Separately derived system

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ctaylo360860

ctaylo360860

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I’m hoping to confirm I’m doing my grounding and bonding right for my separately derived system. I have a switched neutral transfer switch that is fed from a service disconnect on the left. The system is 3phase 208v. The gen set has a 225amp breaker. I plan on setting a small piece of 2 1/2 imc on the ground and using 2 1/2 liquidtight flexible metal conduit to get into the genset and the transfer switch... I’m running 4-4/0 copper conductors, and 1 #4awg cu. “3phases, 1 grounded conductor” and an equipment grounding conductor sized with 250.122. I have a bonding bushing st genset because I’m having to use reducing bushings to get into genset enclosure. There is a bonding jumper installed from the manufacturer in the genset. This bonding jumper is bonding the grounded and grounding conductors, and should be sized on 250.102(c). In the transfer switch I’m making a a concentric whole, but running liquidtight flexible metal conduit to get into the ats enclosure. Will I also need a bonding bushing in ats enclosure as well? I have a set of lugs inside the transfer switch that I planned on landing the equipment grounding conductor on. If I’m understanding 250.30 (a) I also need to run a grounding electrode conductor from frame of my genset to the building steal, this would be sized on 250.66, which should be the largest ungrounded service entrance conductors. These are in the service disconnect and should be paralleled 250kcmill aluminum. Which should be #2 copper. as I can’t set ground rods “everything is sitting on concrete, as this install was not planned out very well imo. It’s going to look like a mess back here because I need to get. 1-2 1/2 raceway, and 3-3/4 raceways 1 for Shilded signal wires, 1-shielded Ethernet, 2- separate circuits for block heater, and battery charger. This was all designed by previous electricians and in the middle of build they quit or were hired, and fired. I am now working with what I have in front of me. Am I missing any other components of the grounding electrical system ? Does anyone have any better ideas or see a problem with my install? Really want to thank everyone on the forum again! Any and all help is very much appreciated!!!!
 
Service disconnect on left
Automatic transfer switch”switched neutral” middle
Main distribution panel right
 

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Service disconnect close up
 

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Gen set enclosure / plan for raceways to Automatic transfer switch.
 

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Just went and looked at the grounding electrode system to see which is closer water main or building steel, and found this. Looks like ester needs to be bonded before and after main shut off. Am I able to jump from a piece of steel down to the water main, or so I need to take it all the way back to the service disconnect. This should be a gec and sized based on 250.66.
 
You won't need bonding bushings as you have a wire type EGC for the flex. You don't have to run each GEC separately. You can jump from one GE to the next as long as the "home run" is sized large enough.
 
texie said:
You won't need bonding bushings as you have a wire type EGC for the flex. You don't have to run each GEC separately. You can jump from one GE to the next as long as the "home run" is sized large enough.
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Okay, great I wasn’t sure, but figured it was better to have the bushing then to not have it... can I come from the frame of the genset to two new ground rods? I will have to core our concrete to set them, but will actually know they’re part of the grounding electrode system.... other option I have is make sure the wire that runs from the Left side of the service disconnect is going actually going to building to steel And is part of ges. Then I should be able to go from genset frame to building steel with a piece of #2 copper sized on 250.66? Will I have to put this gec in a raceway to protect it or can I run it open...
 
texie said:
Just curious, why are they using a switched neutral for a garden variety genset install?
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So I had nothing to do with the design of this install. Everything has been done and and ordered before I got this job.... I’m wondering if they’re doing it because this building is for a tire shop/gas station. I’m not familiar with why you use a non separate derived system vs a separate derives system, and was hoping to gain some clairity on that subject... job seems to be a mess no matter what I do I’ve got to get som many raceways into this small enclosure under the genset...
 
ctaylo360860 said:
Okay, great I wasn’t sure, but figured it was better to have the bushing then to not have it... can I come from the frame of the genset to two new ground rods? I will have to core our concrete to set them, but will actually know they’re part of the grounding electrode system.... other option I have is make sure the wire that runs from the Left side of the service disconnect is going actually going to building to steel And is part of ges. Then I should be able to go from genset frame to building steel with a piece of #2 copper sized on 250.66? Will I have to put this gec in a raceway to protect it or can I run it open...
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GECs can be run without conduit. Best to use PVC to avoid all kings of bonding requirements though. You can even just use sections of PVC to keep it nice looking-it does not need to be a complete conduit system. Since you have all these GECs, I think if it were me, I would put a common ground bar in at a convenient spot a run everything to that. That can even serve as your intersystem bonding point as required in 250.94 and anything that needs to get connected to the GES. Ground bar kits are readily available and are 1/4" X 2" X whatever length you need. Come predrilled and with the mounting hardware.
 
texie said:
GECs can be run without conduit. Best to use PVC to avoid all kings of bonding requirements though. You can even just use sections of PVC to keep it nice looking-it does not need to be a complete conduit system. Since you have all these GECs, I think if it were me, I would put a common ground bar in at a convenient spot a run everything to that. That can even serve as your intersystem bonding point as required in 250.94 and anything that needs to get connected to the GES. Ground bar kits are readily available and are 1/4" X 2" X whatever length you need. Come predrilled and with the mounting hardware.
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Yes I was trying to stay away from metal raceway so I didn’t have to clamp it at both ends of the raceway... I’m not quite following when you say I have all these Gecs... With the genset install I should only be dealing with 1- gec, and 1-egc. Are you saying just set normal ground bar kit? set it say just to the left of the service disconnect on the outside of the building and then run from the service disconnect With #2 copper to the ground bar, then also go from that ground bar to the genset frame with a piece of #2cu?
 
ctaylo360860 said:
Yes I was trying to stay away from metal raceway so I didn’t have to clamp it at both ends of the raceway... I’m not quite following when you say I have all these Gecs... With the genset install I should only be dealing with 1- gec, and 1-egc. Are you saying just set normal ground bar kit? set it say just to the left of the service disconnect on the outside of the building and then run from the service disconnect With #2 copper to the ground bar, then also go from that ground bar to the genset frame with a piece of #2cu?
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Yes. It is a convenient point for all to use. You can take all of your GEs and connections points to it.
 
texie said:
Yes. It is a convenient point for all to use.
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Thank you so much! That’s going to work perfect! Do you think I should try and bond the water main even though they’re not sure if it’s copper or pex coming into the building?
 

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Could I also just add a lug in the service disconnect and run from service disconnect ground lug, back to the gen set frame..
 
ctaylo360860 said:
Could I also just add a lug in the service disconnect and run from service disconnect ground lug, back to the gen set frame..
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No. GECs can not be daisy chained from disco to disco, etc. Daisy chaining only allowed from GE to GE (where conductor is large enough). That is another reason the ground bar is so convenient. It takes away most of the thinking-you just run everything to that. Mechanical lugs are fine for connection.
 
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