Delta Delta transformer grounding?

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emiller233

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pittsburgh, pa
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Controls-Automation engineer
We have a customer who wants to use a 600VAC to 480VAC transformer(50KVA), and i am not sure how to ground this things properly to meet UL508/CSA requirements.

I attached schematics that Eaton sent me for this transformer
Eaton XFMR.jpg

this was Eatons response but I am not clear on what it is telling me:
There should be no ground connection on the line side. Since this is a delta-delta transformer there is no ground connection on the load side either. However the transformer is internally ground per NEC 450.10 and 250.4(B).


The customer does not want this transformer sitting on our main machine due to weight, so they want to put it on the floor right next to our machine and run a short multi-conductor cables(3 hot + 1 GND) to it and use 4-pin connectors on both the load side and the line side (to make shipping this thing easier). The breakers would be back in our main control cabinet.

How do I ground this transformer, if I even have to?
 

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Welcome to the forum... :thumbsup:

You do not have to... but if you do not, you will have to install a ground detector. See 250.21 for starters.

If the transformer has already been purchased (and not returnable without difficulty, exorbitant restock penalty, or such), you can corner ground the secondary, which is not all that uncommon.


If the transformer has not yet been purchased, you could use either a 480/240 center-tapped delta- or 480/277 wye-configured grounded secondary.
 
There should be three hots and a equipment ground on the primary, not to be confused with a grounded/neutral. The secondary can be corner ground or ungrounded, but you still need your overcurrent and grounding electrode and I don't see plopping down a 50kva with some rubber cords and connectors as a good design.
 
I sold transformers for years and try if at all possible to ask why they want a D-D and quite often their answer is because they don't need a neutral. Then the education starts to make sure that they understand what they are doing. Or they call to I ask where the neutral is so they can ground it or how should it be grounded. Scary
 
sorry for my delayed response! i wasn't receiving notifications for this thread...

Smart $
The transformer has not been bought yet and was quoted by our salesman (thru Eaton). It would be a cutom build to meet the UL/CSA Listed requirements, so I think the went with the Delta-Delta for cost savings??? Money is very tight for this project (already over budget).

I looked into the ground detector option (which I know nothing about) and there seems to be a million options! does anyone have any recommendations as to which to use if we had to go that route?

If we corner-ground the secondary, it looks like we would put the ground wires(from both line side and load side connectors) onto the B-leg


I couldn't figure out out to use the 'quote' on here, but in regards to this:
If the transformer has not yet been purchased, you could use either a 480/240 center-tapped delta- or 480/277 wye-configured grounded secondary.
we need 600VAC to 480VAC, is this still the correct option? (I don't deal with transformers much obviously, so I'm trying to learn them realllll quick!)

ActionDave
There should be three hots and a equipment ground on the primary, not to be confused with a grounded/neutral. The secondary can be corner ground or ungrounded, but you still need your overcurrent and grounding electrode and I don't see plopping down a 50kva with some rubber cords and connectors as a good design.
If we go with the corner grounded secondary option, how would we handle the grounding? For equipment grounding, don't we need a ground lug on the chassis of the transformer somewhere, which Eaton is telling me isn't an option on this.
We don't like the idea of plopping this transformer on the floor either, but we aren't being given much of an option... If anyone has a suggestion as to how to do an offline transformer, I am all hears! It Does have to Meet UL/CSA Listed requirements tho, that's why it was suggested to us to use the connector option (to eliminate the need for any wiring after shipping the system)

templdl
I sold transformers for years and try if at all possible to ask why they want a D-D and quite often their answer is because they don't need a neutral. Then the education starts to make sure that they understand what they are doing. Or they call to I ask where the neutral is so they can ground it or how should it be grounded. Scary
I am one of the ones trying to educate themselves on transformers as well, what transformer would you sell me for this UL/CSA 508 Listed project? (not that i expect you to give me a part #, but if you know them well, prefereably Eaton)​
 
emiller233,

If you want to quote a previous post the simplest thing to do is click "reply with quote" at the bottom right of the respective post.

I would get a wye secondary as a general rule although I'm not real sure what your application is and why a delta/delta transformer was recommended.
 
emiller233 said:
We have a customer who wants to use a 600VAC to 480VAC transformer(50KVA), and i am not sure how to ground this things properly to meet UL508/CSA requirements.

I attached schematics that Eaton sent me for this transformer
View attachment 16335

this was Eatons response but I am not clear on what it is telling me:
There should be no ground connection on the line side. Since this is a delta-delta transformer there is no ground connection on the load side either. However the transformer is internally ground per NEC 450.10 and 250.4(B).


