3

I am trying to fix my dryer but I have run into a problem I can't find the answer to. I checked all the fuses with my multi meter and everything seems to be working. Before I rewired a slot in my circuit breaker box for 240 volt slot I had to run my dryer on a 120 slot. It worked and it would dry the clothes but take a lot longer to dry. I rewired and installed a 240 volt plug right next to my 120 volt. Now that I have my 240 volt plug no heat goes to the dryer. I checked and each side of the 3 slot outlet has 120 volts. The plug going to my dryer also shows each side of the plug has `120 going to the dryer. I also tried it with another wire and another outlet to see if that was the issue of why the 240 wasn't working. When I plug the dryer back into the 120 volt outlet it works again but will not heat up as much as it should. I am not sure why it is working on the 120 but not the 240.

**Update I have changed it to a 4 wire 4 socket outlet and plug. I am still only getting 120 from hot to neutral but not 240 from hot to hot. Here are some images of my setup.

Dryer Electric Box Circuit Area Second Bar Outlet Cord

***Update I Measured the voltage on the screws near the factory installed as Nate asked. When I did the the two screws next to factory installed it gave me nothing but when I did one screw at a time with the top neutral line coming in I got 120 Volts on each one. Does that mean I am only getting 120 volts to the box? I also noticed this on my meter that it says 120V 2W. I wasn't sure if that meant 120 for each wire or the 2 wires equal 120V enter image description here

  • 3
    When you measure the voltage between the two hots in your 240V outlet, are you getting 240V? I'm betting you're getting 0, which means your two hots are on the same pole -- they should not be. – Nate S. Nov 13 '19 at 19:02
  • 1
    You say each side has 120v, but is the voltage between the two sides 240v? – JPhi1618 Nov 13 '19 at 19:02
  • 1
    If that's the case, see this question for more details: diy.stackexchange.com/questions/149497/… – Nate S. Nov 13 '19 at 19:04
  • 1
    Shoot us a photo of your service panel breakers, and also if possible the wiring of the dryer socket. Does this circuit have ground? – Harper - Reinstate Monica Nov 13 '19 at 20:11
  • @bosestron, your update with the pictures is helpful, thanks! You're correctly using a 2-pole breaker, so there must be something else going on here. One possibility is that this entire panel is fed from only a single leg, making it a 120V-only panel. Can you measure the voltage between the incoming feeders (i.e. on the screws near where it says "FACTORY INSTALLED")? – Nate S. Nov 18 '19 at 21:34
4

You can't use a 3-wire socket

You're not allowed to use a 3-pin socket anymore (been outlawed since the 1990s). You need to use a NEMA 14-30 cord/plug and socket. There is a procedure for changing this on the dryer that involves removing a jumper between neutral and ground.

If you insist on using a 3-wire connection to a dryer, you need to put it on a GFCI breaker. Those cost about $80. I recommend a 4-wire connection.

Use of /2 cable (2 conductors + ground) is not allowed

You need /3 cable (3 conductors). Dryers need neutral. And you cannot use the bare wire in the cable as a neutral; that can only be used for safety ground. That's because neutral handles current under normal conditions, and that bare wire is not safe to use that way.

Once you have /3 + ground cable, how to hook up the NEMA 14-30 connector is obvious.

Your cable must be 10 AWG not 12

If you are retasking a 120V circuit to be a dryer circuit, it is surely 14 AWG or 12 AWG. Those wires are too small to support the heavy current draw of an electric dryer.

Your breaker must be a 2-pole not a duplex

... and it will not fit in one slot (space).

Fair chance you have a "duplex" or "double-stuff" breaker, with two handles. The breaker fits in one space. The dead giveaway is that the handles throw independently from each other, which means it is absolutely inappropriate for a dryer. Dryers need a breaker with common throw on the handles, and also a feature called "common trip" which assures both sides trip at once.

Further, dryers need a 240V breaker. By definition, a 240V breaker must span across two "spaces", or it wouldn't have 240V!

|improve this answer|||||
3

You've got 120V service, not 240V

As you have found out through the "hot to hot = 0" testing, you appear to have 120V service, not 240V service.

That is rather unusual, though not unheard of. But it severely limits the amount of power you can use. Based on a first look at your panel, you would expect to have 100A x 240V = 24,000W. But instead you sort of have 100A x 120V = 12,000W. But it gets a whole lot messier than that.

The meter picture is the key to determining that this is indeed 120V service rather than 240V service connected wrong. In fact, there have been some questions about how to deal with a single hot out due to various reasons, and temporarily connecting both hots on the panel to a single service hot can be a solution (provided it is done in a safe way). But in this case your meter really is a 120V meter. If you look at the information about this line of meters there is a chart listing 120V 2-wire and 240V 3-wire meters - your meter says "120V 2W".

