# NEC 450 Transformers - Overcurrent Protection Question



## HARRY304E (Sep 15, 2010)

chevywaldo said:


> For XFMR's 600V or less....
> 
> It appears from article 450 that overcurrent protection is required on "both" the primary and secondary side of transformers.
> 
> ...


Read all of 450.3 in the 2011 NEC.

Welcome to the forum.


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## chevywaldo (Oct 25, 2013)

HARRY304E said:


> Read all of 450.3 in the 2011 NEC.
> 
> Welcome to the forum.


 
I just purchased the 2005 code book on ebay for $5.00 - used. Are you saying that the 2011 NEC codebook has changes in it with regard to Article 450 that earlier versions like 2005 did not have? If that's the case, I just wasted $5 and have to get the 2011 edition.

Please let me know.


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## chevywaldo (Oct 25, 2013)

HARRY304E said:


> Read all of 450.3 in the 2011 NEC.
> 
> Welcome to the forum.


 
can you copy those few pages and email it to me?

[email protected]

thanks.


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## BBQ (Nov 16, 2010)

chevywaldo said:


> I just purchased the 2005 code book on ebay for $5.00 - used. Are you saying that the 2011 NEC codebook has changes in it with regard to Article 450 that earlier versions like 2005 did not have? If that's the case, I just wasted $5 and have to get the 2011 edition.
> 
> Please let me know.


:laughing:

Hire someone that knows what they are doing.


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## HARRY304E (Sep 15, 2010)

chevywaldo said:


> can you copy those few pages and email it to me?
> 
> 
> 
> ...


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## chevywaldo (Oct 25, 2013)

HARRY304E said:


> 450.3 Overcurrent Protection. Overcurrent protection of transformers shall comply with 450.3(A), (B), or (C). As used in this section, the word transformer shall mean a transformer or polyphase bank of two or more single-phase transformers operating as a unit.
> Informational Note No. 1:  See 240.4, 240.21, 240.100, and 240.101 for overcurrent protection of conductors.
> Informational Note No. 2:  Nonlinear loads can increase heat in a transformer without operating its overcurrent protective device.
> (A) Transformers Over 600 Volts, Nominal. Overcurrent protection shall be provided in accordance with Table 450.3(A).
> ...


 
does the 2005 NEC code book include these Article 450 revisions, or were these changes made only in the 2011 edition.


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## bkmichael65 (Mar 25, 2013)

chevywaldo said:


> For XFMR's 600V or less....
> 
> It appears from article 450 that overcurrent protection is required on "both" the primary and secondary side of transformers.
> 
> ...


The problem is your "as far as I'm concerned" code reference. Far too many people citing that one and I have yet to see it in print


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## chevywaldo (Oct 25, 2013)

BBQ said:


> :laughing:
> 
> Hire someone that knows what they are doing.


 
what kind of a stupid response is that? I've been in this business 25 years. If I asked all the local 134 electricians here in Chicago those same questions about article 450, I guarantee less than 10% of them would know the answer - probably less than 5%. That is most likely typical across the country. Don't respond to my posts unless you have something worthwhile to contribute.


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## HARRY304E (Sep 15, 2010)

chevywaldo said:


> does the 2005 NEC code book include these Article 450 revisions, or were these changes made only in the 2011 edition.


Each code cycle there are 1,000's of changes we will be on the 2014 NEC 1 January 2014.


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## bkmichael65 (Mar 25, 2013)

FYI the 2011 NEC is available online. Just google 450.3


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## BBQ (Nov 16, 2010)

chevywaldo said:


> does the 2005 NEC code book include these Article 450 revisions, or were these changes made only in the 2011 edition.


Nothing changed regarding over current protection of transformers. 


What about bonding it? Do you know how to do that?

Do you have a GEC run to the transformer?


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## BBQ (Nov 16, 2010)

chevywaldo said:


> what kind of a stupid response is that? I've been in this business 25 years. If I asked all the local 134 electricians here in Chicago those same questions about article 450, I guarantee less than 10% of them would know the answer - probably less than 5%. That is most likely typical across the country. Don't respond to my posts unless you have something worthwhile to contribute.


It's an appropriate response to someone that thinks $5.00 is to much to spend on a code book.


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## macmikeman (Jan 23, 2007)

BBQ Badgering new users again. 

Instead of jumping on the guy you could have said something like " Hi I'm BBQ. How do you like me so far?"


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## chevywaldo (Oct 25, 2013)

BBQ said:


> It's an appropriate response to someone that thinks $5.00 is to much to spend on a code book.


