Tap Rule Confusion

[david luchini]

240.4 (F) and 240.21 (C) 1 will not allow primary only protection on a multi voltage secondary.

I disagree. 240.4(F) and 240.21(C) relate to how to protect the secondary CONDUCTORS, not how to protect the transformer.

I'm not suggesting protecting the secondary conductors with the primary OCPD, I'm suggesting protecting the secondary conductors in ACCORDANCE with 240.21(C). 240.21(C) says secondary conductors are permitted to be connected WITHOUT OCPD at the secondary (as specified in 240.21(C)(1) thru (C)(6)), and 240.21(C)(2) says for conductors not over 10' long, the ampacity of the conductors shall not be less than the rating of the device supplied by the secondary conductors.

 

[Smart $]

I disagree. 240.4(F) and 240.21(C) relate to how to protect the secondary CONDUCTORS, not how to protect the transformer.

I'm not suggesting protecting the secondary conductors with the primary OCPD, I'm suggesting protecting the secondary conductors in ACCORDANCE with 240.21(C). 240.21(C) says secondary conductors are permitted to be connected WITHOUT OCPD at the secondary (as specified in 240.21(C)(1) thru (C)(6)), and 240.21(C)(2) says for conductors not over 10' long, the ampacity of the conductors shall not be less than the rating of the device supplied by the secondary conductors.

First, 240.4(F) is about protecting secondary conductors with the primary OCPD. As such, the primary OCPD must protect the transformer and secondary conductors. It's not an either-or scenario but rather both. However, the OP situation is one not permitted to do so.

As for secondary conductors terminating at a device rather than an OCPD, that would be the scenario where the primary OCPD protects the secondary conductors there is no need for secondary OCPD before the device.

 

[Smart $]

...
Table 450.3 (B) note 2 only allows six breaker rule.

...and the OP stated ten breaker positions. If the breakers occupying those positions were all 2-poles, how many would you have? What about two 3-poles and two 2-poles? ..and three 3-poles and one 1-pole? ...and two 3-poles and four 1-poles?

 

[david luchini]

As for secondary conductors terminating at a device rather than an OCPD, that would be the scenario where the primary OCPD protects the secondary conductors there is no need for secondary OCPD before the device.

This is what I'm trying to get at. 240.21(C) tells you how to protect the transformer secondary conductors. (C)(1) tells you how you can use the primary OCPD to protect the secondary. But it wouldn't apply for a 3-phase delta-wye transformer.

240.21(C)(2) tells you how to protect secondary conductors not over 10' long. It allows you to terminate at a "device" (without an OCPD) if the ampacity of the conductors is not less than the rating of the device, the conductors don't extend beyond the device, the conductors are enclosed in a raceway and the rating of the primary OCPD multiplied by the primary-secondary ratio does not exceed 10 times the ampacity of the secondary conductor.

So by 240.21(C)(2), I can have a primary only protected transformer, where the primary OCPD does NOT protect the secondary conductors, and not require a secondary OCPD as long as I meet the restriction listed above?

 

[iyowanto]

Transformer Secondary Protection

Transformer Secondary Protection

I have 1125.KVA isolated transformer 480V-480V, 3-PH that is protected by 90A fuse in 100A fused disconnect switch on the primary side. I don't have protection on the secondary but the secondary conductors are rated at 95A (#4 at 90C). The secondary conductors have 60ft to feed the panel. Does it violate tap rule 240.21(C)? Or can I use 450.3 for primary protection only and still comply with the code? The reason I'm using 112.5KVA is because the equipment comes in later after the installation is done and the maximum electrical load is 84A on the equipment. My interpretation of the code is the secondary conductors are protected by 90A fuse on the primary side of transformer but I'm not sure if I have to comply with tap rule since the ratio of primary-to-secondary is 1.0. Please help. Thank you.

 

[Smart $]

...

So by 240.21(C)(2), I can have a primary only protected transformer, where the primary OCPD does NOT protect the secondary conductors, and not require a secondary OCPD as long as I meet the restriction listed above?

Not the way I see it.

240.21 general statement requires compliance with (1) through (6). So by (1) you can't have unprotected secondary conductors without a secondary OCPD. (2) through (6) are subsections which must also be complied with when the primary does protect secondary conductors. So (2) through (6) when applicable to primary-protected secondary conductors are going to be written with stipulation(s) regarding connection directly to a device other than an OCPD.

I agree it could be better written, but it is what it is... and I'm quite certain my interpretation is as intended. But I'm always [stubbornly :roll:] open to correction

 

[Smart $]

I have 1125.KVA isolated transformer 480V-480V, 3-PH that is protected by 90A fuse in 100A fused disconnect switch on the primary side...

