Main Beam of a Residential House

Status
Not open for further replies.
umm... The only thing else he said was for 4 tons it requires 40 amp CB and for 5 tons 50 amps.
I'd calll again tomorrow and see what he says.
Thanks for the concern.
 
You need the MCA values. Looking at some vendors equipment can give you a clue. My 4 ton heat pump has an MCA of 29 so #10 wire could be used. But if the HVAC guy picks one that is 31A, then you need #8 wire. Same with the 5 ton, it will probably be just under 40A, but if it goes to 41 you need a wire size upgrade. So I'd run 6-2 for the 5 ton and 8-2 for the 4 ton. Use 30A + 40A in the calculation, plus 5 more amps to cover the two air handlers. This comes to 75A which is 18000 watts and is going to put some hurt on your demand load calculation.
 
Thank you so much Mark.
Without seeing your calculation above I came up with close but not enough without much to go on except your calculation on reply # 25.
You said that a 4 ton AC takes 28 amps plus 3 more for air handlers

4 tons 28 x 240 = 6720w
3 x 240 = 720
_______
7440w

for 5 tons
28amps/4 = 7 amps/ton

7 x5 tons = 35 amps
35 x 240 v = 8400
5 x 240 = 1200 for air handlers
________
9600w
For both would have been 7440 + 9600 = 17,040 w

That''s OK. If I can not use the 200 amp service, I'll have to recommend the 400. And that would be more $$ for me because it's going to take longer to install bigger wires and bigger main.
 
Last edited:
Stickboy:
What is a 320 combo? Where can I buy it? Brand name please?

I called the PoCo ( I don't know what that means) Pacific Gas and Electric here) and I was told to use 320 rated and she said it's a 400 amp panel but 320 rated.
Is there anybody here who can enlighten me what these mean?

I also called the architect and I said I would like to drill a 1 1/2 inch hole at the center of that main beam in question. Now he needs the size of that beam so he can calculate so I need to go to the job site.

Thanks in advance
 
Last edited:
Whats so annoying about engineered beams?... I like that they have pre-punched knockouts you can hit with a hammer to go though and they're less likely to split than conventional lumber not to mention lighter.
 
"But what I was thinking is to drill the (one)hole for the feed wire of the subpanel on top of the cross beam to minimize the load stress but I will do as you said "center third and upper third" . And I will still ask the achitect who drew the plan to be sure."

The following applies to the general type of beams in residences. There are exceptions, so be careful.

The hole should be in the middle third of the height of the beam, and in the center third of the span. (BOTH conditions must be met.)

The rationale is as follows:

Beams are designed to carry the loads in bending, and must be checked for shear stress which is highest at the supports in a simple span (supported at the ends).

You want to avoid cutting anywhere in the upper and lower third of the beam because that will cause high stresses in both bending and shear. You will often see notches at supports, and when you do, you will frequently see splits in wooden joists or beams with such notches.

The middle 1/3 of height of the beam has the highest shear stress, but contributes very little to the bending capability. The shear loads are lowest in the center of the span, and highest at the reactions, so holes in the middle 1/3 of the height and middle 1/3 of the span are in the lowest shear stress areas.

Outside of that, talk to the engineer or architect.
 
bencelest said:
Stickboy:
What is a 320 combo? Where can I buy it? Brand name please?

I called the PoCo ( I don't know what that means) Pacific Gas and Electric here) and I was told to use 320 rated and she it's a 400 amp panel but 320 rated.
Is there anybody here who can enlighten me what these mean?

I also called the architect and I said I would like to drill a 1 1/2 inch hole at the center of that main beam in question. Now he needs the size of that beam so he can calculate s I need to go to the job site.

Thanks in advance
Click to expand...

That's one heck of a hole you're planning to put through that beam. And you've yet to even say what size lumber it is, or how many of them there are, or anything else of the sort. Are you sure you need a hole anything near that size? What are you passing through it?!?
 
I am only guestimating the size of the hole until I get the size of SER 3/0 4 wire which is going to be the feeder of a 200 amp subpanel .
Or can I go with 2/0 4 wire?

BTW I just ordered the 2006 NEC book . I am using the outdated 1996 NEC book that I found which was gatheringdust in my closet.
 
Last edited:
bencelest said:
Again thanks a lot to all of you. All of you are very helpful.

Here's what I come up with for load calculation. This is just APPROXIMATE because I still don't know the kW of the appliances that will be installed. But mainly I would like to know if my load calculation procedure is correct. I will adjust the calculated numbers later.

4200 sq ft Single Dwelling
Computed load
General lighting load

4200sq ft at 3va /sq ft = 4200 x 3 = 12,600
Small Appliances load:
Dishwasher 1500
Garb disp 1500 3000
Laundry 1500 1500
________
Total general light & appliances load 17,100
3000 v-a at 100% load 3,000
17100-3000 = 14,100 v-a at 35% 4,935
_________
Net General Lighting and small appliances load 7,935
Range Load 8,000
Dryer load 5,500
Hot tub load 8,000
Water heater 2,500
Wall Mounted oven/microwave 3,000
Air conditioning 10,080
__________
Total Load 45015

For 120/240-volt 3 -wire single phase service feeder
45015 /240 volts = 187.6 A
Click to expand...


