# Thread: Size of a single service drop and SECs serving multiple service disconnects

1. ## Size of a single service drop and SECs serving multiple service disconnects

What is the rule for sizing a service drop and the SECs serving multiple service disconnects?

For example if three service disconnects, each with 100A OCPDs, are powered from a single service drop, do the drop and the cable to the meters require the capacity to supply 300A, or is there a rule that establishes a lower requirement based on the assumption that a 300A draw is unlikely?

Thanks.

2. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Depending on where the utility considers the point of service to be there are several answers to your question.

It is very unlikely that all 3 services will be drawing maximum load at the same time and there are formulas for determining the wire size based on this. The utility will be using smaller wire yet if the feed is overhead because wire in open air has different ratings than wire in cable or conduit and the service is sized on calculated load, not the OCPD in each service.

The answer will be different if there are 3 masts, 1 for each meter or a single mast that drops into a gutter that in turn feeds 3 meters.

And, the answer will be different depending what the calculated load is on each of the individual services.

3. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Perhaps some pictures of this installation will encourage responses...

4. ## Re: Size of a single service drop and SECs serving multiple service disconnects

MT: The utility has the option to install their drop or lateral according to the diversity of their choosing.
From the service point however, is under the rules of the adopted code for the area. The NEC unfortunately, does not allow this for service conductors whether they are single, multi, paralleled etc.
I am presently installing three (3), 200 amp three phase panels in an industrial building and I will have to install two risers for parallel 350 copper conductors to the CT cabinet.

There is no way, per my experience, that the xfrms the utility will put on the pole and the length/size of their drop would even come close to needing parallel 350's. Nevertheless, there is no exception in the NEC for me to consider this fact in my installation.

Even though the main breakers are down stream of the service conductors, they are still considered as protecting them as the code see it.
Bob Smit, County EI

5. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Originally Posted by bob smit
MT:I am presently installing three (3), 200 amp three phase panels in an industrial building and I will have to install two risers for parallel 350 copper conductors to the CT cabinet
What does "CT cabinet" stand for?

Thanks?

6. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Based on the rope and area history, it's a 100 AMP service. If they were to go for an E permit to get a new service and panels, minimum allowed would be a 200 AMP piped service. Depending on size of building and type of equipment though it could push them up to a 400 AMP service. Overkill but if the numbers come to that...
The Sparky's do a load calc on the permit app. The required numbers vary a bit from the City to the burbs. I've done a few with my Sparky for practice but quite frankly haven't bothered to remember the numbers. It's easier for me just to make a phone call.
The rusty sockets are a Code violation in the City. Don't have to replace, just scrape and paint.

7. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Originally Posted by Michael Thomas
What does "CT cabinet" stand for?

Thanks?
Current transformer. These typically look like donuts around a conductor at the service or in a cabinet near the meters. These are a way to measure a portion of the usage and a multiplier factor is used to get the actual usage. Kind of like scale mileage x factor = actual mileage.

Here is one not installed

8. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Thanks to you both.

9. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Originally Posted by Michael Thomas
Thanks to you both.
Michel, you ever have a problem shopping for hats?

10. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Originally Posted by ROBERT YOUNG
Michel, you ever have a problem shopping for hats?
Robert,

Do you need to switch to decaf ... or maybe you just have not had your coffee yet?

11. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Originally Posted by Jerry Peck
Robert,
Do you need to switch to decaf ... or maybe you just have not had your coffee yet?
I can not do full caffeine.
Decaf is my usual eye opener.

I realize it was an old thread and loved the photo-shop!
But I also think the thread relates to questions I have.
I would like to understand my Fluke A3000 FC Wireless AC Current Clamp
meter to measure the SE feed.
Any help would be appreciated.

12. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Originally Posted by ROBERT YOUNG
I can not do full caffeine.
Decaf is my usual eye opener.

I realize it was an old thread and loved the photo-shop!
But I also think the thread relates to questions I have.
I would like to understand my Fluke A3000 FC Wireless AC Current Clamp
meter to measure the SE feed.
Any help would be appreciated.
Start a new thread for best results.

Also helps for searches in the future. I think?

Re: your question, there are multiple degrees of answers, depending on the situation and accuracy you need.
Current is going to be fluctuating with the load. You isolate one conductor and measure its current in amps. In a vacant house or quiet resident using no appliances, current will be near zero. Evening, everybody home, cold or hot day, current will spike to the max.

13. ## Re: Size of a single service drop and SECs serving multiple service disconnects

Originally Posted by ROBERT YOUNG
Michel, you ever have a problem shopping for hats?
Originally Posted by ROBERT YOUNG
I can not do full caffeine.
Decaf is my usual eye opener.

I realize it was an old thread and loved the photo-shop!
But I also think the thread relates to questions I have.
I was referring to your answer "problem shopping for hats" - which doesn't relate to any question I could think of.

I would like to understand my Fluke A3000 FC Wireless AC Current Clamp
meter to measure the SE feed.
Any help would be appreciated.
Clamp-on ammeter .. as John suggested, start a new thread (makes searching for past information easier).

What questions do you have (recommend starting a new thread with your post of the above information and your questions).

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