IMO, installed as stated, I see it as a violation of 240.21(C). Compliance with 240.219(C)(1) does not relinquish concurrent compliance with (2) though (6). As such, by implication of the requirements under (2) through (6), I believe only a installation complying with subsection (2) is permitted for a primary-protected secondary.

 

[yired29]

Not the way I see it.

240.21 general statement requires compliance with (1) through (6). So by (1) you can't have unprotected secondary conductors without a secondary OCPD. (2) through (6) are subsections which must also be complied with when the primary does protect secondary conductors. So (2) through (6) when applicable to primary-protected secondary conductors are going to be written with stipulation(s) regarding connection directly to a device other than an OCPD.

I agree it could be better written, but it is what it is... and I'm quite certain my interpretation is as intended. But I'm always [stubbornly :roll:] open to correction

This is the way I also see it.

240.21 (C) shall be permitted to be connected to a transformer secondary, without overcurrent protection at the secondary

This is permission to have protection at a location other than where the secondary conductors receive their supply.

 

[david luchini]

240.21 general statement requires compliance with (1) through (6). So by (1) you can't have unprotected secondary conductors without a secondary OCPD. (2) through (6) are subsections which must also be complied with when the primary does protect secondary conductors. So (2) through (6) when applicable to primary-protected secondary conductors are going to be written with stipulation(s) regarding connection directly to a device other than an OCPD.

I understand your point, but I don't see 240.21(C) as requiring compliance with all of the sections (C)(1) thru (C)(6). If I comply with (C)(2) for conductors not over 10ft long, I don't also have to comply with (3), (4), (5) or (6), so why (1)?

240.21(C)(1) PERMITS protection of secondary conductors by the primary OCPD only for certain type of transformers. It does not permit it for a delta-wye transformer, so to my mind 240.21(C)(1) if I have a delta-wye transformer, I won't be applying (C)(1) and MUST apply one of the sections (C)(2) thru (C)(6), depending on my application.

So applying (C)(2), I don't need an OCPD where the secondary conductors receive their supply (at the xfmr). And where the conductors are not longer than 10ft, and the ampacity is not less than the rating of the OCPD at the termination of the secondary conductors OR not less than the rating of the DEVICE supplied by the secondary conductors (the receptacle, in my example) the conductors can land either at an OCPD or a device.

It is interesting to compare the requirements of (C)(2) for 10ft conductors, which allows termination at an OCPD or DEVICE, to (C)(6) for 25 ft conductors, which requires termination at an OCPD (single circuit breaker or set of fuses.)

 

[david luchini]

I have 1125.KVA isolated transformer 480V-480V, 3-PH that is protected by 90A fuse in 100A fused disconnect switch on the primary side. I don't have protection on the secondary but the secondary conductors are rated at 95A (#4 at 90C). The secondary conductors have 60ft to feed the panel. Does it violate tap rule 240.21(C)? Or can I use 450.3 for primary protection only and still comply with the code? The reason I'm using 112.5KVA is because the equipment comes in later after the installation is done and the maximum electrical load is 84A on the equipment. My interpretation of the code is the secondary conductors are protected by 90A fuse on the primary side of transformer but I'm not sure if I have to comply with tap rule since the ratio of primary-to-secondary is 1.0. Please help. Thank you.

You would be fine using the 90A primary OCPD to protect the secondary conductors on your 3Ph, delta-delta transformer with a one-to-one voltage ratio, using section 240.21(C)(1). However, the #4's have an ampacity of only 85, at 75 deg C. I don't believe you can use the 90 deg ampacity per 110.14, unless the equipment is listed and identified for such use.

So you may be violating 240.21(C)(1) by using a conductor which is too small on the secondary.

 

[Smart $]

I understand your point, but I don't see 240.21(C) as requiring compliance with all of the sections (C)(1) thru (C)(6). If I comply with (C)(2) for conductors not over 10ft long, I don't also have to comply with (3), (4), (5) or (6), so why (1)?

240.21(C)(1) PERMITS protection of secondary conductors by the primary OCPD only for certain type of transformers. It does not permit it for a delta-wye transformer, so to my mind 240.21(C)(1) if I have a delta-wye transformer, I won't be applying (C)(1) and MUST apply one of the sections (C)(2) thru (C)(6), depending on my application.

So applying (C)(2), I don't need an OCPD where the secondary conductors receive their supply (at the xfmr). And where the conductors are not longer than 10ft, and the ampacity is not less than the rating of the OCPD at the termination of the secondary conductors OR not less than the rating of the DEVICE supplied by the secondary conductors (the receptacle, in my example) the conductors can land either at an OCPD or a device.

