What's the difference between 240 volts and 220 volts?

Discussion in 'Electrical Forum discussion & Blog' started by Erico, May 13, 2008.

  1. Erico

    Erico New Member

    Messages:
    73
    Location:
    NY
    (besides 20 volts :) )

    I'm thinking of pre-wiring (and pre-plumbing) the bathroom I am building for a future steam generator/shower system.

    The specs I have been reading call for 240 VOLTS. I've heard of 220 but not 240:

    Electrical Rating: 5KW 240Volts 21Amps 1Phase

    Check power voltage. Use 240V rated unit when supply is greater than
    208V. (Most homes have 240V, 1PH service). Use 208V rated unit for
    208V power.
    2. Use minimum 90° C/300V rated insulated copper conductors only,
    sized in accordance with National Electrical Code and local electrical
    code for the Amps in Ampere Chart.
    3. Connect suitably sized equipment grounding wire to ground terminal
    provided.
    4. Install a separate circuit breaker between supply and unit. Provide a
    power supply disconnect within sight of the steam generator or one
    that is capable of being locked in the open position.
    5. For single phase units, use two-wire supply source and equipment
    grounding wire. Neutral (white) wire is not required.


    Question:


    Would I be correct in assuming I can use 10 gage copper wire........and what? a 30 amp. breaker?

    What's a two wire supply source? I'm used to white and black.

    The goal is to pre-wire while I have the walls opened up and MAYBE install a steam system....next year. The extra 1200 dollars isn't in the budget right now but I don't want to kick myself later when I decide I want steam.

    I pulled a new circuit, with the help of this forum, for my neighbor's hot-tub so I'm feeling like I can do it. it's up three floors in a condo building but there should be room in the pipe.

    Thanks in advance for any insight/help.
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    This just about sums it up
    Being that the steam generator would need to be sized at 120% I would say you got all this under control

    both the black and white will be carrying current and have a difference in potential of 240 volts. Neither of these conductors (white/black) will be grounded or neutral.
  3. Erico

    Erico New Member

    Messages:
    73
    Location:
    NY
    Thanks, Jwelectric.

    Should I run two black/hot wires?

    If i end up installing the unit I will probably hire an electrician to make the final connections but I want to wrap my brain around the concept and make sure I run the proper items.

    Will both wires be connected to the breaker? How does the unit ground? Everything here in Chicago is rigid conduit grounded to the conduit (no third wire).

    Also, where would the GFI fit in to the picture? At the breaker? - I've never worked with a GFI breaker but I've seen them mentioned. The breaker box is three floors down - would some sort of junction/mini panel located close to the unit be a better idea?
  4. Billy_Bob

    Billy_Bob In the Trades

    Messages:
    422
    I would check with your local electrical inspector's office. These are the guys who will inspect and approve your work. Best to get it from the horse!

    In my area they have office hours where you can go and ask questions like yours above. Take plenty of pictures of the bathroom, electrical panel, and where you plan to run the wire. Also take the specifications on the steam gizmo.

    There is a national electrical code, but sometimes local areas have their own rules for this or that.
  5. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    Since you have conduit all the way yes, you should run two "hot" colors. Two blacks would be fine.

    Why not just do the "final hookups" yourself?
    Very few real electricians like to do the "final hookups" to someone else's work.

    The circuit gets grounded to the conduit system. You need to run a ground tail from the final box/enclosure to the steam genny.
    The best thing would be to run a ground wire all the way back to the panel with the circuit conductors. I NEVER rely on the conduit alone as a ground, although many people do.

    The GFI would HAVE to go in the main panel. The white tail off the breaker MUST connect to a valid neutral source in the panel where it is installed. It does NOT however need a neutral on the load side to work.
    You are not running a neutral with this circuit.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    It sort of depends on how easy access you have to the breaker. If you wanted to install one up near the steam generator, you'd need to run an additional wire for the neutral. At the cost of copper these days, that would add up. While many people don't do it, you are supposed to test the gfci monthly...you're more likely to do that if it is convenient, and not burried three floors below.

    A 220v breaker is typically twice the width of a 110v one. It will have two screws, one for each side of the transformer (bus bars). It will also have a pigtail when it is a gfci that gets connected to the neutral bus.

    Since it is a multifamily dwelling, many places require electrical work to be done by a qualified, licensed installer. While not particularly hard, it is for the safety of those others in the building if you mess up.
  7. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    "Back in the day" the voltage commonly supplied in residential was 110 volt..and 220. Later, most electric companies upped it to 115, and 230. You still here all 4 of those numbers commonly used in talking about electricity supply. Today, the most common electrical service is 120 volts, and 240. All the terms can be used interchangeably.

    The actual power (watts) delivered to a power consuming device like a motor or heating element is proportional to the actual voltage ( squared ). So a particular heating element for a water heater, for example, may be listed as 4500 watts at 240 volts. If your actual voltage was a little different, the power you would have would be 4130 watts at 230 volts, 3780 watts at 220 volts, and 3380 watts at 208 volts.
  8. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,716
    Location:
    Central Florida
    Why a neutral on a 220VAC GFCI?

