240V and 250V plug.

Discussion in 'General Technical Questions and Answers' started by K4LD, Jun 19, 2010.

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  1. K4LD

    K4LD Ham Member QRZ Page

    Hello All,
    I'd like to wire up a plug on my workbench for working on amplifiers requiring 234/240V. Currently, there is a second dryer in place where I had planned to put the new outlet for 240V. I measured the voltage on the plug, and it's about 250V. Is there anything I have to do to drop the voltage down to 240V? Or am I able to install the plug without having to worry about the voltage difference?

    BTW, the amp I'm working on is an Amp Supply LK-500NTC wired for 234V.
  2. KC8VWM

    KC8VWM Ham Member QRZ Page

    No other modification is needed, "250" will be fine. (220/240)
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Nothing you can do about it. Line voltage in most parts of the country runs a bit high; it should average about 240V under "full load" like when the whole house is loaded fully with air conditioning running, etc. Mine here runs as high as 252V when the house is lightly loaded.
  4. WA4OTD

    WA4OTD Ham Member QRZ Page

  5. W6TMV

    W6TMV Ham Member QRZ Page

    I run my TL922A off of an old dryer socket (with the large three pin plug) and it runs up to 245 VAC and I have noticed no problem with it.
  6. KB9LXP

    KB9LXP Ham Member QRZ Page

    I would change the breaker to 25 amp or 20 amp, whatever MFG. calls for (check manual from Amp) for your safety, Being a Dryer outlet, it is probably on a 30 amp breaker and possibly #8 or #6 Aluminum wire depending on the age of the house (in the 60's cheapskates used Alu. wire) but if it is copper, it is more than likely #10, or for a long wire run, Good electricians used # 8 copper. Don't sweat the voltage, utility has a 5% rule, 240 volt @5% + or -
    Good Luck with the amp, lots of DX to you...:D
  7. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Actually, most major electric companies use 125 VAC +/- 2 volts as the "target" value these days. Especially in hot weather they run on the "+" side to handle all of the air conditioning. Of course, the total voltage run into the residence is twice this so 250 VAC +/- 4 volts is the target.

    TXU, the electric company for almost half the State of Texas, for which I worked for over 10 years, started running 125 VAC as the "target" in the late 1970s.

    Glen, K9STH
  8. W8JI

    W8JI Ham Member QRZ Page

    This has NOTHING to do with the outlet. the standard voltage in the USA has not been 117/234 since the 50's or 60's. The standard is 120/240, and has been for at least 40 years.

    250 volts is only 4% high from the USA standard, and almost always the power companies set the voltage on the high side. 250 is well within tolerance.

    The last thing you would want to do is add a variac or other high ESR system to the line. You could use a 10 volt bucking transformer with a 30 amp or larger secondary, and it would not harm regulation. If the amplifier is designed properly to USA standard voltages, the 250 volts would never hurt a thing.

    The biggest problem you have is outlet is over-fused. This is dangerous, especially if the amplifier does not have fast blow 250 volt rated fuses of the proper amperage. Many people stick 32 volt fuses in 120-240 volt systems, and that is very rough on equipment if there ever is a fault.

    The biggest thing you need to worry about is making sure the amplifier has the correct 250 Vac fuses of proper current rating, especially since the outlet is overkill. Don't worry about 4% over-voltage, it is nothing.

    73 Tom
  9. KM3F

    KM3F Ham Member QRZ Page

    The way around your bench feed is to install a small circuit breaker sub box to feed the 240 bench outlet.
    Use no more than a dual 20 amp "handle linked" breaker in the sub box.
    I have both a 240 amplifier and a 120 hi power amplifier.
    In order not to load down the standard 120 wall outlet in use for the rest of the equipment, with the 120 amplifier, I built a special cord with metal outet boxes, with one 240 and two 120 outlets. One 120 outlet off each side of the 240 line.
    Obviously I only run one amplifier at a time so get the benifit of a hard AC feed for both amplifiers.
    None of this is permant except the original 240 feed, and all purely plugin.
  10. VK6ZGO

    VK6ZGO Ham Member QRZ Page

    In VK6,for many years,the standard mains voltage was 250 volts.

    The story was that it came about when the Electricity supplier changed from

    40Hz to 50Hz.

    The transformers were supposedly more efficient at the higher

    frequency,hence the voltage increased from 240v ,40Hz to 250v,50Hz.

    Anyhow,we ended up with 250v,with the rest of Australia at 240v 50Hz.

    All the sockets & stuff were marked as 240v,but we used them happily for


    (Here ends the part that has any bearing on the OPs question, the

    following is a RANT!:)

    The lightbulbs made in Australia & marked 240v happily worked up to 260v

    for years.

    The "suits" in charge at the light bulb companies discovered that they could

    get "240"volt bulbs made cheaply overseas, & drooling at how much more

    profit they could make,shut down production in VK.

    The new 240volt bulbs had a very much reduced life,often less than a


    The light bulb people came up with an answer,by supplying "260volt" units at

    an increased price. (still imported)

    At this point,a hue & cry arose,led by an Electrical Engineer ( Who should

    have known better), to the effect that our higher voltage was causing vastly

    reduced life to the 240 volt bulbs.

    After much ranting, the decision was made to reduce the supply to 240volts,

    which was duly done,at great cost.

    As all would now be well,the 260 volt bulbs went off the market.

    Shock! Horror!--- the imported 240volt bulbs still had poor life.

    All this was conveniently forgotten when the big push came change us over to

    CFL lamps.

    They quoted vastly improved life for CFLs compared to incandescents.

    They would last about as long as our old Australian made 240volt

    incandescents did!

    I Know this is off topic,but it is a good cautionary tale.

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