The customer does not want this transformer sitting on our main machine due to weight, so they want to put it on the floor right next to our machine and run a short multi-conductor cables(3 hot + 1 GND) to it and use 4-pin connectors on both the load side and the line side (to make shipping this thing easier). The breakers would be back in our main control cabinet.

How do I ground this transformer, if I even have to?
Click to expand...

Neutral may not be required, but is likely least expensive to go with a transformer with 480/277 wye secondary, mostly because this is what has higher sales demand and more likely to be a stock item vs custom build. You need to run an equipment grounding conductor (which can be metal raceway) no matter which method is used - even the ungrounded system still needs an EGC.

Details of "your equipment" that is being supplied may or may not favor or allow ungrounded system, or even a corner ground system to supply it, though the fact it doesn't need a neutral lessens the chance that it can't be on corner ground or ungrounded systems.

If you have surge protectors of any kind they would need to be able to handle 480 volts to ground nominal supply to be on anything but a grounded wye system.
 
kwired said:
Neutral may not be required, but is likely least expensive to go with a transformer with 480/277 wye secondary, mostly because this is what has higher sales demand and more likely to be a stock item vs custom build. You need to run an equipment grounding conductor (which can be metal raceway) no matter which method is used - even the ungrounded system still needs an EGC.

Details of "your equipment" that is being supplied may or may not favor or allow ungrounded system, or even a corner ground system to supply it, though the fact it doesn't need a neutral lessens the chance that it can't be on corner ground or ungrounded systems.

If you have surge protectors of any kind they would need to be able to handle 480 volts to ground nominal supply to be on anything but a grounded wye system.
Click to expand...


This transformer powers a large 330VDC Power Supplyhttp://www.signaltestinc.com/product-p/sga 330-91.htm. the Power supply is mounted in an enclosure. I attached the schematics below. Transformer is on bottom left, the large power supply is on the bottom right.

XFMR wiring.jpg

If we attach transformer to the skid so that i could eliminate the connectors, would i need to run two seperate conduits from the XFMR to the Power supply enclosure(one for Line Side, and one for Load side) so i dont have to de-rate the cables?
 
ActionDave said:
emiller233,

If you want to quote a previous post the simplest thing to do is click "reply with quote" at the bottom right of the respective post.

I would get a wye secondary as a general rule although I'm not real sure what your application is and why a delta/delta transformer was recommended.
Click to expand...

ok, I will see if I can get that quoted then, thanks!

does this change the grounding requirements I assume?
 
I just heard back from Eaton on the transformer. They said I can switch thistop the grounded 480/277 wye secondary for the same price, which puts me back to the grounding to meet a CSA/UL Listing (which is past my knowledge level)

the transformer will be sitting offline of our machine (right next to it due to weight)
there will be a connector on the cable going to the transformer on the Line Side(3 hot + ground)
there will be a connector on the cable going to the transformer on the Load Side(3 hot + ground)

There should now be a ground lug on the transformer chassis since we're switching to a WYE secondary. Do we just land the ground wires coming from both cables/connectors (the Line Side and the Load side) onto the ground lug and its good?
 
emiller233 said:
...
There should now be a ground lug on the transformer chassis since we're switching to a WYE secondary. Do we just land the ground wires coming from both cables/connectors (the Line Side and the Load side) onto the ground lug and its good?
Click to expand...
Connecting a 50kVA transformer with cable and pin connectors is atypical, to say the least... but AFAIK, not a violation.

Grounds of cables will connect to lug(s) <---i.e. if one lug, it has to be rated for two conductors; if not, you'll have to add and use a second lug.

You can put the system bonding jumper (SBJ) and GEC connection in the disconnecting means enclosure.
 
emiller233 said:
I just heard back from Eaton on the transformer. They said I can switch thistop the grounded 480/277 wye secondary for the same price, which puts me back to the grounding to meet a CSA/UL Listing (which is past my knowledge level)

the transformer will be sitting offline of our machine (right next to it due to weight)
there will be a connector on the cable going to the transformer on the Line Side(3 hot + ground)
there will be a connector on the cable going to the transformer on the Load Side(3 hot + ground)

There should now be a ground lug on the transformer chassis since we're switching to a WYE secondary. Do we just land the ground wires coming from both cables/connectors (the Line Side and the Load side) onto the ground lug and its good?
Click to expand...
If transformer does not have the neutral bonded already, (and often they won't) you would have to install a bonding jumper as well. It can be bonded in the transformer or in the first disconnecting means but since you are not utilizing a neutral it basically needs bonded at both, but you wouldn't need to bring a fifth wire (the neutral) to the first disconnect like you would if serving loads that used the neutral.
 
kwired said:
... but since you are not utilizing a neutral it basically needs bonded at both, but you wouldn't need to bring a fifth wire (the neutral) to the first disconnect like you would if serving loads that used the neutral.
Click to expand...
Not running a neutral from transformer to disconnect... so there is no neutral to bond in the disconnect. Have to bond in transformer enclosure.
 
