tap conductors which rules apply

[hhsting]

I have townhome residential that has 400A fused disconnect with 400A fuses outside on the front wall of the townhouse and tap conductors are being brought in Panels A and Panels B. They are about 12 feet in length.

My question is that should 25 feet tap rule apply here or outside tap rule apply here?

 

[infinity]

Either one would apply but regardless it shouldn't change anything. What's your concern?

Eyeballing the tap conductors they appear too be to small.

 

[hhsting]

Either one would apply but regardless it shouldn't change anything. What's your concern?

My concern is outside tap conductors has nearest point of entrance of disconnect and panelboards A and B are not in the nearest point

 

[don_resqcapt19]

My concern is outside tap conductors has nearest point of entrance of disconnect and panelboards A and B are not in the nearest point

So apply the 25' tap rule. The only difference is the minimum size of the tap conductor and that does not come into play with this installation.
I agree with Rob that the tap conductors are too small. They must have an ampacity of at least 200 amps.

 

[infinity]

My concern is outside tap conductors has nearest point of entrance of disconnect and panelboards A and B are not in the nearest point

Ah I didn't see the wall. The 25' tap rule would apply but the nearest point of entrance would not apply.

 

[hhsting]

So apply the 25' tap rule. The only difference is the minimum size of the tap conductor and that does not come into play with this installation.
I agree with Rob that the tap conductors are too small. They must have an ampacity of at least 200 amps.

If 25 feet tap rule is applied should not the tap conductors amapcity be not less than 1/3 of 400A beaker? Meaning not less than 133.33A so it can be 150A so as long as demand load for panel A are less than 150A? Why 200A?

 

[don_resqcapt19]

If 25 feet tap rule is applied should not the tap conductors amapcity be not less than 1/3 of 400A beaker? Meaning not less than 133.33A so it can be 150A so as long as demand load for panel A are less than 150A? Why 200A?

You have to read all of the rule not just part of it. The not less than 1/3 of the rating of the upstream OCPD is only one part of three parts.

(1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.

(2) 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. This device shall be permitted to supply any number of additional overcurrent devices on its load side.

(3) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

 

[infinity]

If 25 feet tap rule is applied should not the tap conductors amapcity be not less than 1/3 of 400A beaker? Meaning not less than 133.33A so it can be 150A so as long as demand load for panel A are less than 150A? Why 200A?

As Don stated the tap conductors would be governed by two factors. The 25' or less in length and the size of the OCPD where they terminate. They must be at least 133 amps for one part of the rule and at least 200 amps for the other part.

 

[hhsting]

So apply the 25' tap rule. The only difference is the minimum size of the tap conductor and that does not come into play with this installation.
I agree with Rob that the tap conductors are too small. They must have an ampacity of at least 200 amps.

Can we apply 25 feet tap rule in this case because fused disconnect is outside a d tap is inside the fused disconnect that is in exterior wall of the town home? I would think outside tap rule would apply no?

 

[infinity]

Can we apply 25 feet tap rule in this case because fused disconnect is outside a d tap is inside the fused disconnect that is in exterior wall of the town home? I would think outside tap rule would apply no?

The outside tap just removes the 25' limit of the 25' tap rule. In this case it is not relevant.

 

[hhsting]

The outside tap just removes the 25' limit of the 25' tap rule. In this case it is not relevant.

I dont follow outside tap rule and 25 feet tap rule are two different rules.

What would apply in my case?

 

[infinity]

I dont follow outside tap rule and 25 feet tap rule are two different rules.

What would apply in my case?

The outside tap rule allows the tap conductors to be more than 25'. At 12' you've complied with the 25' conductor limit of the 25' rule so you've also complied with the outside tap rule.

 

[hhsting]

The outside tap rule allows the tap conductors to be more than 25'. At 12' you've complied with the 25' conductor limit of the 25' rule so you've also complied with the outside tap rule.

But 25 feet rule doesnt say to place tap disconnect nearest the incoming tap conductors?


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[wwhitney]

The outside tap rule allows the tap conductors to be more than 25'. At 12' you've complied with the 25' conductor limit of the 25' rule so you've also complied with the outside tap rule.

Maybe the non location related aspects of the outdoor tap rule, like ampacity. But if the OCPD supplied is not nearest the point of entrance of the conductors, then you can't use the outside tap rule.

