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  1. #1
    Glenn Lawson's Avatar
    Glenn Lawson Guest

    Default Designing Dedicated Computer Circuit

    Here's as much info as I can think of that applies:

    I'm a DIY.

    Circuit evaluation shows we require capacity for 1908 watts, below:
    Computer, 8.0 a., 960 watts
    Monitor, 6.7 a., 804 watts
    Printer, .5 a., 60 watts
    Modem, .3 a., 36 watts
    Table lamps .4 a., 48 watts


    As we all know, but just so you know I'm aware:

    Total capacity for a 15 amp circuit at 120 volts = 1800 watts
    Safe capacity for a 15 amp circuit at 120 volts = 1440 watts

    Total capacity for a 20 amp circuit at 120 volts = 2400 watts
    Safe capacity for a 20 amp circuit at 120 volts = 1920 watts

    We've got six items to plug into receptacles, so we'd like to power three duplex receptacles so we can do this all on one circuit, but obviously that's not required.

    The whole panel is surge-protected at the panel, which we chose over an isolated ground receptacle.

    Here's the question:

    Is there a way to design a circuit utilising four duplex 15 amp receptacles but still gives us safe headroom on capacity?



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  2. #2
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    Default Re: Designing Dedicated Computer Circuit

    I must be very lucky. In my office, on one 20 amp circuit I have:
    1 Desktop computer
    1 printer
    1 fax machine
    3 laptops
    Verizon signal booster
    Comcast modem
    External hard drive
    4 desk lamps
    1 floor lamp
    Power supply for usb hub
    Power supply for cordless phone
    Network Router


  3. #3
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    Default Re: Designing Dedicated Computer Circuit

    It sounds like you have an old CRT monitor, get an LCD they use very little power.

    A PC will not actually use the max listed on the data plate.

    You should be ok anyway, but check the outlet and make sure the connections are under the screws and not just inserted into the holes.
    If you only have a duplex, just get a good quality power strip for everything.

    If you are planning for new construction or have easy access to run a new/extra circuit go for it.

    Bruce King, B.A. King Home Inspections, LLC
    www.BAKingHomeInspections.com
    Certified Master Inspector, Independent Inspectorwww.IndependentInspectors.org

  4. #4
    Glenn Lawson's Avatar
    Glenn Lawson Guest

    Default Re: Designing Dedicated Computer Circuit

    Ahhhh...the perils of communicating via delayed chat.

    Yep, we're doing new construction during a remodel.

    Yep, the studs are all exposed.

    Yep, we're going for it, that's why I joined up here and asked for pro advice.

    Yep, it's cold up here nights and we won't spray in insulation until the AC, data, fax, Cat6, RG6, and phone wires are all roughed.


    No, we don't want strips, but thanks for the suggestion.

    No, I wouldn't dare use EasyCon holes rather than screw connections.

    Eventually we'll get the LCD, but for now, the wattage is what I stated.

    Is there any way to design the circuit--without violating code, of course --using four duplex receptacles?


  5. #5
    Glenn Lawson's Avatar
    Glenn Lawson Guest

    Default Re: Designing Dedicated Computer Circuit

    I hope my office and yours don't share a common wall! LOL

    Seriously, Jack, are you even interested in totalling the wattages of those?


  6. #6
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    Default Re: Designing Dedicated Computer Circuit

    The number of receptacles you install is meaningless (other than you won't have to have triple adapter plugs to give you the number of receptacles to match the number of plugs being plugged in), what is important is that the 20 amp circuit is rated for 80%, or 16 amps, and your calculations show you are almost there.

    Being as you have the studs open, I would recommend 2-20 amp circuits, and install one duplex receptacle for each, then plug in a surge protector 6-plug strip into the each of the receptacle outlets. That will give you 12 receptacle outlets (which simply means more convenience, not more load capacity), then plug a good sized UPS backup into the other receptacle in each duplex, using one UPS for the computer and monitor (display) and the other UPS for the modems, router, etc., to keep your system from shutting off during brief intermittent power surges and drop outs. The larger the UPS the longer your run time on the back up battery, the easier to keep and save work, and shut down safely without losing work.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  7. #7
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    Default Re: Designing Dedicated Computer Circuit

    Here in Canada, our electrical code limits us to no more than 12 duplex receptacles or light fixtures on one 15 amp circuit.
    We are allowed 16 duplex receptacles or light fixtures on a 20 amp circuit.
    AFAIK, there is no restriction on the number of receptacles you can install in the US under the NEC.

    You could consider using fluorescent and LED lighting options to lower the load considerably.

    I would heed Jerry's advice and wire the office with #12 gauge instead of the slightly cheaper #14. Even if your supply can only be 15 amps at this point, the larger gauge wiring will be handle a 15 amp load easily, that is, it will stay cool and therefore be safer.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  8. #8
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    Default Re: Designing Dedicated Computer Circuit

    I usually figure about 1500-1800W for an average office setup.... monitor, cpu, light, modem, printer, etc. So you're at at least one 20A circuit right there absolute minimum. Since you have access JP's advice is sound.... run two 20A circuits so you don't have to worry.

    When I recently did some remodeling to my office area I ran 2- 20A circuits. One for each work "station" in addition to the boderline over-stretched general use circuit that was already in place. It's worked nicely.... it's also really nice to have each station on it's own breaker so you're not having to shut down and reset everything for work elsewhere.


