Tap Rule and Overcurrent Protection

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PowerLink

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I have 3ea single phase RTU @ 8.4a each. on a commercial building, It was necessary to install a new 15kVA 480-208/120 X-former as there was no 208 available in the vicinity. The secondary (40a) over-current device is installed next to the X-former in the roof access closet. From there I made a roof penetration and installed a 3/4 co with 4#8 and a #10gr (neutral for rt-rec only which also got it's own private fuselable pull-out) for about a 130ft run. Nice and clean on the parapet wall. At each RTU I installed a NEMA-3 6X6X4 and tapped the #8s to feed a 30a 1phase pull-out disconnect, fused at 20a which in turn feeds the RTU's which are right there and clearances are all in order.

Now, my Glendale CA inspector turned this system down as he felt that the tap rule pertained to the over-current device at the X-former. My understanding is that the X-former secondary EXO is protecting the #8s throughout the installation and the single phase (fuseable) pullout are the only devices that would exercise and comply with NEC 240.21.

This whole scenario is odd to me because of the great many instances of a feeder set pulled into a gutter and tapped for misc equipment. This is done all the time and I have done it a great number of times not only for HVAC equipment but for various machines and panel-boards. It is very possible that the inspector is merely confused about the installation and wrote a correction which needs to be more clearly understood as I am having trouble finding a clear description of the "tap-rules" in NEC 210-240

Thanks for your help and input.
 

charlie b

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Location
Lockport, IL
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Retired Electrical Engineer
This is not a "tap rule" situation at all! Every conductor (i.e., the #8's coming from the transformer's secondary disconnect and the #12's coming from each fused disconnect) is protected against overcurrent at the point from which it receives its supply. That is all you need. Look at the first sentence of 240.21. You meet that sentence's requirements, without having to deal with the "except as specified" stuff that follows. It is the stuff that follows that constitutes the collection of "tap rules," and you are not dealing with that stuff.

Welcome to the forum.
 

PowerLink

Member
Thank You

Thank You

Thank you for the fast response. Just as suspected, it is a clear cut and valid installation.
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
I don't see a problem, but, can you elaborate a bit on the power for the 120v receptacles.
 
Let me see if I understand this.

Transformer supplies a 40A disconnect from the secondary. (The conductors from the secondary side of the transformer are considered tap conductors)

The 40A disconnect then supplies 8-AWG conductors.

"tapped the #8s to feed a 30a 1phase pull-out disconnect, fused at 20a which in turn feeds the RTU's"

On the load side of the 40A disco, the conductors are considered feeders.


you tapped the feeders, as per your description, which I put in blue.


How did you tap them? What size conductor?

If you used 8AWG, that would not be considered a tap by code. But. how can one supply a 30A rated pullout with a 40A protected feeder?

If you tapped the 8AWG with a smaller conductor (say a 10AWG), then indeed it is a 'tap' conductor, and your installation is code compliant.
 

PowerLink

Member
I don't see a problem, but, can you elaborate a bit on the power for the 120v receptacles.

I simply tapped the #8's at one of the 6x6 gutter boxes and installed a fuseable pullout with a 20a fuse. from there I installed a 20a GFCI rec. with an "in use" cover to accommodate the rt receptacle requirement.
 

PowerLink

Member
Let me see if I understand this.

Transformer supplies a 40A disconnect from the secondary. (The conductors from the secondary side of the transformer are considered tap conductors)

The 40A disconnect then supplies 8-AWG conductors.

"tapped the #8s to feed a 30a 1phase pull-out disconnect, fused at 20a which in turn feeds the RTU's"

On the load side of the 40A disco, the conductors are considered feeders.


you tapped the feeders, as per your description, which I put in blue.


How did you tap them? What size conductor?

If you used 8AWG, that would not be considered a tap by code. But. how can one supply a 30A rated pullout with a 40A protected feeder?

If you tapped the 8AWG with a smaller conductor (say a 10AWG), then indeed it is a 'tap' conductor, and your installation is code compliant.

The taps were made in the NEMA-3 boxes with "polaris" type wire connectors. I suppose blue wirenuts or split bolts would work but I like the polaris connectors better.

The #8's are considered a buss or buss extension protected by the EXO with 40a fuses. Now, anywhere in that conduit run it is acceptable to "tap" and install a fuseable disconnect with smaller conductors eg; #12 and protected at 20a as long as it is within 10ft or within sight of the tap. The HVAC units name-plate stated that the max fuse size is 20a. So, now what you have is protected #12 feeding the equipment with the proper fuse size. The 8's are protected by the 40a fuses at the source.

