3 sets of 350 kcm thhn

Status
Not open for further replies.
3 sets of 350 kcm thhn

have a 1000 amp c/b in a new switch gear Eaton Type can I run 3 sets of 350 thhn to a main lug 1000amp rated panel non- cond. loads any way to use the thhn rating @ 350amps 3 conduits UG
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

Unless all the componets and connections are rated 90 deg, you can only use the 75 deg value which is 310 for a total of 930, and can not be fed from a 1000 amp breaker. See 240.4(C)

Roger
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

I agree with Roger. But I would like to add two things.
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">You can use those conductors, if the total calculated load is less than 930 amps. The fact that the panel is rated for 1000 amps means nothing.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"> </font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">You can use the 1000 amp breaker if it has the ability to dial down its trip setting to a point below 930 amps.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

The fact that the panel is rated for 1000 amps means nothing.
I guess that would depend on if the customer is paying for a 1000 amp panel or a 1000 amps of capacity. ;)
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

Charlie b
quote
You can use a 1000 amp breaker if it has the ability to dial down its trip setting to a point below 930 amps.
What about 240.6(B) which says use the maximum setting unless the breaker has restricted access? If it is under lock and key, you are correct, however the general rule is to use the maximum setting available. Do you want to bet the janitor has a key to the electrical room?
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

Jtester: I have never seen one in which item (1) or (2) wasn't met. Is it common to not comply with (1)?

(C) Restricted Access Adjustable-Trip Circuit Breakers. A circuit breaker(s) that has restricted access to the adjusting means shall be permitted to have an ampere rating(s) that is equal to the adjusted current setting (long-time pickup setting). Restricted access shall be defined as located behind one of the following:
(1) Removable and sealable covers over the adjusting means
(2) Bolted equipment enclosure doors

(3) Locked doors accessible only to qualified personnel
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

ryan_618
I was recently called to look at unexplained tripping of breakers at a 2 year old hospital. The electrician didn't have a key to the electrical room, but the physical plant guys all did. When we got into the switchgear room, every Square D adjustable breaker had its sealable cover removed, and no one knows to this day where they are.
Worse than that, only a fraction of the breakers had the settings specified in the original coordination study. It seems that as the contractor final'd the job, different plug ratings were installed, and then someone took it upon themselves to adjust the breaker settings.
While these breakers come with little plastic windows and seals to discourage tampering, I have been called to more than one job where they didn't even slow down a misguided contractor.
I guess my thought is
Does (C) (1) imply that if the device has the ability to be sealed its OK, or does it say that when the cover is removed and lost, at that point you have a violation?
Since I have very little control over the security of the cover after the job is completed, I always suspected the cover would get removed and the settings would no longer be secured.
Jim T
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

The NEC is not responsible for vandalism. This is a problem for the owner to address. If the staff is not trained to leave the settings alone, and to report any evidence of tampering (e.g., seals are missing), then the owner is placing the safety of the employees at risk.
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

What is the difference between someone changing breaker settings or replacing the fuses in a disconnect with a higher rating, lower AIC, longer time delay etc.

You can not possibly keep idiots from doing the wrong thing. :(
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

Charlie b and iwire
You guys are right, I probably am venting or at least thinking out loud. I thought back to the installations I have been called to, and I don't remember ever seeing seals. I guess no Contractor calls me to show off his good work, only when there is trouble. What experience do you guys have with unsecured covers over the adjustment means?
Secondly, if it is something that I see often, don't you agree that a lawyer would have a heyday with me, given that I should know more about the problems associated with accessible means than most other individuals, particularly in a hospital?
You are right, the NEC considers the seals adequate.
Jim T
 
Re: 3 sets of 350 kcm thhn

Re: 3 sets of 350 kcm thhn

There might be a potential liability issue. Suppose you had been hired to something completely unrelated, but had to do some of the work in that room. Suppose further that after your job was done, an accident took place, and the accident investigation pointed at an incorrect relay setting as being related to a personnel injury. You had been in the room, and could have seen the missing seals. Not a good position, I have to admit.

How do you protect yourself (and by the way, help to protect the public)? The only thing I can offer is to inform the owner, in writing, of any safety concern you observe, any time, every time, regardless of whether it was related to your assigned task. Is this practical? I can?t say. Would it keep them from hiring you again? Again, I can?t say.
 
Status
Not open for further replies.
Top