Cheers, Wayne

 

[wwhitney]

But 25 feet rule doesnt say to place tap disconnect nearest the incoming tap conductors?

Leaving aside the length/location aspects of the two rules, infinity is saying the requirements are the same. [I haven't confirmed.]

But we also have length/location requirements. So for your tap conductors, running from inside from outside, you have two options:

(1) the OCPD inside is nearest the point of entrance. Now you can use the outdoor tap rule, and there is no conductor length limit.
(2) the OCPD is not nearest the point of entrance, so you can't use the outdoor tap rule. That leaves the 25' tap rule, which you can use as long as the total tap conductor length, inside plus outside, is at most 25'.

In other words, when the OCPD is inside and the tap originates outside, there's only a violation on the basis of length/location if both (a) the OCPD supplied is not nearest the point of entrance (so the outdoor tap rule does not apply) and (b) the tap conductor length exceeds 25' (so the 25' tap rule does not apply.

Cheers, Wayne

 

[don_resqcapt19]

Can we apply 25 feet tap rule in this case because fused disconnect is outside a d tap is inside the fused disconnect that is in exterior wall of the town home? I would think outside tap rule would apply no?

You might be able to apply the outside tap rule but it does not change anything for your installation. That is assuming the inside OCPDs are nearest the point of entry of the tap conductors.

The required conductor size under the outside tap rule is the same as required by the 25' tap rule.

The only thing you would get from the outside tap rule would be to have a longer length conductor outside of the building, that you don't need because the length is fixed by the location of the 400 amp fused disconnect.

Also make sure that the load side terminals in the 400 fused disconnect are suitable for two conductors at each termination point. I looked at a couple and the standard lug is only for one conductor. You may have to order the optional lug kit for two conductors per termination.

 

[hhsting]

You might be able to apply the outside tap rule but it does not change anything for your installation. That is assuming the inside OCPDs are nearest the point of entry of the tap conductors.

The required conductor size under the outside tap rule is the same as required by the 25' tap rule.

The only thing you would get from the outside tap rule would be to have a longer length conductor outside of the building, that you don't need because the length is fixed by the location of the 400 amp fused disconnect.

Also make sure that the load side terminals in the 400 fused disconnect are suitable for two conductors at each termination point. I looked at a couple and the standard lug is only for one conductor. You may have to order the optional lug kit for two conductors per termination.

Inside disconnects are not nearest the point of entrance. The tap is made in disconnect inside the exterior wall disconnect and they come inside and they are 12 feet from entrance of the conductors. So would apply 25 feet tap rule would be ok under this situation or not?

 

[Carultch]

If 25 feet tap rule is applied should not the tap conductors amapcity be not less than 1/3 of 400A beaker? Meaning not less than 133.33A so it can be 150A so as long as demand load for panel A are less than 150A? Why 200A?

You can make the tap conductors have as much ampacity as you prefer. There's no issue with tapping a 200A circuit off of a 400A feeder.

Where this governs a design, is if you're tapping to a 100A breaker from a 400A feeder. Instead of running 100A worth of wire, as you'd do by default (and could do if the 10 ft or outside rules could govern instead), you'd promote that section of conductor that classifies as a tap to 134A (minimum). In practice could either be #1/0 Cu at 150A or #2/0 AL at 135A. Once load-side, you'd only need 100A worth of wire

 

[augie47]

Inside disconnects are not nearest the point of entrance. The tap is made in disconnect inside the exterior wall disconnect and they come inside and they are 12 feet from entrance of the conductors. So would apply 25 feet tap rule would be ok under this situation or not?

Since the conductors do not conform to 240.21(B)(5)(4) {They do not terminate nearest the point o0f entrance), you can't use the "outside" tap rule but you are fine with the 25ft tap rule 240.21(B)(2)(1) but to meet 240.21(B)(2)(2) the breakers could not exceed the ampacity of the conductor so, if you keep the 200 amp breakers the conductor must have a 200 amp ampacity {per 240.21,General, the next size up rule" can no be applied.
As an alternative you could go to 150 amp breakers and keep the conductors as shown.

 

[don_resqcapt19]

Inside disconnects are not nearest the point of entrance. The tap is made in disconnect inside the exterior wall disconnect and they come inside and they are 12 feet from entrance of the conductors. So would apply 25 feet tap rule would be ok under this situation or not?

How long are the conductors from the 400 amp disconnect to the inside panels?