Transformer secondary protection required?

[don_resqcapt19]

...
This installation (450.1) has secondary OCPD therefore "Primary Only Protection" doesn't apply in Table 450.3(B). No where in 450.3 does it say "only if the transformer needs it", nor does it say anywhere "only if article 450 requires it". It says in the table that when you have secondary OCPD then you size them accordingly.

It will forever remain my opinion that if the secondary protection is not required by the rule in 450.3, than there is no limit of the size of the secondary conductor OCPD as long as the ampacity of the conductor equals or exceeds that of the OCPD.

 

[don_resqcapt19]

Didn't say it was required by 450. Never said it was required by 450. Said the secondary OCPD was there because of 240. And the secondary OCPD is a part of the transformer installation. Therefore it's covered under the scope. ...

The rule clearly says secondary potection of the TRANSFORMER. That is not the case when the primary OCPD is sized at 125% or less of the rated primary current.

 

[david luchini]

It says in the table that when you have secondary OCPD then you size them accordingly.

That is not what Note 2 of Table 450.3(B) says at all.

It says that where secondary overcurrent protection is REQUIRED by the "Secondary Protection" column of table 450.3(B), then the required OCPD shall consist of not more than 6 devices grouped in one location, and that the total of all the device ratings shall not exceed the allowed value of a single OCPD.

The "Secondary Protection" column of table 450.3(B) gives 4 possible conditions. Two of the conditions are "NOT REQUIRED", one condition is a maximum rating of 125% (or the next standard size up), and the last condition is a maximum rating of 167%.

The "Not Required" for a secondary current of more than 9Amps would be the condition that applies to the OP when the primary OCPD is reduced to 70A.

 

[pfalcon]

The rule clearly says secondary potection of the TRANSFORMER. That is not the case when the primary OCPD is sized at 125% or less of the rated primary current.

Try and quote that Don. No where does it say for the protection (verb) of the transformer. Is says Overcurrent Protection (noun) of the transformer. As in, These are the sizes of OCPD when you install a transformer: Row 1 for transformers that only have primary; Row 2 for transformers that have both. HAVE both, NOT NEED.

 

[pfalcon]

... Two of the conditions are "NOT REQUIRED", ...

But are none the less "PRESENT".

I don't have to second service in my house, but if I do install it then I still have to install it to meet code. REQUIRED OR NOT.
There's a lot of things I can add to a house or building that are NOT REQUIRED. But if they're there then they have to meet code.

You don't HAVE to have secondary OCPD for a transformer but if you HAVE it then you're on row 2 not row 1.

 

[pfalcon]

It will forever remain my opinion that if the secondary protection is not required by the rule in 450.3, than there is no limit of the size of the secondary conductor OCPD as long as the ampacity of the conductor equals or exceeds that of the OCPD.

Then please open a separate thread to debate the merit of "Charlie's rule for reading the NEC".

 

[david luchini]

But are none the less "PRESENT".

I don't have to second service in my house, but if I do install it then I still have to install it to meet code. REQUIRED OR NOT.
There's a lot of things I can add to a house or building that are NOT REQUIRED. But if they're there then they have to meet code.

You don't HAVE to have secondary OCPD for a transformer but if you HAVE it then you're on row 2 not row 1.

The Note #2 doesn't say anything about whether there is an OCPD "PRESENT" on the secondary side of the transformer. It only says where it is "REQUIRED" by the Table. "Present" and "Required" do not have the same meaning.

If the secondary OCPD is "Not Required", then you are on row 1, not row 2. Note 2 says "Where Required", row 1 says "Not Required." It is irrelevant whether you "HAVE" an OCPD on the secondary side of the transformer, because "Have" and "Required" also do not have the same meaning.

 

[don_resqcapt19]

Then please open a separate thread to debate the merit of "Charlie's rule for reading the NEC".

I understand Charlie's rule and I understand the code rule and how it applies. There is nothing in either that leads support to your interpretation of the rule in question. I have nothing more to say on this one.

 

[pfalcon]

... If the secondary OCPD is "Not Required", then you are on row 1, not row 2. ...

Where does the table give you leeway to ignore the presence of the secondary OCPD in order to use row 1? This is NOT a "Primary only protection" installation. There IS a secondary.

 

[ggunn]

Try and quote that Don. No where does it say for the protection (verb) of the transformer. Is says Overcurrent Protection (noun) of the transformer. As in, These are the sizes of OCPD when you install a transformer: Row 1 for transformers that only have primary; Row 2 for transformers that have both. HAVE both, NOT NEED.

