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RE: Are all NST center tapped?

I think that the lower voltage models may not be, but since we generally
prefer to use the higher voltage models, this doesn't matter.  There have
been reports that the newer models that conform to some new safety
requirement do not have an earthed center tap, and there may be some
additional ground-fault protection circuitry that may (or may not?) cause
problems.  If you are buying a new unit you may run into this, but there is
not a lot of experience with these. You may wish to just stick with the
tried-and-true used center-tapped models. But the bottom line is, we do not
require a center tap in our applications.  

If buying a used model, I would suggest finding one with a removable cover
that exposes the asphalt-covered core.  This will allow you to inspect the
asphalt to see if it is cracked.  If and when you do blow your NST, having
one with a removable cover and asphalt potting vs. the un-removable hard
resin potting will make the miserable job of NST resurrection easier.

Gary Lau
Waltham, MA USA

Original poster: "Seth Fischer" <aureo-at-xtra.co.nz> 

I am about to go and look for a NST.  Are they all center tapped?

Is there anything I should look out for (used vs new etc.)?

Seth Fischer