Residential branch circuit wiring in NEC code

[houstonian]

A friend was complaining that her lights dimmed in her fairly new house when she used the vacuum cleaner, and asked me to take a look at it. I found the following loads on the 120V 15A branch circuit, and estimated the VA load (in parentheses):
6 double receptacles (6*180= 1080 VA),
one recessed spot light (100 VA),
one attic light (75 VA),
one closet light (60 VA),
one ceiling fan/light (340 VA),
for a Total of 1655 VA on the circuit.

If I understand the NEC code correctly (no guarantee there...), and all of these are considered continuous loads, then with a 125% safety factor this exceeds the ampacity of the 15A 120V circuit.

Are my assumptions correct? Is it required to treat the receptacle or lighting loads as continuous? If so, does she have a reasonable claim that the builder should modify the wiring? Thanks for the advice!!

 

[pennsy]

Are my assumptions correct?

Not completely. First, this a residence, the 180 va rule applies to commercial wiring not residential.
The code does not consider a residence as having a continuous load.
Since that is the case 1655 VA is not in excess of the circuit device. That said good practice says the circuits should only be loaded to 80% or 1200 va.
From your description the circuit is code compliant, but not well designed. The problem is as you describe seems to be an overly long run whether it is NO. 12 or 14 but especially with no. 14 is voltage drop and when the vacuum cleaner is started there is a large voltage drop ergo the lights dim, momentarily but still an annoyance.
WmColt

 

[resqcapt19]

Are the lights that are "dimming" on the same branch circuit as the vacuum? If so, then as WmColt said, the run may be excessively long resulting in a voltage drop, or there may be a poor connection in the branch circuit wiring. Often times the dimming is related to the size of the utility transformer, the load on the transformer and the voltage drop on the service conductors.
Don

 

[dpc]

My guess is that this installation does not violate the NEC. Keep in mind that the NEC is a safety code, not a design guide. A system in compliance in the NEC still may not function well or efficiently.

As mentioned by pennsy, there is really no restriction on the number of general use receptacles that may be installed on a circuit in a residence.

The use of #14 AWG wire and 15A circuits commonly creates noticeable lamp flicker when the circuit is loaded. But this is still the norm for US residential construction.

I always advise people building new houses to spend a little extra and use strictly #12 AWG and then they can also use 20A breakers instead of 15A.