Job is sold now what ?

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Smash

Senior Member
Objective supply 3phase 480V power for two loads one draws 12 amps will fuse at 30A the other has a 3pole 50amp breaker. Draws 22.5 amps
I already ordered a 208V Delta pri and 480V wye secondary 75KVA step up transformer. Here’s my plan I will run 2/3 MC about 110’ from the 208V panel will install a 3pole 100A breaker voltage drop will be within peramiters with #2 wire, at the load side a 3phase 100A 600V service disconnect to feed trans primary. Out of transformer to a fusible disconnect 10’ away to feed crane. Out of trans again (double lugs) about 15’ to non fusible disconnect to feed the 3pole 50A breaker load. There are no neutrals needed. So I do not plan to use the XO terminal. The 2/3 MC cable has a #8 stranded ground that will go to the HO lug in the transformer than bond to unit case. ? Then will run a separate # 6 EGC back to the source and ground. Little fuzzy on the grounding and bonding and when is it concidered a SDS at the source 110’ away or at the disconnect sitting next to transformer ? Also would run a # 6 solid from trans case to structure steel. Is this install ok once I figure out the grounding aspect. Gets confusing to me when talking delta/wye and SDS. You guys all helped me out to get this job I was able to hold a intelligent conversation of what was needed and now I want to check and double check to make sure I’m correctly doing the install. Ty in advance.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
All else aside, if I had the choice, I would try to locate the transformer nearer the source and run the 480v the long run.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
It's a Separately Derived System when there is no direct connection to circuit conductors of any other electrical source in the building other than grounding and bonding.

A delta wye transformer is an example of an SDS so distance to anything has nothing to do with it.

You bond the HO inside the transformer or the first disconnect and that is where you land you GEC.
 

MD Automation

Senior Member
Location
Maryland
Occupation
Engineer
...So I do not plan to use the XO terminal.

...The 2/3 MC cable has a #8 stranded ground that will go to the HO lug in the transformer than bond to unit case. ? Then will run a separate # 6 EGC back to the source and ground.

...Also would run a # 6 solid from trans case to structure steel.

Smash - glad to hear you picked up this job.

Just to be clear - there is no XO terminal in your transformer, only the HO on the secondary side.

Not sure what the separate #6 back to your 208V source is for? As you indicated, the MC feeding your primary will already have a #8 ground for the bond. The #6 to building steel sounds OK. I am sure someone else, smarter than me, will chime in.

Good luck with it.
 
For the primary, just think of the transformer as being like any other load - gets an egc run with the primary conductors to bond the transformer. The secondary is treated like a service and needs a gec per 250.30(A)(4)
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Objective supply 3phase 480V power for two loads one draws 12 amps will fuse at 30A the other has a 3pole 50amp breaker. Draws 22.5 amps
I already ordered a 208V Delta pri and 480V wye secondary 75KVA step up transformer. Here’s my plan I will run 2/3 MC about 110’ from the 208V panel will install a 3pole 100A breaker voltage drop will be within peramiters with #2 wire, at the load side a 3phase 100A 600V service disconnect to feed trans primary. Out of transformer to a fusible disconnect 10’ away to feed crane. Out of trans again (double lugs) about 15’ to non fusible disconnect to feed the 3pole 50A breaker load.
Depending on which 240.21(C) rule you are using, the load conductors are required to terminate in an over-current device, not a non-fusible disconenct.

There are no neutrals needed. So I do not plan to use the XO terminal. The 2/3 MC cable has a #8 stranded ground that will go to the HO lug in the transformer than bond to unit case. ?
As noted above: Primary EGC connect to the transformer cased only.

Then will run a separate # 6 EGC back to the source and ground. Little fuzzy on the grounding and bonding and when is it concidered a SDS at the source 110’ away or at the disconnect sitting next to transformer ? Also would run a # 6 solid from trans case to structure steel. Is this install ok once I figure out the grounding aspect. Gets confusing to me when talking delta/wye and SDS. You guys all helped me out to get this job I was able to hold a intelligent conversation of what was needed and now I want to check and double check to make sure I’m correctly doing the install. Ty in advance.
I believe 250.20 will require your wye secondary neutral to connect to your Grounding Electrode System and if you are going to use building steel you need to assure it meets the requiremetn sof 250.68 as far a being a GEC>
 
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