My question is about code interpretation, it's not regarding one specific application I have, but rather many applications that I and the other guys in the office run into on a regular basis.

The question is: Is both primary and secondary overcurrent protection required for transformers (600V or less), and if so, is this for all applications or only specific applications.

*Here's a perfect example*. Lets say I have a PLC controlling a large HVAC system in a commercial building. The PLC requires 24VAC (lets say 50 VA). I provide a transformer (120/24V) with a rating of 100VA to power the PLC. Do I have to provide overcurrent protection for both primary and secondary sides of the transformer?


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## BBQ (Nov 16, 2010)

macmikeman said:


> BBQ Badgering new users again.
> 
> Instead of jumping on the guy you could have said something like " Hi I'm BBQ. How do you like me so far?"



Mac, why not go find some links to post, the world needs your insightful link drops.


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## 480sparky (Sep 20, 2007)

chevywaldo said:


> I just purchased the 2005 code book on ebay for $5.00 - used. Are you saying that the 2011 NEC codebook has changes in it with regard to Article 450 that earlier versions like 2005 did not have? If that's the case, I just wasted $5 and have to get the 2011 edition.
> 
> Please let me know.



The reason the Code is updated every 3 years is to include hundreds of changes. Changes based on new technology, long-term studies, etc. It's not updated just so everyone can buy a shiny new book.


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## chevywaldo (Oct 25, 2013)

macmikeman said:


> BBQ Badgering new users again.
> 
> Instead of jumping on the guy you could have said something like " Hi I'm BBQ. How do you like me so far?"


BBQ actually seems like a decent and helpful guy. Perhaps I reacted to strongly to his comment.


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## bkmichael65 (Mar 25, 2013)

*Here's a perfect example*. Lets say I have a PLC controlling a large HVAC system in a commercial building. The PLC requires 24VAC (lets say 50 VA). I provide a transformer (120/24V) with a rating of 100VA to power the PLC. Do I have to provide overcurrent protection for both primary and secondary sides of the transformer?[/QUOTE]


Secondary protection is not needed, but I would probably put an inline fuse on the secondary since it's cheaper to replace a fuse than a transformer


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## HARRY304E (Sep 15, 2010)

chevywaldo said:


> BBQ actually seems like a decent and helpful guy. Perhaps I reacted to strongly to his comment.


He needs a good forum beating now and then please feel free to nail him good.:whistling2::laughing:

However he is one of the best when comes to the NEC.


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## BBQ (Nov 16, 2010)

chevywaldo said:


> The question is: Is both primary and secondary overcurrent protection required for transformers (600V or less), and if so, is this for all applications or only specific applications.


Protection of the *transformer* on both sides depends on the application. 

Protection of the *conductors* on both sides is always required and covered in Article 240.




> *Here's a perfect example*. Lets say I have a PLC controlling a large HVAC system in a commercial building. The PLC requires 24VAC (lets say 50 VA). I provide a transformer (120/24V) with a rating of 100VA to power the PLC. Do I have to provide overcurrent protection for both primary and secondary sides of the transformer?



For that transformer installation no secondary side transformer protection is required. 

You may still have to provide protection for the secondary conductors.


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## BBQ (Nov 16, 2010)

HARRY304E said:


> He needs a good forum beating now and then please feel free to nail him good.:whistling2::laughing:


:thumbup:












> However he is one of the best when comes to the NEC.


Thanks


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## KGN742003 (Apr 23, 2012)

chevywaldo said:


> BBQ actually seems like a decent and helpful guy. Perhaps I reacted to strongly to his comment.


BBQ is knowledgeable about the code and installation, he can be quite helpful. Let's not play to fast and loose with the word decent though.:jester:


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## chevywaldo (Oct 25, 2013)

KGN742003 said:


> BBQ is knowledgeable about the code and installation, he can be quite helpful. Let's not play to fast and loose with the word decent though.:jester:


Not my first rodeo. I've been on many forums over the years, most dealing with computers, car restoration, motorcycles, physics, chemistry, etc. It seems whenever a "newbie" makes a post, there is always some "forum cop" that has like 30,000 posts, that has to chime in and makes a remark that sets me off a bit. They usually don't answer the question, but instead provide some kind of comment that is irrelevant to the posted question, as if to say "you're in my house now and you will follow the rules and policies that I have set forth in this forum - because I am a senior member around here" which we all know is ridiculous.  It' all good.


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## Awg-Dawg (Jan 23, 2007)

macmikeman said:


> BBQ Badgering new users again.