It is interesting to compare the requirements of (C)(2) for 10ft conductors, which allows termination at an OCPD or DEVICE, to (C)(6) for 25 ft conductors, which requires termination at an OCPD (single circuit breaker or set of fuses.)

Once under 240.21(C), you have to comply with (1) through (6) per the general statement.

(1) is for transformer secondary permitted to be protected by the primary OCPD. So let's say this is the case for the time being. Now you still have to comply with (2) through (6). We'll skip (2) for now.

(3) mentions only overcurrent devices, and not device or load, so you would not be able to have only primary protection even in an industrial environment.

Both (4) and (6) specifically require secondary conductors terminate [load end] at a single OCPD.

With (5) you are excepted to 240.21(B)(3) for feeder tapped transformer. Under 240.21(B)(3)(5) the secondary conductors must terminate [load end] in a single OCPD.

Getting back to (2), we see that other than (1) it is the only other condition of the six which does not stipulate a single OCPD at the load end of the secondary conductors... and in permitting such, (2) was written to specifally allow termination to a [load-type] device or an OCPD.

In summary so far, to have a compliant installation where the secondary conductor are protected only by the primaty OCPD, conditions of 240.21(C)(1) & (2) must be met. The requirements of (3) through (6) are rendered moot by exclusionary conditions. However, I must say IMO the structuring and wording could be better.

Now, when we look at requirement (2) again, but in the case where secondary conductors are not protected by the primary OCP, we cannot connect directly to a load-type device without first having an OCP device in line because the general statement of 240.21(C) states only under the specified conditions of (1) through (6) are the secondary conductors permitted to not be protected with an OCPD at the supply end. Since (1) is exclusionary, under any of the remaining conditions there must be an OCPD at the load end.

 

[david luchini]

Getting back to (2), we see that other than (1) it is the only other condition of the six which does not stipulate a single OCPD at the load end of the secondary conductors... and in permitting such, (2) was written to specifally allow termination to a [load-type] device or an OCPD.

I guess we'll have to agree to disagree. The code does not say you can terminate to a "load-type" device, it says a device. A device is a unit of an electrical system that carries or controls electric energy as its principal function. A device is not required to have any type of internal OCPD. A receptacle is a device.

If the code intended all secondary conductors to terminate at an OCPD, except where they permit protection by the primary OCPD, they wouldn't have included the language of terminating on a device in (C)(2). 240.21(C)(3) thru (C)(6) ALL require the secondaries to terminate on an OCPD, but (C)(2) does not.

Once under 240.21(C), you have to comply with (1) through (6) per the general statement.

Yes, and my example complies with (C)(2) by virtue of terminating on a DEVICE. You cannot be expected to comply with ALL of the requirements of (1) through (6), but must apply (1) through (6) separately. For instance, if I am using section (2) and must also comply with (1), then why must I not also comply with (6)? If my secondary conductors are less than 10 ft long, then they are also less than 25 ft long. So if I must comply with (1) thru (6), by your reasoning, I'd have to apply (1), (2) and (6) to any indoor secondary conductors that are less than 10 ft long. I don't think that is what the code intends.

 

[RB1]

I agree with David. Prior to the 2008 Code it would have been feasible to have the bus of a power panel supplied from a ten foot secondary conductor without overcurrent protection at the secondary of the transformer. That is why there is a FPN referencing 408.36 located below 240.21(C)(2). The changes to Article 408 in the 2008 Code really make this a moot point, but it doesn't have anything to do with the protection of the secondary conductor, it has to do with the protection of the panelboard bus.

SMART$ I think you are misreading the code. 240.21(C) "specifies" six conditions where the overcurrent protection is permitted to be located other than where the secondary conductor receives its supply. If you remember, prior to the 1993 Code these rules were separate exceptions that applied both to feeders and secondary conductors. Subparagraphs (2) through (6) stand alone based on the conditions specified in that paragraph. Just my opinion.

 

[Smart $]

...

SMART$ I think you are misreading the code. 240.21(C) "specifies" six conditions where the overcurrent protection is permitted to be located other than where the secondary conductor receives its supply. If you remember, prior to the 1993 Code these rules were separate exceptions that applied both to feeders and secondary conductors. Subparagraphs (2) through (6) stand alone based on the conditions specified in that paragraph. Just my opinion.

Believe me, I would like to think so. But the wording doesn't support that conclusion.