Consider using the alternate method of 220.82 and Example D2(b) in Appendix D.

Everything but the A/C, including making the water heater 4500 VA, comes to 46,100 VA.

Use 100% of the first 10,000 VA + 40% of the balance:
10,000 + 0.4 x 36,100 = 24,440 VA
Add A/C load = 10,080.
Total is now 34,520 VA

Amps = 34,520/240 = 143.8 Amps ==> 144 Amps

Well within 200 amp service.
 
DaveTap said:
Whats so annoying about engineered beams?... I like that they have pre-punched knockouts you can hit with a hammer to go though and they're less likely to split than conventional lumber not to mention lighter.
Click to expand...

Personal preference.

My father swears by OSB, I think it stinks. Some people like engineered beams, I don't much care for them. For one thing, I think engineered beams create problems in second story floors, and OSB on decking is more prone to sagging. But that's a completely unprofessional, unscientific opinion I have no intentions of backing up with facts, beyond that an all-wood engineered beam is weaker than a dimensionally identical piece of solid lumber.

I like wood. Giant chunks of wood, not pieced or glued or stapled or anything else of the sort. Except plywood, but that's kinda unavoidable ...
 
at 144 amps total load if you add the nca of the 2 AC units:
26.2amps + 34.2 amps = 60.4 + 144 = 204.4 amps
plus the 4 bathroom fans and the 2 garage door openers which would go over the 200 amps limit more.
The HO gave me the OK for the 400 amp service anyway and I told him that it will be about $550 more from my original estimate vs th 200 amps.
 
I found out that the main beam 's measurement is 5 1/2" x 14" x 19' and I have to pass through to 2 of them. When I called the architect he asked exactly which beam I was reffering to. He was looking at the plans and I did not have one.
I was lucky enough to talked to the plumber who gave me all sorts of advice. It did really made me concern working with those prefab lumbers.
I also found ways that I can run my wires so that I can bypass those prefabs. And the architect thank me for not touching it.
Had I opt to drill a hole to the main beam I would have used a 1 1/2" hole for a 4/0 aluminum 3 wire with ground. It's the diameter of the cable.
Thanks a lot to all who respond to my querry.
You all helped me a lot.
 
Last edited:
bencelest said:
Stickboy:
What is a 320 combo? Where can I buy it? Brand name please?

I called the PoCo ( I don't know what that means) Pacific Gas and Electric here) and I was told to use 320 rated and she said it's a 400 amp panel but 320 rated.
Is there anybody here who can enlighten me what these mean?

The panel comes with two 200a breakers and distribution but the meter is plug in. not CT's and is only rated at 320 amps . Try millbanks , circle AW . In your area Royal wholesale is near by and has them.
Click to expand...
 
acrwc10 said:
bencelest said:
Stickboy:
What is a 320 combo? Where can I buy it? Brand name please?

I called the PoCo ( I don't know what that means) Pacific Gas and Electric here) and I was told to use 320 rated and she said it's a 400 amp panel but 320 rated.
Is there anybody here who can enlighten me what these mean?....
Click to expand...

THIS means that the assembly is 400 Amp, but with a continuous rating of 320 Amps (80%).
Click to expand...
 
tallgirl said:
Personal preference.

My father swears by OSB, I think it stinks. Some people like engineered beams, I don't much care for them. For one thing, I think engineered beams create problems in second story floors, and OSB on decking is more prone to sagging. But that's a completely unprofessional, unscientific opinion I have no intentions of backing up with facts, beyond that an all-wood engineered beam is weaker than a dimensionally identical piece of solid lumber.

I like wood. Giant chunks of wood, not pieced or glued or stapled or anything else of the sort. Except plywood, but that's kinda unavoidable ...
Click to expand...

I used to think OSB was junk till a gc showed me that if you take a piece of OSB and lay it in water,then take a piece of plywood and lay it beside the OSB.Come back in 2 days and the OSB held together while the plywood was junk.And OSB is alot cheaper to buy.
 
allenwayne said:
I used to think OSB was junk till a gc showed me that if you take a piece of OSB and lay it in water,then take a piece of plywood and lay it beside the OSB.Come back in 2 days and the OSB held together while the plywood was junk.And OSB is alot cheaper to buy.
Click to expand...

That depends on the grade of plywood and whether or not the OSB was cut. Once OSB is cut, it's water resistance is much lower than plywoods. I'd rather a leaky roof, or leaky toilet or bathtub, could be fixed without having to remove parts of the roof or floor, and it's more likely that the lumber will be damaged by water if OSB rather than plywood. Plus, I don't know if it's misapplication (since most OSB specs I see require 16" OC framing) or poor quality, but OSB roofs seem to be wavier than plywood roofs (before plywood became all but extinct). This also corresponds to more homes being framed 24" OC, but that's an entirely different rant.

Fact is, the commonly used glued-wood products have a poor track record with long-term water resistance in actual application. The less glue and the more wood, the better. OSB is one heck of a lot of glue ...
 
Status
Not open for further replies.
Top