83 % rule apply with feeder taps?

[Sparky38]

Contractor has a 320 meter feeding into a 400 amp transfer switch with 400 amp main breaker double tapped parallel 4/0 al se cables off of load side of breaker and runs 25’ to two 200 amp panels with main breakers. Would I be wrong if I said that This is in violation of 240.21 (B2,2) Where it specifically states “The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors” 4/0 is rated for 180 amp @ 75 deg, An OCPD is not permitted to be supplied by a tap conductor having an ampacity less than its rating, I don’t believe that the 83 percent rule would apply here what do you guys think? Also they ran SE Cable through the wall and attic without the use of a raceway which would be another violation of 240.21(B2,3) Correct?

 

[infinity]

Yes tap conductors cannot use the next size up rule in Article 240.

Welcome to the Forum.

 

[Sparky38]

Yes tap conductors cannot use the next size up rule in Article 240.

Welcome to the Forum.

Thank you! So just to be clear the 83% rule and the next size up standard breaker size is out with tapped conductors correct? What do you think about running the SE Cable through wall and attic without a raceway? I’m thinking the tapped conductor needs to be enclosed In a raceway correct, We are still in the 2017 NEC

 

[kwired]

First thing in order to be able to use the 83% is you must be supplying an entire dwelling unit. So for single family dwelling you won't have any feeder tap that supplies the dwelling. For multiple dwelling applications you possibly could though. Whether or not you could consider that 83% of what is normal to be "full ampacity" for this application, I'm not certain. If so what you need is an 83 amp or greater conductor (after any required adjustments) when the load end OCPD is 100.

 

[Sparky38]

First thing in order to be able to use the 83% is you must be supplying an entire dwelling unit. So for single family dwelling you won't have any feeder tap that supplies the dwelling. For multiple dwelling applications you possibly could though. Whether or not you could consider that 83% of what is normal to be "full ampacity" for this application, I'm not certain. If so what you need is an 83 amp or greater conductor (after any required adjustments) when the load end OCPD is 100.

The two 4/0 se cables are routed to two 200 amp panels so basically these feeders are feeding the entire dwelling unit, But what is confusing to me is the code says you can’t go up to the next breaker size when dealing with tap conductors so I figured the 83% rule does not apply here either

 

[don_resqcapt19]

The two 4/0 se cables are routed to two 200 amp panels so basically these feeders are feeding the entire dwelling unit, But what is confusing to me is the code says you can’t go up to the next breaker size when dealing with tap conductors so I figured the 83% rule does not apply here either

You can't use the 83% rule with two feeders feeding the dwelling unit.

 

[Sparky38]

You can't use the 83% rule with two feeders feeding the dwelling unit.

I didn’t think so either but not all people read the code book and understand it the same way lol, Thanks for the responses!

 

[jaggedben]

You can't use the 83% rule with two feeders feeding the dwelling unit.

More precisely, you can't use it for the feeders when they are rated lower than the service. You can use it only for the service conductors.

 

[jaggedben]

The two 4/0 se cables are routed to two 200 amp panels so basically these feeders are feeding the entire dwelling unit, But what is confusing to me is the code says you can’t go up to the next breaker size when dealing with tap conductors so I figured the 83% rule does not apply here either

It's two independent questions.

You cannot use the 83% rule on the feeders because neither feeder by itself supplies the whole dwelling and they are smaller than the service conductors. That's the end of that discussion, taps or not.

Now you also have taps. They can't use the next size up rule so with 4/0 Al they can't be on more than a 175A breaker.

If, say, you instead had a 400A distribution panel with a main breaker and two 200A breakers, 4/0 Al would be okay if the calculated loads were 180A or less.

 

[Sparky38]

More precisely, you can't use it for the feeders when they are rated lower than the service. You can use it only for the service conductors.