  9. #9
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    Default Re: Designing Dedicated Computer Circuit

    Adding the wattage? No thanks.
    I just realized that there are probably two circuits for my office.


  10. #10
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    Default Re: Designing Dedicated Computer Circuit

    Quote Originally Posted by Glenn Lawson View Post
    Yep, we're doing new construction during a remodel.

    Yep, the studs are all exposed.

    Yep, it's cold up here nights and we won't spray in insulation until the AC, data, fax, Cat6, RG6, and phone wires are all roughed.

    I guess I don't see the issue. The walls are open, your adding data lines, phone lines, A/C rough-in, etc, etc, so just add one more cable or wire for a second circuit.


  11. #11
    Glenn Lawson's Avatar
    Glenn Lawson Guest

    Default Re: Designing Dedicated Computer Circuit

    Thanks for all your responses! I'm learning lots here.

    @Jerry, I'm not arguing or discounting what you say, just trying to understand. So may I ask a further question or two?

    I get what you're saying, and the UPS idea will be used. So will the two-circuit concept. But I don't understand if you just missed my saying previously that I intend to use a surge protector at the panel, and that's why you're recommending a local one at the receptacle, or if there is another reason behind your suggestion.

    Would you explain why you're recommending a local one? Should I use both types of surge protectors, one at the panel, and one local?

    Further, if I may, (and not intending to complicate things) I already own a Pass & Seymour Isolated Ground receptacle, which I considered using in this circuit but was waiting to see if anyone recommended that. No one did. Have there been problems with Isolated Ground receptacles?

    @ Dom, the issue is that I am not a licensed electrician. I am an advanced DIYer who knows quite a bit about actually wiring to prevent fires and hotspots, but not so much on circuit design for specific tasks. Thanks for your help.

    Last edited by Glenn Lawson; 12-14-2011 at 06:17 PM.

  12. #12
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    Default Re: Designing Dedicated Computer Circuit

    Quote Originally Posted by Glenn Lawson View Post
    @Jerry, I'm not arguing or discounting what you say, just trying to understand. So may I ask a further question or two?

    I get what you're saying, and the UPS idea will be used. So will the two-circuit concept. But I don't understand if you just missed my saying previously that I intend to use a surge protector at the panel, and that's why you're recommending a local one at the receptacle, or if there is another reason behind your suggestion.

    Would you explain why you're recommending a local one? Should I use both types of surge protectors, one at the panel, and one local?
    I like redundant protection for things like that, i.e., my UPS is plugged into a surge protection, and the UPS also offers surge protection - if the surge craps out the surge protection strip, it will protect my UPS system, but if the surge craps out the surge protection strip AND my UPS system, it still protects my computer, printer, displays, etc., which are plugged into the UPS.

    I'd rather throw $20 away than $200 for the UPS, but I'd rather throw the $200 UPS away than the hundreds/thousand for everything plugged into the UPS.

    Further, if I may, (and not intending to complicate things) I already own a Pass & Seymour Isolated Ground receptacle, which I considered using in this circuit but was waiting to see if anyone recommended that. No one did. Have there been problems with Isolated Ground receptacles?
    No need for an isolated ground to that equipment and if not done correctly, the isolated ground can lead to grounding problems and you could create ground loops and other issues. Isolated grounds have limited uses, and I would not use one for this type of circuit.

    It is best to just use grounding-type receptacles and to make sure that all is properly grounded. If you are concerned about it, just use PVC and non-metallic boxes, with an insulated grounding conductor run with the circuit conductors, that way the grounding contact will be limited to that at the receptacle end and at the panel end where the circuit terminates, and no place in between.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  13. #13
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    Default Re: Designing Dedicated Computer Circuit

    That printer must be a dinky one with disposable type cartridges. Some day you might want a drum type or laser printer, etc. Go with 2 circuits minimum, keep the printer on a separate circuit from the tower & display, along with the modem transformer, and compact fluorescants or other off the tower supply circut as well as keep the wireless phone base unit off the computer tower supply circuit. Some time later you might want to add a router, wireless or not, and whatever the next generation of new thingy comes out - so you'll have capacity. Best is to avoid the non-related motors and inverters off the CPU circuit - and keep the connections from communications cables to the outside to electrical interface devices on a circuit other than that directly powering the computer. Those interconnections to the computer itself can be done via a surge monitoring and battery backup power supply unit interfaced with its supplied hardware.

    Suggest 15A duplex receptacles on 20A circuits. Multigang boxes for your dedicated computer circuit with at least two locations, you can use a reducing plaster ring if you'd prefer to mount just two duplex receptacles at each box location for now, also suggest using two-gang boxes with a reducing plaster ring for the second circuit's duplex location receptacles for the occasional use, and other devices all around the rest of the room including every wall 2' or longer and at every 6' of wall space, including near your computer outlets locations. Keep in mind you may wish to reconfigure the furniture arrangement at some point.

    Continuous use items are calculated at 125% as are lighting outlets. Although newer computer equipment may have defaults set for energy reductions, also know these can be overridden, and to have up and in use 3 hrs+ not uncommon.

    Perhaps I missed it, but I didn't see any reference to the dimmensions of the room.


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