Isolated Ground for home office/rec rm?
I’m planning to finish a bonus room (about 21X15 unfinished room over garage) in my house. The house is a 2-story colonial built in 2000. This room will be used as an office/ family room. It will contain several computers and a modest home theater system. While this room is open, it offers an excellent opportunity to pull wires from the basement to the attic. (Yes, I’m wiring for network and putting in some conduit for future use).
Right now, this room has a 15A circuit that was pulled when the house was built. It has been suggested that while the walls are open, I should pull a second circuit to support the electronic gear. It has also been suggested the the second circuit be an isolated ground to reduce noise for the stereo and/or computers.
Questions:
Is 15A enough?
What are the advantages of an isolated ground circuit and is it worthwhile?
Pete
Replies
15 amp plenty for computers and such. I wouldn't worry about the isolated ground. maybe a 20 amp circuit for the home theatre if your going to use a monster amp and huge powered subwoofer but in most cases 15 amp is plenty. Im a electrician my home theatre is on two 15 amp circuits. and my computer is plugged in to any old wall outlet. I think most people use isolated ground systems just for show. the best thing i think you can do is use high quality speaker wire and good equipment (spend heavy on the tuner/amp) Talk to many people on speaker placement. I once got two different rear channel speaker locations from the same audio store.
A dedicated computer circuit is a good idea. I usually go with a 20A. Some people report fewer mystery glitches after a separate circuit is installed. I understand that the computer components last longer and operate more smoothly not having to deal with the spikes and noise from appliances and other loads.
If you install a separate circuit all the way back to the first point of disconnect, not a sub panel, adding a separate, isolated, ground will not give you better performance.
A few ideas:-Plug all connected computers and peripherals into the same circuit. This would be another reason to go for a 20A circuit. This limits the possibility of ground differentials and circulating currents.
-Install a whole house surge arrestor. This is a good idea just about anywhere even if you don't have a computer.
-At the end of the dedicated circuit install a high quality surge arrestor strip one with a arrestor for the telephone line is usually a good idea even if you don't dial up your ISP because it keeps you covered for FAXes. Replace this strip every year, two years for a really heavy duty one, or so.
Marking the unit with the month and year on a strip of tape placed on the bottom of each unit helps. Don't throw the older ones away. Move them to less important equipment. 1st year - computer. 2nd year - home theater system. 3rd year - Stereo system. Etc. The more of these units in a house the better the overall protection.
-If you loose power regularly, utility companies or thunder storms, plug a good quality UPS, Uniterruptable Power Supply, into the power strip to carry your computer through momentary sags and power loss.
What exactly do you need to do to isolate the ground, on an individual circuit?
Edgar76b,An isolated ground receptacle, typically orange in color with an isolated ground symbol, have two ground connections. The equipment ground, intended to provide a return path for faults and shorts in both the system leading to the receptacle and the receptacle itself, and a reference ground that provides both functions to the equipment plugged into the special receptacle.
The reason this is necessary is that some equipment drain a small, sometimes not so small, but regular current into the ground system. While this is normal and generally not harmful it is often enough to throw off delicate electronics as to what a true ground level really is. This problem is common when there is unrelated equipment, especially motor loads and older refrigerators, on the same circuit as the computer. This is made only worse when the ground is terminated into a subpanel as all the branch circuit grounds to the subpanel share the same ground conductor back to the next panel. In some cases, a separate building, the ground will also be routed back to the parent panel on the neutral.
In a correctly installed isolated ground receptacle the isolated ground conductor is not terminated at any subpanel. It is electrically isolated, thus the name, from the normal ground bar at any subpanel and continues on to the first point of disconnect, the main panel. This provides a more accurate ground reference by avoiding the noise and transient currents common to the equipment ground.
Most of these problems are found where the computer shares a circuit with other equipment or where powered through multiple subpanels. Both of these problems are avoided by installing a dedicated circuit to the main panel. In this case, a dedicated circuit run to the main panel, an isolated ground receptacle and the extra wiring are largely a waste of money and effort. In fact while a few years ago isolated ground receptacles were commonly specified as a cure for unrelated problems. More recently, as the engineering has caught up with the mythology, I have seen isolated ground circuits less frequently and more intelligently specified.
