I'm considering an A-to-A Heat Pump, small 2.3-3kW for on-demand heat.

The metal piping introduces a potential from outside (extraneous
conductor), but unless the HVAC external unit is in contact with the
ground OR 500V resistance is 23k-ohms it does not require bonding
back to the MET. Vis., the use of brackets for external units even if
mounted 1ft off the ground.

Is my reading correct or has there been alternative guidance / errata?

js.b1 wrote:
I'm considering an A-to-A Heat Pump, small 2.3-3kW for on-demand heat.

The metal piping introduces a potential from outside (extraneous
conductor), but unless the HVAC external unit is in contact with the
ground OR 500V resistance is 23k-ohms it does not require bonding
back to the MET. Vis., the use of brackets for external units even if
mounted 1ft off the ground.

Is my reading correct or has there been alternative guidance / errata?

I think your reading is correct - however you will have bonding by
default via its supply CPC presumably anyway. (assuming the heat pump is
not class II and the ducting is not isolated from it)

--
Cheers,

John.

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