RES Technical Corner by Brett Eliasz, PE

Technical Corner

For the article this month we will take a look at mounting surge protection devices (SPDs) within the piece of electrical equipment it is associated with or mount it external.

IEEE Standard 1100 (Emerald Book) recommends the SPD to be installed outside of the electrical equipment for the following reasons:

1. If the SPD were to require replacement, then an outage would likely need to happen to repair or replace.

2. SPD product failure can contaminate the panel internally with ionized gases which can cause collateral damage to the panel itself along with compromising the insulation system of the panel and the wiring residing within.

The best way to accomplish external mounting is to provide a branch circuit breaker within the panel it is associated with to feed an externally mounted SPD device. In this instance, the breaker can simply be shut off to allow maintenance to occur instead of a full building shutdown. This also eliminates the risk associated with contamination of the panel with ionized gases.

One of the benefits to mount SPD’s integral to the panel is to minimize the length of SPD conductors which optimize the effectiveness of the device.

One of the best places to install SPD is at the main switchgear, where the service enters the building. Also, as you may already know, NEC 700.8 requires SPD to be installed on all emergency system switchboards and panelboards. Note that NEC 701 & 702 are silent to this requirement.

Since SPD typically gets installed in critical areas of a building electrical system, I would have to agree that the best practice is to install SPD’s external to the equipment it is associated with.

Code references courtesy of NEC 2017 Code version

Hopefully this article finds you well and can be used as a reference for your project needs. If anyone would like to contribute to the RES magazine and add an article or would like to request information on a specific topic (not limited to Electrical) just email me at beliasz@bergmannpc.com. As always, any comments are appreciated…! Thank you for reading.

Brett Eliasz, P.E., LEED AP BD+C , RES Director