310.15(B)(2) Adjustment Factors

Status
Not open for further replies.

tryinghard

Senior Member
Location
California
Carl, thanks but I'm still wondering what constitutes/qualifies load diversity and when to use it instead of Table 310.15(B)(2)(a)?

It appears with your link that some circuits - that are limited and controlled as to not allow operation at the same time as others - may not have to be counted as CCC's?
 

iwire

Moderator
Staff member
Location
Massachusetts
Unless you are an engineer you never use Table B.310.11. (or you live in MA :) )

See B.310.15(B)(1) at the start of Annex B.
 

cadpoint

Senior Member
Location
Durham, NC
... thanks but I'm still wondering what constitutes/qualifies load diversity and when to use it instead of Table 310.15(B)(2)(a)?

It appears with your link that some circuits - that are limited and controlled as to not allow operation at the same time as others - may not have to be counted as CCC's?
I had to back up to 2005, other one on the job.

How can you get by 310.15(B)(2)(a), last sentence.... "Each current carrying conductor of a parellel set of conductors shall be counted as a current carrying conductor."

So for example: (what I think your trying to do is)
Take five wires, of those a hot and a ground and the others are signal wires on a device. Your asking if you use 3 wires for your count in raceway fill but installing five?

Maybe ... :grin:
 

tryinghard

Senior Member
Location
California
cadpoint said:
I had to back up to 2005, other one on the job.

How can you get by 310.15(B)(2)(a), last sentence.... "Each current carrying conductor of a parellel set of conductors shall be counted as a current carrying conductor."

So for example: (what I think your trying to do is)
Take five wires, of those a hot and a ground and the others are signal wires on a device. Your asking if you use 3 wires for your count in raceway fill but installing five?

Maybe ... :grin:

Actually I was just trying to understand what "load diversity" is and when to apply it. It all started when recently using 310.15(B)(2) on one of our jobs I just noticed the fine print note.
 

SEO

Senior Member
Location
Michigan
iwire said:
Unless you are an engineer you never use Table B.310.11. (or you live in MA :) )

See B.310.15(B)(1) at the start of Annex B.
There are ways to apply this section. The examples are very easy to work out. But in my experience "use iwires "advice. I have seen many cases where it was used wrong and cost lot's of money to change.
 

iwire

Moderator
Staff member
Location
Massachusetts
tryinghard said:
Actually I was just trying to understand what "load diversity" is

IMO, Load diversity means the conductors in a single raceway or cable will never have peak loading at the same time.

That said, the question has come up before and no one was able to find an offical answer.

tryinghard said:
and when to apply it.

You can apply it when your an engineer, not trying to be wise guy here, it's just how I see it. :smile:
 

iwire

Moderator
Staff member
Location
Massachusetts
Maybe this will help show where I get my view about load diversity from. In MA they amended the NEC and have us use Table B.310.11 (They don't call it that but it is)

They also add a FPN

FPN: Overheating may occur where continuous, fully loaded conductor diversity is less than 50 percent and the number of current carrying conductors exceeds nine. See 310.10
 

SEO

Senior Member
Location
Michigan
iwire said:
Sure would like to hear how without 'engineering supervision'.
I don't see a reference to engineering supervision. Load diversity could be used where you have heating and cooling units and the heating and cooling could not be on at the same time. You may have a situation where you have several motors and have an interlock where not all the motors could run at the same time. By using the formula and examples under table B.310.11 in the annex it can be done. There has to be a way to ensure that not all conductors are loaded at the same time and then apply the adjustment factors. I still say be careful and stay away if possible.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Speaking as an engineer, I would not want to try to use ?load diversity? in any real application, with the NEC wording in its present state. For starters, the NEC itself does not define that phrase. Nor will it be found in Webster?s Collegiate Dictionary. But more importantly, it is not a common phrase in the realm of electrical power systems engineering. This topic has come up several times on this forum, and I have said this before: I literally do not know what that phrase means.

It might be talking about non-coincident loading, as some of you are discussing. But in my view, if you have interlocks to prevent two machines from running at the same time, you only count one for the purposes of service load calculations, and you only count one for the purposes of conductor derating (i.e., for more than three current-carrying conductors in a raceway), and you don?t call it ?load diversity.?

It might also be talking about the fact that even if two machines are both operating simultaneously, they likely will not be both running at maximum rated HP at all times, and nor will all the other machines in the building.

There is a well-defined phrase, in the realm of electrical power systems engineering, called ?diversity factor.? I have talked about it before. All I will say for now is that it does not seem to fit the intended use of the phrase ?load diversity,? as that phrase appears in the NEC.

Bottom line: Yes, you need an engineer, to take advantage of ?load diversity.? But you need a different engineer, as yours truly is not willing to undertake that task for you. :D
 

iwire

Moderator
Staff member
Location
Massachusetts
SEO said:
I don't see a reference to engineering supervision.

Table B.310.11 (the one used that can be used with 'load diversity) is located in Annex B of the NEC.

The very first section of Annex B is B.310.15(B)(1) which explains the use of Annex B is reserved for installations under engineering supervision.
 

SEO

Senior Member
Location
Michigan
iwire said:
Table B.310.11 (the one used that can be used with 'load diversity) is located in Annex B of the NEC.

The very first section of Annex B is B.310.15(B)(1) which explains the use of Annex B is reserved for installations under engineering supervision.
Thanks iwire I knew I was going to get a response from you when I gave some examples in my post. I do agree with you.:smile:
 
Status
Not open for further replies.
Top