Just to pick a nit, the word "protection" is a noun in both instances as it nearly always is; with a bit of a stretch I can think of a way to use the word as an adjective, but not as a verb.

 

[david luchini]

Where does the table give you leeway to ignore the presence of the secondary OCPD in order to use row 1? This is NOT a "Primary only protection" installation. There IS a secondary.

The OCPD on the secondary side which is providing protection to the secondary conductors is not relevant to the TRANSFORMER protection. The Table is titled "Maximum Rating or Setting of Overcurrent Protection for TRANSFORMERS 600V and less (as a Percentage of Transformer-Rated Current)"

The table is referenced in section 450.3, which says: "Overcurrent protection of TRANSFORMERS shall comply with..."

Table 450.3(B) only tells us what the requirements for protecting the TRANSFORMER are.

The Table gives you two Methods for protecting the Transformer (see the left most column):

.....Method 1: "Primary Only Protection"

.....Method 2: "Primary and Secondary Protection"

For Method 1, the Maximum Rating of the Primary OCPD can be 125% of the primary rated current (or next size up.) If the primary OCPD meets this maximum rating, then no secondary protection is required, and you have a "Primary Only" protected transformer.

If the Primary OCPD is greater than 125% (or next size up), such as the 80A primary OCPD in the OP, then you must look at the second method. For method 2, the Maximum Rating of the Primary OCPD can be 250% of the primary rated current. In this case, the Secondary OCPD can have a Maximum Rating of 125% of the secondary rated current (or next size up), and you have a "Primary and Secondary" protected transformer.

In the case of the OP, the Primary OCPD (80A) exceeded the allowable 125% (or next size up) for the "Primary Only" method, BUT the secondary also exceeded the allowable 125% (or next size up) required for the Secondary Protection in the "Primary and Secondary" method, so the installation was non-compliant with 450.3(B).

There are two options to correct the non-compliance. Make the transformer protection comply with Method 1 "Primary Only", or comply with Method 2 "Primary and Secondary" protection.

Reducing the Secondary OCPD to 175A would make the installation comply with Method 2. The primary OCPD would still be greater than 125%, but less than 250%, and the Secondary OCPD would be less than 125%. Therefore, the Requirements for TRANSFORMER protection in T450.3(B) would be met, and assuming the primary and secondary conductors were already properly protected by the 80A and 200A OCPDs, reducing the secondary OCPD to 175A, the CONDUCTORS will still be properly protected per 240.4 & 240.21(C).

Reducing the Primary OCPD to 70A would make the installation comply with Method 1. The primary OCPD would be at 125% (or next size up) and there would be NO REQUIRED protection for the secondary of the transformer. Therefore, the Requirements for TRANSFORMER protection in T450.3(B) would be met, and assuming the primary and secondary conductors were already properly protected by the 80A and 200A OCPDs, reducing the primary OCPD to 70A, the CONDUCTORS will still be properly protected per 240.4 & 240.21(C).

You are trying to force the presence of an OCPD on the secondary side of the transformer for the protection of the secondary conductors as meaning that the Transformer is "Primary and Secondary" protected. But Table 450.3(B) tells us that the method of protecting the Transformer as "Primary Only" or "Primary and Secondary" is related the Maximum Rating or Setting of the Transformer OCPDs as a Percentage of Transformer Rated current. In the OP, with a 70A primary OCPD, the "Protection Method" for the transformer would be "Primary Only," and no Secondary Protection would be required for the TRANSFORMER. In this case, the OCPD on the secondary side will only be providing protection to the conductors, not to the transformer. As such, the rating of the OCPD must be only lower or equal to the ampacity of the secondary conductors. There is no limit to the OCPD relating to the Percentage of the Transformer secondary current.

 

[pfalcon]

I understand Charlie's rule and I understand the code rule and how it applies. There is nothing in either that leads support to your interpretation of the rule in question. I have nothing more to say on this one.

Okay Don. Let's get off the hook on this one. I've read the handbook as well. It's obvious that 450.3 was intended for the sole purpose of protecting the transformer. Wryly from the bottom of page 666:

The requirements for overcurrent protection of transformer secondaries in 450.3 apply only to the protection of transformers, not to the protection of conductors. ... It is possible that the overcurrent protection required by Article 450 also satisfies the requirements in Article 240 for protection of the conductors, and vice versa, but it is also possible that they do not.

E'en so, those are notes in the handbook not in the code.

