) exception #2 and 250.30 A(2) exception. System bonding jumper and grounding electrode are required at both location.

 

[Isaiah]

If your Xformer outdoor and Xformer/SWG are separated enclosure, then you can connect to XO terminal and call it reducing neutral, SSBJ are not required to bring to SWG IAW NEC 250.30 A(1) exception #2 and 250.30 A(2) exception. System bonding jumper and grounding electrode are required at both location.

If located in SWGR and XFMR are located in separate buildings the SSBJ must be bonded at the XFMR XO. There is no such thing as a “reducing neutral”. Calling it such would be very misleading - it would mean a white or gray grounded conductor that is current carrying….which it is not.
Also the system bonding jumper is not required at both locations—only at the XFMR in this case.


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[Jpflex]

We have a 3MVA, 13.8kV-480V 3PH, 3W solidly grounded power transformer that was shipped from the manufacturer with an XO bushing on 480V side - however there are NO neutral loads. The secondary feeds a 480V switchgear with 14, 500kCMIL per phase and a supply side bonding jumper in each conduit, sized per table 250.102(C)(1).
Construction connected ALL 14 of the supply side bonding jumpers to the XO bushing in the transformer and to the ground buss in the switchgear. QA/QC is saying the SSBJ cannot be connected at the transformer XO because the transformer may read “residual voltage” on the XO. I don’t see this as an issue - but they want to see the SSBJ’s removed from the XO bushing. Thoughts?


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I don’t get your SSBJ TOTAL at 14 conductors which should run from the separately derived source enclosure to the first point of disconnect enclosure or bus

If you you are paralleling every ungrounded conductor and SSBJ into one massive conduit ok

However if you have 3 conduits equally separating pairs of ungrounded and grounded conductors in 3 conduits from source to first disconnect then you could not get the required even number of SSBJ in 3 conduits. 14 SSBJ / 3 = 4.66 SSBJ conductors in each of the conduits (not possible)

Also if you don’t have neutral loads you may be able to go with an ungrounded system and not run a neutral (which I think you call 14 SSBJ?) from XO to the first disconnect. Instead you leave xo without anything terminating to it. The SSBJs would not connect at the xo neutral but to the source cabinet ground to first point of disconnect

Here’s the math I got for your project

Primary 125.15 I = 1 AWG @75 deg c

Secondary 3608.54 I = 14 of 250 kcmil conductor parallel x 255i = 3570i

(What the heck are you powering for this many amps a small town or meth lab lol?)


SSBJ 14,500,00 x .125 = 1,812,500 mil

1,812,500 mil / 14 conductors = 129,464.286 mil individual SSBJ X 14 or 2/0 at 133,100 cm each x 14 (would only work in a single conduit as 14 SSBJ can not divide evenly into 3 conduit runs)

 

[Jpflex]

I don’t get your SSBJ TOTAL at 14 conductors which should run from the separately derived source enclosure to the first point of disconnect enclosure or bus

If you you are paralleling every ungrounded conductor and SSBJ into one massive conduit ok

However if you have 3 conduits equally separating pairs of ungrounded and grounded conductors in 3 conduits from source to first disconnect then you could not get the required even number of SSBJ in 3 conduits. 14 SSBJ / 3 = 4.66 SSBJ conductors in each of the conduits (not possible)

Also if you don’t have neutral loads you may be able to go with an ungrounded system and not run a neutral (which I think you call 14 SSBJ?) from XO to the first disconnect. Instead you leave xo without anything terminating to it. The SSBJs would not connect at the xo neutral but to the source cabinet ground to first point of disconnect

Here’s the math I got for your project

Primary 125.15 I = 1 AWG @75 deg c

Secondary 3608.54 I = 14 of 250 kcmil conductor parallel x 255i = 3570i

(What the heck are you powering for this many amps a small town or meth lab lol?)


SSBJ 14,500,00 x .125 = 1,812,500 mil

1,812,500 mil / 14 conductors = 129,464.286 mil individual SSBJ X 14 or 2/0 at 133,100 cm each x 14 (would only work in a single conduit as 14 SSBJ can not divide evenly into 3 conduit runs)

If you you are paralleling every ungrounded conductor and SSBJ into one massive conduit ok

However if you have 3 conduits equally separating pairs of ungrounded and grounded conductors in 3 conduits from source to first disconnect then you could not get the required even number of SSBJ in 3 conduits. 14 SSBJ / 3 = 4.66 SSBJ conductors in each of the conduits (not possible)

***correction above I meant SSBJ but not grounded conductors as you said there are no line to neutral loads

However I believe it is typical to run a derived ungrounded conductor from neutral to first point of disconnect even if you will not run line to neutral loads.

On an ungrounded system however ground detectors would have to be installed

 

[Jpflex]

14.66 conductors x 255 = 3,738.3 i but 14.66 conductors is not practical

 

[ramsy]

2/0 at 133,100 cm each x 14 (would only work in a single conduit as 14 SSBJ can not divide evenly into 3 conduit runs)

Is grounding metallic conduit with bonding jumpers simpler, if not underground?

 

[Jpflex]

If located in SWGR and XFMR are located in separate buildings the SSBJ must be bonded at the XFMR XO. There is no such thing as a “reducing neutral”. Calling it such would be very misleading - it would mean a white or gray grounded conductor that is current carrying….which it is not.
Also the system bonding jumper is not required at both locations—only at the XFMR in this case.


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But if this were a delta delta 480 volt system with no line to neutral loads then this I believe could be installed as an ungrounded system. The system bonding jumper would have to be installed nearest the grounding electrode conductor.

This occurs at two locations, at transformer cabinet and to the first point of disconnect. As for whether code requires SBJ at outdoor source transformer xo to grounding electrode conductor to grounding electrode maybe? But could SBJ system bonding jumper also be only at first disconnect to its grounding electrode conductor and electrode?

 

[Jpflex]

Is grounding metallic conduit with bonding jumpers simpler, if not underground?

You could not use 2/0 in my example but I was just making calculations based on your stated 14 number of SSBJ as an example

I’m not exactly sure what you meant by bonding jumpers for metal conduit not underground being easier but if you told me more info on your underground set up such as if you have one big conduit for all feeders or 3 conduits would be helpful

Also I’m working on a 4800 p to 480 s delta delta ungrounded system at my job site but can’t go to work at the moment due to the storm