Delete 252.11

[ryan_618]

Substantiation:
This change to the 2005 edition of the code should never have been accepted. There was no technical substantiation.
Are there any documented cases of this being a problem?
Where did 12? come from? Is 11? unsafe? Is 12?1? safe?
Also, this requirement is so vague in its language that it is impossible to create uniform interpretation. What is to bonded together here? The generators? The attractions? The rides?
How do I bond them? 500Kcmil copper? 6 AWG? What portions of Article 250 apply? Do I base the size on 250.122? Do I use Table 250.66?
What happens when a voltage is imposed from one system (during a fault) to the metal, non-current carrying parts of the other system and its rides and attractions? Why are we energizing attractions that were safe until we bond them to something that is under fault? Isn?t isolation safer than bonding? I don?t want to be touching a ferris wheel that is perfectly safe, only to get shocked because a different generator had a fault and imposed its voltage on me for the time duration of the overcurrent device to open. I would rather just not get shocked! Isolation is the answer, not bonding.
I urge the members of Panel 15 to delete this proposal that never should have passed in the first place.

 

[bphgravity]

Re: Delete 252.11

I don't have a 252?

The 12' makes sense to me. If a bare foot man that happens to be 8'4" puts his foot on one ride and stretches out to another ride that is supplied by a separate service, he would be potentially exposed to step/touch voltage. And since the probability is around 1 in a billion of this happening, it needs to be in the code.

Doesn't this same problem exist in 250.58?

 

[ryan_618]

Re: Delete 252.11

Originally posted by bphgravity:
I don't have a 252?

Doesn't this same problem exist in 250.58?

Actually, I don't think it does. If there was a lighting event at the builing. and the two services were grounded to different electrodes, it is very likely that a surface arc would occur between the two electrodes. I think this is the reason that 250.106 is in the Code as well.
I guess there is that possibility at the carnival as well, but I don't think it should be required, considering the temporary nature of the installation.

 

[don_resqcapt19]

Re: Delete 252.11

Ryan,
I think that if the non current carrying parts that are supplied from two different power sources are within "touch" distance that they should be bonded. I think that 12' makes sure that a person cannot be touching both items at the same time.
Don

 

[ryan_618]

Re: Delete 252.11

Don, I understand what you are saying, but it seems to me that there are very derious pro's and con's to this argument.

If the generator (and its bonded equipment) are energized, bonding them to something else will energize more things. I think that is my biggest issue (other than panel 15 passing something with no technical data or substantiation).

 

[bphgravity]

Re: Delete 252.11

Originally posted by ryan_618:
If there was a lighting event at the builing. and the two services were grounded to different electrodes, it is very likely that a surface arc would occur between the two electrodes. I think this is the reason that 250.106 is in the Code as well.

So we are going to suppose that a lightning strike event is more probable than a open grounded neutral from one of the two services?

I do agree the benefits of 250.58 and certainly 250.106 outweigh the cons, but not by alot. I feel this section is the same situation. A happy medium or at least compromise has to be made when two potential hazards could arise.