1) The scope (450.1) specifically says the article covers the installation rather than the protection of the transformers. That broadening of the scope means the conductors and OCPD associated with the transformer are covered not just those things intended for its protection.

2) Both article 240 and article 450 call the protection for the secondary conductors "Secondary Overcurrent Protection". There is nothing except the transformer for that OCPD to be secondary to. Both articles address it as though it's part of installing the transformer by giving them a name associated with that installation. It requires ignoring a rational relationship to claim the 240 OCPD is not a part of the installation. Especially since if you elect to use a 450 OCPD then it's one and the same component as the 240 OCPD.

3) Article 240 lays claim to the transformer primary OCPD for D-D (with direct reference to 450.3) to avoid a secondary. Thereby reinforcing that protection of the secondary conductors is part of the transformer installation.

4) 450.3 creates its table without regard for how the OCPD became part of the installation. It doesn't care whether 450 required the secondary OCPD; it just tells you how to size what's there. There's no exclusionary statement allowing you to use the "primary only" row when you have an installation that includes a secondary - regardless of why the secondary got installed.

And that's where Charlie's rule does come in. When I first read this article I wasn't pre-disposed to an interpretation. I wasn't pre-baptized into its intent. The first transformer I looked at did have a 240 OCPD present and there is nothing in 450 to even imply that it isn't part of the transformer installation. It was a surprise when I read the handbook and saw their take on it. So I reread the articles. Several times. In all honesty, I was hoping you and David would find a clause I'd missed. That hasn't happened. Both your arguments rely on unwritten intent that the secondary concerned must have been installed under article 450. But it doesn't. It only says what it says - not what it was intended to say.

So to be clear: I understand the INTENT and PRACTICE being used that if Row 1 is used to size the primary then the secondary is independant of article 450. So in this specific case either

Row 1: 450 Primary sizing per row 1 of 450.3(B); 240 not 450 secondary sizing.
or
Row 2: 450 Primary sizing per row 2 of 450.3(B); 240 and 450 secondary sizing

 

[pfalcon]

The OCPD on the secondary side which is providing protection to the secondary conductors is not relevant to the TRANSFORMER protection.
... _{<Clipping the spammy part that we've already agreed upon>} ...
You are trying to force the presence of an OCPD on the secondary side of the transformer for the protection of the secondary conductors as meaning that the Transformer is "Primary and Secondary" protected.

Exactly, though I wouldn't have said I'm trying to force it. I think it does that on its own. And not IS ... protected but HAS ... protection. As in HAS "Primary and secondary protection" whether it needed it or not.

But Table 450.3(B) tells us that the method of protecting the Transformer as "Primary Only" or "Primary and Secondary" is related the Maximum Rating or Setting of the Transformer OCPDs as a Percentage of Transformer Rated current.

"Maximum Rating or Setting for Transformer OCPDs as a Percentage of Transformer Rated current." specifies the units in the table not a restriction/relationship on the row requirements. Units in the body are dependent on the rows not the other way around.

Unfortunately the word "for" in the title is the best I can see for your argument. And since the secondary OCPD is named for its position in the installation of a transformer that argument is very weak.

 

[pfalcon]

Just to pick a nit, the word "protection" is a noun in both instances as it nearly always is; with a bit of a stretch I can think of a way to use the word as an adjective, but not as a verb.

Lol, okay. Object noun.

 

[david luchini]

Exactly, though I wouldn't have said I'm trying to force it. I think it does that on its own. And not IS ... protected but HAS ... protection. As in HAS "Primary and secondary protection" whether it needed it or not.

But the Note 2 that is driving your argument says nothing about whether the transformer HAS an OCPD on the secondary side, only whether it is REQUIRED or not. And it is the Table 450.3(B) which tells us whether it is REQUIRED or not.

"Maximum Rating or Setting for Transformer OCPDs as a Percentage of Transformer Rated current." specifies the units in the table not a restriction/relationship on the row requirements. Units in the body are dependent on the rows not the other way around.

Yes, the units in the body are dependent on the rows. The rows say "Primary Only Protection" or "Primary and Secondary Protection." If I want to protect the Transformer with "Primary Only Protection" row, the I must follow the units in that row, which are 125% for the Primary, and Not Required for the Secondary. That is what allows me to protect the 45kVA transformer with a 70A primary ocpd, and allows the transformer secondary conductor OCPD to be any size, as long as the conductors are properly protected.