Smart $ said:
Connecting a 50kVA transformer with cable and pin connectors is atypical, to say the least... but AFAIK, not a violation.

Grounds of cables will connect to lug(s) <---i.e. if one lug, it has to be rated for two conductors; if not, you'll have to add and use a second lug.

You can put the system bonding jumper (SBJ) and GEC connection in the disconnecting means enclosure.
Click to expand...
Scratch that last line. There's no neutral to bond.
 
Smart $ said:
Not running a neutral from transformer to disconnect... so there is no neutral to bond in the disconnect. Have to bond in transformer enclosure.
Click to expand...
This is where you need to pay attention to terminology and exactly how things are done. If you bond to the neutral at the transformer - all you need to leave the transformer with is the three ungrounded and an equipment grounding conductor (which can be metal raceway) if you have no neutral load. But if your system boning jumper is actually in the first disconnect then you actually should need a white or gray grounded conductor from XO to the first disconnect and an EGC (again can be metal raceway) back to the transformer enclosure.

Bond same conductor in both enclosures to the case - technically only the transformer end has the system bonding jumper, the other one is just a bonding jumper that bonds the first disconnect enclosure to the EGC.
 
schematic PDF is attached...

the correct terminalogy is what I am trying to give myself a crash-course in and learn quickly..!!! haha

i think i have gotten the schematics correct, or at least close to it, from reading the feedback here, as well as watching some of Mike Holts videos on Youtube...

I have attached a copy of them with they Delta Wye transformer which shows the grounding in it. We are not using the Neutral on the WYE side, so i connected that to PE on my schematics (which i think the correct term for it is EGC-Equipment grounding conductor).

Delta-Wye XFMR grounding.jpg

the wire going from the neutral terminal on the WYE side of the transfomer is called the SBJ - System Bonding Jumper???

assuming i got this portion correct, now i need to figure out the correct way to tie it back to the Power enclosure via the connectors/cables. I know this isnt typical to have connectors on the transformer, but this is a UL Listed project so pir Inspector that signs the UL certificate is telling us that no wiring can be done/modifed once this system leaves our shop, hence the need for connectors to detach this Transformer for shipping...

Everything on the schematics except for the Transformer and the Line and Load side cables for it, are inside of a single enclosure, which i call the Power Box on the schematics that i attached. teh connectors for this transformer will be mounted on the power enclsure
 

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emiller233 said:
the wire going from the neutral terminal on the WYE side of the transfomer is called the SBJ - System Bonding Jumper???

assuming i got this portion correct, now i need to figure out the correct way to tie it back to the Power enclosure via the connectors/cables. I know this isnt typical to have connectors on the transformer, but this is a UL Listed project so pir Inspector that signs the UL certificate is telling us that no wiring can be done/modifed once this system leaves our shop, hence the need for connectors to detach this Transformer for shipping...

Everything on the schematics except for the Transformer and the Line and Load side cables for it, are inside of a single enclosure, which i call the Power Box on the schematics that i attached. teh connectors for this transformer will be mounted on the power enclsure
Click to expand...
Your connections look okay, my understanding is PE is the same as EGC too.

A 50 kva transformer is going to need a big ole' plug on the secondary if you are using some kind of rubber cord. What did you have in mind? Cam locks or something like a Meltric plug and recpt?
 
Looks pretty much okay to me, too. The only thing I note at issue is the NEC requires a connection to a grounding electrode... nearest of metal water pipe or structural steel electrodes, and if neither of those exist, any other building or structure electrode. See 250.30(A)(4).
 
ActionDave said:
Your connections look okay, my understanding is PE is the same as EGC too.

A 50 kva transformer is going to need a big ole' plug on the secondary if you are using some kind of rubber cord. What did you have in mind? Cam locks or something like a Meltric plug and recpt?
Click to expand...
not sure what the schematics I've uploaded are, but i have upsized it to a 75KVA transformer.. :cool:
I have been pushing for the Meltric connectors since they are Arc Flash rated, 60A on Line, 100A on load side. but the customer wants el-cheapo Amphenol connectors (screw-on connection)_ since that's what they have elsewhere on their system that this will integrate into. they are cheaper for me to buy, and the customer is correct in saying that the connectors 'should' never be disconnected live under power We'll see what happens..? haha

is it OK/acceptable to have two PE/EGC wires (in parallel) connecting the transformer to the power enclosure. one for the line side connector, and the other for the load side connector? I am seeing a lot of conflicting info on this as there could potentially be a ground loop created? If, i have to isolate the two, how do i do it? There will be like 10-feet of cable between them if its relevant?
 
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