I hope you will let me rexplain this, in my terms so i understand. Thank you by the way, But If I understand correctly, The important thing is that the circuit is dedicated, To nothing but the intended Recepticles, or equipment. With its ground terminated at the first point of disconnect. (the Breaker / not a breaker in a sub panel in between somewhere )
My Question: Is the recepticle important for any reason other than its color?
Edited 7/28/2002 10:00:07 PM ET by Edgar76b
You have it. A dedicated computer circuit is, IMHO, a sound investment that will pay dividends and save you trouble for the life of the house. Even if you don't go with a whole house surge arrestor and a UPS do get a high quality surge strip with telephone line protection, about $40. If you have a choice an external modem offers additional protection over internal models. I use a USR ext 56k as cable is unreliable and DSL unavailable.
The orange dedicated ground receptacles would not be any improvement over a good industrial duty model. The orange color might help identify the dedicated computer circuit but I think a grey industrial duty model, they have heavier contacts and construction over residential grade, looks better and does the same job for a bit less money. In most cases the extra ground connection does no good so why pay extra for it.
Edited 7/28/2002 10:19:38 PM ET by 4LORN1
i still think its overkill but if you must have one IG receptacles come in all colors
In IG receptacle outlets, the device strap is electrically isolated from the equipment grounding terminal/ground slot on the outlet.
This is necessary ONLY if you're using metallic conduit as a wiring method. It isolates the equipment grounding conductor from the conduit, which is grounded.
If you are using NM (romex) and you're running a dedicalted circuit, the IG outlet is money down the drain. I am especially amused by audiophiles who think the orange outlet with the triangle is essential for best performance of their systems!
Cliff
I am especially amused by audiophiles who think the orange outlet with the triangle is essential for best performance of their systems!
There's alot to be amused with those dudes! They also frequently want "hospital grade" outlets, which they somehow think will make a difference, in combination with their >$500 power cords (I kid you not). There's one company selling a box which the "audio purist" is supposed to plug into an outlet in the house, which magically makes all the electrons flowing through the house power "coherent", with a fantastic effect on the sound, according to the manufacturer.
'always wondered why they never stop to consider that run-of-the-mill Romex is feeding that hospital-grade outlet, which is fed by a standard panel, etc. 'there may be a niche market for electricians to do whole-house rewiring with stainless-steel conduit and gold-plated silver conductors. After all, these guys seem gullible enough to buy anything.
Audiophiles are an interesting lot.
I had one who specified double runs of 12-2 speaker cables. It struck me as a little bit odd until I learned that all of the cables where made up of silver coated, "oxygen free" and ultrafine stranded copper at $5 a foot.
We installed the cabling, all 12 runs, and left the customer overjoyed with the set up. The guy claims that it "sounds better". I couldn't tell the difference but then again I'm not an audiophile. The way I figure it my "tin" ear has saved me $20,000. compared with this guys system.
Wow, I bought my oxygen free 10 ga wire in 1983 when it was only a buck a ft. And yes, it does make a difference. It connects my tube amp to my transmission line speakers. As with other things, there is hype and gimmickry with audiophile gear, but there are also some legitimate issues out there. My favorite catch phrase is "digital-ready." Hmm, I wonder if my Clark-Eisenson tube pre-amp, which has a 0.5-400KHz response and can put out +/- 40V swings, is digital ready? ;-) You guys might laugh, but I guarantee that after you hear "Smiling Phases" off of the direct-disk lab's pressing of BS&T's second album, you'll come away with a new appreciation for the difference between real and good.
If you have a decent amp, them it should have a power supply that is able to filter out "anything" that comes in over the line. That is why God created huge capacitors. If you are depending on line voltage stability, you are already screwed. The problem with most audiophiles is that they don't have a clue about what is real and imaginary, and they spend beaucoup bucks trying to solve imaginary problems. A dedicated 15A circuit for the equipment should be sufficient. Anything else is imaginary overkill.
