derating-residential circuits

[powermac36]

derating-residential circuits

Can table B.310.11- adjustment factor for >3 current carrying conductor in a raceway ( with load diversity)? - annex b- be utilized in derating residential conductors

Example:
200 amp service upgrade,1-ph,120/240v,75-deg lugs,24 ckt power panel.
The elec cont, installed 24 current carrying conductors in a 2" raceway.

12 conductors are #14 THWN.

does residential wiring fall under load diversity?

OK or derate wires??

[ March 27, 2005, 11:58 AM: Message edited by: powermac36 ]

 

[mhulbert]

Re: derating-residential circuits

Re: derating-residential circuits

If the conduit is longer than 24", you have to derate, even if it's residential.

 

[George Stolz]

Re: derating-residential circuits

Re: derating-residential circuits

How could someone demostrate load diversity? I think I understand what it means--different circuits will carry load at different times, such as lights from photoeyes will be off when computers inside an office would be on, something like that. Feel free to correct me if that's wrong.

How could you demonstrate diversity in a residence?

 

[iwire]

Re: derating-residential circuits

Re: derating-residential circuits

Originally posted by powermac36:
Can table B.310.11- adjustment factor for >3 current carrying conductor in a raceway ( with load diversity)? - annex b- be utilized in derating residential conductors

I would think you would need an engineer to sign off on that in order to use the annex.

 

[charlie b]

Re: derating-residential circuits

Re: derating-residential circuits

Originally posted by georgestolz: I think I understand what it means--different circuits will carry load at different times,

That is the basic idea. But the term ?load diversity? is not defined in the NEC, nor is it a standard industry term. So I do not know how the NEC authors intend that it be applied. My inclination would be to use the concept of ?load factor? in place of ?load diversity.? That term is basically ?average load divided by peak load.? But getting a 50% factor is not easy. If a facility runs at 100% load for 12 hours and is turned completely off for 12 hours, then the average load for the entire day is 75%, the peak load is 100%, and the ?load factor? is 75%.

Originally posted by georgestolz: How could you demonstrate diversity in a residence?

The same way you would demonstrate it an any type of occupancy. Load measurements for a sufficiently long period to get a representative sample. Then do the math. But first you need a definition of ?load diversity.?

Originally posted by iwire: I would think you would need an engineer to sign off on that in order to use the annex.

I think this is true. But this is one engineer who would not accept the assignment without an allowance for the time needed to get agreement with the AHJ over how the calculation is to be performed.

 

[Snape]

Re: derating-residential circuits

Re: derating-residential circuits

I'm an Electrician in the Uk and we have a good section on diversity in out IEE Electrical Regulations.
For cookers (Ranges) you apply diversity as it is unlikely all the resources will be used at full load, so you can work out a smaller cable size based on the diversity.

Does the NEC work on the same principles as this.

I will be moving to Canada, Ontario in the next few months i have purchased the Ontario Electrical code would it be worth buying the NEC code too.

Thanks
Ian

 

[charlie]

Re: derating-residential circuits

Re: derating-residential circuits

Ian, if you are going to stay in Canada, I see no reason, other than curiosity, to purchase the NEC. As far as diversity, the NEC does take it into account in some circumstances and not in others. For instance, a 10.5 kW range is counted as 8 kW but a run of conduit for a three way switch (two travelers and a return) leg is counted as three conductors even though only two will carry current at any one time.