If I have a 277/480 panel that I’m piping out of into a transformer, and then piping out of the transformer into a secondary 120/208 panel where do I need ground bushings? Both panels and both sides of the transformer? And do i always need a bonding jumper from X0 to my ground lugs on transformer?
Proper Transformer Bonding / Grounding?
- Thread starter Palmer
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If there are no concentric or eccentric KO's on the 480 primary conductors then no bonding bushings are required. If the GEC is in a metal raceway a bonding bushing is required on that raceway. Yes the X0 is bonded with a system bonding jumper (SBJ) sized according to T250.102(C). If flexible raceway are used then there are other requirements.
I used a knockout set from a 480v panel, left with compression emt connector and went all the way to the transformer, changed over to greenfield and used grounding bushings on both ends of that run. I did the same thing from the transformer to the secondary panel, used ground bushings at both spots. Did I need to or did I not need to use them at all locations?
Im curious as to why I had to bond the neutral and ground. I had a tripped breaker and it sent my neutral all whacked out at 47 volts to ground and once I installed the SBJ it cleared and worked as should. I have always done them inside the transformer and never at the secondary panel, does it matter?
xformer
Senior Member
- Location
- Dallas, Tx
- Occupation
- Master Electrician
the Xo bonding can occur in the Transformer enclosure or at the first means of disconnect.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Bonding bushing are not required on any of the raceways mentioned in this installation.
:thumbsup:
Keep in mind with the grounding limitations of greenfield (from 250.118) adding a bond bushing is not a lot different than doing so to a piece of PVC as the bond path through greenfiled is so limited.
Last question, how come in one picture it shows ground coming from primary and in secondary, and then in another it shows no ground in the secondary? or in another picture i’ve seen no ground coming in on primary side but there is a ground on sexondaryz
Not sure what pictures you are referencing.
This one pretty well sums it up.
You will see the primary has the primary equipment ground, The secondary will have thesystem bonding jumper, supply side bonding jumper and grounding electrode conductor to address.
This one pretty well sums it up.
You will see the primary has the primary equipment ground, The secondary will have thesystem bonding jumper, supply side bonding jumper and grounding electrode conductor to address.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
You would need to show those pictures to get the right answer but I can only guess by what you've written that the metal raceway is being used as an EGC. This is fine if there is no FMC in the run. You should brush up on the terminology as it makes it easier for someone to understand what you're describing. The conductor in the primary circuit is an EGC, the conductor in the secondary circuit is an SSBJ (supply side bonding jumper), it's incorrect to call either of those just a ground.
There was this same picture that showed no ground on secondary panel and another that showed no ground from primary panel but was on in secondary.
Can the EGC go onto a mechanical 2 hole lug with the SSBJ? Or does it have to be in a lug by itself like shown and building steel, neutral and SBJ are on X0.
Not sure I follow completely but it appears the equipment ground and supply side bonding jumpers are the raceway itself rather than a actual conductor.
Multi-port lugs are acceptable for terminations.
Multi-port lugs are acceptable for terminations.
If you use a terminal bar, be careful where you mount it
450.10 Grounding.
(A) Dry-Type Transformer Enclosures. Where separate equipment grounding conductors and supply-side bonding jumpers
are installed, a terminal bar for all grounding and bonding conductor connections shall be secured inside the transformer
enclosure. The terminal bar shall be bonded to the enclosure in accordance with 250.12 and shall not be installed on or over
any vented portion of the enclosure.
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