SELECTIVE COORDINATION - EQUIPMENT BRANCH

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PE (always learning)

PE (always learning)

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Hey everyone,

I know I've been asking a lot of questions today, so thank you everyone for the responses. I am working on a power systems study for an assisted living facility and the standby generator feeds an ATS switch that feeds a main lug only switchboard that is supporting roof top and DOAS units. The ATS switch is labeled equipment branch. The breaker that feeds the automatic transfer switch is rated for 600 amps and it does not coordinate with a 450 amp breaker located on the main lug only switch board down stream. This was a bad design on the engineers part. My question is am I required to selectively coordinate loads on the equipment branch or is selective coordination only required for life safety loads?

Best Regards
 
I do not do hospital work so I cannot answer your question but as you are finding it is quite unlikely you will coordinate a 600af breaker with a 600af breaker. If you can get it coordinated to 0.1s maybe just note it to engineer as that me be acceptable (doubtful you can). If you can’t, strongly note to engineer in submittal and let him worry about it.
 
One other thing to note is what is your SCA? I don’t have a one-line but I assume you want coordinated both when on normal power and on standby/emergency power.

You only need to coordinate to the higher short circuit availability. If it is 10 kA for example, you can stop looking at the TCC to the right of 10 kA. Most software does this automatically but you should verify.
 
My available short circuit current on the normal side is 24,571 amps at the main distribution panel labeled MDP-1. I have attached the TCC for your viewing. The two breakers that I had issue with are labeled "MDP-1 (480V): ATS-EQ" (600A breaker) and "DP1: RP1" (450A breaker). As you can see I was able to coordinate the breakers in the instantaneous region, but they will obviously not coordinate in the long time region. This seems like bad design on the engineers part. I'll just note it on the final study as you said and the manufacturer and the engineer can try to come to an agreement.
 

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The Equipment Branch is considered part of the Essential Electrical System.

517.31 Requirements for the Essential Electrical System.
517.31(G), in which coordination is required only for faults that exceed 0.1 second in duration.

Be sure you check manufacturer's tables if they are of the same manufacturer in case they are selective but not necessarily reflected that way in the TCC, but from a tested combination.
I can't see due to resolution but here is a generic Siemens table https://www.downloads.siemens.com/download-center/download?BTLV_41386
But almost impossible to coordinate trips that close. You would need 2 really good LSI adjustable trip units..
 
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ron said:
The Equipment Branch is considered part of the Essential Electrical System.

517.31 Requirements for the Essential Electrical System.
517.31(G), in which coordination is required only for faults that exceed 0.1 second in duration.

Be sure you check manufacturer's tables if they are of the same manufacturer in case they are selective but not necessarily reflected that way in the TCC, but from a tested combination.
I can't see due to resolution but here is a generic Siemens table https://www.downloads.siemens.com/download-center/download?BTLV_41386
But almost impossible to coordinate trips that close. You would need 2 really good LSI adjustable trip units..
Click to expand...

517.31(G) is for hospitals. If the facility falls under 517.40, I don't see any coordination requirements mentioned in 517.40 through 517.44
 
So even though there are no requirements for coordination for nursing homes under 517.40, I think I'm still required to abide by NEC 701.27 and NEC 700.28. NEC 701.27 and NEC 700.28 says "Legally required standby and Emergency system(s) overcurrent devices shall be selectively coordinated with all supply-side overcurrent protective devices. Selective coordination shall be selected by a licensed professional engineer or other qualified persons engaged primarily in the design, installation, or maintenance of electrical systems."
 
I'm pretty sure that selective coordination is not required for the normal source.
 
engineerintraining12 said:
So even though there are no requirements for coordination for nursing homes under 517.40, I think I'm still required to abide by NEC 701.27 and NEC 700.28. NEC 701.27 and NEC 700.28 says "Legally required standby and Emergency system(s) overcurrent devices shall be selectively coordinated with all supply-side overcurrent protective devices. Selective coordination shall be selected by a licensed professional engineer or other qualified persons engaged primarily in the design, installation, or maintenance of electrical systems."
Click to expand...

I am inclined to agree with you. And 701.27 would require selective coordination not just coordination.
 
packersparky said:
700.28 and 700.28 states "all supply side overcurrent devices." I believe that the overcurrent devices of the 701/700 systems have to selectively coordinate with the normal system overcurrent devices.

https://iaeimagazine.org/magazine/2...oordination-what-the-inspector-needs-to-know/
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From the article referenced


For the emergency system, we must assure all overcurrent protective devices from the load to the alternate source are selectively coordinated. However, we must also assure the emergency system overcurrent protective devices on the load side of the automatic transfer switches are also selectively coordinated with the normal source overcurrent protective devices. However, the overcurrent protective devices ahead of the automatic transfer switch on the normal side are not required to be selectively coordinated. Figure 3 explains where selective coordination is required, and where it is not required for emergency systems.
 
dkidd said:
From the article referenced


For the emergency system, we must assure all overcurrent protective devices from the load to the alternate source are selectively coordinated. However, we must also assure the emergency system overcurrent protective devices on the load side of the automatic transfer switches are also selectively coordinated with the normal source overcurrent protective devices. However, the overcurrent protective devices ahead of the automatic transfer switch on the normal side are not required to be selectively coordinated. Figure 3 explains where selective coordination is required, and where it is not required for emergency systems.
Click to expand...

