parallel conductors

[AKwiring]

I think I have a pretty straight forward question here. I am running parallel 4/0 URD conductors over 400' underground to a meter w/ disconnect 200 amps. For my grounding conductor do I size it based on the size of the two 4/0 conductors which looks like it would be a 1/0 grounding conductor. Or is the grounding conductor based on 200 amps? I'm looking at table 250.122 which is stating the overcurrent device should be before the conductors. Before the conductors in this run is the utility transformer.
Thanks- I do mostly small resi work, haven't had to do much with large parallel conductors.

 

[iwire]

I think I have a pretty straight forward question here. I am running parallel 4/0 URD conductors over 400' underground to a meter w/ disconnect 200 amps. For my grounding conductor do I size it based on the size of the two 4/0 conductors which looks like it would be a 1/0 grounding conductor. Or is the grounding conductor based on 200 amps? I'm looking at table 250.122 which is stating the overcurrent device should be before the conductors. Before the conductors in this run is the utility transformer.
Thanks- I do mostly small resi work, haven't had to do much with large parallel conductors.

When you say 'grounding conductor' are you asking about a grounding electrode conductor (GEC) or an equipment grounding conductor (EGC) ?

 

[chris kennedy]

Before the conductors in this run is the utility transformer.

Maybe I'm not following you here, but from the POCO tranny to main disco would not require an EGC.

 

[Pierre C Belarge]

Sounds like you have service entrance conductors. Service entrance conductors do not have overcurrent protection ahead of them.

Typically one does not install a bonding/grounding conductor on the supply side of a service. If you do, you need to see 250.102(C), which references Table 250.66, not Table 250.122.


If you decide to continue and install the bond conductor, the size is based on the SE cable in each raceway or cable. Table 250.66 requires a 2 AWG copper conductor for 4/0 Copper conductors....that is if you are installing copper conductors.

 

[AKwiring]

I am talking grounding electrode conductor at the 200 amp meter disconnect. #2 would be appropriate correct?

 

[Cavie]

250.122 is for EGC and 250-66 is for GEC. The EGC (ground wire in conduit with current carying conductors) is based on 200 amps 250.122. GEC (Ground wire going to grounding system) is based on the service wire size 250.66. The breaker/fuses can be at the switchgear. Not required to be at the transformer. Either outside the building or imeadeatly after entering the building depending on your AHJ.

 

[iwire]

I am talking grounding electrode conductor at the 200 amp meter disconnect. #2 would be appropriate correct?

The GEC is sized per Table 250.66 and the size of your service conductors.

You have two 4/0 AL per phase?

Table 8 tells us 4/0s are 211,600 circular mills two those and you have 423,200 circular mils.

Table 250.66 shows us a 1/0 AL or 2 copper would be the required GEC size for 423 Kcmil of service conductor.

However, what is the GEC running to?

250.66(A) requires no more than 6 copper to a ground rod. pipe or plate

250.66(B) requires no more than 4 copper to a concrete encased electrode

250.66(C) requires no more than the size of the ground ring it connects to.

 

[Pierre C Belarge]

250.122 is for EGC and 250-66 is for GEC. The EGC (ground wire in conduit with current carying conductors) is based on 200 amps 250.122. GEC (Ground wire going to grounding system) is based on the service wire size 250.66. The breaker/fuses can be at the switchgear. Not required to be at the transformer. Either outside the building or imeadeatly after entering the building depending on your AHJ.

From the transformer to the service disconnecting means, the conductors are service entrance conductors. The overcurrent device at the service disconnecting means is not how one would size the bonding conductor on the supply side of the service disconnecting means. One uses 250.102(C), which references Table 250.66.

A general rule that is fairly easy to remember is:

On the supply side of the service disconnecting means, one uses Table 250.66. On the load side of the service disconnecting means, one uses Table 250.122.

 

[AKwiring]

OK I think I have it. I would use the total circular mils area and I am using aluminum wires so I just make the limit to use #2copper according to table 250.66. I am connecting the GEC from the meter to two ground rods.

 

[AKwiring]

OK I think I have it. I would use the total circular mils area and I am using aluminum wires so I just make the limit to use #2copper according to table 250.66.

I am connecting the GEC from the meter to two ground rods. According to 250.66(A) I could use #6 copper, but our local codes call for #4 so that would be appropriate in this situation. Is this correct? When you have a 200 amp service do you normally use #6 as your GEC connected to two ground rods? Is that your sole grounding method?

 

[Pierre C Belarge]

OK I think I have it. I would use the total circular mils area and I am using aluminum wires so I just make the limit to use #2copper according to table 250.66.

I am connecting the GEC from the meter to two ground rods. According to 250.66(A) I could use #6 copper, but our local codes call for #4 so that would be appropriate in this situation. Is this correct? When you have a 200 amp service do you normally use #6 as your GEC connected to two ground rods? Is that your sole grounding method?

Sounds like you now have a grip on the situation.

 

[iwire]

I am connecting the GEC from the meter to two ground rods. According to 250.66(A) I could use #6 copper, but our local codes call for #4 so that would be appropriate in this situation. Is this correct?

Sounds like it.

When you have a 200 amp service do you normally use #6 as your GEC connected to two ground rods?

The only 200 amp services I do that have only grounding rods are temps and I could use 6 AWG but then there is the psychical protection aspect so 4 bare works out easier.

NEC wise you could have a 5000 amp service in middle of nowhere and the GEC to the ground rods could still be 6 AWG.

 

[AKwiring]

Thanks for all of your help. I've only been on my own for a little over a year. I did my apprenticeship with a master who's been around a long time. We did mostly small residential work. He's a great guy but I'm always trying to learn more to expand the business!

Do you mind me asking what you all usually do to terminate the two parallel 4/0 aluminum conductors to the meter socket terminals?

 

[iwire]

If you can not get a socket equipped for two 4/0s you will likely have to bring the two 4/0s into a splice can first and finish the last few feet with one 4/0 per phase.

 

[michaelstrttn]

#6 is all required its in code 250.122 F