Similarly, I wonder why people want a 20A circuit for computers. Is there a combination of computer gear out there that draws even 4 amps? If anything, I'd want less capacity in a branch circuit that likely supplies numerous devices through 18 gauge zip cord.
FWIW, this site reminds me of the internet of the 1980's in the pre-AOL days, before "me too" was ever uttered in a usenet posting.
bob
20A because it is only about $.02/ foot more.
Besides with 5A for the power supply (600w for the 2 CPUs, 3 HDs, CD, CDRW, DVD, and high end video card. Soon to be 2 cards.), 1.7A for the 19" monitor (Soon to be a 21" at 2.5A) (Within a year it will be 2-21"monitors or a total of 5A), 2A for an ancient but cheap and reliable impact printer and another 1.7A for a multifunction device and an additional .6A for the audio amp. All these are nameplate values. If I add all this up correctly it comes in at 14.3A. That's mighty close to 15A. I'm glad I installed a 20A circuit.
You are correct in that the MOVs failing is designed to blow, in most surge strips, a fast blow fuse. Unfortunately the fuse is not fast enough and blows after a surge is let through. The fuse is added to disconnect the MOVs from power and prevent them from cooking in case of a partial short not to protect the equipment plugged into the strip.
You are also correct that the surge strips would be less abused in areas that have fewer lightning storms. I'm in Florida so around here 1 to 2 years is all I recommend for important computers. Even without thunder storms some power quality references claim that most houses receive something like 6 surges large enough to damage electronics every day. These are from line switching and some motor loads primarily and tend to be very small compared to what lightning can produce.
Telecommunication sites have arrestors with MOVs the size of a brick and weighing about 12 lbs each. A direct strike will often vaporize one or more of these blocks and make replacement of the entire surge box necessary. At $6000 a pop for the box and another $1000 for replacement, mostly overtime, the companies are glad to pay for it compared to the alternative. The $6000 box protects a $1000,000. in equipment that is doing $25,000. an hour in business.
Also if you have a Laser printer they draw lots of current.
My 10 year old IBM (Lexmark) is rated at 6.5 amps. But that is average running current.
When first fires up the fusing heater I know that it draws a lot more, but I have not tried to measure it.
I'm a scientist by day and therefore it is my nature to question numbers rather than just accept them. You presented a situation that justified a 20A circuit. My calculated power consumption is WAY lower than yours and more in line with my suggestion of 4 Amps. For the PC, the ATX PS is rated at 250 watts, but to calculate the load component by component, figure 45 watts for the MB/memory, 25 for the CPU, 12-15 per HD, and 12-15 per CD drive. Maybe 10-15 for the video card, 5-10 watts per fan. So an average PC is probably drawing 120-180 watts, or 1-1.5A . And these are max values. A CD at rest only consumes 2 watts. My 17" monitor draws 1.5 A and the 21" 2.0A. The HP printer draws a whopping 28 watts, the cisco modem 20 watts, and the linksys router 9 watts. So even with 2 puters, monitors, TV, window fan, and misc electrical in the office, I'm well within the limits of a 15A circuit, even with everything running at once.
I use 20A circuits where they are required by code (bath, kitchen, DR, laundry, garage) or appropriate, and use 15A where the power consumption isn't that great. Most of the 15A circuits in my house feed small devices with thin power cords. I'd rather have a breaker trip quickly if one of these shorts out, hence my preference for 15A to feed circuits in living spaces and bedrooms. Now if I were running space heaters in those rooms, then I would have considered putting in 20A circuits. In fact, I did put in a 20A circuit to run just the window AC units in the 2 south side bedrooms. I know we were required to put a 20A circuit in the dining room, but I still don't know why the cordless phone and cordless dustvac need so much capacity. ;-)
Just went by nameplate ratings. I install 600w power supplies in most of the computers I build. They are less sensitive to surges, run cooler, have plenty of overhead for devices and are very reliable. It would be rare to have any of the devices actually draw the rated amperage. For the extra 2 cents per foot I go for #12 on all the dedicated computer circuit that I put in. If a customer objected to the added expense of using #12 instead of #14 I would gladly write off the $2 difference. None has ever objected. More head room and lower ground resistance and a small savings in power usage. The lower ground resistance helps the surge arrestor strip do its job.