If I am missing something, please speak up as I use this system alot and it is very cost effective.
 
The taps were made in the NEMA-3 boxes with "polaris" type wire connectors. I suppose blue wirenuts or split bolts would work but I like the polaris connectors better.

The #8's are considered a buss or buss extension protected by the EXO with 40a fuses. Now, anywhere in that conduit run it is acceptable to "tap" and install a fuseable disconnect with smaller conductors eg; #12 and protected at 20a as long as it is within 10ft or within sight of the tap. The HVAC units name-plate stated that the max fuse size is 20a. So, now what you have is protected #12 feeding the equipment with the proper fuse size. The 8's are protected by the 40a fuses at the source.

If I am missing something, please speak up as I use this system alot and it is very cost effective.

i'm unfamiliar with "within sight of"
is that in the tap rules
 

PowerLink

Member
i'm unfamiliar with "within sight of"
is that in the tap rules

This is something that I have been having trouble finding in NEC yet it is something that I was taught 20+ years ago. It may have stated it in a 1980s NEC and has since been omitted. There is however in 240.21 (4) and (5) a description of industrial or exterior application yet does not directly state "within sight"

I can foresee an application where the buss or gutter is located high up and would not allow for a means of conductor protection within 10ft. With the source at that height the EXO would be mounted at a serviceable area within sight of the "tap". Alternately, you could bring fully rated conductors to your over current protection which may be prohibitive due to source sizing and would be beside the point.

Any help in locating this rule would be greatly appreciated.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
This is something that I have been having trouble finding in NEC yet it is something that I was taught 20+ years ago. It may have stated it in a 1980s NEC and has since been omitted. There is however in 240.21 (4) and (5) a description of industrial or exterior application yet does not directly state "within sight"
Since I entered the trade in the 70's, I have never seen any "within sight" rule except for motor and appliance disconnects, although I have heard many of them mentioned often.:grin:

In reality, the tap rules in 240.21 do not define the physical distance between devices, they only address the conductor length.

The two 'most common' tap rules are for 10' and 25'.
Because your #10 tap from the #8 feeder is more rated more than 30% of the feeder 40A device, your tap conductors can be up to 25' long.
 

Smart $

Esteemed Member
Location
Ohio
Since I entered the trade in the 70's, I have never seen any "within sight" rule except for motor and appliance disconnects, although I have heard many of them mentioned often.:grin:
Perhaps he is referring to the RTU disconnecting means being located within sight of the unit served. Ref: 440.14
 

PowerLink

Member
Perhaps he is referring to the RTU disconnecting means being located within sight of the unit served. Ref: 440.14

This is very possible, Interesting how the human will stretch a concept to fit the need.

I wonder how this will can be viewed in a non HVAC application such as a hydraulic lift or a compressor?
 

benaround

Senior Member
Location
Arizona
Where 'within sight from', ' In sight from', or 'Within sight' is used in the code, a distance

of not more than 50' is also in the requirement.
 

PowerLink

Member
Where 'within sight from', ' In sight from', or 'Within sight' is used in the code, a distance

of not more than 50' is also in the requirement.

Do you have the specifics of NEC sighting the "within sight" of the site? Does that only pertain to HVAC equipment or is it a broad definition?
 
The taps were made in the NEMA-3 boxes with "polaris" type wire connectors. I suppose blue wirenuts or split bolts would work but I like the polaris connectors better.

The #8's are considered a buss or buss extension protected by the EXO with 40a fuses. Now, anywhere in that conduit run it is acceptable to "tap" and install a fuseable disconnect with smaller conductors eg; #12 and protected at 20a as long as it is within 10ft or within sight of the tap. The HVAC units name-plate stated that the max fuse size is 20a. So, now what you have is protected #12 feeding the equipment with the proper fuse size. The 8's are protected by the 40a fuses at the source.

If I am missing something, please speak up as I use this system alot and it is very cost effective.


The red highlighted items are not permitted in the NEC as code compliant.


I have not heard this type of setup for the installation you are installing, so I believe it is language you learned in the field

You are using language that is not code language as found in the NEC, but slang language found in the field. The casual reader of the NEC has a difficult time finding information in the NEC, as they are trying to find slang in the NEC, where there is no slang used.
I feel you are using your field training and language to try and match to the NEC, which is difficult at best.
 
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