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

  1. #1
    DIY Member Erico's Avatar
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    Default What's the difference between 240 volts and 220 volts?

    (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. #2
    Electrical Contractor/Instructor jwelectric's Avatar
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    Default

    Quote Originally Posted by Erico View Post
    (besides 20 volts )
    This just about sums it up
    Quote Originally Posted by Erico View Post
    Question:
    Would I be correct in assuming I can use 10 gage copper wire........and what? a 30 amp. breaker?
    Being that the steam generator would need to be sized at 120% I would say you got all this under control

    Quote Originally Posted by Erico View Post
    What's a two wire supply source? I'm used to white and black.
    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. #3
    DIY Member Erico's Avatar
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    Default 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. #4

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    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. #5
    Licensed Electrical Contractor Speedy Petey's Avatar
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    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. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Plumber jimbo's Avatar
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    "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. #8
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Default 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. #9
    Moderator & Master Plumber hj's Avatar
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    Default 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. #10
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by hj View Post
    false tripped.
    Would you please take a minute and explain just what a "false trip" is?

  11. #11
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Mikey View Post
    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?
    Quote Originally Posted by hj View Post
    To power the GFCI circuitry.
    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. #12

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    Quote Originally Posted by jwelectric View Post
    Would you please take a minute and explain just what a "false trip" is?
    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. #13
    Moderator & Master Plumber hj's Avatar
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    Default 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 by hj; 05-17-2008 at 07:43 AM.

  14. #14
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Default

    Quote Originally Posted by hj View Post
    Resistive devices such as water heaters lose capacity in direct relationship to the loss of voltage.
    Actually, it's a voltage-squared relationship, I think.

  15. #15
    Retired Defense Industry Engineer jadnashua's Avatar
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    Power = amps x volts, so linear...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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