Surge Suppressors, Arresters,
I was wondering if you could clarify what the difference is between a surge suppressor,
a surge arrester, and a surge protector. I have read your article in EC&M; however,
you only separated the arresters from the TVSSs by simply stating that if they are on
the line side of the meter, then they are arresters; if they are located on the load side,
then they are TVSSs. Based on my reading, the National Electrical Code doesn't seem to
take that point of view. Could you please clarify for my case below?
I am presently working on a project that has a main switchboard with severe damage due
to lightning strikes. The side is half burnt by arcing, the copper bus is nicely rounded
at the corners, and the bus is missing some attachments for support (or the copper has
been removed around the supports). Based on my first site visit, the owner has indicated
that the main switchboard was stricken by lightning three times; however, they seem to
think it is fine because it still supports the load they are connecting to it.
At this time, we have not found any
damage done to the owner's primary 2,500 kVA oil-filled transformer, which is located
approximately 7 ft from the main switchboard. The primaries on the "H" frame
above the transformer appear to be in good shape, along with the secondaries to the switchboard.
The problem I am having is that the transformer and service is a 480V, three-phase, 3-wire
delta, UNGROUNDED service. There is a partial equipment ground; I mean partial in that
there is a ground bus connected to a grounding grid. However, most of the feeders are
not carrying ground wires and some are using PVC conduit. No MEGGER test has been conducted.
I am proposing to replace the existing switchboard with new at a new location and provide
new service conductors, and I would like to also provide some form of lightning protection.
I was going to originally propose a TVSS at the new switchboard location because the new
service conductors will be run on the roof; however, per Article 285 of NEC 2002, TVSSs
are not allowed for ungrounded systems (Article 285.3(1)). So, my next proposal is to
provide a surge arrester (per Article 280 of NEC 2002) at the main switchboard. However,
while searching for the proper equipment to specify, I got turned around trying not to
violate Article 285. Per some manufacturers, they can supply surge arresters that can
meet my requirements (460V, three-phase, 3-wire ungrounded delta surge arrester, 40 kA
current limit with LED or alarm indication). Yet, when I read the UL listing, it is listed
as a TVSS (UL 1449).
The NEC 2002 has not been accepted yet in the state I am working in; however, I try to
make it a good habit in designing the system to the most stringent situation between the
NEC code that is accepted by LAHJ and the latest Code. If you could maybe clarify to me
why the Code has changed to separate TVSSs and surge arresters, that may also be of great
help. Based on my reading of Article 280.5 of NEC 1999, I would be allowed to install
a UL listed TVSS for this system.
Mike, maybe your newsletter readers
can help me out.
Daniel Vigeant, E.I.T.