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 Post subject: NEC 700.27 Breaker Coordination
PostPosted: Sat Mar 06, 2010 7:30 am 
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A recent coordination/SC/AF study we had performed by an EE has recommendations to modify an existing (15 y/o) emergency generator distribution system based on a change in the 2008 NEC 700.27

"Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices."

This practice of reducing the emergency feeder and OCPD to an ATS for the elevators is very common in my area and this is twice now I have seen this recommendation. Unfortunately, with the existing circuit breakers we are not able to achieve coordination without replacing circuit breakers at a large expense to the customer.

I would not think this would be a requirement for the customer to upgrade to meet the current 2008 code. I realize it would be a good recommendation because the change was made for a reason but I need to validate if it would be a requirement?

Thanks for your help.


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PostPosted: Sun Mar 07, 2010 5:35 pm 
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First, the NEC is not a legal building requirement. Each State has to adopt the NEC before it becomes State building code - then its law. Most States, unless it is something that is a known risk, does NOT require facilities - built to the prevailing code at the time of construction - to upgrade every time the NEC changes. This is knwon as 'grandfathering'. So check to see if what you have was legal for the year it was installed, if it was, then check if there is a mandate to upgrade, if not, then its legal.


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PostPosted: Mon Mar 08, 2010 3:14 pm 
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will40 wrote:
A recent coordination/SC/AF study we had performed by an EE has recommendations to modify an existing (15 y/o) emergency generator distribution system based on a change in the 2008 NEC 700.27

"Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices."

This practice of reducing the emergency feeder and OCPD to an ATS for the elevators is very common in my area and this is twice now I have seen this recommendation. Unfortunately, with the existing circuit breakers we are not able to achieve coordination without replacing circuit breakers at a large expense to the customer.

I would not think this would be a requirement for the customer to upgrade to meet the current 2008 code. I realize it would be a good recommendation because the change was made for a reason but I need to validate if it would be a requirement?

Thanks for your help.


These articles are creating quite a stir. My understanding is the required coordination requirement was introduced by a major fuse company. Same thing with the elevator coordination requirement.

Interesting.... it turns out you can not easily completely coordinate circuit breakers but in most cases you can completely coordinate fuses. :eek:

Somewhere else in this forum I mentioned I was interviews a few years ago (I think 2007) for an article in EC & M magazine about this issue. I was pretty direct about the implications of the article and why it was likely written.

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PostPosted: Mon Mar 08, 2010 5:37 pm 
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Thanks guys, then I found the attached that mentions it was first introduced in the 1993 NEC.

And yes, the major fuse company :)

Guess I have some homework to do.


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