Try to follow it all the way through, instead of starting at the Table. Section 450.3 says "Overcurrent protection of Transformers shall comply with...450.3(B)." Section 450.3(B) says "Overcurrent protection shall be provided in accordance with Table 450.3(B)." There is nothing that says lets see where we have protection and then lets work the settings to make T450.3(B) comply. It says provide protection in accordance with T450.3(B). Table 450.3(B) gives us two Protection Methods, "Primary Only" and "Primary and Secondary." If I provide a Primary OCPD which is less than 125% of the primary rated current, then I am Providing Overcurrent Protection for the Transformer in accordance with T450.3(B), "Primary Only" method.

Unfortunately the word "for" in the title is the best I can see for your argument. And since the secondary OCPD is named for its position in the installation of a transformer that argument is very weak.

You are again confusing "Transformer Secondary Overcurrent Protection," and "Transformer Secondary Conductor Overcurrent Protection." The position of "Secondary" is named in both, but these are two separate issues. In most (if not all) conditions where "Transformer Secondary Overcurrent Protection" is required, the OCPD that provides Transformer Secondary Protection will also provide Transformer Secondary Conductor Protection. In the OP, with a 70A primary OCPD and a 200A secondary OCPD, there is no "Transformer Secondary Overcurrent Protection," because non is required by T450.3(B), but there is still a "Transformer Secondary Overcurrent Protection" because it is required by 240.21(C).

 

[don_resqcapt19]

...

2) Both article 240 and article 450 call the protection for the secondary conductors "Secondary Overcurrent Protection". ...

This is where I don't agree. There is nothing in Article 450 that has anything to do with the protection of any conductor. The rules in that article only cover the protection of the transformer windings. Likewise there is nothing in Article 240 that covers the protection of the transformer.

 

[pfalcon]

But the Note 2 that is driving your argument says nothing about whether the transformer HAS an OCPD on the secondary side, only whether it is REQUIRED or not. And it is the Table 450.3(B) which tells us whether it is REQUIRED or not.

My apologies for ever bringing up note 2. You have to be ON the table before the note applies. Required is in note 2 and doesn't apply until AFTER you select a row. We agree, since I've conceded that.
"Has (already) or requires (by 450) a secondary" applies to select the row.

... If I want to protect the Transformer with "Primary Only Protection" row, ...

You can if it doesn't already have a secondary OCPD. So on a D-D you can choose, but a D-Y already HAS a secondary - the choice was made for you.

... There is nothing that says lets see where we have protection and then lets work the settings to make T450.3(B) comply. It says provide protection in accordance with T450.3(B). Table 450.3(B) gives us two Protection Methods, "Primary Only" and "Primary and Secondary." ...

Table lookups do not permit you to arbitrarily ignore something that's already present. They permit you to add optional components only.

You design the system first and set sizes second. On a D-D you can elect to add or omit a secondary THEN you look up the appropriate row to select values. On a D-Y it's already been forced on you. You can't omit or ignore it just because you want to use the first row.

You are again confusing "Transformer Secondary Overcurrent Protection," and "Transformer Secondary Conductor Overcurrent Protection." The position of "Secondary" is named in both, but these are two separate issues. In most (if not all) conditions where "Transformer Secondary Overcurrent Protection" is required, the OCPD that provides Transformer Secondary Protection will also provide Transformer Secondary Conductor Protection. ...

Not confusin' nuthin'. I know the INTENT in 450 is to protect the transformer but no where does it say that. It says the scope is the INSTALLATION of the transformer. The install includes the secondary OCPD if present.

 

[pfalcon]

This is where I don't agree. There is nothing in Article 450 that has anything to do with the protection of any conductor. The rules in that article only cover the protection of the transformer windings. Likewise there is nothing in Article 240 that covers the protection of the transformer.

I wholly agree that nothing in Article 450 has anything to do with the protection of conductors.

The emphasized part is where we disagree. The INTENT was to only cover the protection of the transformer windings. But no where in the article does it actually SAY that. It's in the handbook and followed by practice but it's not in the code. The code says INSTALLATION. That number (2) argument is rationale that both articles are referring to the same device - nothing more. In 450 that device is considered part of the installation and therefore inside the scope of the article. Therefore it can't be ignored when choosing a row on the table.

 

[david luchini]

1) The scope (450.1) specifically says the article covers the installation rather than the protection of the transformers. That broadening of the scope means the conductors and OCPD associated with the transformer are covered not just those things intended for its protection.

The broadening of the scope does not mean the conductors. The scope (450.1) say the installation of all transformers. Reading through Article 450, you will see that this includes Overcurrent Protection of Transformers, Guarding of Transformers, Ventilation of Transformers, Accessibility of Transformers, Transformer Vaults, etc.

