300.3

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chris kennedy

chris kennedy

Senior Member
Location
Miami Fla.
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60 yr old tool twisting electrician
I have an existing MTS that I believe is in violation of 300.3. Normal power comes in with just 2 4/0's. I believe there is an exception for switches that allows this install without the grounded conductor run with them. I cant find this exception in 300 or 400. Where is it???

The load leaves in the same nipple but with the 4/0's and the #3 grounded conductor from the generator inlet device goes to the MDP. This I believe is in violation.

Also, I need to submit a riser diagram to the building dept on Monday. How would you list the conductors in that conduit??? 4-4/0's, 1-#3, and 1-#4EGC in 2" conduit???

Thanks

MTSLibertyBell001.jpg


MTSLibertyBell002.jpg
 
Pierre C Belarge said:
In looking at that install, and from what I can see in the pictures, I am willing to bet there may ampacity adjustment issues and grounding/bonding issues at the generator.
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Granted, but my real issue is how to represent this conduit on a riser diagram without raising eyebrows at plans review. 4-4/0's, 1-#3, and 1-#4EGC in 2" conduit
 
How is that ground lug attached to the can? It does not seem to be against the back wall but yet I see a bond screw going out the back?. seems to be sitting on some sort of insulating material. Is that switch service rated?
 
Cavie said:
How is that ground lug attached to the can? It does not seem to be against the back wall but yet I see a bond screw going out the back?. seems to be sitting on some sort of insulating material. Is that switch service rated?
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The bond screw hits a metal 'L' bracket thats welded to the bottom of the can. Not service rated, 200A switch feed form 225A normal power breaker in the MDP.:roll:
 
Well .... is it supposed to be a 'separately derived system' or not? That's what defines whether the neutral is switched.

From a design point, there's no reason NOT to switch the neutral. That is, if you switch the neutral you keep the two systems completely apart; all manner of goofy things might happen if you leave the two neutrals (generator and PoCo) connected to each other.

Yet, there is no code requirement that the systems be 'separate.'
 
chris kennedy said:
I have an existing MTS that I believe is in violation of 300.3. Normal power comes in with just 2 4/0's. I believe there is an exception for switches that allows this install without the grounded conductor run with them. I cant find this exception in 300 or 400. Where is it???
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Look at art. 250.24(C) for the grounded conductor brought to service equipment.
 
Your Line diagram might reflect the code conflict of 230.7?
Well is it or isn't it, with the excetpion(s)!

You might also need to include 230.2(E) or does that exist, not shown?
 
chris kennedy said:
The bond screw hits a metal 'L' bracket thats welded to the bottom of the can. Not service rated, 200A switch feed form 225A normal power breaker in the MDP.:roll:
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Why do you say the transfer switch is not service rated? Typically a green bonding screw for the neutral bus bar is only provided with equipment that is marked 'suitable for use as service equipment".
 
chris kennedy said:
I believe there is an exception for switches that allows this install without the grounded conductor run with them.
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Pierre C Belarge said:
" I believe there is an exception for switches that allows this install without the grounded conductor run with them. I cant find..."

His question was about switches, of which 200.7(C)(2) is applicable
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200.7(C)(2) is in regards to re-identifying white/gray insulation for switch loops. I don't think that is was he was thinking. I think he was looking for the exceptions to 300.3(B) which are in 300.3(B)(1) through (B)(4).
 
don_resqcapt19 said:
Why do you say the transfer switch is not service rated? Typically a green bonding screw for the neutral bus bar is only provided with equipment that is marked 'suitable for use as service equipment".
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I'm sorry Don, I should have stated this is not being used as service equipment.

Twoskinsoneman said:
I think he was looking for the exceptions to 300.3(B) which are in 300.3(B)(1) through (B)(4).
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You are correct.
 
don_resqcapt19 said:
Then the green bonding screw should not be installed as the transfer switch does not switch the grounded conductor.
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I agree all the grounded conductors should be terminated on this buss without the bonding screw. EGC's should have been bonded to the enclosure. What can I do? This was installed by the company I work for and was told by the owner, "just get this through plan review".
 
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