Service Tap?

[charlie b]

I am performing an independent review of a design package. The building has a second service (300 amps) for standby loads. I am OK with that. The same service provides power to both legally required standby and optional standby loads. I am OK with that too.

Here is my problem with the design. The designer is bringing 310 amps worth of service conductor into the building. The conductors are then spliced within a junction box, from which 200 amps worth of wire is run to a 200 amp fused disconnect, and 100 amps worth of wire is run to a 100 amp MCB panel. The two overcurrent devices are close enough to each other to be considered “grouped,” and we are within the “2 to 6 disconnecting means” limit. But the requirement for overcurrent protection for service conductors doesn’t say you can downsize the wires that lead to each of the “2 to 6 disconnecting means.” I would call this a poor design, but I can’t find a code article that forbids it. If the 310 amps worth of wire came from an upstream panel that had a 300 amp breaker protecting the wire, then we would be within the 240.21 tap rules. But those rules apply to tapping a feeder, not a service.

Is this proposed design code compliant? Why or why not?

 

[augie47]

IMO. completely compliant.
230.42 requires that the service conductors be sized to handle the load.
230.90 requires that each conductor be protected at it's amapcity.
In your case those requirements are met for the primary conductor as well as the ones connected to it (I hesitate to use the word "tap" as they don;t technically meet the NEC definition)
Fairly common design in this area where you have multiple service disconnecting means. I often see a polaris set up in a wireway branching to 4 or 5 disconnects.

 

[mwm1752]

Where doe it say you cannot downsize the conductor, as long as it carries the load & terminates into a properly sized OCPD you should be ok --

 

[charlie b]

Thanks for the comments. My basic problem is that 240.21 starts by saying that overcurrent protection must take place at the point at which a conductor gets its power, except at noted below. The "below" part only talks about branch circuits and feeders. So I am left to understand that service conductors have to have overcurrent protection at the source. But then, 230.90 only requires the overcurrent protection to be in series with the service conductors, without saying whether they go at the supply end or the load end.

Now let me return to my more practical self. :happyyes: I never see a design that protects the service conductors at the source. However, when I have seen more than one service disconnecting means, each one has received a separate set of conductors from the utility. This is different, in that there is only one set of conductors from the utility, and that set is split internal to the building into two smaller sets. I just haven't seen that before.

 

[Smart $]

...I hesitate to use the word "tap" as they don;t technically meet the NEC definition...

The only definition is in 240.2, and it starts, "As used in this article..."

Then we have...

230.33 Spliced Conductors. Service conductors shall be
permitted to be spliced or tapped in accordance with
110.14, 300.5(E), 300.13, and 300.15.

IMO, a service tap conductor has less calculated load and ampacity than the supplying service conductor.

 

[iwire]

In my opinion you do not have any taps at all, you have service conductors and more than one service disconnect.

To me it sounds like a compliant installation based on exception 3 of 230.90

 

[Smart $]

Thanks for the comments. My basic problem is that 240.21 starts by saying that overcurrent protection must take place at the point at which a conductor gets its power, except at noted below. The "below" part only talks about branch circuits and feeders. So I am left to understand that service conductors have to have overcurrent protection at the source. But then, 230.90 only requires the overcurrent protection to be in series with the service conductors, without saying whether they go at the supply end or the load end.

Now let me return to my more practical self. :happyyes: I never see a design that protects the service conductors at the source. However, when I have seen more than one service disconnecting means, each one has received a separate set of conductors from the utility. This is different, in that there is only one set of conductors from the utility, and that set is split internal to the building into two smaller sets. I just haven't seen that before.

Compliance with any pertinent definition and requirement makes it impossible to have service conductors with ocpd at their source.

Here's some logic that applies to allow the installation IMO:

230.42 as mentioned by Gus

230.40 Exception No. 2 permits one set of service entrance conductors to supply each of the two to six disconnecting means in separate enclosures, while the general requirement only permits one set of service entrance conductors from each drop or lateral. That logically requires a "Y" transition at or after the drop or lateral... while a drop or lateral is also comprised of service conductors. All that is left is whether one is permitted to "tap" as opposed to "splice"...

230.33, quoted earlier.

 

[electrofelon]

230.33 Spliced Conductors. Service conductors shall be
permitted to be spliced or tapped in accordance with
110.14, 300.5(E), 300.13, and 300.15.

In my opinion you do not have any taps at all, you have service conductors and more than one service disconnect.

To me it sounds like a compliant installation based on exception 3 of 230.90

Yeah I have always hated that use of the word "tap" in 230.33....

 

[nickelec]

This reminds me of a thread I created in regards to a situation where and Inspector failed me for this. 240.21 doesn't apply to SECs period is how I understand it and what I got out of the discussion

Sent from my SM-G986U using Tapatalk

 

[charlie b]

This is a 5 year old thread. It should not have new issues raised. I will close this thread. A new thread can be started, if you wish.