Service Bonding

[Plumbob]

Greetings,
I am inspecting a new 400 amp service. The 400 amp service disconnect is attached to the outside of the building. There are two 200 amp panel boards located just inside and connected with non metal raceways. These are main breaker panels. Since the panel boards are down stream and in seperate enclosures from the service disconnect are they treated as main panels or sub-panels. I have been trying to evaluate whether the bonding conductors are sized properly. There are #4 AWG bare copper conductors routed with the feeder conductors and originating at the aluminum lug where the system grounded and GEC are landed in the service disconnect enclosure and landed on the equipment grounding terminals in the panel boards. Are these system bonding jumpers or ?

 

[ActionDave]

Greetings,
I am inspecting a new 400 amp service. The 400 amp service disconnect is attached to the outside of the building. There are two 200 amp panel boards located just inside and connected with non metal raceways. These are main breaker panels. Since the panel boards are down stream and in seperate enclosures from the service disconnect are they treated as main panels or sub-panels

Anything after the service disconnect is a sub panel, grounds and neutrals separate. I don't know what you mean by Main Panel.

I have been trying to evaluate whether the bonding conductors are sized properly. There are #4 AWG bare copper conductors routed with the feeder conductors

This makes no sense. There needs to be an Equipment Grounding Conductor sized per 250.122 run with the circuit conductors inside the same conduit or cable system.

and originating at the aluminum lug where the system grounded and GEC are landed in the service disconnect enclosure and landed on the equipment grounding terminals in the panel boards.

This makes no sense. You can't mix aluminum and copper on the same lug. By system ground do you mean Grounded Conductor, ie neutral?

Are these system bonding jumpers or ?

Don't know what they are yet. They are not system bonding jumpers because you don't have a separately derived system.

 

[Plumbob]

ActionDave,
Thank you for responding to my question. Just to follow up, your confirmation that the GEC connection to the Service Grounded Conductor in the Service Disconnect Enclosure defines the downstream panel boards as sub panels clears up some of my confusion.


My reference to Main Panel was meant differentiate between a Main Breaker type panel serving as the Service Disconnect and a sub panel.

As the panel boards in this discussion are sub panels its in now clear to me that the conductors connecting the grounding terminals in the panel boards to the system grounded conductor in the service disconnect enclosure are equipment grounding conductors that need to be sized based on table 250.122.

The aluminum lug I mentioned is located in the 400 amp Service disconnect enclosure. The service supplied neutral is landed there along with the GEC and the feeder neutrals and EGC's top the sub panels. All are copper conductors. The aluminum lug is bonded to the enclosure by a manufacturer supplied metal strap. If used as a service disconnect the strap is rotated into contact with the enclosure and bonded with a supplied screw. There is a sticker supplied to be used to identify the unit as a service disconnect however there is no label that identifies the disconnect as "suitable for use as service equipment"

I think I am up to speed here but I still have a difficult time with all the various bonding jumpers, when to call them supply side or service or equipment bonding etc.

Any wisdom will be gratefully received and liberally shared.

 

[Dennis Alwon]

Not sure if the definitions in the nec will help you but here they are. The main and system bonding jumpers can be one and the same.

Bonded (Bonding). Connected to establish electrical continuity
and conductivity. (CMP-5)


Bonding Conductor or Jumper. A reliable conductor to ensure
the required electrical conductivity between metal parts
required to be electrically connected. (CMP-5)


Bonding Jumper, Equipment. The connection between two or
more portions of the equipment grounding conductor.
(CMP-5)


Bonding Jumper, Main. The connection between the grounded
circuit conductor and the equipment grounding conductor
at the service. (CMP-5)


Bonding Jumper, System. The connection between the grounded
circuit conductor and the supply-side bonding jumper, or
the equipment grounding conductor, or both, at a separately
derived system. (CMP-5)

 

[Plumbob]

Thank you, the definitions actually do help if you (I) pay attention to the details. I will keep these in mind as I encounter services in the future. For me there is no substitute for actually seeing an installation in person and connecting what I see with what I have read in the NEC and also clarified through participation in professional forums like this one. I read through other peoples experiences on this forum and it helps to clarify code and application for me.

Y'all ride hard and keep your powder dry

 

[MasterTheNEC]

Greetings,
I am inspecting a new 400 amp service. The 400 amp service disconnect is attached to the outside of the building. There are two 200 amp panel boards located just inside and connected with non metal raceways. These are main breaker panels. Since the panel boards are down stream and in seperate enclosures from the service disconnect are they treated as main panels or sub-panels. I have been trying to evaluate whether the bonding conductors are sized properly. There are #4 AWG bare copper conductors routed with the feeder conductors and originating at the aluminum lug where the system grounded and GEC are landed in the service disconnect enclosure and landed on the equipment grounding terminals in the panel boards. Are these system bonding jumpers or ?

I guess all the others cleared up the majority of this question. I do have to ask, based on what you have presented I would think that 4 AWG is an EGC....but since the OCPD ahead of it is 400A why would it be a 4 AWG and not a 3 AWG based on T250.122. Even if I used 250.122(G) I would still expect it to be no less than what is in T250.122 based on the OCPD ahead of the EGC. But alas...maybe it isn't an EGC And I am just lacking my afternoon coffee fix.

 

[rojay]

I guess all the others cleared up the majority of this question. I do have to ask, based on what you have presented I would think that 4 AWG is an EGC....but since the OCPD ahead of it is 400A why would it be a 4 AWG and not a 3 AWG based on T250.122. Even if I used 250.122(G) I would still expect it to be no less than what is in T250.122 based on the OCPD ahead of the EGC. But alas...maybe it isn't an EGC And I am just lacking my afternoon coffee fix.

I would agree with you on this. Sounds like the feeders are essentially parallel 3/0 taps feeding two separate panelboards and the EGC needs to be sized according to the OCP ahead of it.

I believe the main service GEC should be a 1/0 landing at the service disconnect switch.

I’m used to seeing the service disconnect inside in the form of 2- 200 amp MCB panelboards with separate #4’s running from each back to the GEC.