Feeder vs Tap Feeder

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Design: Multi-Family
208Y/120 distribution - Apartments are 120/208V-1P-3W
Riser 4W feeder from distribution panel...vertically or horizontal to serve 3, 4, 5 and even 6 apartments.
Each apartment served via 3W "Tap Feeder" connected to riser.
Apartment load sized via 220.82
Is this not a violation of 220.82(A)

Riser load sized via table 220.84
Is this not a violation of 220.84(1)

Tap Feeders serving 4, 5, and 6
Is this not a violation of 215.4(A)
 
Welcome to the forum... :thumbsup:

MyCleveland said:
Design: Multi-Family
208Y/120 distribution - Apartments are 120/208V-1P-3W
Riser 4W feeder from distribution panel...vertically or horizontal to serve 3, 4, 5 and even 6 apartments.
Each apartment served via 3W "Tap Feeder" connected to riser.
Apartment load sized via 220.82
Is this not a violation of 220.82(A)
Click to expand...
In what way? While the supply conductors are taps, they are by themselves still technically a feeder per the Article 100 definition.

Riser load sized via table 220.84
Is this not a violation of 220.84(1)
Click to expand...
Again, in what way? 220.84(A)(1) states each dwelling unit is supplied by no more than one feeder. According to your description, only one feeder (or one feeder tap) supplies power to each unit.


Tap Feeders serving 4, 5, and 6
Is this not a violation of 215.4(A)
Click to expand...
How many sets utilize a common neutral? You made no mention of the feeders having a common neutral. 208Y/120 being a 4 wire system, you can run two feeder sets with one common neutral (7 circuit conductors total).
 
My opinion...from the information given...

MyCleveland said:
...
Apartment load sized via 220.82
Is this not a violation of 220.82(A)
Click to expand...

No.

Riser load sized via table 220.84
Is this not a violation of 220.84(1)
Click to expand...

No.

Tap Feeders serving 4, 5, and 6
Is this not a violation of 215.4(A)
Click to expand...

Not per se. If you're concern is that the riser neutral supplies multiple taps, that is not a violation.

What you are describing is one feeder that supplies multiple other feeders through taps. The main feeder must be sized for the total load of all units. Each feeder supplied by a tap must be sized for the dwelling unit it supplies. The tap rules must be followed to make this a compliant install. But I don't see anything that you've described as a violation in and of itself.
 
Smart $ said:
Welcome to the forum... :thumbsup:


In what way? While the supply conductors are taps, they are by themselves still technically a feeder per the Article 100 definition.

Again, in what way? 220.84(A)(1) states each dwelling unit is supplied by no more than one feeder. According to your description, only one feeder (or one feeder tap) supplies power to each unit.

How many sets utilize a common neutral? You made no mention of the feeders having a common neutral. 208Y/120 being a 4 wire system, you can run two feeder sets with one common neutral (7 circuit conductors total).
Click to expand...
Supply conductors to apartment, "Tap Feeder" is then the same as "Feeder"
Does not a Tap Feeder (3W), connected to a 4W riser result in apartment served via TWO feeders

Same for 220.84A)((1), apartment is serviced via two feeders, and therefore access to derating table 220.84 is not allowed

All 3W Tap Feeders are connected to the 4W riser, therefore you end up with 3-6 3W Tap Feeders SHARING a common neutral....215.4(A) states this is not allowed.
 
jaggedben said:
My opinion...from the information given...



No.
Supply conductors to apartment, "Tap Feeder" is then the same as "Feeder"
Does not a Tap Feeder (3W), connected to a 4W riser result in apartment served via TWO feeders


No.
Same for 220.84A)((1), apartment is serviced via two feeders, and therefore access to derating table 220.84 is not allowed


Not per se. If you're concern is that the riser neutral supplies multiple taps, that is not a violation.
All 3W Tap Feeders are connected to the 4W riser, therefore you end up with 3-6 3W Tap Feeders SHARING a common neutral....215.4(A) states this is not allowed.

What you are describing is one feeder that supplies multiple other feeders through taps. The main feeder must be sized for the total load of all units. Each feeder supplied by a tap must be sized for the dwelling unit it supplies. The tap rules must be followed to make this a compliant install. But I don't see anything that you've described as a violation in and of itself.
Click to expand...
What I am describing is a 4W riser serving 3-6 3W Taps, ALL of which SHARE the 4W riser NEUTRAL, does this not violate 215.4(A)
 
MyCleveland said:
What I am describing is a 4W riser serving 3-6 3W Taps, ALL of which SHARE the 4W riser NEUTRAL, does this not violate 215.4(A)
Click to expand...

