Question about NEC 2017 I can't figure out if its an error or not

Below is a picture of TABLE 230.51.(C) Supports. Is that first "maximum volts" column really supposed to be 1000 then 1000 under it? looks like it would be around 300 or 600 V.

I could be reading it all wrong. 

For giggles, I pulled out Boyfriend's NEC 2011 to see what it said.

It shows 600, 600, 300, 600*  with all of the other numbers matching. I can't get my copy of NEC 2014 to open (file corrupted - boo).

But I'm leaning towards it's not a mistake and just confusing AF. 

And then I asked him, and he's not sure.

So then I googled it and got this:
https://forums.mikeholt.com/threads/table-230-51-c.37282/ 



I can also ask my drafter on Monday - he was an electrician for 18yrs and quotes the NEC to my underling at least one month 

Attached is 2014. The numbers are highlighted so that means they changed from 2011 to 2014. I don't see how it can be confusing and not be an error. Unless they just brought it upon themselves to make a random chart that isn't like other charts. I use IEEE all the time at work doing clearances for substations. 

If you read the Mike Holt forum post, that table has been laid out like that for over 30 years

LyceeFruit PE said:

If you read the Mike Holt forum post, that table has been laid out like that for over 30 years

Click to expand...

Yeah considering the numbers changed once (2011/2014) that means it was messed up for the last 20 years. I tried to send an email to them but their website is giving me an error when uploading the question lol. I think it said they have a live support chat mon-fri 9-5 so im excited to see what they say. I'm sure whoever is on the other end of that doesn't answer code questions.

@SparkyBill

The reason is because this table is for individual open conductors. There are various support/clearance options for voltages < 1000 V.

Greater clearances are required for larger support spans to prevent the conductors from interfering with each other when exposed to weather.

The table having multiple 1000 V options is just to allow flexibility when the conductors are installed.

For instance, if you have 480 V conductors and your support spans are 8ft apart, the clearance between conductors must be at least 6in.

If you have 480 V conductors and your support spans are 14ft apart, the clearance must be at least 12in between conductors.