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Old house, ungrounded outlets...

Discussion in 'Amps and Cabs [BG]' started by ndrifka, Sep 6, 2008.

  1. ndrifka


    Aug 14, 2008
    Hey everyone. I'm new to TB and this is my first thread, so please be gentle. After doing some searching here about ungrounded outlets, I still have questions. I recently purchased a LMII and two 151HR cabs (love 15" speakers), and would like to know if plugging my amp into an ungrounded outlet could cause damage to the amp...or myself. I realize a grounded outlet is best, but I live in an old house with ungrounded outlets. Any help/advice would be appreciated.:help:
  2. Dogbertday

    Dogbertday Commercial User

    Jul 10, 2007
    SE Wisconsin
    Blaine Music LLC
    you need to get an adapter and then screw the little tab to the middle of the outlet plate. that will ground it
  3. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks
    I've got the same issue in my old house - don't worry, you're not going to hurt the amp by plugging it in to an ungrounded outlet. Just get yourself a ground lift adaptor plug and you're all set.
  4. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    It's not too difficult to just change the outlets, either, but a ground lift will have you up and running. Just be sure to screw in the ground tab.
  5. You should be OK but you will need to be careful and there are several things to keep in mind. You will need to check the polarity of your wiring, that house sounds old enought to be before there were wiring standards. The center pole may or may not be grounded again consider the age. Be sure your amp is not on the same circuit as any other high draw electrics like a washing machine, dryer, refrigerator or freezer which can cause brown out or noise. The gauge of the wiring as well as the voltage and amperage of the original service may also not be up to snuff, especially if you crank up or have other musicians also plugged in. If your amp or other electrics start acting incorrectly or if there is excessive heat of the appliance, cord or outlet be sure to have an electrician out to check the service.
  6. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks
    Yes, but the outlets still won't be properly grounded. In order to do that, he'd have to rewire the entire house.
  7. Joeykun

    Joeykun pronounced ジョーイくん

    Jun 22, 2007
    Shirley, MA
    The nice thing about Markbass amps is that it will shut down signal to your cabs if it is not powered correctly.
  8. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    All outlets are grounded, the problem is with 2 prong outlets. An electrician can replace them with three prong outlets with the existing wire. The trick lies in making sure that the ground lug ends up connected to ground and not to the hot wire, but doing so correctly is why you'll have to pay him at least $40 per outlet, though he may give you a better deal if he does the whole house.
  9. ndrifka


    Aug 14, 2008
    Thanks for the info so far. I just searched for every outlet in the house and I did find a couple outlets in the house that must have been upgraded to the 3 prong grounded type. The bad news is that they are in the living room and dining room, not in the upstairs bedrooms where I want to have the jam sessions. It looks like the sessions might need to take place in the dining room, or maybe I'll get a few 3 to 2 prong adapters for the upstairs like suggested. The house is up for sale and a band's gear sitting in the dining room might be an eyesore...at least to those not among us. ;)
  10. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Bargain of the century.
  11. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks
    Well, sort of. Technically the neutral and the ground go to the same place, but your're not going to be able to wire up a three prong outlet to two wires and be able to pass electrical inspection. New construction houses are wired with three wires: hot, neutral, and ground. Old construction just has the hot and neutral. The only way to properly ground the outlets is to replace all the old wiring with new wiring - something that could cost thousands and thousands of dollars.

    Ground plug adaptors are about $1 each.
  12. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    This is quite dangerous mis-information, except for the "call an electrician" part.

    Old houses may have any of three common wiring types in the US.

    1) "knob and tube" wiring. This has separate hot and neutral wires (insulated) run at a distance from each other, held by porcelain "knobs" and run through wood (studs, floors) inside porcelain tubes. Boxes are NOT grounded. It is actually much safer than it seems, but CAN NOT be grounded in any effective way. it must be replaced to get grounded wiring.

    2) OLD STYLE "Romex" or "NM" cable. This has two wires only, and has no ground. Boxes are NOT grounded, and the only way to provide a ground is by pulling in new wire, which is difficult without knocking holes in the walls, because the wire is required to be stapled to the walls inside.

    3) OLD STYLE "armored cable". Nominally the metal armor is grounded, but in fact the connections have probably corroded or loosened, and grounding cannot be counted on, EVEN IF a ground checker lights up correctly for a good ground. The ground checker can't find high resistance connections, it lights up if there is any sort of contact.
    In fact, bad connections and basic high resistance of the "armor" are a possible cause of a house fire if the ground ever gets "used" due to a short etc.

    As you can see, ONLY with #3 do you have a CHANCE of grounding with the screw on the outlet, and even there YOU CAN'T BE SURE.

    Newer houses with real grounded outlets have either improved "armored cable" with a shorting wire that lowers resistance, plastic insulated wire with ground (new type "NM" with ground), or "type MC" armored cable that includes a ground wire.

    Most units with a 3 prong plug do need the ground, because they are not double-insulated the way modern units with a 2 -wire plug are.

    Touching the amp and a radiator or hot air register, etc, at same time may give you a shock.
  13. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It depends how old. Most built after 1960 have three wires, with the ground connected to the box. Older houses built with BX cable are grounded via the metal jacket. The point in hiring a licensed electrician is that he'll know what can be safely done, and what can't.
  14. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    +1 to Jerrold's reply.

    An electrician definitely has to take a look so you know which of the three options you have. The BX cable situation is option #3; it may be OK or may not.

    FYI on the meaning of double insulated power tools and appliances. These are built so that no metal part can possibly be touched. Thus, if there is a short inside the unit, you can't possibly touch the "hot" metal part.

    A device with exposed metal, however, needs the third prong to ground that metal. A fault would then short to ground, blowing the fuse/tripping the breaker.
  15. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Actually, a double-insulated device CAN have exposed metal. Like a portable drill motor. But the MAINS wiring is all protected by a double layer of insulation.

    The voltage rating of the insulation is higher for double-insulated than for an item with grounding, since the ground (earth) connection is "counted" as protection equal to added insulation.

    The option #3, which is BX cable, with the OLD cable, is really not much safer than un-grounded, because the grounding is not reliable. That cable type is no longer allowed by the electrical code, replaced by "MC" with ground, or in certain cases with an improved type of BX having a "shorting wire" to ensure the spirals of the armor are shorted together.

    Bottom line is that

    1) UNLESS your wiring has a actual earthing wire, you cannot be sure anything is earthed, even if you use the grounding screw on an adapter.

    2) IF you use a 3 wire device and do not use the earthing wire, you may have trouble with electric shocks touching it and other equipment or grounded objects. These probably will only be leakage current, but you don't know........ You have "defeated" the backup protection built into the unit.

    I know, people have done it for donkey's years, but that doesn't make it safe, just typical. Half of all sound equipment in the US probably has the 3rd pin cut off.......... but usually SOMETHING in the system IS grounded (earthed).

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