I get what you are saying, but I dont see it that way. IMO the feeder taps end where they connect to the single feeder (riser) which is just 1 feeder. I dont see the feeder taps (which as pointed out by smart$ are a type of feeder) as sharing a neutral.
 
Riser utilizing Table 220.84

Riser utilizing Table 220.84

100A apartment load example could result in a common riser beingsized SMALLER than the TAPS serving each apartment.
Three apartments of 20.8kW load, which equates to exactly a 100A – 120/208V-1P-3WTAP feeder serving each apartment.
20.8 x 3 = 62.4kW
Access to derating table 220.84
62.4 x 0.45 = 28.1kW
Total load for sizing riser = 28.1kW
Riser ampacity = 28,100/(208)(1.73) = 78.1 amps
Result is I can serve THREE 100A single phase apartments with an 80A (PHASE& NEUTRAL conductors) 4W common riser feeder.Please NOTE that apartments are DELTA loads on a Y system, each apartment, reflectsback onto the riser (increase) by a factor of 1.73.
 
electrofelon said:
I get what you are saying, but I dont see it that way. IMO the feeder taps end where they connect to the single feeder (riser) which is just 1 feeder. I dont see the feeder taps (which as pointed out by smart$ are a type of feeder) as sharing a neutral.
Click to expand...

Feeder tap, is feeder number one (3W), approximately one foot in length, connected via TAP (No Overcurrent Prot), to common 4W riser (3-6 floors in length) which is feeder number two.
How is the riser Neutral NOT common to ALL taps (3-6).
The 3W Tap feeder has different characteristics than the 4W riser, so they cannot be considered together as ONE feeder.
One feeder is the rule stated in both 220.82(A) and 220.84(A)(1) in order to have access to the optional calc and derating table 220.84.
 
MyCleveland said:
100A apartment load example could result in a common riser beingsized SMALLER than the TAPS serving each apartment.
Three apartments of 20.8kW load, which equates to exactly a 100A – 120/208V-1P-3WTAP feeder serving each apartment.
20.8 x 3 = 62.4kW
Access to derating table 220.84
62.4 x 0.45 = 28.1kW
Total load for sizing riser = 28.1kW
Riser ampacity = 28,100/(208)(1.73) = 78.1 amps
Result is I can serve THREE 100A single phase apartments with an 80A (PHASE& NEUTRAL conductors) 4W common riser feeder.
...
Click to expand...


I think you're missing something there.

220.82 allows a calculation based on 100% of the first 10kVA plus 40 percent of the remainder. If that number is 20.8kVA (requiring a 100A feeder), then your total summation of considered loads was 37kVA to start with.

220.84 applies to the total considered load without any allowance like the one in 220.82. Thus if you had 3 units requiring a 100A feeder you'd have 37kVA*3=111kVA. Apply 45% to that and you get 50kVA, which when you divide by 208V and 1.73 requires a 138A feeder.

Note: None of this has anything to do with whether you have a feeder that gets tapped, or taps vs feeders. You could have a service with a main breaker and three feeder breakers to dwelling units; no taps, but the calculations would be the same.

Also note: if the main feeder (riser) ungrounded conductors are protected properly at their ampacity then as long as the neutral is sized the same it cannot see an unbalanced current that's greater than its ampacity. The fact that the downstream feeders might be 3W instead of 4W is quite irrelevant to that.
 
MyCleveland said:
What I am describing is a 4W riser serving 3-6 3W Taps, ALL of which SHARE the 4W riser NEUTRAL, does this not violate 215.4(A)
Click to expand...

No, I don't believe that's what 215.4 refers to. If each of the tapped off feeders has a neutral tapped with it, then those are the neutrals for those feeders, and none are shared. The 'riser' is a separate feeder and its neutral only belongs to the riser.
 
MyCleveland said:
Supply conductors to apartment, "Tap Feeder" is then the same as "Feeder"
Does not a Tap Feeder (3W), connected to a 4W riser result in apartment served via TWO feeders

Same for 220.84A)((1), apartment is serviced via two feeders, and therefore access to derating table 220.84 is not allowed
Click to expand...
No. The feeder tap is a feeder in and of itself. What differs is that its protection is at the load end rather than the source end. Only this last feeder is the one that counts whether the dwelling unit is served by more than one feeder. Think of it like this... would it be two feeders if the protection (breaker, fuses) was where it taps the riser feeder?

