Does the NEC mandate the use of ATSs?

[mbrooke]

Looking at article 517 and article 700, the NEC keep referring to stand alone automatic transfer switches but make no mention of automatic circuit breakers as part of auto-throw over. Does that mean switch-gear with motorized breakers and PLCs is not allowed for these applications? This seems to go against the NEC's intent of not being a design manual. But then again I'm wondering if the code making panels know something?

 

[hillbilly1]

Put in plenty of them, they are electrically and mechanically interlocked.

 

[mbrooke]

Put in plenty of them, they are electrically and mechanically interlocked.

Right, but does code allow them for life safety, critical and legally required?

 

[romex jockey]

maybe in art 705 MBrooke?

~RJ~

 

[paulengr]

Nothing wrong per se. It’s just that for backup power applications ATSs are a lot more common due to the fact that inherently there is just one double throw switching device instead of two single throw devices. With breakers you are effectively building double ended switchgear whether or not that is the intent.

I would caution you however about the thinking that switchgear is just like any other control system and that generic off the shelf PLCs and control equipment is perfectly acceptable to the task. From experience it’s not. There are a lot of issues to be concerned with in switchgear. Caterpillar has built a lot of switchgear over the years using Schneider or Eaton breakers and GE or AB PLCs. Cat uses their reputation and buying power with the genset side of things to sell this stuff to larger municipalities, prisons, and federal facilities. Durham, Raleigh, and several state facilities in North Carolina have them so I have quite a bit of experience with them. In terms of reliability there are a lot fewer problems with ASCO ATSs, or switchgear using multifunction relays. These solutions are both purpose built for the application. You just don’t have “the usual” PLC problems, even if they buy an embedded/OEM style PLC and repackage it as a generic looking breaker control.

DCS control is popular with larger power plants. Or more specifically they typically have a layer of multifunction relays that handle faults and the DCS is little more than an outrageously overpriced HMI. The multifunction relays came about from the evolution from induction disc to today’s microprocessor units.

Don’t get me wrong here. You can certainly write your own PLC program to do everything inherent in say an SEL 751. But then you need to do type testing...throwing thousands of automated function tests generated by software at it to test every possible outcome plus analysis of the results. There is specialized relay testing gear specifically for this. But you won’t save any money doing it and it’s so much easier to just accept an off the shelf solution.

This is like burner controls. Most large burners have two levels of controls. The lowest level is almost invariably either a Honeywell or Fireye branded burner safety relay. It handles the actual burner lighting process and actively monitors everything at all times. The PLC sits on top of this and controls the overall process, adjusting heat output, and making pretty operator displays.

So just saying...go with the road well traveled here.

 

[mbrooke]

maybe in art 705 MBrooke?

~RJ~

Anything specific you have in mind?

 

[mbrooke]

Nothing wrong per se. It’s just that for backup power applications ATSs are a lot more common due to the fact that inherently there is just one double throw switching device instead of two single throw devices. With breakers you are effectively building double ended switchgear whether or not that is the intent.

Understood.

I would caution you however about the thinking that switchgear is just like any other control system and that generic off the shelf PLCs and control equipment is perfectly acceptable to the task. From experience it’s not. There are a lot of issues to be concerned with in switchgear. Caterpillar has built a lot of switchgear over the years using Schneider or Eaton breakers and GE or AB PLCs. Cat uses their reputation and buying power with the genset side of things to sell this stuff to larger municipalities, prisons, and federal facilities. Durham, Raleigh, and several state facilities in North Carolina have them so I have quite a bit of experience with them. In terms of reliability there are a lot fewer problems with ASCO ATSs, or switchgear using multifunction relays. These solutions are both purpose built for the application. You just don’t have “the usual” PLC problems, even if they buy an embedded/OEM style PLC and repackage it as a generic looking breaker control.

DCS control is popular with larger power plants. Or more specifically they typically have a layer of multifunction relays that handle faults and the DCS is little more than an outrageously overpriced HMI. The multifunction relays came about from the evolution from induction disc to today’s microprocessor units.

Don’t get me wrong here. You can certainly write your own PLC program to do everything inherent in say an SEL 751. But then you need to do type testing...throwing thousands of automated function tests generated by software at it to test every possible outcome plus analysis of the results. There is specialized relay testing gear specifically for this. But you won’t save any money doing it and it’s so much easier to just accept an off the shelf solution.

This is like burner controls. Most large burners have two levels of controls. The lowest level is almost invariably either a Honeywell or Fireye branded burner safety relay. It handles the actual burner lighting process and actively monitors everything at all times. The PLC sits on top of this and controls the overall process, adjusting heat output, and making pretty operator displays.