    If there's no neutral to the load, why would you need a neutral off the GFCI to the neutral bus? Or is it supplied just in case it's a 3-wire circuit?
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,811
    Location:
    Cave Creek, Arizona
    neutral

    To power the GFCI circuitry. I would want a GFCI in the area of the tub rather than having to go down to the basement any time it false tripped.
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    Would you please take a minute and explain just what a "false trip" is?
  11. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    The neutral is NOT there "to power the GFCI circuitry".
    It is there because that is what GFI's do. They monitor the load for imbalance.
    A two-pole unit monitors line-to-line and line-to-neutral simultaneously.
    Any (noticeable) imbalance anywhere and it will trip.

    So in a sense it really is there for potential 120/240v circuits.
  12. Billy_Bob

    Billy_Bob In the Trades

    Messages:
    422
    I always wonder about the common situation where a GFI keeps tripping and people blame the GFI and not whatever is plugged into the GFI.

    Seems to me if most things plugged into a GFI work ok, but one appliance causes the GFI to trip constantly, then there is a problem with that appliance...
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,811
    Location:
    Cave Creek, Arizona
    Gfci

    Devices with motors, or more specifically compressors such as freezers and drinking fountains seem to cause GFCI's to trip randomly. This is why a freezer ir freezer should NEVER be plugged into a GFCI. It can trip and without a temperature alarm the user will not know about it until the contents have thawed and spoiled. I had one customer who had it happen, but since the outlet was dead they just ran an extension cord to a working outlet. When I was there for a different problem, the situation came up and I told them it sounded like a GFCI problem, even though that outlet was not a GFCI one. After an extensive search, I found the tripped GFCI under a bench in their bathroom. They had not even known it was there. It is also the reason that many receptacles for certain appliances are installed with a single device outlet without GFCI protection, so that an extension cord cannot be used in that outlet when the location would normally require a GFCI for the extension cord. As far as 220/240 is concerned most devices will tolerate a 10% variation between the design voltage and the supplied voltage, without creating problems. Resistive devices such as water heaters lose capacity in direct relationship to the loss of voltage.
    Last edited: May 17, 2008
  14. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,716
    Location:
    Central Florida
    Actually, it's a voltage-squared relationship, I think.
  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    Power = amps x volts, so linear...
  16. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,716
    Location:
    Central Florida
    Resistive load... P=E*I but I=E/R, so P=E^2/R.
  17. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    also

    P= I squared times R

    BUT

    of course this only holds true in prue resistive circuits with DC voltages.
    For AC circuits we must also do a Power Factor calculation.
  18. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,716
    Location:
    Central Florida
    Or use the RMS voltage if it's an AC circuit with a resistive load. The possibilities are endless...
  19. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    Could you give us the source for this information. In more than 29 years of experience in the field with GFCI devices I have never run into this except through conversations where no data was produced to back such information.


    Under the 2008 code cycle this would mean that freezers can no longer be in unfinished basements, attached or detached garages or any remote (storage) buildings served electrically from another building.

    Did you also check out the freezer to find the reason there was a difference between the two conductors?

    Again this will no longer be allowed by the 2008 code

    Not meaning to sound mean or anything but this is not a true statement. The 240 GFCI devices conform to the same standard as a 120 volt device. Both trip when there is a 5 milliamp difference between the two current carrying conductors.

    I wouldn’t totally agree with this statement either. The lower voltage does not mean that a water heater won’t heat water to the desired temperature it just means it will take it a few seconds longer to get the job done.
  20. Furd

    Furd Engineer

    Messages:
    446
    Location:
    Wet side of Washington State
    You're all wrong! :D

    In the case of the water heater let's assume a 4500 watt element operating at 240 volts. Since this is virtually a totally resistive load we can ignore impedance and power factor.

    Current draw in the above example would be 18.75 Amperes. By Ohm's law the resistance would be 12.8 Ohms. The resistance of the heating element is a fixed quantity and is based on the materials and method of manufacture.

    Now let's change the voltage to 120. The resistance is the same (12.8 Ohms) so the Amperage has now dropped to 9.38 Amperes, exactly 1/2 of the amperage at 240 volts, which certainly seems logical. HOWEVER, multiplying that 9.38 Amperes by the 120 volts to get the power gives us an answer of 1125 Watts, exactly 1/4 of the wattage at 240 volts. Therefore, the BTU output of the heating element is also 1/4 as much when run on 120 volts as compared to the design voltage of 240.

    Since there are 3414 BTUs per kilowatt it is easy to see that at 120 volts the heat output is 3840 BTUs and at 240 volts it is 15,363 BTUs or that at the lower voltage the heat output is, like the wattage, 1/4 of the design output.


    As for compressors (refrigerators) causing GFCIs to trip...my refrigerator has been connected to a GFCI circuit breaker for more than eight years and I have NEVER had the breaker trip. Yes, I have tested the GFCI function and it works as it should.
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