 
Did you plan that?:laughing:


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## seabee41 (Dec 21, 2010)

chevywaldo said:


> what kind of a stupid response is that? I've been in this business 25 years. If I asked all the local 134 electricians here in Chicago those same questions about article 450, I guarantee less than 10% of them would know the answer - probably less than 5%. That is most likely typical across the country. Don't respond to my posts unless you have something worthwhile to contribute.


This is not true . Get a Chicago code book at look at article 450 ( page 341) table 18-27-450.3b


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## BBQ (Nov 16, 2010)

Awg-Dawg said:


> Did you plan that?:laughing:


Stop doging me.


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## seabee41 (Dec 21, 2010)

seabee41 said:


> This is not true . Get a Chicago code book at look at article 450 ( page 341) table 18-27-450.3b


Also I suggest if your working in Chicago get a Chicago code book. There are differences between NEC and Chicago


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## SteveBayshore (Apr 7, 2013)

BBQ said:


> Nothing changed regarding over current protection of transformers.
> 
> 
> What about bonding it? Do you know how to do that?
> ...


He said the largest was 500va, not 500kVA, he is talking about CPTs not power transformers.


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## chevywaldo (Oct 25, 2013)

*Still Don't Have a Straight Answer*

I was just at several jobsite and saw control transformers installed with a variety of scenarios with regards to overcurrent protection. This is very confusing. Let's just stick with the NEC (< 600V) - nevermind chicago code for now.

I saw a hot water boiler control panel with a control transformer where only the secondary was fused. The primary (3-phase 208) was NOT fused. It even confirmed it on the wiring diagram. No overcurrent protection on the primary side. I see similar scenarios all the time. 

I also see hundreds of control transformers (typically 120/24V) under 100 VA, installed with NO primary overcurrent protection. I called (2) transformer companies and talked to their tech support people and both of them said they DO NOT provide primary side integral overcurrent protection on the transformers they make. Some modyels they offer are built with "secondary" overcurrent protection (via circuit breaker), but NO primary overcurrent protection. The tech support guys said, it's up to the contractor and the NEC code to determined if and when primary overcurrent protection is required. The way I interpret NEC 450.3 is that Primary overcurrent protection is "always" required for transformers. Yet, when I am on jobsites looking at installed transformers, in most cases there is NO overcurrent protection on the primary side. Why?

So I am back at square one. I have to make a presentation on this subject to our engineering staff and field electricians soon, and I'm trying to get to the bottom of this.

When is Primary overcurrent protection required for transformers and when is Secondary overcurrent protection required for transformers. Similarly, when is it NOT required? Again, were talking <600V, and in my case, small control transformers only (less than 500VA, typically with 24V secondaries)

thanks. :001_huh:


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## wildleg (Apr 12, 2009)

chevywaldo said:


> I was just at several jobsite and saw control transformers installed with a variety of scenarios with regards to overcurrent protection. This is very confusing. Let's just stick with the NEC (< 600V) - nevermind chicago code for now.
> 
> I saw a hot water boiler control panel with a control transformer where only the secondary was fused. The primary (3-phase 208) was NOT fused. It even confirmed it on the wiring diagram. No overcurrent protection on the primary side. I see similar scenarios all the time.
> 
> ...


you need to get up to speed with the code. if you had bothered to read 450 at all you would have found a huge help in the table that has already been referenced (450.3). In addition, if you are dealing with class I or II, you should be reading 725. If you can't afford a codebook and the time to read it, no one here is going to be able to help you. If you want a treatise on the subject, buy one of mike holt's cds on article 450 of the code and it will take you through most of it, but not necessarily your exact scenario. you need to do your homework.

just my 02, take it any way you like


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## don_resqcapt19 (Jul 18, 2010)

chevywaldo said:


> ...
> 
> I saw a hot water boiler control panel with a control transformer where only the secondary was fused. The primary (3-phase 208) was NOT fused. It even confirmed it on the wiring diagram. No overcurrent protection on the primary side. I see similar scenarios all the time. ...


If those transformers were provided and installed by the control panel or equipment manufacturer, the NEC rules do not apply. 

In general, if the control power transformers are field installed, that is not part of manufactured listed equipment, then primary and secondary overcurrent protection will be required per Table 450.3(B). Note that there are conditions in the table that only require primary protection for the transformer.

It is important to understand that the rules in Article 450 only cover the protection of the transformer itself. You also have to apply the rules in Article 240 to the protection of the conductors.


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## don_resqcapt19 (Jul 18, 2010)

SteveBayshore said:


> He said the largest was 500va, not 500kVA, he is talking about CPTs not power transformers.


