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About Bruce Grant
Expertise
I can answer any questions about residential electrical wiring and most questions about commercial wiring. In my own business, I insist on using best practices in all work we do (which to me means "to Code" or BETTER, using the most recommended ways to do things).
Experience
I'm 65, but learned wiring basics as a teenager. I only used this knowledge for myself, friends and family until early 2002, when economic downturns suddenly made my 30 years in IT irrelevant. Through the Internet, I bought many books on wiring and electrical code and switched careers, becoming an unlicensed electrical contractor, carpenter, and handyman. I now know, after 7 years in the industry, everything I need to get a California C-10 License except some of the Industrial wiring stuff (which I'll probably never use, but need to pass the test). The main reason I haven't yet obtained the License is lack of funds to pay for it and the required insurance. Eventually, I'll get it.
Education/Credentials
* BS in Physics and Mathematics from Oregon State University, 1967
* Primarily self-taught from books written for electrical and construction pros, but also informal training from more experienced pros
Past/Present Clients
homeowners and small businesses in the San Francisco Bay Area, mainly on the S.F. Peninsula
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You are here: Experts > Home/Garden > Home Improvement/Repair > Electrical Wiring in the Home > 30 Amp Service installed
Expert: Bruce Grant - 11/3/2009
Question
QUESTION: My wife and I bought a 1927s house that we are remodeling. It has a 3 car garage that I intend on turning one half into a work shop. I am ready to install flourescent T2 shop lights and run a few plugs for power tools. While looking at the electrical situation I notice there are two service wires running from the house panel.
it runs into a old style panel box that uses screw in fuses. I imagine I should replace this with a newer breaker style box, correct? The fuse box has a 15 amp and a 30 amp fuse in it. The 15amp wire looks to be 12-3 and the 30 amp looks to be 8. Not sure if it 8-3 or 8-4 but does that make a difference?
The 15 mp will run my over head lights, 4 4'T12 fixtures and a outside security light with 2-75 watt floods. The 30 amp service does not have anything on it other then a wall plug. I would like to run this line over to the work shop side for power tool plugs.
I will be running a Sear table saw, thickness planner and some other various small tools like routers, drill press and planners on this line. I have used these tool before on a 15 amp service with no problems.
What size wire would you recomend for me to run from the the 30 amp panel box. Also, who I be better off changing the breaker in the house to a 20 amp service and saving the cost of 8-3 wire if that is required to use 10-3?
Any advice on this situation would be helpful. Also since wire is so costly right now I would prefer the less expensive route without giving up saftey and failure of the service.
ANSWER: Terry,
Your concern about safety and doing things correctly is one that most people should have -- you are a positive exception. Your basic intentions are definitely correct, so you only need help on the details.
You don't mention anything specific about the main panel, so I will assume, unless you tell me differently in a follow-up, that it is a modern panel with circuit breakers. If it's not, maybe you should consider replacing it AND the sub-panel with a larger, modern box and merge the circuitry from both old boxes into the new one (unless they are in separate locations, something else not mentioned).
National Electrical Code (NEC) allows your older, fused sub-panel to be "grandfathered", so you do not HAVE to replace it unless it's defective or dangerous for some other reason. If the wire to it is as old as the house, it has lower current carrying capacity than modern wire because of its type of insulation, so the wire should be replaced, but the box is probably perfectly safe. If the wire has modern insulation, then it is more than sufficient unless the wire run is over 160 feet on either circuit. Something often forgotten is LABELING each fuse box receptacle with both the correct fuse value and a description of what is on the circuit; this is a good time to do that.
AWG size 14 is usually used for 15A circuits unless the wire run is over 100 feet. Size 12 is used for 20A circuits. The requirement for a 30A circuit is size 10 wire. Using larger sizes than these is not only allowed in any case, but is also required if the voltage drop anywhere in the circuit is greater than 5% and is recommended if greater than 3%, since larger wire reduces voltage drop.
If the only things connected to those circuits are what you've listed, then you have a large safety factor built in on the 15A circuit. Your prior experience with the shop tools indicates the same for the other circuit. If you have to run new wiring on the 30A circuit, then compare the cost difference between #10 wire and #12 wire with the cost of a new 20A breaker to replace the 30A breaker. I would not reduce that circuit to a 15A one.
