What is the reasoning/intent behind NEC 285.25 for Surge Protection Devices?

[HarryHomeowner]

Hi All - thanks in advance for any light you can shed on this issue.

I have a customer who wants me to install a TVSS receptacle (Hubbell 5360SA) in his basement that will serve computer equipment (routers, switches, modems, etc.). The receptacle needs to be mounted in a location that's about 10 feet away from the panel. The manual for this receptacle clearly states:

"CAUTION: Do not install this device if there is not at least 10 meters (30 feet) or more of wire between the electrical outlet and the electrical service panel."

In my situation, there will only be 10 feet, not 30. I called Hubbell and they referred me back to NEC 285.25, which states this requirement for all Type 3 SPD (I think SPD is Surge Protection Device). Apparently the code was recently revised to state that only Type 3 SPDs which specifically state the requirement for being installed at least 10 meters / 30 feet must actually be installed that way -- so if the manufacturer doesn't state this requirement for their Type 3 SPD, then the installer doesn't have to follow the requirement. But since this Hubbell receptacle (and other similar TVSS receptacles I've looked at) all do seem to have this requirement, I'm stuck.

QUESTION- What is the intent behind requirement? What could go wrong if the receptacle is installed closer than 30' to the panel? I asked the Hubbell support person this question, and they started to get very nervous because I was "asking them how to deliberately go around NEC code" -- not true. I just want to know why this is considered dangerous.

Thanks!
-Brian

 

[charlie b]

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.

 

[HarryHomeowner]

The resistance may very well have something to do with it.


Regarding your other question - the panel in question is the main service panel for the house. However, the panel is an older Eaton CH split-bus panel with no main breaker (I don't think this would make any difference). From there, the service entrance cable extends up and out of the panel to the meter outside, which is probably about a 5' run.

 

[jim dungar]

The distance requirement has to do with the fault current rating of the SPD (part of its 'Type' class). The relevant NEC requirement is 110.10.

 

[tom baker]

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. A better solution may to be use a quality plug ($50) with built in RJ45 jacks. This creates a single point ground at the point of use and prevents a voltage difference.

Anyway with SPDs two rules
You get what you pay for.
More is better.

Just a SPD receptacle won't get you much protection.

 

[Ponchik]

I have always used SQUARE-D whole house SPD.

Any other manufacturer recommendations?

 

[GoldDigger]

I would amend your first rule to read:
"You do not get more than you pay for."

Tapatalk!

 

[Little Bill]

I have a possible solution to the OPs problem. If there is room, with the needed location of the SPD, just run at least 25' of wire more than the needed 10'. Run it around the ceiling if you need to.
Receptacle is already 10' away, add the 25' of wire and you exceed the 30' requirement!:thumbsup:

Remember, the requirement is for 30' of wire, not 30' away from the panel!