240V Appliances

As you already discovered, you can't run 240V appliances because you simply don't have 240V service! The good news is that most of these appliances are large resistive loads (clothes dryers, water heaters, etc.) so they will work and be safe. But they won't work as effectively on 120V, as you already know. However, I would definitely not count on a 240V air conditioner or heat pump to work correctly on 120V.

Paralleling Conductors

You have an interesting problem because instead of connecting the single hot and neutral (= two wires = 2W on your meter, which is normal for 120V), you have 3 wires - two hots and a neutral - connected to the panel as if it was 3-wire 240V service. The result is confusion (as you know) but also possibly a dangerous situation with paralleling conductors. You have 100A x 2 wires. But instead of it all going to one place, it goes to 2 breakers (in a pair, but they are still really 2 breakers) and the power is divided up on the panel bus.

The result is that you could actually pull 200A, if the loads are well balanced, without causing a trip of your main breaker! That would normally be fine - 100A x 240V. But in your case it would really be 200A x 120V. That would be OK for the hot wires. But it would absolutely NOT be OK for:

  • The meter and wires from the meter back to the pole - they are all sized based on 100A service.
  • The neutral wire - it is only sized for 100A. With 240V service, the most it will ever have is 100A. In fact, if you have 100A x 240V in use then the neutral carries no current. But with 120V, that one neutral can end up carrying a full 200A, which will cause it overheat, which is not a good thing.

Talk to your Electric Utility

The power company is the only one that can truly solve the problem by upgrading you to 240V service. Properly installed, that will solve your dryer problem and give you a lot more power to work with for other things too.

If that just can't be done - either 240V service is not available or you are on a subfeed from somewhere else (e.g., one of a pair of houses, each getting a single hot from a 240V feed) then some changes to your panel are in order. The simplest safe thing to do would be to switch the 100A main breaker for 50A. However, that would be limiting because if your load isn't exactly balanced (and it rarely is) you might find that you trip the breaker even when using far less power than 100A. Another alternative is to only use one hot in the panel. That is easy to do - just use alternate rows. However, you will run out of spaces to connect all your loads so then you would need a larger panel that would be half empty.

|improve this answer|||||
  • 1
    Yeah, that meter is a Form 1S, which is a surefire giveaway that their service is 120V-only :/ – ThreePhaseEel Nov 19 '19 at 5:06
  • 1
    Good write-up manassehkatz. I'd also note that the neutral feeder looks very undersized for 120V-only service. Perhaps it was intended that one of the two "hots" be neutral, and the smaller wire ground, but whoever wired it up thought they had 240V. – Nate S. Nov 19 '19 at 17:24
  • 1
    @NateS-ReinstateMonica It looks pretty clear to me that whoever installed this panel had no idea it wasn't 240V. Which sounds crazy. But could be as simple as: Building was built and wired up and then connected to 120V instead of 240V and nobody bothered to think about the problems at the time. – manassehkatz-Moving 2 Codidact Nov 19 '19 at 17:30
  • 2
    @manassehkatz-ReinstateMonica, agreed; that looks like exactly what happened. If a service upgrade is impossible, it'd be easy enough to make safe by rearranging the existing wires, but it definitely needs some work -- I'm surprised that neutral hasn't melted already. – Nate S. Nov 19 '19 at 17:37
  • 2
    Oh my -- good call the MWBCs ThreePhaseEel; I didn't spot those at first either. This panel is a fire waiting to happen. – Nate S. Nov 20 '19 at 19:22
2

HOLY SMOKES! You have a much bigger problem here than you thought!

Somehow, between your electric utility and whoever wired your house, something didn't get communicated correctly, and the results are frankly, a hot mess. Your utility provides a 120V, 2-wire, single phase service to your house; this is shown both by the voltage readings you are getting at your main breaker, and by the fact that your meter is Form 1S (look below the right end of the long line of text, and it says "FM 1S" on the second of 3 short lines of text there), which is what is used for a 2-wire service like yours. (A normal 3-wire service uses a Form 2S meter, by the way.)

However, whoever wired your house wired it as if they had a normal, 120/240V, 3-wire, split-phase service coming in; we can tell this both from the undersized service neutral coming in (for a 100A service, normally, the neutral will be the same size as the hots, but Code allows it to be smaller than the hots on a split-phase service for reasons that are explained below), and the fact that they made extensive use of multi-wire branch circuits when wiring your house (I count 5, not including your new dryer circuit).

The reason this all is a problem is because in a 3-wire, split-phase setup, service and multi-wire branch circuit neutrals only carry the difference in current between the two opposite legs of the service or circuit. This is useful, because it lets us save wire, and also downsize service and feeder neutrals if large load imbalances are not expected, as normally, single-phase branch circuits are roughly balanced across phases/legs by the layout of North American loadcenters/panelboards, where no two directly adjacent spaces are on the same phase or leg.

