Hi Everyone,
Have a 1940’s era rental house that I want to rehab and thought it would be a fun exercise to scope out it electrical needs. Electrician will do the actual work, but I’m planning for a full kitchen and bath remodel and in general upgrading it to this century, so I’m trying to see how close my plan is to reality. This is located in the Bay Area, CA
House has a newer (1992) main panel with a 90 amp main, with 5 breakers, which include 2 – 15 amp, 2 – 20 amp, and 1 – 50 amp for an electrical stove. 90% of the house is knob & tube with only a couple of exceptions.
The house as a 1250 square foot main level with 2 bedroom, 1 bathroom, formal dining room, living room/foyer, and eat-in kitchen. Lower level includes a garage and a 500 square foot basement with laundry area.
The house also has natural gas that can run a stove, furnace, water heater and clothes dryer and plan to keep it that way. My preference is to convert the 50-amp breaker that runs to the kitchen stove into a sub panel that will power the new kitchen remodel, further freeing up any of the other circuits that it is currently using. Although the kitchen will use a gas stove, this 50-amp panel will still power a number of appliances, including frig, dw, disposal, microwave, hood etc.
Here are a some of my questions, assuming a reletively generic remodeling, no hottubs, whirlpools, or other devices that require a lot of additional power:
1. Should a 90 amp main be enough or do I need to consider upgrading this panel. If 90 amps is not enough, and if this panel can accept a 100-amp breaker, is there really a differnet gauge SE cable used between a 90amp and 100amp service. What gauge SE cable should I be looking for to support a 100-amp service.
2. If I can keep the 90 amp main, and convert the 50 amp breaker that runs to the kitchen to a sub-panel (assuming that this is legal to do) can I run second sub-panel to run the rest of the house. Would it only be a 40 amp panel (40 + 50 = 90) or could I run a larger panel? I would consider doing this for wiring efficiency and because I do not believe the main panel can support no more than another 3 or 4 curcuits. I would have the existing 15/20 amp circuits removed from the main panel and power off of this second sub-panel if this is a possibility.
I might have more questions, but until I know what I’m thinking is rooted into some sense of reality, I think I should hold off for now.
Thanks,
Tark
Replies
Without electric range or dryer then 100 amps (or even 90) should be plenty.
Here is a checklist/article on how to figure load.
http://www.taunton.com/finehomebuilding/pages/bh0019.asp
If needed here is an article on service entrances.
http://www.taunton.com/finehomebuilding/pages/bh0007.asp
And one on sub-panels.
http://www.taunton.com/finehomebuilding/pages/h00176.asp
"2. If I can keep the 90 amp main, and convert the 50 amp breaker that runs to the kitchen to a sub-panel (assuming that this is legal to do) can I run second sub-panel to run the rest of the house. Would it only be a 40 amp panel (40 + 50 = 90) or could I run a larger panel? I would consider doing this for wiring efficiency and because I do not believe the main panel can support no more than another 3 or 4 curcuits. I would have the existing 15/20 amp circuits removed from the main panel and power off of this second sub-panel if this is a possibility."
Yes, you can run one or more sub-panels.
It does not work by just adding up the size of the breakers. You need to figure the demand on each side. But you can always go with bigger panesls. In fact small panels usually don't have many breaker spaces to it would not be unusal to use 100 amp panels for the subs.
But youcan feed them from a smaller breaker so that you can run smaller wire and save $$$ with the cost of copper.
I have no idea why they used 90 amp breakers. Look at the panel, but I am sure that it is rated for 100 or 125 amps (or even more), unless they overloaded the panel and it is only a 60 or 80 amp panel.
As to the wire size. If you using the special table for service entrances #4 AL or #2 copper is rated for 100 amps.
But if you use the regular tables #4 CU is rated for 85 (which can be rounded up to 90) and #2 AL is 90 amps. So that might be what they used. Or local code or uninformed inspector requred the lower rating at the time.
