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Selecting the generator

The TB guidance allows use of three types of genset

  1. an RCD-protected genset; or
  2. a centre-tapped genset in conjunction with an RCD; or
  3. an isolated-output genset, modified to provide a polarised output.

In fact, the TB specifically forbids us from using an isolated output genset. Which may seem odd; because that’s the only type that’s suitable for supply to an MEN-type installation. But they TB also includes a requirement that, if there’s not a connection within the genset between N & E, we must make one. And if we follow that instruction, it will no longer be an isolated output.

It is likely that the guidance will be amended to require an RCD with this option, as for RCD-protected gensets.

How do we know what sort of genset output we have? Asking the supplier isn’t likely to help; most won’t understand the question, let alone know the answer. And it isn’t likely to be written on the tally-plate.  But we need to know; and not just so we can follow the TB’s guidance.

There can be serious issues if we get it wrong.