However, if you accidentally connect both legs or phases of such a split-phase service or circuit to the same leg, as whoever wired your house did when they connected the service-entrance conductors to the meter base, not only will you not be able to get 240V out of the circuit or service as you expected, but the current flow in the two hots has only one way to get back to where it came from, and that's the single neutral, which is now carrying twice the current. Since neutrals don't have circuit breakers (they're assumed to be protected because their corresponding hot wires are protected), this leads to the neutral wire slow-cooking itself whenever the circuit is heavily loaded, and eventually your house as well!

This gets worse when you have a service that is wired with an undersized neutral, only meant to handle load imbalances. Now, you have a neutral wire that is already too small for 100A, trying to handle up to 200A of current, before the main breaker in your panel will ever notice anything is wrong!

Fixing this will require your utility to help, so call them NOW!

Since this problem is an issue with the service to your house, you will need your utility to intervene, at minimum to pull the meter so that the service wiring can be safely replaced with something that can handle the situation it's been placed in. Furthermore, while the service-entrance conductors and service disconnecting means in your house technically comply with the letter of NEC 230.42(B) and 230.79(C), the installation as a whole does not comply with the NEC. In particular, using a 120/240V, 3-wire distribution panel with a utility-supplied 120V, 2-wire (Form 1S metered) service is forbidden, as if it were allowed, NEC 710.15(C) would then be superfluous:

(C) Single 120-Volt Supply. Stand-alone systems shall be permitted to supply 120 volts to single-phase, 3-wire, 120/240-volt service equipment or distribution panels where there are no 240-volt outlets and where there are no multiwire branch circuits. In all installations, the sum of the ratings of the power sources shall be less than the rating of the neutral bus in the service equipment. This equipment shall be marked with the following words or equivalent:

                  WARNING:
 SINGLE 120-VOLT SUPPLY. DO NOT CONNECT MULTI‐
            WIRE BRANCH CIRCUITS!

The warning sign(s) or label(s) shall comply with 110.21(B).

As a result of this, I would be seriously asking the utility to get you on a proper 120/240V, 100A, 3-wire (Form 2S metered) service, as that would simplify things greatly, requiring only a new 10/3 run for the dryer circuit (to handle the full load of your dryer) and some handle-ties in the panel (to make it so the MWBCs have common maintenance shutoffs, as required by Code). If your utility refuses to upgrade your service, not only will you need to switch your dryer back to 120V, you will need to have the house rewired to rid it of the multi-wire branch circuits!

|improve this answer|||||
  • 1
    Great answer. I wonder, if the utility refuses to upgrade the service, if it might be cheaper/easier to put a large transformer between the meter and the panel to generate the split phase 240 locally. It'd be an expensive transformer, but possibly not as expensive as a full house rewire. But hopefully the utility will be reasonable and that won't be necessary. – Nate S. Nov 20 '19 at 19:29
  • @NateS-ReinstateMonica -- the problem is that you'd need a 25kVA transformer for that, which'd draw ~200A@240VAC at full load, far too much for the OP's metering hardware. (I seriously doubt that 200A Form 1S meters exist...) – ThreePhaseEel Nov 20 '19 at 23:59
  • I was thinking 12kVA with a 100A breaker in front of it on the 120V, meter-connected side, which would match to what OP is actually getting from the utility. – Nate S. Nov 21 '19 at 0:09
  • @NateS-ReinstateMonica -- then you'd have to have a 50A main in the panel, which is unlikely to be quite enough for the house especially with the dryer taking up a reasonable chunk of the load. – ThreePhaseEel Nov 21 '19 at 0:13
  • Oh agreed, more would be better, but if that's all the utility will give them, then I think having it arranged as 2x50 120V lines would be better than 1x100, since it'll at least let them use that dryer (and not much else at the same time) and they won't have to re-wire all their MWBCs. But provisioning more from the utility would be the best option, if that's available. – Nate S. Nov 21 '19 at 0:29
0

How did you run the 240V? You said 3 wires? If you ran 2 "Hots" and a Ground, the dryer likely needs 120V from line to NEUTRAL to make the control system function. No control system, no drying. You will MEASURE 120V from Line to GROUND, but that is not the same as Line to Neutral because INSIDE of the dryer, there is no (or should not be) any connection from Neutral to Ground, that is only taking place in your service panel (as it should). Such is the danger of measuring line power to ground; it does not tell you what's missing, only what's there.

You needed to run a 4 wire cable to the dryer outlet; 2 Hots, a Neutral and a Ground. In SOME cases, if the wire was run in metal conduit, the conduit can serve as the ground connection rather than having a separate wire. But if the circuit was run with cable only, you need 4 wires.

|improve this answer|||||

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.