2020 NEC 242.14(C): TYPE 2 SPD, separately derived system

Location
Texas
Occupation
Student of Electrical Engineering
Per 2020 NEC 242.14(C), it appears after every transformer, you require a SPD, correct, even if I already have an SPD at the service disconnect or anywhere ahead of the transformer (separately derived system)?

ex: 480V service with a SPD, distribution panelboard, transformer, SPD, utility panelboard.

Thank you for your help.
Sincely,
NSL
 
Location
Texas
Occupation
Student of Electrical Engineering
Maybe some additional details regarding my design:
5 Story Building in Texas (municipality, multiuse building).
Service Transformer: 2000kVA 12.4k - 480/277V
At the building, I have a NEMA 3R service disconnect, with a built-in (factory installed) Type 1 SPD, which should satisfy 242.12(A) & (B).
Then my service enters the building and terminates at the Main Distribution Switchboard.
From there it goes to my 480V distribution panelboards (each floor).
Afterward, there are 480V - 208/120V utility transformer and 208/120V utility panelboards (each floor).

Per 242.14(C), it appears I need a Type 2 SPD within the 208/120V panelboards, correct?

Now that I re-read the entire 242 section, and Table 242.3, it does not appear I am required to have a SPD at the service entry. I would require one @ COPS, elevators/escalators, Fire Pump, IT equip, and modular data center (all of which are within the building). Maybe it is better to supply SPDs at the MDP & each utility panelboard rather than for each category listed (cover everything with SPD, so I don't have to worry about the individual needs)?

Thank you for your help with trying to interpret this new/rearranged NEC section.
Sincerely,
NSL
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I suppose it is a little unclear, but I do not believe 242.41 requires an SPD to be installed for a separately derived system. It only places a requirement on the SPD connection location if you decide to install one.
 
Location
Texas
Occupation
Student of Electrical Engineering
Okay got it. Only 230.67 has a mandatory requirement for an SPD, otherwise if one is installed, it must comply with 242.

Thank you for your help and input!
 
Location
Texas
Occupation
Student of Electrical Engineering
I guess ultimately I am asking:

If I provide a factory installed Type 1 SPD on my service entry equipment, everything downstream will be protected by a SPD and it should make the entire installation comply with any SPD requirements (code, spec, customer, etc.), correct?

There is very little to zero chance of anything past the service entry SPD which would cause a voltage spike, correct (negating the need for a second SPD anywhere within the building past the first SPD provided). If there is a SPD installed on my service entry equipment, then there is no need to add another SPD on the 5th floor 208V panelboard because it would never see a voltage spike because the original SPD will stop all spikes.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I mean, who knows. SPDs are an insurance policy against unexpected things going wrong. It all depends how much insurance you think you need and for what scenarios. Some surges are too big for any SPD. Also, you are correct that to some extent an SPD at the service protects separately derived systems from overvoltage that comes from the utility. But if you had a fault on the premises from your 480V service to the conductors of your 208V system, the service SPD wouldn't protect against that.
 
Location
Texas
Occupation
Student of Electrical Engineering
Correct, internally if something goes wrong there would be no surge protection, but the likelihood of that happening should be extremely minimal (commercial installation, so all electrical equipment is behind locked doors only accessible to qualified personal, etc.).

I believe the only true threat would come from the utility side, so with my above described scenario (SPD @ service entry) I should be good regarding code requirements.

Thank you for talk with me about this. I appreciate your input.
 
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