Outdoor feeder tap

[bobwright]

My first post on the forum, I read the NEC rule regarding the feeder taps ( 10ft, 25 ft rules ). However the situation is like this.

4 single family dwellings connected to one service feeder. After the entrance to the houses the cables run about 40 feet in the house then enter distrubition panels and protected by 125A circuit breakers. The problem is when you want to change any of the breakers you need to turn off all 4 houses from a 400A breaker. The 4/0 cable comes in front of the 4 houses and is spliced to the four houses with 1/0 cable which they run like 100 ft.
Isn't this a code violation ? What can be done to fix the issue ? My concern would be , the 400A breaker protecting 1/0 cables, in case of a overload in the house side ( say 160A ) the 400A breaker won't trip but the cable will heat up.

Any comments appreciated.

 

[George Stolz]

Can you be more specific? The installation is a bit hard to imagine.

For example, here's what I envision:

Utility Transformer > 4/0 AL USE > Direct-buried junction box > 1/0 AL USE > Riser for meter socket > PVC under slab > rises from slab into Main Breaker Panelboard w/ 125A OCPD.

If this is how this is installed, it can be legal. Where does the installation you're dealing with deviate from what I described? Where is the 400A breaker?

 

[infinity]

If the panels are protected by the 125 amp CB's why would you think that the #1/0 feeders could be overloaded? Having said that, if I'm understanding your set up there are many problems.

 

[bobwright]

Utility Transformer > 400 A breaker 4/0 AL USE > Direct-buried junction box > 1/0 AL USE > Enters the house > PVC under house > rises from slab into Main Breaker Panelboard w/ 125A OCPD.

This is how exactly it is. Thanks for clearing up. So it might be legal ? I thought the 25 ft rule would violate that ( more than 25 ft between the junction box and the breaker in the house ).

 

[George Stolz]

Depending on what you mean by "enters the house" in the fifth step of your one line, this could be legal.

If by that you mean, it dives under the house without entering, then these conductors could fall under 240.21(B)(5). Note 230.6.

That said, I think it's a horrible design. Provided that they have done load calculations and determined that the load on the 4/0 supplying the four houses will not exceed 180 amps - which simply defies the imagination - I believe it would leave absolutely no room for expansion at all.

I'd be amazed if the single 4/0 run could even handle 4 houses to begin with.

Tap rules are to be used sparingly and when necessary, IMO. They should protect the 4/0 on a 200A breaker at the least, or should upsize their wire for a true 400A. Are you sure it's not 2 sets of 4/0 in parallel?

Where are the electric meters in this situation? Are all these conductors under the control of a utility? Who installed this?

 

[Pierre C Belarge]

Depending on what you mean by "enters the house" in the fifth step of your one line, this could be legal.

If by that you mean, it dives under the house without entering, then these conductors could fall under 240.21(B)(5). Note 230.6.

That said, I think it's a horrible design. Provided that they have done load calculations and determined that the load on the 4/0 supplying the four houses will not exceed 180 amps - which simply defies the imagination - I believe it would leave absolutely no room for expansion at all.

I'd be amazed if the single 4/0 run could even handle 4 houses to begin with.

Tap rules are to be used sparingly and when necessary, IMO. They should protect the 4/0 on a 200A breaker at the least, or should upsize their wire for a true 400A. Are you sure it's not 2 sets of 4/0 in parallel?

Where are the electric meters in this situation? Are all these conductors under the control of a utility? Who installed this?

I agree with George on this...but, something does not smell right here. I would have to see the installation to be really sure. It is interesting how some can come up with an installation that I have never seen. (quite a few years of "not seen")

 

[kbsparky]

Utility Transformer > 400 A breaker 4/0 AL USE > Direct-buried junction box > 1/0 AL USE > Enters the house > PVC under house > rises from slab into Main Breaker Panelboard w/ 125A OCPD.

This is how exactly it is. Thanks for clearing up. So it might be legal ? I thought the 25 ft rule would violate that ( more than 25 ft between the junction box and the breaker in the house ).

You would not need to invoke the 25 foot rule here. Instead, look at 240.21(B)(5) Outside Taps of Unlimited Length.

No limitation on the length, provided the other rules are complied with. From your description, the job is compliant, although a bit inconvenient as you have discovered.

 

[bobwright]

Entering the house issue, ( enters the building concrete, continues to run in pvc conduit under the concrete , then enters the house panel ).

My concern would be 400A breaker protecting 1 / 0 cable that is spliced to houses.

4 / 0 is not in paralell.

And just for opinion how would you do the installation ?

 

[kbsparky]

.... And just for opinion how would you do the installation ?

I would have used a 4-position meter stack (or I-line panel, in the event you are not individually metering these houses) at the main service location. You would not even need a 400 Amp main breaker in this case.

Installing the feeders in underground PVC conduit and having them emerge inside of each dwelling would be my preferred choice as well.

 

[bobwright]

Outside taps rule :

(5) Outside Taps of Unlimited Length Where the conductors are located outdoors of a building or structure, except at the point of load termination, and comply with all of the following conditions:
(1) The conductors are protected from physical damage in an approved manner. ( protected )
(2) The conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side. ( conductors terminate in 125A breaker that protects the load side )
(3) The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto. ( didn't understand this part )
(4) The disconnecting means for the conductors is installed at a readily accessible location complying with one of the following:
a. Outside of a building or structure
b. Inside, nearest the point of entrance of the conductors
c. Where installed in accordance with 230.6, nearest the point of entrance of the conductors

Section 240.21(B)(5) permits outside conductors to be tapped from a feeder without any limitations on the length of the tap conductors. The tap conductors must be protected against physical damage and must terminate in a single, fused disconnect or a single circuit breaker with a rating that does not exceed the ampacity of the tap conductors. Also, this fused disconnect or circuit breaker must be installed at a readily accessible location either inside or outside a building or structure. Furthermore, if the fused disconnect or circuit breaker is installed inside a building or structure,it must be located nearest the point of entrance of the tap conductors.

Although the installation is weird, except the 3rd rule which i didn't understand it looks ok.

 

[George Stolz]

Actually, I think you have a violation of the second condition - where do the 4/0 conductors terminate? If I'm right, the 400A main would have to be swapped out for a 200A breaker (240.4(B)).

(3) The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto. ( didn't understand this part )

The disconnecting means is the actual handle you grab to shut something off.

It means the device that opens under overcurrent (the breaker or the fuse, the OCPD) is either a part of the disconnecting means (a circuit breaker) or located right next to it (as fuses would be).