SPD Type 3, 10 meters, 30ft minimum branch circuit conductor length from the main service equipment panel.

[Jamesco]

Type 3- Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to the point of utilization, for example cord connected, direct plug-in, receptacle type SPDs installed at the utilization equipment being protected. The distance (10 meters) is exclusive of the conductors provided with or used to attach SPDs.

Wouldn't the minimum branch circuit length 30ft rule also apply to a sub panel?

Example, a 100A sub panel fed with #2 copper. 100A breaker in main panel.

 

[Jamesco]

Doing a search I found this thread that somewhat addresses my question.
https://forums.mikeholt.com/threads...c-285-25-for-surge-protection-devices.110537/




Here is a quote from charlie b

• Feb 27, 2014

• #2

I don't know how the SPD functions, so I can't answer the question. My only thought is that the device needs the resistance that extra wire would provide.

I can, however, pose a question of my own. Is the panel that is 10 feet from the desired SPD location the main panel for the house, or is it a sub panel located some distance from the main panel? The 10 meter requirement has to do with the distance from the main service disconnect to the SPD location, not the distance to the branch circuit panel.

Sub Panel ...

What if the electrical service is a 400A (320A continuous) and there are two 200A sub panels.

Wouldn't this UL1449 rule apply?

"Type 3- Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to the point of utilization, for example cord connected, direct plug-in, receptacle type SPDs installed at the utilization equipment being protected. The distance (10 meters) is exclusive of the conductors provided with or used to attach SPDs."

For NEC references I looked at 110.10 Circuit Impedance,

Also 2020 NEC 230.67 Surge Protection.
Installation of Type 1 or Type 2 SPD. Therein at Main service panel or Sub Panel Location(s).

Quote from tom baker

• Feb 27, 2014

• #5

Type 3 SPDs are not cabable of absorbing a large surge of energy as they are small. The Type 2 SPDs I install have 70mm mov;s and can handle a lot of "Joules". So with the type 3, the manufacture is using the impedance of the 30 ft of wiring to reduce the surge to a level the device can absorb.
I would recommend a high quality SPD ($300)at the service entrance, and then a SPD at the point of use.

To me I think this goes to the heart of my question. But why this specific language? "Type 3- Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to ...
Why isn't a sub panel included in the language as well?

 

[don_resqcapt19]

...

To me I think this goes to the heart of my question. But why this specific language? "Type 3- Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to ...
Why isn't a sub panel included in the language as well?

They are just trying to increase the impedance from the high fault current that may be available from a service. The conductor length can be any combination of "x" feet of feeder conductors to a panel, and "x" feet of branch circuit conductors to the SPD.

 

[Jamesco]

They are just trying to increase the impedance from the high fault current that may be available from a service. The conductor length can be any combination of "x" feet of feeder conductors to a panel, and "x" feet of branch circuit conductors to the SPD.

Thanks Don