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

[Sparky Bill PE]

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. 

 

[LyceeFruit PE]

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 

 

[Sparky Bill PE]

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. 

 

[LyceeFruit PE]

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

 

[Sparky Bill PE]

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

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.

 

[Orchid PE]

@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.

 

[Orchid PE]

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.