bonding after xfmr

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-=PEAKABOO=-

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112.5 kva 480 primary, 120/208 secondary. I have 1/0 ground from building steel to the xfmr can then to the XO tap. I have two 2" flex 4' long with four 3/0 in each. This is a 2 piece panel board with a 400 amp main breaker. What the best way to bond the nuetral to ground in this panel?
thanks
 
-=PEAKABOO=- said:
112.5 kva 480 primary, 120/208 secondary. I have 1/0 ground from building steel to the xfmr can then to the XO tap. I have two 2" flex 4' long with four 3/0 in each. This is a 2 piece panel board with a 400 amp main breaker. What the best way to bond the nuetral to ground in this panel?
thanks
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Since you have already bonded them in the transformer you will not bond them again in the panel. You would add an EGC from the XO tap to an isolated ground bar in the panel.

Roger
 
-=PEAKABOO=- said:
so I can go to the neutral bar with a 1/0 from xo and take my branch circuit grounds to the nuetral bar?
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No, you will land your parallel 3/0 neutrals on an isolated (not bonded to the enclosure) neutral bar in the panel and all the branch circuit neutrals will land here also.

You will need to add an appropriate sized EGC in both of your 2" flexes, these two EGC's will land on an ground bar (bonded to the enclosure) in the panel and all of the branch circuit EGC's will land on this bar.


Roger
 
-=PEAKABOO=- said:
That is the way I normally do it. I was confused about bonding in 2 locations, xfmr and panel boards. Can I run #4 in 2" condiuts instead of 1/0?
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You would never bond at two locations when dealing with a seperatly derived systems unless you could meet the requirement of 250.30(A)(1) Exception No. 2 and even if you could, it would not be a good idea.

As far as your EGC size, see Table 250.122


Roger
 
roger said:
As far as your EGC size, see Table 250.122


Roger
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Roger, Coming off the transformer, the ground wire would be called an equipment bonding jumper and need to follow table 250.66.for each of the derived phase conductors in each set.#4 with the 3/0.The system bonding jumper in the transformer would be the # 2awg minimum (1/0 the op is using).
Rick
 
RUWired said:
Roger, Coming off the transformer, the ground wire would be called an equipment bonding jumper and need to follow table 250.66.for each of the derived phase conductors in each set.#4 with the 3/0.
Rick
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You're correct Rick. (That's what happens when I try to talk on the phone and complete a post at the same time
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)

Roger
 
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