HVAC Grounding and Wire sizing of existing power

[deharoj]

I was asked a couple of questions and not sure if my anwers are correct.

1. A big box (A/C unit ) was replaced for a like unit. Power was existing from original build. All in conduit up to the unit then the last few feet are in sealtight for vibration. There is no ground wire, so they used the race way as a grounding means back when it was installed. If no changes were made to the existing power source do i still have to worry about a ground wire? Can it be grandfathered in the way it was?

2.The same unit has XHHW 250mcm in aluminum which is rated for 205 amps. However the unit MCB and disconnect both are rated at 225amps. This is how it was originally installed. Is there something in the code that allows for the wire not to be rated at the same amperage as the overcurrent protection?

Thanks in advance guys.

 

[don_resqcapt19]

A bonding jumper will be required around the sealtight, assuming that the conduit is metallic.
As far as the wire rating and the OPCD, the wire for an AC unit is often smaller than the rating of the protective device. There should be a name plate on the unit giving the minimum circuit ampacity and the maximum OCPD. The code permits you to size the wire to the minimum circuit ampacity and protect it with the maximum OCPD listed on the name plate.
Don