Thank you, What do you guys think about the 2 sets of 4/0 Al SE cable coming off a 400 amp breaker and feeding two 200 amp panels with 200 amp mains (1 4/0 feeder to each panel) Cables are running up the wall from service through attic and down a interior wall, about 25’ total length, Would you say the cables need to be installed inside a raceway per 240.21(B2,3) NEC 2017

 

[LarryFine]

Thank you, What do you guys think about the 2 sets of 4/0 Al SE cable coming off a 400 amp breaker and feeding two 200 amp panels with 200 amp mains (1 4/0 feeder to each panel) Cables are running up the wall from service through attic and down a interior wall, about 25’ total length, Would you say the cables need to be installed inside a raceway per 240.21(B2,3) NEC 2017

There's no problem with having no raceway, but the cables should be SER, not SE.

 

[Sparky38]

There's no problem with having no raceway, but the cables should be SER, not SE.

Tapped conductors do not need a raceway? The way I’m reading 240.21(B2,3) NEC 2017 it would be required, even the 10’ rule requires this, This falls under the 25’ rule

 

[infinity]

Tapped conductors do not need a raceway? The way I’m reading 240.21(B2,3) NEC 2017 it would be required, even the 10’ rule requires this, This falls under the 25’ rule

Yes they require a raceway or another form of protection from physical damage. IMO SE cable does not qualify.

 

[Dennis Alwon]

If you have 2 feeders as you stated and it is 4/0 aluminum then you still can use section 240.4(B) (next size up) and install it on a 200 amp breaker. The actual capacity will only be 360 amps instead of 400 amps

 

[infinity]

If you have 2 feeders as you stated and it is 4/0 aluminum then you still can use section 240.4(B) (next size up) and install it on a 200 amp breaker. The actual capacity will only be 360 amps instead of 400 amps

These are tap conductors so how would the next size up rule apply?

 

[Dennis Alwon]

These are tap conductors so how would the next size up rule apply?

It would apply if the op stated what I was thinking. haha. I am 72 yrs old and still can't read.. I read post 5 and 6 and was responding to the standard 1- 400 amp meter with service conductors to 2- 200 amp panels. I guess I flew past the first post

 

[wwhitney]

For an interesting twist on the OP, suppose one of the two 4/0 Al cables did carry the entire load of the dwelling unit, and the other goes to, say, a woodshop in an outbuilding. They both need to comply with the tap rules, and so the latter clearly needs to land on a 175A breaker. But can the former land on a 200A breaker?

Cheers, Wayne

 

[don_resqcapt19]

For an interesting twist on the OP, suppose one of the two 4/0 Al cables did carry the entire load of the dwelling unit, and the other goes to, say, a woodshop in an outbuilding. They both need to comply with the tap rules, and so the latter clearly needs to land on a 175A breaker. But can the former land on a 200A breaker?

Cheers, Wayne

That is a problem with the code as there is nothing that permits a rule in one chapter 1-4 article to modify another rule found in chapters 1-4.
My take would be that the most restrictive would apply and that would be the tap rule.

 

[kwired]

For an interesting twist on the OP, suppose one of the two 4/0 Al cables did carry the entire load of the dwelling unit, and the other goes to, say, a woodshop in an outbuilding. They both need to comply with the tap rules, and so the latter clearly needs to land on a 175A breaker. But can the former land on a 200A breaker?

Cheers, Wayne

Kind of similar to my earlier mentioned multi family situation where each is supplied via a tap. I think it is ok. Taps can't utilize the next size up rule and this is mentioned in 240.21(B).

conductors supplying a dwelling get a special adjustment so to speak with the 83% which effectively makes the ampacity of 4/0 aluminum 216 amps - 200 amp OCPD does not exceed the ampacity of the conductor.

 

[kwired]

Kind of similar to my earlier mentioned multi family situation where each is supplied via a tap. I think it is ok. Taps can't utilize the next size up rule and this is mentioned in 240.21(B).

conductors supplying a dwelling get a special adjustment so to speak with the 83% which effectively makes the ampacity of 4/0 aluminum 216 amps - 200 amp OCPD does not exceed the ampacity of the conductor.

When they changed from the table to the 83% they kind of made it clear they intend ampacity adjustments to apply to these conductors before final conductor selection. The 83% allowance for the base is an adjustment as well from the way I see it. When we had the table it said 4/0 was a 200 amp conductor but didn't really tell us if we needed to or how to make adjustments when needed. With the 83% rule adjustments are same as usual you just start out with a different base ampacity for a particular conductor.