The rules that require a grounded system are not based on the size of the transformer. If the system is one that is required, by 250.20, to be a grounded system, then there will be some connection to a grounding electrode no matter how small the transformer is. Exception #3 to 250.30(A)(5) permits a grounding method that does not require a grounding electrode conductor.


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## Dennis Alwon (May 9, 2009)

I removed the last few posts. Please lets stop the attacks on each other. If you can't respond without calling someone a name then please don't respond.


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## chevywaldo (Oct 25, 2013)

Dennis Alwon said:


> I removed the last few posts. Please lets stop the attacks on each other. If you can't respond without calling someone a name then please don't respond.


 
agreed. thanks for steppin in - sometimes were like a bunch of kids fighting (sort of like our U.S. Congress) boys will be boys.


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## SteveBayshore (Apr 7, 2013)

don_resqcapt19 said:


> The rules that require a grounded system are not based on the size of the transformer. If the system is one that is required, buy 250.20, to be a grounded system, then there will be some connection to a grounding electrode no matter how small the transformer is. Exception #3 to 250.30(A)(5) permits a grounding method that does not require a grounding electrode conductor.


You would run a #8 GEC (250.66)to a 500Va transformer that has a current rating of 4 amps?
*Your* code reference has an exception about installing GECs for transformers of less than 1000VA. I agree, the secondary has to contain a grounded conductor in most installations, but not a GEC.


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## Speedy Petey (Jan 10, 2007)

seabee41 said:


> *Also I suggest if your working in Chicago get a Chicago code book.* There are differences between NEC and Chicago


I really think this is the best advice you can get. 
Places like Chicago and NYC are in their own little world.


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## seabee41 (Dec 21, 2010)

Speedy Petey said:


> I really think this is the best advice you can get.
> Places like Chicago and NYC are in their own little world.


Based off of NEC and the physical size of the handbook too


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## don_resqcapt19 (Jul 18, 2010)

SteveBayshore said:


> You would run a #8 GEC (250.66)to a 500Va transformer that has a current rating of 4 amps?
> *Your* code reference has an exception about installing GECs for transformers of less than 1000VA. I agree, the secondary has to contain a grounded conductor in most installations, but not a GEC.


Isn't that exactly what I said in my post?????


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## SteveBayshore (Apr 7, 2013)

don_resqcapt19 said:


> Isn't that exactly what I said in my post?????


So we are both arguing the same point that was in my original post. You're not required to install a grounding electrode conductor or bond a transformer of 500 VA, just ground one of the circuit conductors?:thumbsup::thumbsup:


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## BBQ (Nov 16, 2010)

SteveBayshore said:


> *You're not required to install a grounding electrode conductor or bond a transformer of 500 VA*, just ground one of the circuit conductors?


No, that is not what the exception says. It only allows the elimination of the GEC, a bonding jumper is still required. 



> Exception No. 3: A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, *provided the grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Exception No. 3,* and the transformer frame or enclosure is grounded by one of the means specified in 250.134.


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## don_resqcapt19 (Jul 18, 2010)

SteveBayshore said:


> So we are both arguing the same point that was in my original post. You're not required to install a grounding electrode conductor or bond a transformer of 500 VA, just ground one of the circuit conductors?:thumbsup::thumbsup:


How do you ground one of the circuit conductors without bonding it?


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## SteveBayshore (Apr 7, 2013)

don_resqcapt19 said:


> How do you ground one of the circuit conductors without bonding it?


Definition of bonding is different than definition of grounding in article 100. Two different animals in my opinion.


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## don_resqcapt19 (Jul 18, 2010)

SteveBayshore said:


> Definition of bonding is different than definition of grounding in article 100. Two different animals in my opinion.


The conductor that is used to connect one side of the transformer to the "conducting body that extends the ground connection" is a bonding conductor. You cannot create grounded system without using either a grounding electrode conductor or a bonding conductor.


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## BBQ (Nov 16, 2010)

SteveBayshore said:


> Definition of bonding is different than definition of grounding in article 100. Two different animals in my opinion.


Steve, They are different and the exception you are hanging your hat on in this thread specifically says that _bonding_ is still required.


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## RIVETER (Sep 26, 2009)

chevywaldo said:


> For XFMR's 600V or less....
> 
> It appears from article 450 that overcurrent protection is required on "both" the primary and secondary side of transformers.
> 
> ...


Sometimes on this forum you have to just get "REAL"... and that means HONEST with us and yourself. If you only have a 1987 code book...you don't really care.


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