A TVSS should be install. On the Load side or line side of the breaker.
The term TVSS (Transient Voltage Surge Suppressor) is no longer used. Now it is called a
Surge-Protection Device (SPD).
We can't answer your question because we don't know what you have there. It depends upon the product you have. Be sure to double-check, and read manufacturer's installation instructions. Take a look at definition for SPD:
"Surge-Protective Device (SPD). A protective device for limiting
transient voltages by diverting or limiting surge current; it also prevents continued flow of
follow current while remaining capable of repeating these functions and is designated as follows:
Type 1: Permanently connected SPDs intended for installation between the secondary of the service
transformer and the line side of the service disconnect overcurrent device.
Type 2: Permanently connected SPDs intended for installation on the load side of the service
disconnect overcurrent device, including SPDs located at the branch panel.
Type 3: Point of utilization SPDs.
Type 4: Component SPDs, including discrete components, as well as assemblies. (CMP-5)
Informational Note: For further information on Type 1, Type 2,
Type 3, and Type 4 SPDs, see UL 1449, Standard for Surge Protective Devices."
Depends on what type of SPD you have and for the sake of argument I'll assume that your question is about Type 1 and Type 2 SPD's. Listed Type 1 SPD's are manufactured with integral overcurrent protection and are permitted to be installed on the line side (supply side) of the service disconnecting means.
Listed Type 2 SPD's do not have any integral overcurrent protection and are required to be installed on the load side of the first overcurrent device (typically the service OCPD). Type 2 SPD's are required to be connected to their own OCPD in accordance with the manufacturer's installation instructions.
Type 1 SPD's are permitted to be installed as a Type 2 SPD where they are connected to an OCPD on the load side of the first OCPD.
Someone out there will have to explain that to me, because it all depends upon the SCCR rating (285.7), whether or not one can install a Type 1 or a Type 2.
110.10: Not every Type 2 can be installed on the load side, if this is the case (at least at the main switchgear section). Otherwise the AIC rating of the entire electrical system is going to be inadvertently lowered. I see this issue as an SCCR issue, and not so much as a "Type 1" or "Type 2" issue.
The SCCR rating can be up to 200 kA with some Type 2 SPD's. It really depends on the SPD, some of cheap ones from the big box stores and online retailers are complete garbage. The link below is for Eaton's SP-2 Type 2 SPD.
It would all depend on SPD being debated, you can't blanket say all Type 2's are 200kA SCCR nor all Type 1's have 10kA SCCR. I've always been under the impression the decision between Type 1 and Type 2 really comes down to how or where it can be installed on your system. Interestingly enough, do you often see an issue where the SCCR of the SPD is less than the maximum available fault current? Even low-end residential models often have relatively high SCCR's.
UL 1449 has marking requirements for a number of values including SCCR.
If anyone wants to read the UL Standards they are visible for free on their web site, just create an account.
It is a bit clunky in that you cannot search, copy or download, but it beats paying the $716.00 for sure.
Hope this helps,
To be honest Chris, I'm thinking that most inspectors may not be paying attention to this. I'm going to scrutinize this item more on plan review, maybe ask for the manufacturer and model (although the engineer will hate me for doing it).
The National Electrical Code, 2017 ed, [Handbook]
Article 285 and referenced articles has variable approaches as to
connections of type's 1,2,and 3 SPD devices with informative discussions that are more definitive as to the specific
I highly recommend that a review of NEC 285 and its referenced articles be reviewed for each proposed installation.
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