All 3W Tap Feeders are connected to the 4W riser, therefore you end up with 3-6 3W Tap Feeders SHARING a common neutral....215.4(A) states this is not allowed.
Click to expand...
Again, no. You'd have to have a seven wire riser, i.e. 2 feeder sets of ungrounded conductor to share a common neutral: A1, A2, B1, B2, C1, C2, N.

Taps off the feeder neutral conductor are not counted as sharing the neutral for this requirement.

The way I see it, you have a good mind set. But you are lacking in your Code training. As stated in 90.1 "This Code is not intended as a design specification or an instruction manual for untrained persons."
 
jaggedben said:
No, I don't believe that's what 215.4 refers to. If each of the tapped off feeders has a neutral tapped with it, then those are the neutrals for those feeders, and none are shared. The 'riser' is a separate feeder and its neutral only belongs to the riser.
Click to expand...

Just because I have a 1' tap extended to the N on the 4W riser does not negate the fact that ALL taps share the 4W riser N.
What if I simply looped the N up the riser rather than tapping it on each floor, the result is the same.
 
There are no common neutrals in this application. You have one feeder circuit with a neutral. You have multiple tap circuits each with their own neutral.
 
Smart $ said:
No. The feeder tap is a feeder in and of itself. What differs is that its protection is at the load end rather than the source end. Only this last feeder is the one that counts whether the dwelling unit is served by more than one feeder. Think of it like this... would it be two feeders if the protection (breaker, fuses) was where it taps the riser feeder?


Again, no. You'd have to have a seven wire riser, i.e. 2 feeder sets of ungrounded conductor to share a common neutral: A1, A2, B1, B2, C1, C2, N.

Taps off the feeder neutral conductor are not counted as sharing the neutral for this requirement.

The way I see it, you have a good mind set. But you are lacking in your Code training. As stated in 90.1 "This Code is not intended as a design specification or an instruction manual for untrained persons."
Click to expand...

Your (A1, A2, B1, B2, C1, C2, N) scenario describes exactly a 3 apartment riser with taps connected to the 4W riser and ALL sharing a common N.
Visualize the N simply looping its way up the riser.

untrained persons - first day on the site, should I sign off ?
 
MyCleveland said:
Your (A1, A2, B1, B2, C1, C2, N) scenario describes exactly a 3 apartment riser with taps connected to the 4W riser and ALL sharing a common N.
...
Click to expand...
There is no common neutral shared with multiple circuits. You have one neutral for the feeder circuit and a neutral with each tap circuit. None are common to more than one circuit. The feeder circuit does not extend into the tap circuits. A new tap circuit neutral starts at the point of connection to the feeder circuit neutral.
 
don_resqcapt19 said:
There are no common neutrals in this application. You have one feeder circuit with a neutral. You have multiple tap circuits each with their own neutral.
Click to expand...


Can we take this back to the your first post regarding feeder vs tap feeder
In the text of 220.82(A)...single set of 3W...feeder & 220.84(A)(1)...no dwelling supplied by more than one feeder
In both of these statements are you saying a feeder and tap feeder are equivalent ?

Does not the entire scope of art 220 demand that the single or one feeder be capable of delivery the designed ampacity whether it is from the standard calc or optional calc ?

I content, if you allow the 4W riser to be derated, it would be impossible to deliver design amps without tripping out riser OCD.
Again, Delta 3W loads tapped from a 4W riser, reflect back onto the riser at a factor of 1.73.
 
jaggedben said:


I think you're missing something there.

220.82 allows a calculation based on 100% of the first 10kVA plus 40 percent of the remainder. If that number is 20.8kVA (requiring a 100A feeder), then your total summation of considered loads was 37kVA to start with.

220.84 applies to the total considered load without any allowance like the one in 220.82. Thus if you had 3 units requiring a 100A feeder you'd have 37kVA*3=111kVA. Apply 45% to that and you get 50kVA, which when you divide by 208V and 1.73 requires a 138A feeder.

Note: None of this has anything to do with whether you have a feeder that gets tapped, or taps vs feeders. You could have a service with a main breaker and three feeder breakers to dwelling units; no taps, but the calculations would be the same.

Also note: if the main feeder (riser) ungrounded conductors are protected properly at their ampacity then as long as the neutral is sized the same it cannot see an unbalanced current that's greater than its ampacity. The fact that the downstream feeders might be 3W instead of 4W is quite irrelevant to that.
Click to expand...
I see your point with the math...simply change the apartments to standard calc design at 20.6kW each.
You still end up with three 99amp apartments served via a 80amp 4W (derated N relative to each tap) riser
 
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