SPD in both panels or just one?
- Thread starter sw_ross
- Start date
If it’s two separate panels….one SPD for each panel!
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Considering the short, straight wires the instructions usually state, I'd say one in each panel.
I am assuming you have a 400A main service with two 200A main disconnects? One disconnect has a branch breaker distribution under it and the other main feeds a sub panel in the house or another structure on the property?
IMO and if I am interpreting the NEC correctly, if the feeder goes out to another separate structure, then it needs one additional SPD. If no feeder leaves the main structure then one is required usually by the main service
The situation I’m referring to is a 400-amp service (referred to as a 320 service) that has (2) 200-amp disconnect’s in the meter/main outside of the residence. From there is (2) feeders running into the structure to feed (2) 200-amp Main Lug panels.
We’re trying to understand if (1) SPD in 1 panel suffices for the residence , or do you need 1 in each panel?
I understand the concept of “just to be safe put one in each panel”, but I truly want to understand why 1 SPD in 1 of the panels doesn’t “do the job” of absorbing the surges from power companies as well as environmental surges (lightning, etc).
I’m not being cheap, these are design/build projects that are generally T&M jobs. I will put one in each project if necessary.
We’re trying to understand if (1) SPD in 1 panel suffices for the residence , or do you need 1 in each panel?
I understand the concept of “just to be safe put one in each panel”, but I truly want to understand why 1 SPD in 1 of the panels doesn’t “do the job” of absorbing the surges from power companies as well as environmental surges (lightning, etc).
I’m not being cheap, these are design/build projects that are generally T&M jobs. I will put one in each project if necessary.
It is not a matter of being cheap, I agree.
I still think you need one, either at the main service, if you have slots for branch breakers, otherwise install one at one of the subs.
The place I’m working at is still trying to figure out this situation.
The supply house told us, based off their conversations with the Square D rep, the SPD only needs to be place “somewhere” in the setup to work?!
On one job since the main panel was full the SPD was placed in downstream a sub-panel. That doesn’t make sense to me?
How is that going to protect devices that are fed from the main panel?
The supply house told us, based off their conversations with the Square D rep, the SPD only needs to be place “somewhere” in the setup to work?!
On one job since the main panel was full the SPD was placed in downstream a sub-panel. That doesn’t make sense to me?
How is that going to protect devices that are fed from the main panel?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Technically your two panels are connected in parallel with the source. The panels experience basically the same voltage at the same time (yes I know there is some slight voltage drop). This means a surge protective device placed in parallel will provide protection for voltage rise to your panels.
The problem with using downstream locations include a significant voltage drop preventing the SPD from seeing the voltage surge. Also, there is a lack of protection for the system if the panel containing the SPD is 'turned off'.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
(B) Location. The SPD shall be an integral part of
the service equipment or shall be located
immediately adjacent thereto.
Exception: The SPD shall not be required to be
located in the service equipment as required in
(B) if located at each next level distribution
equipment downstream toward the load.
The way I read that, you would need one in each sub.
the service equipment or shall be located
immediately adjacent thereto.
Exception: The SPD shall not be required to be
located in the service equipment as required in
(B) if located at each next level distribution
equipment downstream toward the load.
The way I read that, you would need one in each sub.