As for the 15A circuit being safer. I don't think so. Inverse time circuit breakers are both less sensitive and more reliable than you think. If you really want to be safer with the smaller cords install an arc-fault circuit breaker. I agree that in most bedrooms even 15A is overkill.
With media centers, computer rooms, home offices and shops it is hard to provide too many receptacles and even sometimes circuits. When I wire houses one dedicated circuit to each is the minimum for me. These are in addition to the code minimums. You did know the code is an absolute minimum. For anyone who cooks regularly an additional SABC is smart. Also the refrigerator and any freezers in anything but a spec house deserve a dedicated circuit. Finding out that $2000 in meat went bad because your kid got creative where she plugged in the hair drier tends to ruin the day and leave you with a nasty clean up.
In new house wiring its close to 5 cents on the dollar to add these versus adding them after the fact. I would rather have ampacity that I don't use than need what I don't have.
I'll ask my EE friend about 15 vs 20 reaction times. I did put in arc-faults on the two circuits which use either 2-wire non-grounded romex or the first floor lights which I'm sure are knob and tube. This house is on its third generation of wire. And I hear ya on the cost of putting it in while the walls are open vs after the fact. I lucked out and located an abandoned duct from the basement to the second floor which had access to the third floor attic. That saved us from a lot of 3-story wire pulling time around the vent stack. The time I took to draw up an accurate floor plan has really helped in figuring out what connects to what. I keep reminding Princess though that the outlet in her craft room cost about $175.*
When we moved in, the first floor was served by (2) 15 A fused branches. The outlet for the fridge was off the basement light circuit. The house was grounded through the water pipe since either someone didn't connect the neutral at the house in the first placeor it just rusted loose. The inspection sticker on the old fuse box said 1949, and i believe it. Now we have a dedicated 20 for the fridge, (2) GFI 20's for the counters, a 20 for the DR, a 20 GFI for the bath, and 15's for the LR and the sunroom. And not a single extension cord in use!
The Willamette Valley seems to be pretty surge free. We seem to get a few lightning bolts each Spring and thats about it. Most houses have a single window AC unit for those few days where it gets above 90. Its not at all like the terrors we experienced in the spring in NC and MD when all Hell would break loose with those 95 degree, 95% humidity late afternoon thunderstorms. Sure do miss the beauty of the lightning.
* Princess wanted an outlet in one particular spot. But to get there, the electricians had to drill down closer to a window than they wanted because of the finished wall in the third floor attic space. So they had to drill through 2 top plate 2x4's, 2 window header 2x4's, and a sill plate 2x4. All of these were full-dimension old-growth 2x4's, and you could really hear the hole hawg struggling as the drill bit grew to 8 feet with extensions. Then it turned out they were right next to a stud, and had to drill laterally from the box opening cut in the trim to access the stud bay with the dropped wire. Someone had put in an extra short stud under the sill plate. They were not pleased. When I drop a wire now, I check the stud locations in several places just to make sure before I cut the first hole.
My plan calls for one 15 amp circuit, dedicated for smoke detectors. All the rest are 20 and up. The work is the same, and the cost difference between #12 vs #14 wire is trivial. Box and conduit fill counts are based on the biggest wire, so there's no advantage to using #14 except where the load is guaranteed always to be so low that #12 would be ridiculous.
-- J.S.
This is from an commercial EE friend of mine who does high end building designs re: our discussion.
Bob,
First of all, sorry I didn't get back to you sooner. No, it's not worth
talking about, however... There are 2 things a breaker protects against,
overload and short circuit. In the case of overload, the 15A will certainly
trip first. Therefore, from a safety standpoint, you are correct. In the
case of short circuit there is a minute difference, only noticable to a test
instrument. Your friend is on the right track with "overhead," our designs
today always use 20A circuits and 20A rated receptacles. They are the
receptacles with the horizontal slot as well as the vertical, on one prong.