You mention that there is currently only one receptacle on the 30A circuit; it is probably a different type than the standard 15A and 20A receptacles elsewhere in the house, so if you decide to reduce the circuit to 20A, you should replace that with a 20A receptacle to prevent future use of a 30A device (with its special plug) on that circuit.
If the existing 30A circuit wiring is all #8 or even #10 (panel to sub-panel and sub-panel to receptacle), then I would recommend that you merely add multiple 20A receptacles onto the circuit from the existing receptacle box, using #12 or #10 wire. The first new receptacle wiring-wise after the original receptacle should be a 20A GFCI connected on the "Line" side. The remaining receptacles would be connected in parallel to the "Load" terminals of the GFCI (see the attached diagram, also available on my website at http://www.costeffective.us/img/GFCIplus.gif). Under current Code, the *new* receptacles require GFCI protection since they are in a garage., and it's always a good idea in a workshop, anyway.
If any of my assumptions are incorrect, or if you need additional info or clarification, please let me know in a follow-up. Good luck, Terry.
Bruce
IMAGE: GFCI protection of standard receptacles
---------- FOLLOW-UP ----------
QUESTION: Hi Bruce,
Sorry for no reply or any follow up. Since I last ask you a question we have put new siding on a three car garage, started a 7x22 additon to the house to expand the kitchen, started shingling the house on the 29th and will start the vinyl siding next week. Oh yeah and jacked up the house center supports 3/4".
The wiring is one of the last on the list to tackle until we can open ip some walls and get a handle on it. Our main box is a 125 amps service. We have natural gas cooking and heating so they only require minimal lectric to turn on lights bulbs or run the blower. We do use an electric dryer right now and thats on a 30 amp I think maybe a 40 by itself.
All the other lights in the house seem to run off two lines. Nor ure who the heck ran the new wiring but they fed off the old style wires in the walls it seems. We cut a few really old cloth wire in the addition add on that didn't seem to be connected to the box but show them hot. They will have to be chased down and replaces or disconnected.
The garage wiring I asked about is a doing worse then a nightmare and has been disconnected so I could sleep at night. They had a wire running from the downstairs lights, two bedroom lights and the kitchen lights running out to the garage service fuse box. Then they had a seperate wire running from the house service box out to the same garage service box.
The line running from the house box was feeding a single light mounted on the outside of the garage and one plug. The line running from all the house lights was feeding 6 other plugs and 6 pull string lights. The only smart thing they did was put in two 1" underground plastic pipes and the wire pull freely threw. So running two new 12-2 and 10-2 wire out to the garage from the house box will be a snap.
Now I am good at connecting plugs. switches, GFIs and that kind of stuff. But I think I will leave connecting the wire to the main box to an expert. Bad enough messing up a 15 amp line but I don't play with 125 amp service.
I thanks you for your suggestions and answers to my question. They helped out a lot in looking more closely at what I had to work with. For now, I need to straighten out the mess they had running wires all over the place with no purpose. They have old 1927s wiring hooked up to new wirng, to many things ran to one breaker and only 1-2 low voltage items running to a 20 amp service.
Your answer back to me was top notch and I appreciated your concern. I also appreciated your respect toward a DIYer just trying to do a home repair that had some electrical experience. I know their some out there that have no reason doing any electrical work. They scare the hell out of me and the person that did this job surely shouldn't be touching anything electrical.
Answer
Terry,
I'm glad I could help you. I'm amazed at just how much work you are doing in such a short time. I appreciate getting the blow-by-blow descriptions! It sounds like a previous owner did some really Mickey Mouse wiring, plus a few good things (different owners, maybe?).
FYI -- It is legal to extend old knob-and-tube wiring with modern wiring if the circuit has sufficient capacity. Be aware that the typical cloth-insulated wiring of that era connected to a 10- or 15-Amp circuit has a maximum actual capacity of only 13 Amps, so anytime you can easily replace it with modern wiring, you should do it.
The electric dryer (240-Volt) is required to be on a separate circuit from everything else.
Good luck with everything.
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