Transformer XO

[Smash]

I know this topic has been discussed at length and I finally maybe I think understand the bonding and grounding of transformers in general. Some of the different exceptions and scenarios can still be confusing. My problem or question I’m hooking up a large saw from China I mean really from China not just made there. The manual, controls, everything Chinese. It’s Designed to run at 200V 3phase I’m installing a 3phase 45KVA 480V/277V to 208/120 transformer. Saw rep said quote“208 very good “ Did all the calculations 70Amp breaker on the primary side 125amp fusable disconnect on the secondary side. There is 3 lines and a equipment ground on the primary side EG on a lug at the service entrance. I pulled 5 total lines from the secondary to my disconnect. X1 X2 X3 X0 neutral and a #2 ground wire which I fed thru XO to aid as my bonding jumper and terminated at the ground lug I installed on the transformer metal frame. Here’s my question inside the saw which arrived last night after all other work is done there are only four terminals L1 L2 L3 and PE which is used as green ground then jumps to terminal block for all control grounds for the machine. There is no neutral do I need to use the XO terminal at all do I carry it through to the unit and terminate it at the machine ? I’m just not sure which I should be using. Right now I’m using both through the disconnect with no where to terminate my last 5th wire in the saw. I also have both on the combination block in the disconnect with the bonding screw intstalled. ( I know that needs to come out to keep a fault traveling back to the source) Is XO even needed ? If not I just continue the EGC straight from the source to the machine bonding transformer and disconnect along the way. Clear fault path machine to source. Is a bonding jumper still required at XO in this case. My brain hurts

 

[jumper]

I have a hard time with reading large blocks of text. Please break it up next time.

XO has to still be bonded to the case and connected to the GES even if do not need a neutral at the equipment.

A neutral does not have to be ran to equipment if not needed.

I think you were asking about that?..

 

[Smash]

I currently have XO to the disconnect from disconnect to the saw. Smaller #2 ground from transformer frame lug to disconnect combination lug then both to the saw. I used the #1 AWG from disconnect to the PE terminal on saw. All work was completed with a whip off disconnect waiting for saw. I’m just questioning the use of the XO back to the saw. Sounds like XO should have stopped with the bonding jumper only and only carry ground thru disconnect to saw. Wouldn’t removing bond screw in disconnect be the same thing ? It carries straight thru just using multiple wires to accomplish the same thing.

 

[jumper]

I currently have XO to the disconnect from disconnect to the saw. Smaller #2 ground from transformer frame lug to disconnect combination lug then both to the saw. I used the #1 AWG from disconnect to the PE terminal on saw. All work was completed with a whip off disconnect waiting for saw. I’m just questioning the use of the XO back to the saw. Sounds like XO should have stopped with the bonding jumper only and only carry ground thru disconnect to saw. Wouldn’t removing bond screw in disconnect be the same thing ? It carries straight thru just using multiple wires to accomplish the same thing.

I am sorry, I do not follow.

XO is a transformer terminal. XO at the disco?

 

[infinity]

I currently have XO to the disconnect from disconnect to the saw. Smaller #2 ground from transformer frame lug to disconnect combination lug then both to the saw. I used the #1 AWG from disconnect to the PE terminal on saw. All work was completed with a whip off disconnect waiting for saw. I’m just questioning the use of the XO back to the saw. Sounds like XO should have stopped with the bonding jumper only and only carry ground thru disconnect to saw. Wouldn’t removing bond screw in disconnect be the same thing ? It carries straight thru just using multiple wires to accomplish the same thing.

Smash,
Like Jumper I'm having a hard time following your installation. You need to clarify these few terms:

SBJ -system bonding jumper, from X0 to frame
SSBJ- supply side bonding jumper, from the X0 to the disconnect
EGC- equipment grounding conductor, from the disconnect to the saw
GEC- grounding electrode conductor, X0 to the ground electrode

Since your SBJ is in the transformer then you do not need to bring a neutral conductor to the disconnect switch since it's not being used. The SSBJ will be used to bond the disconnect switch and will be used for all equipment grounding purposes on the load side of the disconnect switch.

 

[Smash]

Smash,
Like Jumper I'm having a hard time following your installation. You need to clarify these few terms:

SBJ -system bonding jumper, from X0 to frame
SSBJ- supply side bonding jumper, from the X0 to the disconnect
EGC- equipment grounding conductor, from the disconnect to the saw
GEC- grounding electrode conductor, X0 to the ground electrode

Since your SBJ is in the transformer then you do not need to bring a neutral conductor to the disconnect switch since it's not being used. The SSBJ will be used to bond the disconnect switch and will be used for all equipment grounding purposes on the load side of the disconnect switch.