Some copiers have 20A plugs with one vertical and one horizontal prong. On
the subject of surge suppression, the larger phase wires will also allow the
surges an easier path to your device, so that argument is sort of moot.
Lower energy costs is correct from an absolute standpoint, however, from ####practicle standpoint it won't be noticed. The only place that I know of
where 15A circuits and receptacles are used is in residential. Incidently,
the code requires 2- 20A receptacle circuits in the kitchen. I would advise
anyone doing their own wiring to use 12AWG wire and 20A circuits with 20A
receptacles. You will have more capability and flexibility for future
changes.
And that's all the advice for today!
Sparky
-----Original Message-----
Subject: 15 vs 20A breakers
I'm in a friendly argument with a guy right now over 15 vs 20 A branch
circuits in an office/media room. I contend the 15 is safer since so
many devices are run off 16 and 18 gauge cords which are prone to damage
and shorting, and less energy to start a fire gets out of a 15 before it
blows than a 20. He contends there is no difference in the reaction
time and that it is better to have a 20 for overhead, better surge
supression grounding, and lower energy costs due to less wire
resistance.
Is it even worth our time to think about this? ;-)
You say to replace the individual surge arrestor every year: why ?
AND, if you have to change the individual surge arrestors so frequently, then why not the whole-house arrestor ?.
Phill Giles
The Unionville Woodwright
Unionville, Ontario
The reason I recommend changing out the surge arrestor strips, one year for cheap ones and two for heavy duty units, is that, especially with cheaper units, that the components, primarily MOVs (Metal Oxide Varisisters) necessary to drain away voltage spikes are damaged by every surge. These component are impossible to test effectively for remaining capacity and may fail at any time. If they fail during a surge they let through any remaining spikes.
Don't discard the older units. Any remaining capacity can be used to protect all of the other electronics you own. Saving a $1000 computer and letting your $5000 home theater system cook might not be much of a bargain. Even after many years these strips still are useful on job sites long after any protection capabilities has been expended.
Higher quality, expensive, units usually include other components, such as spark gaps, high speed high current transistors and chokes that augment the MOVs and preserve their capacity and may even replace the MOVs but these components are also subject to failure with heavy use and daily wear.
The costs of these units, even the good ones, has spiraled down. What was a $100+ for a very good unit is now $50 for an even better unit. The same can be said of the computers being protected. Computers have become less valuable as objects and more vital to the operation as a business and valuable primarily for the information they hold. If all you do is surf the web, answer e-mails and you keep no important information on it there is little need to worry about extra protection.
The reason I recommend the whole house unit is that it, as the name implies, protects the entire house and knocks the top off of any of the larger surges. This provides a second layer of protection, spreads the damage around and may provide a longer life to your household appliances.
"If they fail during a surge they let through any remaining spikes." - this phrase is somewhat misleading.
Just a note to clarify this for some not fully familiar with MOVs. Small MOVs will fuse open its lead or pop open at about 3X to 10X its "new rating" for a single big pulse, and thus can let thru the surge. Below the 3Xto 10X level the MOV will short and ground the surge and trip the breaker. Both Siemens and Panasonic web sites have full data on MOVs, including the surge lifetime curves (e.g if you live in Tampa, the replacement is an excellent idea, on the West coast MOVs will likely last longer than any other equipment ).
BTW: MOVs used in military systems generally are installed with tabs instead of wire leads and physically constrained (as in a slot in a metal box) so that they do not physically fly to pieces for a big surge. As an example, the MOV used to protect Minuteman silos from Nuclear lightning is a 2 inch dia MOV in a 1/2 thick steel housing with 1/2" dia 4340 studs holding it together. As tested, #4/0 wire breaks from magnetic forces (about 400,000 amps for a few milliseconds) long before the MOV fails open (it fails short providing full protection at a few kA transient level so that the UPS operates without fail). -