Mod House

[User Name]

Hey guys, rolled up on a new modular/prefab house today to start doing the service tomorrow for it. I was kind of scratching my head at the wiring job here out of the factory, the sales rep told me they wire the houses to 2020 code, I just kind of said ok for the moment. But how is notching the floor truss, jamming in as many wires as you can and plating them up to code? Is a nail plate listed as nm supporting means? Looking at 334.80 basically says you got to make amperage adjustments when more than two nm's are installed together, so the one bundle through the framing has 11 romex's bundled, probably would need to derate that like 45%? Looking at 300.4(A)(2) Notches in wood, seems to allow for this type of installation. I thought at one point there was a code you could only have 2 romex's per hole with a minimum size hole of 3/4" but I must be mistaken, can't find it.

Also the company gave me an 1 1/4" pvc pipe to jam at least 6 basement/utility circuits into, I thought there was something of a code that you weren't allowed but 1 romex per conduit? Maybe I'm wrong on that too.

I don't mean to criticize anyone that wires their houses like this, I've just never seen it done like this and at first glance it doesn't look right but maybe it's totally acceptable. More than one way to skin a cat as they say I guess lol.

 

[User Name]

Oh also I don't understand how they had 3 notches per board and only used 1 for those whole length, why not divide them up? 25 cents for a nail plate adds up but yikes, times can't be that tough.

 

[kwired]

How is support any different than if you drilled holes and pulled through them? Not an electrical inspection fail for that aspect IMO, maybe structural/framing fail though, drilling or notching that close to upper or lower portion of a floor joist will lessen it's load carrying ability.

That all said, I would think drilling would be faster than notching then plating anyway.

The 1-1/4 PVC - I likely would have installed a junction box on it and pulled THHN/THWN conductors through it instead of NM cables. Deration does come into play. 10-20 conductors is 50% adjustment if you pulled 6 two wire circuits in there NM probably doesn't fit so well after ampacity adjustments are made.

 

[User Name]

I'm just guessing by the notches they have a tool or machine that notches them out before they get installed. Don't know that for a fact, but that's how I'd do it. There's a code I read some where back you're allowed to remove a certain percentage of a 2x4 or whatever before it impacts the structural integrity.

Thanks for the tip for my branch circuits, I'll definitely put a pull box on that pipe and do thhn!

 

[kwired]

I'm just guessing by the notches they have a tool or machine that notches them out before they get installed. Don't know that for a fact, but that's how I'd do it. There's a code I read some where back you're allowed to remove a certain percentage of a 2x4 or whatever before it impacts the structural integrity.

Thanks for the tip for my branch circuits, I'll definitely put a pull box on that pipe and do thhn!

I was thinking about mentioning that those notches maybe were cut before they even installed the framing members. They might do similar on wall studs as well. Might even be every one of them has notches but not every notch gets used.

The floor joist maybe they did figure out mechanical loading and did figure out what size can be used even after the notches are cut? If all joists are notched before ever installed might save them some labor even though they possibly increased width to account for mechanical strength?

Lots of repetition in these homes, even with different floor plans, still a lot of things are same from one model to another and any way they can find to make it go together faster lowers their costs.

 

[LarryFine]

I'm just guessing by the notches they have a tool or machine that notches them out before they get installed.

They were most likely gang-cut, stacked together and dado-cut in one pass.