Hi,

I’m planning on installing a 240v, 30A circuit in my garage. I’ll be pulling (3) 10AWG wires in 3/4” conduit, about 30’ with 3-4 90’s along the way. I’m fairly comfortable with this sort of work. I wired my backyard, which included running conduit, pulling wire (smaller gauge), installing circuits, basically the same thing but for 110.

I was wondering if there’s anything different about installing a 240 circuit besides the wire and breaker size? Or if it’s all the same steps?
thanks

 

Not really except 240vac has 2 120 vac hot wires with respect to neutral. Whether you terminate the 240 vac in a sub panel or outlet, pull a forth wire for tying the main panel ground to the sub panel or outlet.

 

Let's see; no white wires, 2 pole breakers, no GFCI or AFCI (usually) for straight 240V installs.

 

Fundamentally, installing 240 volt circuits is the same as installing 120 volt circuits.

You just have to use components and wires intended for or compatible with 240 volts.

Household and commercial wire is generally rated for 250 volts or 600 volts. You only need to look out for the rarely encountered 150 volt wiring.

Receptacles and plugs are specially shaped (slot and prong arrangements) for 120 volts or 240 volts and also amperage. You need to get the proper kind for each branch circuit.

Many 240 volt branch circuits and most 240 volt feeds to subpanels are actually for both 120 volts and 240 volts. Here you have the two hots, usually red and black, plus ground and a white neutral.

Running to a separate building, if you need both 120 volts and 240 volts, you must have only one feed, with the two hots, neutral, and ground.

Most 240 volt appliances, tools, heaters, etc. consume more than half the amperes of the maximum amperes rated branch circuit to which they may be safely connected. So it is rare for a 240 volt branch circuit to have more than one receptacle or outlet.

Occasionally a black/white (2 conductor) Romex cable will be used for 240 volt only circuits, both conductors being hot.For Romex with more conductors or for individual conductors such as THWN, white may not be a hot conductor in either 120 volt or 240 volt circuits.

The same piece of wire will carry the same number of amperes at either 120 or 240 volts.

For very long runs, tolerable voltage drop is evaluated using percent as opposed to number of volts. So the formulas are different for 240 volt circuits versus 120 volt circuits. It will be found that a long run at 240 volts can carry twice the amperes as at 120 volts (but not allowed to violate the rule for short runs such as 20 amps for 12 gauge, 30 amps for 10 gauge etc.). So at 240 volts you can get up to 4 times the watts at the far end compared with at 120 volts.

 

Thanks for all of the responses. I should have said that I’m installing this for a new electric water heater. It will be hard wired to the circuit. Does that change anything? Do I need to have a switch in the middle so that there’s a disconnect? Something like the attached picture? Or can I just run the wires to a junction box and then run a short run of flex down to the water heater from there?

Here’s what I’m getting from the responses:

• There’s an extra hot wire, so all together I’ll have: two hot wires, a ground, and a neutral. I’m a visual person, so I looked up a wire diagram (attached). Makes sense.
  
• 2 pole breaker - does it need to be 2 pole? I have a 30A spare in my panel, but I dont believe it’s a 2 pole (see attached pic). And I dont know if poles and phases are related? But I only require single phase.
  
• Any pro/cons of using romex vs 4 single wires? Seems like it would be easier to get a 10/3 romex and just pull that through
  

Thanks!

 

You have a few issues there. A water heater does not need neutral. So, no 3rd white wire. 10/2 romex with ground is fine. The disconnect needs to be 240V 30A. that is not what you have pictured. Fuses not required at the disconnect.

If romex, mark the white conductor with a red sharpie for a couple inches of exposure at each end of the run.

No romex in the conduit. Internal wires should be THHN. RED/BLACK/GREEN would be great.

What is the rated wattage of the new water heater?

 

You're showing a single pole 30A breaker. That would need to be changed to a 2P30A breaker.
As mentioned you only need three conductor..... two hots and a ground.
You can use a basic HVAC disconnect as the splice point by the water heater.
The 60A non fused is a good choice from depot.
They also offer a 30A switch that is even better.

 

Thanks guys.
it's 5000 watts
Do I need to have a disconnect installed? (is it required?) the directions call for a "suitable disconnecting means". Could this be the breaker?
Why don't water heaters need a neutral?
is a "overcurrent protective device" another way of saying circuit breaker?

 

A basic all electric water heater has two terminals to connect to the power supply.

A few water heaters are 120 volt only. These require one hot and neutral. These are usually small in size.

Most are 240 volt only and you connect the two hot wires from the 240 volt branch circuit to those two terminals.

A few modern electric water heaters have a third terminal for neutral because they have 120 volt control circuitry in addition to the 240 volt heating circuitry inside.

Plus a screw in the framework or on the outer shell to attach the ground wire.

An overcurrent protective device can be a fuse or a circuit breaker. There are a few other things it could be but I am not familiar with any of those.

 

A service disconnect is required for servicing a hard wired appliance. If your electrical panel is within sight of the water heater..... no disconnect is required.

Fuses or a circuit breaker is overcurrent protection.

Most electric water heaters have two 4800w heating elements. An upper element and a lower element. Only one runs at a time. Top one first and then the bottom one.

 

Are there exceptions to the disconnect rule for hardwired appliances?
For instance: 120v disposers, dishwashers, 240v wall ovens, ranges, etc?
Also, do circuit breaker lockout devices full fill that function?

 

The cords on many appliances are the disconnect. A hardwired dishwasher should have a breaker lock or a local disconnect switch.

I have never seen the oven require a disconnect besides the breaker.

 

Almost always, a Romex cable is harder to pull and takes up more space in a conduit compared with the same number of separate (e.g. THHN) conductors of the same sizes.

There is a maximum amount of cross sectional space that may be occupied by the wires and/or cables in a conduit.

There is additional "de-rating" for the allowable number of amperes in Romex cables inside conduit due to the extra layers of "material" in a Romex cable and the ability to dissipate heat naturally generated by the passage of current. I don't have the formulas handy now.

For simplicity, some experts and some building codes say no Romex in cables.

 

The NEC specifically allows NM in conduit, and in some instances like where subject to physical damage it is required.

No additional derating factors in conduit.

 

Thanks for all the responses. got it installed last weekend and everything seems good.