The general statement in 240.21(C) says, "A set of conductors feeding a single load, or 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 (C)(6)."

So unless each of the six requirements excludes itself from consideration, it applies. In the case of a (1) installation, (2) does not exclude itself from consideration and the other four do in that they all require an OCPD at the load end of the conductors.

As I said earlier, it could be structured and worded better.

 

[david luchini]

The general statement in 240.21(C) says, "A set of conductors feeding a single load, or 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 (C)(6)."

Yes, and my example has a "set of conductors" "connect to a transformer secondary" "without overcurrent protection at the secondary" "as specified in 240.21(C)(2)." By the plain language of the code, that is acceptable.

Nowhere does the general statement in 240.21(C) say that the secondary conductors MUST be protected by an OCPD. It says they are permitted to be connected WITHOUT an OCPD.

If the secondary conductors are "not considered to be protected" by the primary OCPD (as in (C)(1)) then that is fine. They are considered to be protected by meeting all of the requirements of (C)(2) parts (1) a & b, part 2, part 3 and part 4.

 

[M. D.]

I agree....

SMART$ I think you are misreading the code. 240.21(C) "specifies" six conditions where the overcurrent protection is permitted to be located other than where the secondary conductor receives its supply. If you remember, prior to the 1993 Code these rules were separate exceptions that applied both to feeders and secondary conductors. Subparagraphs (2) through (6) stand alone based on the conditions specified in that paragraph. Just my opinion.

 

[Smart $]

Yes, and my example has a "set of conductors" "connect to a transformer secondary" "without overcurrent protection at the secondary" "as specified in 240.21(C)(2)." By the plain language of the code, that is acceptable.

Just to confirm, your example is secondary [tap] conductors with a receptacle connected on the load end. The secondary configuration is one which does not qualify for primary OCPD protecting secondary conductors. Correct?

Nowhere does the general statement in 240.21(C) say that the secondary conductors MUST be protected by an OCPD. It says they are permitted to be connected WITHOUT an OCPD.

That is correct, but it implies such because it only permits secondary conductors OCPD to be located somewhere other than where they receive their supply. Refer to 240.12 general statement. 240.21(A) through (H) are exceptions to the general statement and establish the conditions and location(s) of the OCPD when not located where they recieve their supply.

If the secondary conductors are "not considered to be protected" by the primary OCPD (as in (C)(1)) then that is fine. They are considered to be protected by meeting all of the requirements of (C)(2) parts (1) a & b, part 2, part 3 and part 4.

Not if they terminate to a device which is not an OCPD. Regardless of 240.21, you must still meet the requirement of...

240.15 Ungrounded Conductors.
(A) Overcurrent Device Required. A fuse or an overcurrent
trip unit of a circuit breaker shall be connected in
series with each ungrounded conductor. A combination of a
current transformer and overcurrent relay shall be considered
equivalent to an overcurrent trip unit.

 

[Smart $]

...
That is correct, but it implies such because it only permits secondary conductors OCPD to be located somewhere other than where they receive their supply. Refer to 240.12 general statement. 240.21(A) through (H) are exceptions to the general statement and establish the conditions and location(s) of the OCPD when not located where they recieve their supply.

Ooops!!!

That was supposed to be 240.21

 

[Volta]

Yes, and my example has a "set of conductors" "connect to a transformer secondary" "without overcurrent protection at the secondary" "as specified in 240.21(C)(2)." By the plain language of the code, that is acceptable.

Nowhere does the general statement in 240.21(C) say that the secondary conductors MUST be protected by an OCPD. It says they are permitted to be connected WITHOUT an OCPD.

If the secondary conductors are "not considered to be protected" by the primary OCPD (as in (C)(1)) then that is fine. They are considered to be protected by meeting all of the requirements of (C)(2) parts (1) a & b, part 2, part 3 and part 4.

Sure, not there, but in the first sentance of 240.21. "Overcurrent protection shall be provided in each ungrounded circuit conductor . . ."

They then go on to specify or allow the locations.

 

[david luchini]

Not if they terminate to a device which is not an OCPD. Regardless of 240.21, you must still meet the requirement of...

Quote:
240.15 Ungrounded Conductors.
(A) Overcurrent Device Required. A fuse or an overcurrent
trip unit of a circuit breaker shall be connected in
series with each ungrounded conductor. A combination of a
current transformer and overcurrent relay shall be considered
equivalent to an overcurrent trip unit.

And how does that apply to 240.21(C)(1)? The secondaries from a transformer that are protected by the primary OCPD do NOT have a fuse or overcurrent trip unit of a circuit breaker connected in series with each ungrounded conductor.