High Leg Dryer

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Wire_nutz

Member
I have a new single phase 240 volt electric dryer to replace an existing dryer. The existing dryer receptacle and supply cord is 3-wire without ground. The supply power is 240/120 volt 3-Phase 4-wire High-Leg. This is an existing outlet with with all 3 voltages present, 240/120/208. When the cord was installed on the old existing dryer, the high leg (208volt lead) had to be installed on the terminal block of the dryer that is not connected to the internal electrical parts that operate on 120 volts.

NEC Rules Only,

Question #1: Is it acceptable to hook up the new dryer this way also?

Question #2: Does the new cord and receptacle have to be replaced with 4-wire devices.
 
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lakee911

Senior Member
Location
Columbus, OH
So, the cord plugged in and then there was an additional wire run to the dryer terminal block for 208V only? Are you sure? That sounds odd.:-?

It doesn't matter that 208VAC (with respect to ground) is present because that same connection will be 240VAC with respect to another phase. Provided that the 120VAC equipment has 120VAC and the 240VAC equipment has 240VAC, you are fine. If you study the internal schematic, it should be apparent which lead needs to be connected where.

I don't see why it wouldn't be code compliant and I don't see why you would need to change to 4W if you're not changing anything else.
 
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J

jim dungar

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Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Your system is 240/120 3PH 4W, also called a high leg or center-tapped delta. While the high leg to ground is 208V, it is not proper to mention it when describing your available system voltages as it usually leads to a misunderstanding.

You dryer has internal parts that work off of 120V L-N which is only available from the non-high legs, so you need to hook up the new dryer the way the old one was.
 
W

Wire_nutz

Member
If I had wired the existing outlet I would have used the neutral and the two 240 volt phases to supply the 120/240 volts necessary for the dryer.

My concern is, someone may plug another dryer into the outlet not knowing a high leg is present. Normally dryer receptacles are 120/208 or 120/240.

Is the dryer receptacle code compliant with a HIGH LEG?
 
W

Wire_nutz

Member
jim dungar said:
Your system is 240/120 3PH 4W, also called a high leg or center-tapped delta. While the high leg to ground is 208V, it is not proper to mention it when describing your available system voltages as it usually leads to a misunderstanding.

You dryer has internal parts that work off of 120V L-N which is only available from the non-high legs, so you need to hook up the new dryer the way the old one was.
Click to expand...
If I had wired the existing outlet I would have used the neutral and the two 240 volt phases to supply the 120/240 volts necessary for the dryer.
My concern is, someone may plug another dryer into the outlet not knowing a high leg is present. Normally dryer receptacles are 120/208 or 120/240. Is the dryer receptacle code compliant with a HIGH LEG?
 
W

Wire_nutz

Member
The present voltages are as follows:

L1 ? L2 ?L3 = 240 volts between phases

Neutral to L1 = 120 volt

Neutral to L2 = 120 volt

Neutral to L3 = 208 volt
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
Wire_nutz said:
If I had wired the existing outlet I would have used the neutral and the two 240 volt phases to supply the 120/240 volts necessary for the dryer.

My concern is, someone may plug another dryer into the outlet not knowing a high leg is present. Normally dryer receptacles are 120/208 or 120/240.

Is the dryer receptacle code compliant with a HIGH LEG?
Click to expand...

If you have a single phase dryer, 2 hots and a neutral, then this

Wire_nutz said:
The present voltages are as follows:

L1 ? L2 ?L3 = 240 volts between phases

Neutral to L1 = 120 volt

Neutral to L2 = 120 volt

Neutral to L3 = 208 volt
Click to expand...

is confusing me.:-?
 
W

Wire_nutz

Member
jumper said:
If you have a single phase dryer, 2 hots and a neutral, then this



is confusing me.:-?
Click to expand...
I have a new single phase 120/240 volt dryer. The power distribution panel is 240/120 3-Phase 4-Wire with a High-Leg. The existing dryer receptacle that is installed has a neutral and two hot wires, one being the High-Leg.