So just saying...go with the road well traveled here.

This is hands down one of the best posts I've read on here!

If you had the option, would you go with switchgear or a stand alone ATS for larger systems?

 

[romex jockey]

Anything specific you have in mind?

i'm bouncing around , 445, 702, 250......i'm sure someone will zero it in here soon.....~RJ~

 

[mbrooke]

i'm bouncing around , 445, 702, 250......i'm sure someone will zero it in here soon.....~RJ~

I'm sure you're onto something, but I don't have that level of brain power like the other guys here.

 

[don_resqcapt19]

Looking at article 517 and article 700, the NEC keep referring to stand alone automatic transfer switches but make no mention of automatic circuit breakers as part of auto-throw over. Does that mean switch-gear with motorized breakers and PLCs is not allowed for these applications? This seems to go against the NEC's intent of not being a design manual. But then again I'm wondering if the code making panels know something?

700.5 Transfer Equipment. (A) General. Transfer equipment shall be automatic, listed, and marked for emergency use, ...

701.5 Transfer Equipment. (A) General. Transfer equipment shall be automatic, listed, and marked for emergency system or legally required standby use,

If the installation is covered by Articles 700 or 701, the transfer switch must be automatic and listed for the purpose. Note that all of the rules in 700 and 701 do not always apply to Articel 517. You have to dig into that article to see what applies.

The switchgear with motorized breakers and PLC control would only be permitted if that combination is listed as an emergency or legally required transfer switch.

 

[hillbilly1]

All of those type I have put in were for optional standby systems. Can’t think of one that was used as an emergency system. Can’t remember if it was listed for such. Fire pumps always had their own downstream, but they usually were tapped ahead at the transformer, and directly off the generator ahead of its main.

 

[mbrooke]

700.5 Transfer Equipment. (A) General. Transfer equipment shall be automatic, listed, and marked for emergency use, ...

701.5 Transfer Equipment. (A) General. Transfer equipment shall be automatic, listed, and marked for emergency system or legally required standby use,

If the installation is covered by Articles 700 or 701, the transfer switch must be automatic and listed for the purpose. Note that all of the rules in 700 and 701 do not always apply to Articel 517. You have to dig into that article to see what applies.

The switchgear with motorized breakers and PLC control would only be permitted if that combination is listed as an emergency or legally required transfer switch.

Alright. The pictures of single pole double throw ATSs is throwing me. Also the wording. But ultimately the definition is what matters.

 

[paulengr]

Understood.




This is hands down one of the best posts I've read on here!

If you had the option, would you go with switchgear or a stand alone ATS for larger systems?

Switchgear hands down. But with ASCO you pretty much start with the application...pick what you want it to do. You buy the parts they tell you and wire it up and program it the way they tell you. Simple. With switchgear it is more generic and you can make it do more but it’s less idiot proof. At least the built-in programming does all the basics though which is where PLC designs tend to fail.

I mean programming 50/51 overcurrent relay code is not trivially easy. It’s built into a relay and ASCO modules. Operating on 125 VDC or even diesel battery voltages is built into ASCO and relays. It requires special options with PLCs that are generally 24 VDC or 120 VAC. How often does a PLC issue come down to a power supply?

 

[paulengr]

700.5 Transfer Equipment. (A) General. Transfer equipment shall be automatic, listed, and marked for emergency use, ...

701.5 Transfer Equipment. (A) General. Transfer equipment shall be automatic, listed, and marked for emergency system or legally required standby use,

If the installation is covered by Articles 700 or 701, the transfer switch must be automatic and listed for the purpose. Note that all of the rules in 700 and 701 do not always apply to Articel 517. You have to dig into that article to see what applies.

The switchgear with motorized breakers and PLC control would only be permitted if that combination is listed as an emergency or legally required transfer switch.

Very few installations are legally required. They are virtually all nice to have, best effort, etc. NECcis articulating NFPA 110. A legally required standby system has a lot more requirements. If it’s not legally required you have a lot more options. Even a full blown cogen or the station bus in a power plant doesn’t require this. Very few backup or even online systems are legally required.

 

[mbrooke]

Switchgear hands down. But with ASCO you pretty much start with the application...pick what you want it to do. You buy the parts they tell you and wire it up and program it the way they tell you. Simple. With switchgear it is more generic and you can make it do more but it’s less idiot proof. At least the built-in programming does all the basics though which is where PLC designs tend to fail.

