Hello all it’s been a long time since I’ve posted here but I’ve got a question.
I inspected a 1953,1300 sqft property with 4 electric panels today (sheesh).
The main panel next to the meter is a newer panel with no main shutoff and 3 circuits. Two circuits are 20amps and irrelevant to my question.
The last circuit is a 100amp breaker used to feed a sub panel that does not have its own shutoff but basically serves the rest of the house (two other sub panels and some smaller circuits).
In the attic I found the sub panel feeder conductors coming from the main panel to the sub panel.
it is type NM-B , 4 wire, size 4AWG.
I’m calling this out because this is feeding a sub panel not a main panel, and the wire size should be larger for 100amps, since it is technically a feeder not a service entrance, it is also type NM and as a result has to use the 60degree column (even though it is type NM-B).
This is my understanding for feeder and branch circuit wire sizing as opposed to service entrance cable sizing but I wanted to check with any sparkies first
You are correct, the sub-panel is being fed by a feeder and that the OCPD (100 amp) is too large for #4 NM cable which has a 60° C ampacity of 70 amps. NM cable comes in sizes from #14 to #2 AWG. At 60° C, #2 AWG copper NM cable has an ampacity of 95 amps. That cable can be used with a 100 amp OCPD if the calculated load of the sub-panel is 95 amps or less due to the next size up rule in 240.4(B).
Service conductors for a single dwelling can be sized to 83% of the service disconnect size but that is not relative to the sub-panel in this case.
So you could end up with two problems:
The OCPD is too large for the feeder conductors.
Or the calculated load on the sub-panel larger than the 70 amps ampacity of the feeder conductors. For case #1 you could change the OCPD to 70 amps but that is only if case #2 would allow a 70 feeder for this sub-panel. If the calculated load is greater than 70 amps then the conductors must be changed.
Screw that!
Call it out for… “All Repair(s) to the homes electrical system, (which may include replacement of multiple electrical components), as deemed necessary for function and safety, by a Licensed and qualified Electrical contractor”!
“Further evaluation and correction” comes off as… you’re not sure about the problem… so a lazy tradesperson may not give it the full attention that you obviously did. “In and Out”… “Wham Bam Thank You Ma’am”!
Whereas… specifying “To make necessary repairs”… put’s the onus onto the tradesperson to do his/her job, and figure out the problem so they can repair it properly and completely!
Yeah I agree… I think sometimes the wording I use either sounds boring or makes the issue sound unimportant. Got to remember who will be reading it too