702 vs. 710

[markhorst]

We are having an intense (yet fun) discussion in our office as to whether a generator with an auto transfer switch can be sized using 710.15(A) according to the 2020 code or if it must be sized according to article 702.4(B)

Argument A says that article 702 is obviously written specifically for generators and therefore is how they should be sized.

Argument B says that a generator can be sized according to 710.15(A) because

• 710.1 states, "... systems that operate in island mode... "
• Article 1 defines Island Mode as "The operational mode for... an isolated microgrid..."
• Isolated Microgrid is not defined in the 2020 NEC, but since the function of an ATS is to isolate the loads and create a micro-grid the system would be "operating in island mode".
• The informational note in 710.15(A) specifically calls out a generator as a part of a stand-alone system

It seems like the code includes generators with an ATS in both sections... anyone have thoughts?

 

[tortuga]

Thats very interesting I am going to look both those up in my 2020 code book later.

 

[Carultch]

I would expect that it depends on whether your backup sources are exclusively generators, or whether you have a mix of energy sources during off-grid mode. 702.4(B) seems to be written for generators only, while 710.15(A) would apply for multiple types of sources during off-grid mode.

 

[markhorst]

I would expect that it depends on whether your backup sources are exclusively generators, or whether you have a mix of energy sources during off-grid mode. 702.4(B) seems to be written for generators only, while 710.15(A) would apply for multiple types of sources during off-grid mode.

It does seem like that was the intent, but then in the informational note below 710.1 it specifically states "Stand-alone systems often include a single or a compatible interconnection of sources such as engine generators, ..."

 

[Rock86]

I voted 702... primarily because it identifies that the code is specifically for Transfer Equipment, but given enough conversation, I could probably say either or.