Nec 200.3

[Nate Scott]

Could you explain what NEC 200.3 means and its reason for being in the NEC.

 

[George Stolz]

That's an utterly original question, very cool.

200.3 Connection to Grounded System. Premises wiring shall not be electrically connected to a supply system unless the latter contains, for any grounded conductor of the interior system, a corresponding conductor that is grounded. For the purpose of this section, electrically connected shall mean connected so as to be capable of carrying current, as distinguished from connection through electromagnetic induction.

Premises wiring is defined in 100. Essentially, what this is saying is that if there are L-N loads in the structure, then the service can't be hooked up without supplying a neutral for those loads.

The last sentence is making it clear that the rule governing the service in question doesn't cross boundaries of seperately derived systems.

At least, that's how I read it.

As for why it's in this section of the NEC, I'm not really sure. We're already given similar requirements in 250.20, I didn't even know this section existed until you asked this question. I always figured 250 did this job.