The emergency OCPD has to be selectively coordinated with the upstream OCPD in the normal system. Figure 3 shows that OCPD "E" has to be selectively coordinated with OCPD's "A", "B", "C", and "D". But OCPD's "A" and "B" do not have to be selectively coordinated with each other. Maybe we are saying the same thing.
 
packersparky said:
I am inclined to agree with you. And 701.27 would require selective coordination not just coordination.
Click to expand...

NEC 517.26 specifically requires the life safety system to meet the requirements of ARticle 700, except as amended by 517.

NFPA 99 says something similar:

6.4.2.2.1.5 For the purposes of this code, theprovisions for emergency systems in Article 700 of NFPA70, National ElectricalCode, shall be applied only to the life safetybranch.
6.4.2.2.1.6 The following portions of Article 700 ofNFPA70 shall be amended as follows:(A)  700.4 shallnot apply.
(B)  700.10(D)(1) through (3) shall not apply.
(C)  700.17Branch Circuits for Emergency Lighting. Branch circuits that supplyemergency lighting shall be installed to provide service from asource complying with 700.12 when the normal supply for lighting isinterrupted or where single circuits supply luminaires containingsecondary batteries.
(D)  700.28shall not apply.

But I don't see anything that requires the equipment branch to meet the requirements of any other article including 700,701,702, or 708.

I would agree it would be good design to have coordination, but I'm not sure I agree there is a code requirement for it.




​
 
steve66 said:
NEC 517.26 specifically requires the life safety system to meet the requirements of ARticle 700, except as amended by 517.

NFPA 99 says something similar:

6.4.2.2.1.5 For the purposes of this code, theprovisions for emergency systems in Article 700 of NFPA70, National ElectricalCode, shall be applied only to the life safetybranch.
6.4.2.2.1.6 The following portions of Article 700 ofNFPA70 shall be amended as follows:(A)  700.4 shallnot apply.
(B)  700.10(D)(1) through (3) shall not apply.
(C)  700.17Branch Circuits for Emergency Lighting. Branch circuits that supplyemergency lighting shall be installed to provide service from asource complying with 700.12 when the normal supply for lighting isinterrupted or where single circuits supply luminaires containingsecondary batteries.
(D)  700.28shall not apply.

But I don't see anything that requires the equipment branch to meet the requirements of any other article including 700,701,702, or 708.

I would agree it would be good design to have coordination, but I'm not sure I agree there is a code requirement for it.




​
Click to expand...

I guess it comes down to: Is the equipment branch a legally required system? 517.44 seems to say it is.
 
I think it's worth noting that the NEC says "Selective coordination shall be selected by a licensed professional engineer or other qualified persons engaged primarily in the design, installation, or maintenance of electrical systems. Leading me to believe that it is up to interpretation as well.
 
I’m glad ron pointed out checking the mfr’s charts. Always a good idea if both breakers are by same mfr. I don’t think it will help with coordinating your MDP1 & DP1 in this case though. This generally only held when overlap on TCC is in instantaneous region in my experience. Certainly worth the check still though.



dkidd said:
I'm pretty sure that selective coordination is not required for the normal source.
Click to expand...
As for this I do believe code requires the coordination of both sources. Makes it tough but makes sense in my opinion. Think about a pumping station with 2 pumps and a main circuit breaker. Short circuit on load side of one of the pump occurs and due to miscoordiabtion both main and shorted pump breakers trip. After ATS transfer, you only have one pump available.Not great example but you can postulate others where miscoordination on normal brings bad scenarios even when legally required standby or emergency source is fully coordinated.

I think it is funny code allows .1s for healthcare but not article 701 legally required standby. I’ll be honest NEC is due for a rip on this IMO. Arc flash and coordination are often in direct contradiction and allowing >40 cal/cm2 to try and meet ‘selectively coordinated’ is a bad trade off.
 
smoothops10 said:
I’m glad ron pointed out checking the mfr’s charts. Always a good idea if both breakers are by same mfr. I don’t think it will help with coordinating your MDP1 & DP1 in this case though. This generally only held when overlap on TCC is in instantaneous region in my experience. Certainly worth the check still though.

As for this I do believe code requires the coordination of both sources. Makes it tough but makes sense in my opinion. Think about a pumping station with 2 pumps and a main circuit breaker. Short circuit on load side of one of the pump occurs and due to miscoordiabtion both main and shorted pump breakers trip. After ATS transfer, you only have one pump available.Not great example but you can postulate others where miscoordination on normal brings bad scenarios even when legally required standby or emergency source is fully coordinated.

I think it is funny code allows .1s for healthcare but not article 701 legally required standby. I’ll be honest NEC is due for a rip on this IMO. Arc flash and coordination are often in direct contradiction and allowing >40 cal/cm2 to try and meet ‘selectively coordinated’ is a bad trade off.
Click to expand...

If you keep things the way they are, then it is a big tug o war between selective coordination and arcflash protection!
But things are not fixed in stone! if devices can't be selectively coordinated at the existing fault levels, perhaps they would if you tweaked the setup and lower the available fault in the point of installation. Perhaps you have the luxury of raising the trip settings of the breakers that you have! Or maybe you can change the elements/devices so you can achieve both goals. Ever wondered why fuses are selectively good when used with others fuses also? JMHO.
 
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