# 600V 3 phase to 208/120V transformer bonding question



## Gatekeeper (Mar 20, 2017)

So I have 2 transformers. one is a 300kva and the new one is a 45kva. They are both 600V 3 phase 4 wire on the primary side and 208/120V 3 phase 5 wire on the secondary side. These transformer are hooked up via a 600V breakered disconnect on the primary and will be fed into another breakered disconnect on the secondary which will power equipment. Is the XO (neutral) on the (120/208) secondary inside the transformer supposed to be bonded to the transformers casing or ground lug inside the casing? Since there is no white wire (neutral) going into the transformer but one coming out I believe this is creating a new system? Many people are confused with this and i would like to help prevent any hazards. T


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## active1 (Dec 29, 2009)

Separately derived system.
It would be nice if XFMRs came with a ground bar already on the case.
So you can pick up your EG IN, EG out, XO, electrode, sec neutral, and 2 ground bushings.
I know some you can loop through.
Just saying be nicer than scrounging for chair lugs and hardware.


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## telsa (May 22, 2015)

Gatekeeper said:


> So I have 2 transformers. one is a 300kva and the new one is a 45kva. They are both 600V 3 phase *3* wire on the primary side and 208/120V 3 phase* 4* wire on the secondary side. [ The equipment bond// green wire// grounding wire is NOT counted as a conductor. It's still a wire. But not a conductor. So no-one uses your terminology.]
> 
> These transformer are hooked up via a 600V breaker disconnect on the primary and will be fed into another breaker disconnect on the secondary which will power equipment.
> 
> ...


This is referred to in the NEC as an SDS. ( Separately Derived System )

This is NOT the time or place for novices.

Bring in a j-man// EC.

These are easy peasy for him -- but not you. 

*You'll screw things up - when doing so kills people.*

No-one can solve the matter over the phone -- or over the Internet.


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## Gatekeeper (Mar 20, 2017)

telsa said:


> This is referred to in the NEC as an SDS. ( Separately Derived System )
> 
> This is NOT the time or place for novices.
> 
> ...


Tesla my intention is to bring this to the red seals in charge but I wanted to understand what is right or wrong first hence me asking here. Dont assume im some cheap contractor doing a hack job skipping safety and procedures. Let me add a retired city inspector who works here knows our existing 600 to 120/208 transformers have no neutral to ground bonding jumper and continues to use them as such.


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