Type 1 SPD At Branch Circuit Level

[yesterlectric]

Other than cost is there a reason not to install a type 1 SPD at the branch circuit level where a type 3 SPD would be acceptable to use? For example is there a higher clamping or let through voltage that comes as a tradeoff for the high fault current capabilities of the type 1 SPD which would make its use nearest to the equipment it protects less desirable? Asking because an engineer requested a particular type 1 SPD at a branch circuit.

 

[synchro]

SPD's typically have multiple MOV devices connected in parallel internally. Each MOV has individual over-current protection in some form to prevent a failed device from starting a fire, while allowing the others to maintain their surge protection function. One thing that comes to mind is that if a type I SPD is used on a branch circuit, then the source impedance seen by the SPD could be significantly higher than it was designed for due to the resistance of the branch circuit conductors. That might impact how well an internal overrcurrent device can function in disconnecting a faulty MOV. Granted, such faults will probably be less likely with an oversized SPD. However, MOV degradation is cumulative and so failures could still eventually occur. Also, early failures due to latent manufacturing defects are possible.

This is speculation on my part, and the manufacturer of the SPD under consideration should be consulted for more definitive information.

 

[yesterlectric]

I think the code should be more clear. It says where a type 3 SPD MAY be installed. We know this means it can not be installed where a type 1 or type 2 would be, because it isn't rated for the fault current. However te code doesn't say this is the reason. It also says where we MAY install type 1 and 2 devices without saying we can/can't install them at the branch circuit level.