You will not see anything there about conductors. You will see, however, in the scope of Article 215 "This article covers the installation requirements, overcurrent protection requirements, minimum size, and ampacity of conductors for feeders.."

The scope for conductors is found elsewhere in the Code, not in Article 450.

2) Both article 240 and article 450 call the protection for the secondary conductors "Secondary Overcurrent Protection". There is nothing except the transformer for that OCPD to be secondary to. Both articles address it as though it's part of installing the transformer by giving them a name associated with that installation. It requires ignoring a rational relationship to claim the 240 OCPD is not a part of the installation. Especially since if you elect to use a 450 OCPD then it's one and the same component as the 240 OCPD.

This is not true. The term "Secondary Overcurrent Protection" does NOT appear anywhere in Article 240. In fact, you will only find that term in Tables 450.3(A), 450.3(B) and in 695.5(B) which relates to Fire Pumps fed via a Transformer

3) Article 240 lays claim to the transformer primary OCPD for D-D (with direct reference to 450.3) to avoid a secondary. Thereby reinforcing that protection of the secondary conductors is part of the transformer installation.

Article 240 does not lay claim to the Transformer primary OCPD to avoid a secondary OCPD. 240.4(F) and 240.21(C)(1) permit transformer secondary conductors to be protected by the primary OCPD on a D-D transformer, under the conditions specified therein. Both of those two section specify that the protection of the Transformer must be in accordance with 450.3. In other words, the Transformer Protection and the Conductor Protection are separate issues.

For example, if the transformer in the OP was 45kVA, 480-240 D-D, and the primary OCPD was 80A, then 240.4(F) and 240.21(C)(1) do not allow for a "Primary Only Protection" installation. T450.3(B) will required a Transformer Secondary OCPD.

4) 450.3 creates its table without regard for how the OCPD became part of the installation.

Again, not true. Table 450.3(B) is TELLING us how the Transformer OCPD becomes part of the installation. 450.3(B) says "Transformers 600V, Nominal, or Less: Overcurrent protection shall be provided in accordance with Table 450.3(B)." This is a Mandatory rule in the Code. Protection shall be provided in accordance with Table 450.3(B), not shall be provided in accordance with Article 240.

It doesn't care whether 450 required the secondary OCPD; it just tells you how to size what's there. There's no exclusionary statement allowing you to use the "primary only" row when you have an installation that includes a secondary - regardless of why the secondary got installed.

The words "NOT REQUIRED" are right there in black and white in Table 450.3(B). But you're telling us to just ignore them.

There is no "inclusionary" statement to say that transformer secondary conductor OCPDs automatically become Transformer Secondary OCPDs, even though the primary OCPD is less than 125%, in accordance with "Primary Only Protection."

And that's where Charlie's rule does come in. When I first read this article I wasn't pre-disposed to an interpretation. I wasn't pre-baptized into its intent. The first transformer I looked at did have a 240 OCPD present and there is nothing in 450 to even imply that it isn't part of the transformer installation. It was a surprise when I read the handbook and saw their take on it. So I reread the articles. Several times. In all honesty, I was hoping you and David would find a clause I'd missed. That hasn't happened. Both your arguments rely on unwritten intent that the secondary concerned must have been installed under article 450. But it doesn't. It only says what it says - not what it was intended to say.

There is nothing unwritten about it. What it says it that for Transformer Protection, if the Primary OCPD is not greater than 125%, then Secondary Protection of the transformer is NOT REQUIRED. That's the way it is written, plain and simple.

 

[david luchini]

Not confusin' nuthin'. I know the INTENT in 450 is to protect the transformer but no where does it say that.

It says it explicitly, you're just chosing to ignore it:

450.3 Overcurrent Protection. Overcurrent protection of Transformers shall comply withg 450.3(A), (B), or (C).

450.3(B) Transformers 600V, Nominal, or Less. Overcurrent Protection shall be provided in accordance with Table 450.3(B).

Table 450.3(B) Maximum Rating or Setting of Overcurrent Protection for Transformers...

It says the scope is the INSTALLATION of the transformer. The install includes the secondary OCPD if present.

It most certainly does NOT. It includes the secondary OCPD if it is required to protect the transformer. If a secondary OCPD is present but has nothing to do with the transformer, but is only there to protect the conductors, then that secondary OCPD is not part of the transformer installation. It is NOT REQUIRED to be part of the transformer installation by Table 450.3(B).