GEC on Multiple Service Entrance Conductors

[1madison]

Given; A 4000 amp 120/208 3 phase service that has 10 sets of 500 kcm conductors from poco to the 4000 amp main service dis-connect switch.What is the correct size of the grounding electrode conductor.I'm getting a strange number from the EE' s drawings.Thanks

 

[charlie b]

Re: GEC on Multiple Service Entrance Conductors

You are over 1100 MCM. So Table 250.66 says you can use 3/0 copper. What does the EE's drawing say?

 

[spsnyder]

Re: GEC on Multiple Service Entrance Conductors

What is the GEC connected to?

 

[1madison]

Re: GEC on Multiple Service Entrance Conductors

GEC from MDS to cold water POE. EE says use 1-500 kcm.I think he might be confusing the equipment grounding conductor with the GEC.

 

[roger]

Re: GEC on Multiple Service Entrance Conductors

I think the EE might want to look at his service entrance conductor ampacity again too.

Roger

 

[charlie b]

Re: GEC on Multiple Service Entrance Conductors

Originally posted by 1madison: I think he might be confusing the equipment grounding conductor with the GEC.

Sounds reasonable. Please tell me he is not asking for a 500 MCM to go into each conduit.

Originally posted by roger: I think the EE might want to look at his service entrance conductor ampacity again too.

Good point. If the calculated load is more than 3800 amps, or if there is no calculation, or if the plan is to take advantage of all 4000 amps of the equipment's rating, then you need either one more conduit or to replace the 500's with 600's.

 

[iwire]

Re: GEC on Multiple Service Entrance Conductors

Originally posted by charlie b:

Originally posted by roger: I think the EE might want to look at his service entrance conductor ampacity again too.

Good point. If the calculated load is more than 3800 amps, or if there is no calculation, or if the plan is to take advantage of all 4000 amps of the equipment's rating, then you need either one more conduit or to replace the 500's with 600's.

Actually with 10 sets of 500 the OCP will have to be 3800 or less regardless of the load.

There is no 'rounding up' at this level.

 

[charlie b]

Re: GEC on Multiple Service Entrance Conductors

Ah, that old argument again:

Person 1:

The sky is blue.

Person 2:

No, you are wrong, the grass is green.

I wasn't talking about the OCP. I was talking about the ampacity of the conductors. If the calculated load is under 3800, then you can use 10 sets of 500 MCM copper.

 

[iwire]

Re: GEC on Multiple Service Entrance Conductors

Originally posted by charlie b:
I wasn't talking about the OCP. I was talking about the ampacity of the conductors. If the calculated load is under 3800, then you can use 10 sets of 500 MCM copper.

No, not with 4000 amp service, had he said a 3,800 amp service than we could agree.

10 sets of 500 copper does not equal a 4000 amp service which IMO is what Roger was getting at.

 

[charlie b]

Re: GEC on Multiple Service Entrance Conductors

Originally posted by iwire:10 sets of 500 copper does not equal a 4000 amp service which IMO is what Roger was getting at.

That does not disagree with what I said in my first post:

Originally posted by charlie b: If the calculated load is more than 3800 amps, or if there is no calculation, or if the plan is to take advantage of all 4000 amps of the equipment's rating, then you need either one more conduit or to replace the 500's with 600's.

If you know nothing about the load, if you are just saying "4000 amp service," then you need more copper.

I also said that you pick the copper before you pick the OCP. I trust you are not disagreeing with that?

 

[iwire]

Re: GEC on Multiple Service Entrance Conductors

Typically (at least from this electrician's experience) a '4000 amp service' is a service with a single 4000 amp OCP.

Regardless of the load being 1 amp or 4000 amps ten 500 kcmil CU service conductors can not be protected by a single 4000 amp OCPD.


Originally posted by charlie b:

If the calculated load is more than 3800 amps, or if there is no calculation, or if the plan is to take advantage of all 4000 amps of the equipment's rating, then you need either one more conduit or to replace the 500's with 600's.

4000 amp rated service equipment rarely comes with less than a 4000 amp OCP.

IMO, whatever it was you where trying to say came out sounding like a 4000 amp OCP protecting ten 500 kcmil CU would be acceptable if the load was less than 3,800 amps.

Can you see why I would question that?

 

[iwire]

Re: GEC on Multiple Service Entrance Conductors

Originally posted by charlie b:
I also said that you pick the copper before you pick the OCP. I trust you are not disagreeing with that?

Actually in my world I sometimes disagree with that.

Customer calls us and says "I need a 200 amp feed to this new machine".

Right there the OCP has been picked, now it is up to me to pick a conductor, raceway or cable to do the job. You can safely bet that the conductor will have a rating greater than 200 amps.

 

[roger]

Re: GEC on Multiple Service Entrance Conductors

Charlie, Bob knows me pretty well, I was hinting at 240.4(C)

Roger

 

[iwire]

Re: GEC on Multiple Service Entrance Conductors

Originally posted by roger:
Charlie, Bob knows me pretty well, I was hinting at 240.4(C)

Hi Roger, I was also thinking of 240.4(C) in my first post, by my third post I realized 230.90(A) may be more appropriate but the result is much the same.

 

[infinity]

Re: GEC on Multiple Service Entrance Conductors

Typically (at least from this electrician's experience) a '4000 amp service' is a service with a single 4000 amp OCP.

Regardless of the load being 1 amp or 4000 amps ten 500 kcmil CU service conductors can not be protected by a single 4000 amp OCPD.

Bob, I agree. Add a set or increase the conductor size.

 

[infinity]

Re: GEC on Multiple Service Entrance Conductors

Originally posted by 1madison:
GEC from MDS to cold water POE. EE says use 1-500 kcm.I think he might be confusing the equipment grounding conductor with the GEC.

Sounds to me like he's confused about the main bonding jumper. This would be sized for 12.5% of the service entrance phase conductors.

(500Kcmils)(10)(12.5%)=625Kcmils

 

[roger]

Re: GEC on Multiple Service Entrance Conductors

Hello Bob, I was going to mention 230.90 but decided to cut right to the final point.

Trying to stay with my new concise ways .

Roger

 

[charlie b]

Re: GEC on Multiple Service Entrance Conductors

Originally posted by iwire: IMO, whatever it was you where trying to say came out sounding like a 4000 amp OCP protecting ten 500 kcmil CU would be acceptable if the load was less than 3,800 amps. Can you see why I would question that?

That was not my intent, and yes I do see why you would question that. I knew that you could not "biggie size" the OCP if the OCP is over 800 amps. We are not disagreeing on anything here, as I was talking about conductors and not OCPs. That was the point of my "blue versus green" analogy.

I chose not to take for granted that "4000 amp service" automatically means 4000 amp OCP. I would not have known if that was the "industry standard" interpretation of that phrase. Instead, I took the designer's perspective, which would call for a load calculation as a first step. But to put this discussion to bed, let's suppose a load calculation was performed, and that the results were 3750 amps. I believe you will agree that 10 sets of 500 MCM copper would be acceptable (good design practice would call for more copper, but the NEC would not require it). I agree with your statement that this would require a 3800 amp OCP.