Need consensus among code pros

[EEC]

Situation: Service 3phase 208/120 Split between a 400 amp MCB panel no neutral and a 200 amp panel with neutral. What's the size of the grounding electrode to water pipe? 400 amp panel fed with 3-500kcmil copper conductors and 200 amp with either 4-4/0 or 4-3/0 copper conductors.

 

[Ponchik]

I would say the GECKO is based on the largest service conductors.

 

[iwire]

What is the size of the service conductors supplying both disconnects?

 

[EEC]

Just to be clear

Just to be clear

I would say the GECKO is based on the largest service conductors.

Are you saying add the 500kcmil to the size of the 4/0 and base the size on the sum?

 

[EEC]

more info

more info

The 200 amp panel is a main circuit breaker panel too

 

[EEC]

Something to consider

Something to consider

Yea its either add the two sizes together or don't use the 500kcmil at all to calculate the size of the grounding electrode conductor because it does not have neutral and may only need to be sized for equipment grounding

 

[Smart $]

Yea its either add the two sizes together or don't use the 500kcmil at all to calculate the size of the grounding electrode conductor because it does not have neutral and may only need to be sized for equipment grounding

Probability says this is a grounded service and as such, the neutral is required to be brought to service equipment... which means it has to be brought to the 400A panel also, whether it is used for line-to-neutral loads or not. The rules for sizing the main bonding jumpers then kick in for each separate panel, in addition to the GEC rules for multiple disconnecting means.

 

[Smart $]

Probability says this is a grounded service and as such, the neutral is required to be brought to service equipment... which means it has to be brought to the 400A panel also, whether it is used for line-to-neutral loads or not. The rules for sizing the main bonding jumpers then kick in for each separate panel, in addition to the GEC rules for multiple disconnecting means.

250.24(C)
250.28(D)(2)
250.64(D)

 

[augie47]

First, I agree with Smart$, if the 400 amp panel is a Service a neutral must be brought to it also
As far as the grounding electrode conductor the size will be determined by the location of connection. It (they) will be size per 250.66 according to the size of the service conductors at the point they, the GEC, are connected.\
Do you plan on one common GEC from the meter or tap point or one from each panel (disconnect)?

This thread may help also:
http://forums.mikeholt.com/showthread.php?t=173978

 

[EEC]

Do you plan on one common GEC from the meter or tap point or one from each panel (disconnect)?

This thread may help also:
http://forums.mikeholt.com/showthread.php?t=173978

Yes one common GEC, also I agree the 400 amp panel needs to have a grounded conductor

 

[augie47]

Where does your grounding electrode conductor originate (at the meter, in a wireway, etc) and what size are the service conductors at that point ?

 

[EEC]

The service conductors entering the CT cabinet are parallel 500 each phase from PCO. Then one single set of 500 to 400 amp panel and a single set of 4/0 to 200 amp panel and only one 4/0 grounded neutral to 200 amp panel also the 4/0 has a tap for equipment grounding to 400 amp panel

 

[augie47]

The service conductors entering the CT cabinet are parallel 500 each phase from PCO. Then one single set of 500 to 400 amp panel and a single set of 4/0 to 200 amp panel and only one 4/0 grounded neutral to 200 amp panel also the 4/0 has a tap for equipment grounding to 400 amp panel

I'l try one more time Where is the system will your GEC originate ???
If your POCO supply is (2) 500s then you have to size a common GEC based on 1000 kcmil which will be a 2/0 Cu connected to the grounded conductor termination in the CT cabinet (based on 250.66 )
The detail may change slightly if you are connecting at a point other than the CT cabinet.

IMO, regardless of the point of connection, the GEC to the water and steel needs to be 2/0 min based on 1000 kcmil of service conductiors (#6 mion to rod, $4 min to UFER).
If you decide to originate your GEC at your disconnects you can tap to the 2/0 with a 1./0 from the 400 amp and #2 from the 200 amp panel based on the 500 and 4/0 feeding them (see the sketch in the referenced thread)

 

[EEC]

I'l try one more time Where is the system will your GEC originate ???

Before the panels in the trough below the panels

 

[augie47]

Before the panels in the trough below the panels

simplifies things, Thanks. Based on 250.66, Parallel 500s would require a 2/0 Cu GEC to building steel and water with a #6 to any ground rods available and a #4 to UFER ground.

 

[Smart $]

Before the panels in the trough below the panels

Where is your CT can with respect to panels and [wireway] trough?

Connecting to the grounded conductor(s) in the trough will be more troublesome than connecting in the panels or CT can... IMO.

 

[EEC]

Where is your CT can with respect to panels and [wireway] trough?

Connecting to the grounded conductor(s) in the trough will be more troublesome than connecting in the panels or CT can... IMO.

I'm using the neutral bar in existing 400 amp panel that's not being used for neutral because the 400 amp panel only has line to line loads.

 

[Smart $]

I'm using the neutral bar in existing 400 amp panel that's not being used for neutral because the 400 amp panel only has line to line loads.

If you run your GEC(s) to the 400A panel, you have to run GEC(s) to the 200A panel also.

You have three choices of how to run your GEC(s):

1. Run single GEC(s) from electrodes to any point before where service conductors split into 400A and 200A taps,
2. Run separate GEC(s) from each panel (or the taps supplying them) to the grounding electrodes, or
3. Run common GEC(s) to the grounding electrodes, then tap off that separately to each panel.

 

[lauraj]

I'm using the neutral bar in existing 400 amp panel that's not being used for neutral because the 400 amp panel only has line to line loads.

You still need to terminate the neutral in your 400A panel: 250.24(C) - "the grounded conductor shall be routed with the ungrounded conductors to each disconnecting means and shall be connected to each disconnecting means grounded conductor terminal or bus"