Thanks Bill. This gives me food for thought.I have one really "dumb" question. I've noticed that the plugs and lights in the bedrooms are under one 15-amp circuit. I was always under the impression that plugs and lights had to be under separte circuits. Is this more of a best practice or are separate circuits required.
you need to upgrade to a 200 amp.
No requirements at all for them to be on separate circuits.But I would put it as a good practice or maybe even better practice. But I don't think that it rises as high as needing a best practice, not in bedrooms.Now areas used with power tools, and that includes kitchens, it is best practice. And required in kitchens, but code does not address it in workshops or garages.
Thanks again.
I've never even seen a 90A breaker, or sen refereces to them in the wiring capacity charts.
Local usage/practices?
WalkerIs this another one of your incornations?Table 310-15(b)(6) which is limited to Residential Serivce Entrances using USE cable, or RHx or THxx wire is only shows listings for 100, 110, 125, 150, etc up to 400 amps.Of coruse by the time that table was writen (in my 99 MEC) the miniumum service allowed was 100 amps, so no lower is shown.But the basic wire tables show in 310-16 list all kinds of ampacities from 20 to 2000 bepending on the wire size, type, and tempature rating.As far as breaker size you are allowed to go up to the next higher STANDARD size. The NEC list standard sizes, but I don't wnat to search for them.But looking at a list of SQ D breakers they show 15 to 50 amp in 5 amp steps, 50 to 110 in 10 amp steps, and 125, 150.IIRC those are the standard sizes and then some higher ones.I while back I need was working on a house that had 30 amp for the AC (and furacne). Split off the furance to a separate circuit. But the BB and hardware stores only had 15, 20, 30, 50 amp breakers, while the AC called for a max of 25.But the electrical supply house had them up on their front display so they are not that rare.Typically you won't find a 90 in a home. Just not that much of loads that require them.Maybe some resistive heat backups for HP's. But I think that they are typically much smaller.There are some on dempand electric WH that use 90 amps (from what I have heard people mention), but it if it like the 120 amp ones them it is really a collection of 30 amp modules.And a feeder to a sub-panel would normally use a more common size such as 60 or 100. But it just might be that based on the wire that was available, temp deratings or some odd combination that it was more reasonable to go with a 90 rather buying larger wire for the 100.Some large welding equipment might need a 90. But while BB might have one in his home workshop that certainly is not common residential.
Edited 8/12/2006 11:57 am by BillHartmann
Well, I'm not sure you're going to like my answers. To keep this post short, I'll just hi the high points.
Things have changed a lot since the house was built. Not just codes; also our lifestyles. You're in a situation where the quickest, easiest and best way to remodel is to knock it all down and start over! Failing that, a complete gut now will save you all the aggravations caused by half-measures.
Here are some of the code requirements you'll need to meet:
- A residence requires 100 amp service. This will also need to have a ground in addition to the "water bond;"
- Your circuits will need to be "grounding"; this usually means new wiring, with a ground wire;
- Additional circuits will be needed to be added for the bath and kitchen. Bedrooms will need AFCI protection. Outdoor receptacles are needed; and,
- Chances are, lighting will have to comply with an 'energy code.'
Another thing to consider is that every gas appliance SHOULD also have a receptacle at it. This is for the electric igniter that is replacing the pilot light.
Your stove circuit probably has three wires right now; a sub-panel will need four.
Whatever panel you use, make sure there are plenty of extra spaces for adding future circuits. Indeed, you might also run some extra pipes from the panel, into the attic and crawl spaces, for the convenience of future electricians.
You'll need to add permanently wired smoke alarms. Every outside door will be required to have a switch-controlled light.
You really need to sit down with some pros and sort things out before the first nail is pulled.
Good catch on the four wire vs three on sub vs stove!
Actually he was only talking about reusing the breaker, not the feeder. But he might have had that in mind.
If you have K&T wiring, be ready to upgrade it as soon as you open the walls.