L1 to L3 = 240 volts
Neutral to L1 = 120 volts
Neutral to L3 = 208 volts
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
Wire_nutz said:
I have a new single phase 120/240 volt dryer. The power distribution panel is 240/120 3-Phase 4-Wire with a High-Leg. The existing dryer receptacle that is installed has a neutral and two hot wires, one being the High-Leg.

L1 to L3 = 240 volts
Neutral to L1 = 120 volts
Neutral to L3 = 208 volts
Click to expand...

Okay, now that makes sense.

High leg should be L2, but no matter.

I would move the breaker to A and C phase and get rid of the high leg.

You said EMT, is it installed as suitable as being an EGC?
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Wire_nutz said:
If I had wired the existing outlet I would have used the neutral and the two 240 volt phases to supply the 120/240 volts necessary for the dryer.

My concern is, someone may plug another dryer into the outlet not knowing a high leg is present. Normally dryer receptacles are 120/208 or 120/240.

Is the dryer receptacle code compliant with a HIGH LEG?
Click to expand...
This is why labeling equipment is available.:)

If the outlet is the proper configuration for a 240/120 4W system, then yes it is compliant. Your dryer would then be connected to the appropriate plug terminals, and the high-leg one would be left unused.

I would prefer to see the receptacle changed to be a 120/240V configuration, with the high leg "safed off" in the box, but I cannot quote a code section that mandates it.
 
O

ote

Member
Location
NC
IMO, I would try to swap positions of the breaker in the panel to different phases to get rid of the Hi leg to the dryer. I wouldn't think you would have to change to 4-wire because you are reusing the same circuit, not running a new circuit.If you can't change the breaker position, then I you better make sure the 120v controls are not off the hi leg.
 
mxslick

mxslick

Senior Member
Location
SE Idaho
One thing to keep in mind:

How will you KNOW which leg a new dryer's 120v equipment is connected to? I don't think there is an industry standard that all manufacturers follow, so there is a 50% chance you can connect a dryer on the wrong leg and let the smoke out of the motor/timer/drum light (the most common 120v dryer loads).

I second the idea of moving the dryer's breaker so it is off of the high leg..and do it before something gets fried.
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
jim dungar said:
This is why labeling equipment is available.:)

If the outlet is the proper configuration for a 240/120 4W system, then yes it is compliant. Your dryer would then be connected to the appropriate plug terminals, and the high-leg one would be left unused.

I would prefer to see the receptacle changed to be a 120/240V configuration, with the high leg "safed off" in the box, but I cannot quote a code section that mandates it.
Click to expand...

OP does not have a 240/120 3PH 4W circuit, he has 120/208/240 1PH 3W circuit with one hot on B phase.

I think he has to rework the circuit the exception in 250.140 says:

The exception in 250.14 to leave an existing install says

(1) The supply circuit is 120/240-volt, single-phase,
3-wire; or 208Y/120-volt derived from a 3-phase,
4-wire, wye-connected system.
 
W

Wire_nutz

Member
This is an existing installation. The panel board is full except for some of the High-Leg spaces are open.

Multiple other dryer receptacles are wired this way also.

This is a main lug panel board and left to right respectively, the far right lug is the High-Leg.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
jumper said:
OP does not have a 240/120 3PH 4W circuit, he has 120/208/240 1PH 3W circuit with one hot on B phase.
Click to expand...
My bad.:mad:

Actually he has a 240/120 1P 3W circuit with one high leg.
120/208/240 is not an industry, nor ANSI, standard way to describe a circuit.
 
W

Wire_nutz

Member
jim dungar said:
My bad.:mad:

Actually he has a 240/120 1P 3W circuit with one high leg.
120/208/240 is not an industry, nor ANSI, standard way to describe a circuit.
Click to expand...
I did not check the voltage rating of the breakers yet.

I only checked the voltages at the main lugs of the panel board and the neutral bar and at the existing dryer outlets.

I did not check at the transformer or source of supply to the panel board yet.
 
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