I mean programming 50/51 overcurrent relay code is not trivially easy. It’s built into a relay and ASCO modules. Operating on 125 VDC or even diesel battery voltages is built into ASCO and relays. It requires special options with PLCs that are generally 24 VDC or 120 VAC. How often does a PLC issue come down to a power supply?

Why switchgear? A stand alone ATS is just so much simpler, especially when you can do multiple smaller units.

Also, what about Russel Electric?

 

[don_resqcapt19]

Very few installations are legally required. They are virtually all nice to have, best effort, etc. NECcis articulating NFPA 110. A legally required standby system has a lot more requirements. If it’s not legally required you have a lot more options. Even a full blown cogen or the station bus in a power plant doesn’t require this. Very few backup or even online systems are legally required.

The original question was about Article 517 and 700 applications. Most of the loads on standby power for a 517 installation are emergency loads or legally required standby loads. All of the loads covers by Article 700 are emergency loads. The transfer equipment for those two articles is required to be specifically listed for those purposes.

 

[mbrooke]

The original question was about Article 517 and 700 applications. Most of the loads on standby power for a 517 installation are emergency loads or legally required standby loads. All of the loads covers by Article 700 are emergency loads. The transfer equipment for those two articles is required to be specifically listed for those purposes.

Its ok, he can ask Not taking sides or anything. Just curious about all aspects of the NEC even those that may slightly "side track" a thread.

 

[garbo]

Looking at article 517 and article 700, the NEC keep referring to stand alone automatic transfer switches but make no mention of automatic circuit breakers as part of auto-throw over. Does that mean switch-gear with motorized breakers and PLCs is not allowed for these applications? This seems to go against the NEC's intent of not being a design manual. But then again I'm wondering if the code making panels know something?

I retired from a large hospital/research/ambulatory care center that had well over 75 ATS switches. They liked throwing money away and the 25 newest ones were either rated 1200 or 1600 amps @ 48p volts. Could not understand how or why you would feed 6 or 8 1600 amp ATS switches from a 3000 or 4000 amp normal or emergency switchgear. Best thing in hospital's is they are now installing closed transition ATS switches. All the ones we had had a bypass function so tech could perform yearly PM and some testing on them during normal hours. Hospitals always or should have dual incoming primary service. That along with numerous generators provided dependable power. I was the only one who argued with clueless engineers who insisted on using NO ( Normal open contacts ) to turn in generators when a ATS lost normal power. I wanted NC contact so if a wire broke between the 10th floor generator and lowest level basement ATS generator would come on. They said it could waste fuel if it was only a control manfunction and I said rat her waste some deisel or natural gas fuel then a patients life in the OR. Guess you can not fix stupidity.

 

[mbrooke]

I retired from a large hospital/research/ambulatory care center that had well over 75 ATS switches. They liked throwing money away and the 25 newest ones were either rated 1200 or 1600 amps @ 48p volts. Could not understand how or why you would feed 6 or 8 1600 amp ATS switches from a 3000 or 4000 amp normal or emergency switchgear. Best thing in hospital's is they are now installing closed transition ATS switches. All the ones we had had a bypass function so tech could perform yearly PM and some testing on them during normal hours. Hospitals always or should have dual incoming primary service. That along with numerous generators provided dependable power. I was the only one who argued with clueless engineers who insisted on using NO ( Normal open contacts ) to turn in generators when a ATS lost normal power. I wanted NC contact so if a wire broke between the 10th floor generator and lowest level basement ATS generator would come on. They said it could waste fuel if it was only a control manfunction and I said rat her waste some deisel or natural gas fuel then a patients life in the OR. Guess you can not fix stupidity.

75 ATS? I can assure you I've seen a few hospital prints with that same amount if not more. One has close to 86, each being rated 100-225 amps in size.

Me personally I would do at least two contacts- two red wires that start the engine when shorted and two yellow wires that start the gen when opened. Each independent of the other. On top of that I've even drawn up a third pair- two blue wires that must close for the engine to shut down.

 

[m sleem]

700.5 Transfer Equipment. (A) General. Transfer equipment shall be automatic, listed, and marked for emergency use, ...

701.5 Transfer Equipment. (A) General. Transfer equipment shall be automatic, listed, and marked for emergency system or legally required standby use,

If the installation is covered by Articles 700 or 701, the transfer switch must be automatic and listed for the purpose. Note that all of the rules in 700 and 701 do not always apply to Articel 517. You have to dig into that article to see what applies.

The switchgear with motorized breakers and PLC control would only be permitted if that combination is listed as an emergency or legally required transfer switch.

Aside from that, ATS has a maintenance bypass switch which is very important for emergency power