tap at secondary
- Thread starter hienlam
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charlie
Senior Member
- Location
- Indianapolis
Re: tap at secondary
"Substantiation:
As 240.21(C)(3)(1) is now written, it is unclear whether or not it is referring to a single set of secondary conductors or multiple sets of secondary conductors going to different overcurrent devices. For example, a transformer secondary feeding two unequally-rated overcurrent devices. I believe the NEC intent is to have these two sets of conductors be the same size, however, the existing wording can lead someone to install two sets of differently sized conductors whose combined ampacity is more than the secondary current rating of the transformer.
Panel Meeting Action: Accept in Principle
Revise existing 240.21(C) to read as follows: "Each set of conductors feeding separate loads shall be permitted to be connected to a transformer secondary, without overcurrent protection at the secondary, as specified in 240.21(C)(1) through (6)."
Panel Statement:
By revising the text in the main body of 240.21(C), the panel has met the intent of the Submitter and is also clarifying the requirement for multiple loads in general."
In other words, yes is the panel's intent as reflected in the change above that will be in the 2005 edition of the NEC, assuming this goes through in the comment stage (the panel vote was 12 - 0).
From the ROP
"Substantiation:
As 240.21(C)(3)(1) is now written, it is unclear whether or not it is referring to a single set of secondary conductors or multiple sets of secondary conductors going to different overcurrent devices. For example, a transformer secondary feeding two unequally-rated overcurrent devices. I believe the NEC intent is to have these two sets of conductors be the same size, however, the existing wording can lead someone to install two sets of differently sized conductors whose combined ampacity is more than the secondary current rating of the transformer.
Panel Meeting Action: Accept in Principle
Revise existing 240.21(C) to read as follows: "Each set of conductors feeding separate loads shall be permitted to be connected to a transformer secondary, without overcurrent protection at the secondary, as specified in 240.21(C)(1) through (6)."
Panel Statement:
By revising the text in the main body of 240.21(C), the panel has met the intent of the Submitter and is also clarifying the requirement for multiple loads in general."
In other words, yes is the panel's intent as reflected in the change above that will be in the 2005 edition of the NEC, assuming this goes through in the comment stage (the panel vote was 12 - 0).
Re: tap at secondary
240.21(C)(3)(1) is listed as Industrial installations only. The poster did not say this was industrial. If not, I think 240.21(C)(2)(1a & b) might be interepted to allow this installation.
1a would assume the ampacity of the conductor to each panel would be adequate for the load.
1.b the conductors to each breaker would have ampacity equal to rating of each breaker. I would add that the sum of the breaker ratings would not exceed the rating of the transformer. You would also apply the logic that the panels should be grouped together.
[ July 22, 2003, 01:31 PM: Message edited by: bob ]
240.21(C)(3)(1) is listed as Industrial installations only. The poster did not say this was industrial. If not, I think 240.21(C)(2)(1a & b) might be interepted to allow this installation.
1a would assume the ampacity of the conductor to each panel would be adequate for the load.
1.b the conductors to each breaker would have ampacity equal to rating of each breaker. I would add that the sum of the breaker ratings would not exceed the rating of the transformer. You would also apply the logic that the panels should be grouped together.
[ July 22, 2003, 01:31 PM: Message edited by: bob ]
- Location
- Illinois
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- retired electrician
Re: tap at secondary
Bob,
I don't see any limit on the number or taps that can be supplied from a transformer as long as each set of tap conductors are installed per the rule. Remember that you do not have transformer secondary overcurrent protection and that the transformer must have an primary OCPD equal to or less than 125% of the primary rated current. Also 240.21(C)(2) is limited to 10' of conductor.
I wonder why that a 10' feeder tap in 240.21(B)(1) requires a single OCPD at the end of the tap and the transformer tap rule lets you terminate to a "device" with a rating not less than the ampacity of the tap conductors? Why are these installations treated differently?
Don
Bob,
I don't see any limit on the number or taps that can be supplied from a transformer as long as each set of tap conductors are installed per the rule. Remember that you do not have transformer secondary overcurrent protection and that the transformer must have an primary OCPD equal to or less than 125% of the primary rated current. Also 240.21(C)(2) is limited to 10' of conductor.
I wonder why that a 10' feeder tap in 240.21(B)(1) requires a single OCPD at the end of the tap and the transformer tap rule lets you terminate to a "device" with a rating not less than the ampacity of the tap conductors? Why are these installations treated differently?
Don
Re: tap at secondary
Charlie, thanks for clarifying...
Bob, it's certainly for industrial installations...
Don, your interpetation is the same with my...
to answer to your concerning about these articles. (no idea why)...i've little knowlegdes on NEC...reading this book make me wonder why they used such language that so hard to understand...(wording like lawyer language and i really hate lawyer...)
Charlie, thanks for clarifying...
Bob, it's certainly for industrial installations...
Don, your interpetation is the same with my...
to answer to your concerning about these articles. (no idea why)...i've little knowlegdes on NEC...reading this book make me wonder why they used such language that so hard to understand...(wording like lawyer language and i really hate lawyer...)
charlie
Senior Member
- Location
- Indianapolis
Re: tap at secondary
We have addressed this topic on other threads but the upshot is that the Code is a legal document and has to be written in the concise language of legaleze so it will stand up in court.
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