I apologize the confusion comes in because the transformer the disconnect and a load side whip I installed weeks ago in prep for this saw being delivered. That’s where my contract ended. Everything was set up with the belief a neutral was needed. Saw rep was there to bolt down, level, and tie in the whip I supplied. He used the full sized #1 AWG neutral XO in this case to the PE ground at the saw. Is this a problem since I did install the bonding jumper inside the transformer ? This job is 3hr drive for me and my contract is done. If it’s not correct I will return and fix it but if it’s ok it will save me a day.

 

[jumper]

So, PE at the saw is connected to the XO in the tranny.

XO to case.
XO to GES

Yes?

 

[Ingenieur]

I think this is what you are asking
480 to xfmr 3 ph and a gnd, no x0
208 to switch 3 ph and gnd, no x0
208 to machine 3 ph, a gnd, no x0

in xfmr
bond 480 gnd lug to 208 gnd lug and to enclosure (lug may already be grounded)
bond sec x0 to gnd lugs (prim x0 is not used)

at disconnect
3 ph in
3 ph out
bond ground to case and continue to machine

machine
land 3 phases
land ground to pe lug

this assumes the machine does not need 120
if so add neut from sec gnd lugs thru switch to machine
only connect at machine, not switch

 

[LarryFine]

Allow me:

I know this topic has been discussed at length and I finally maybe I think understand the bonding and grounding of transformers in general. Some of the different exceptions and scenarios can still be confusing. My problem or question I’m hooking up a large saw from China I mean really from China not just made there. The manual, controls, everything Chinese.

It’s Designed to run at 200V 3phase I’m installing a 3phase 45KVA 480V/277V to 208/120 transformer. Saw rep said quote“208 very good “ Did all the calculations 70Amp breaker on the primary side 125amp fusable disconnect on the secondary side. There is 3 lines and a equipment ground on the primary side EG on a lug at the service entrance.

I pulled 5 total lines from the secondary to my disconnect. X1 X2 X3 X0 neutral and a #2 ground wire which I fed thru XO to aid as my bonding jumper and terminated at the ground lug I installed on the transformer metal frame. Here’s my question inside the saw which arrived last night after all other work is done there are only four terminals L1 L2 L3 and PE which is used as green ground then jumps to terminal block for all control grounds for the machine.

There is no neutral do I need to use the XO terminal at all do I carry it through to the unit and terminate it at the machine ? I’m just not sure which I should be using. Right now I’m using both through the disconnect with no where to terminate my last 5th wire in the saw. I also have both on the combination block in the disconnect with the bonding screw intstalled.

( I know that needs to come out to keep a fault traveling back to the source) Is XO even needed ? If not I just continue the EGC straight from the source to the machine bonding transformer and disconnect along the way. Clear fault path machine to source. Is a bonding jumper still required at XO in this case. My brain hurts

 

[KnightPower]

I think I understand. Pull out neutral to disconnect and leave bond screw there. Done.

Sent from my SM-G930V using Tapatalk

 

[Smash]

I think I understand. Pull out neutral to disconnect and leave bond screw there. Done.

Sent from my SM-G930V using Tapatalk

It’s a 3 hr drive one way. I was hoping not to make another trip. But of course I want it to be safe. My job was completed 3 weeks before the saw arrived. I should have simplified what I was after. I can have the factory rep remove the bond screw which would basically carry the white neutral thru to the saw just needs to be identified as ground. Clear path lug from transformer straight thru to the lug on saw.

 

[kwired]

You are overthinking things. Your load doesn't utilize a neutral so you have no need to connect one to anything. Cap your white wire in the saw and forget about it. You didn't need it, but won't hurt to leave it either.

You still need same grounding/bonding regardless, and on a wye system that must be done with the neutral conductor.

Had you supplied a panelboard with other 120 volt loads as well as this saw instead of just a single disconnect then the saw, you simply would have left the panel with three ungrounded and an equipment grounding conductor.

 

[MBLES]

I have a similar but not so similar question so Ill just piggy back off this post. Would the XFMR need a GEC to ground rod if installed on 10th floor? I have the transformer grounded to the raised platform but the platform isnt attached to building. The platform floats on roof with equipment. Do i need a GEC from 1st floor to roof?

 

[GoldDigger]

I think that a bonding jumper (not GEC) to closest building steel (if qualified) should be all you need.

But the platform will need an EGC in the feeder to the transformer.

 

[MBLES]

I think that a bonding jumper (not GEC) to closest building steel (if qualified) should be all you need.

But the platform will need an EGC in the feeder to the transformer.

Yes Sir. Is there an address in NEC you can point me to?