Single phase 250V load fed half by single phase 125V source

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Nycedreemz

Nycedreemz

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I just wanted to get a few opinions on a certain setup.

I have had quite a few customers ask for a plug adapter with this setup. A 125V plug to a 250V connector.

( Example ) L5-20P (Single phase 125V line) to L6-20R (Single phase 250V load). Now i know to do this in reverse is a major no no. The person only needs to run half of the 250V load to do what they need to do. I have had plenty order this set up and have been pleased with its performance.

I'm just a little uncertain about how this works due to the supplied equipment needing 250V and someone running half of this on 125V. My whole hangup on this is that 125V line side of this is 1-hot, 1-neutral, and the ground. The 250V is 2-hots and a ground. (I know that most if not all reading this already knew that, just being thorough.)

In my mind, when this setup is connected, one of the hots in the 250V equipment are now connected to the neutral of the 125V source. While the other hot is connected to the 125V hot and of course the ground is to ground on both sides. Like i said before, I have built this and all customers who received this adapter were pleased. I just don't understand electrically exactly what is going on here. Please don't beat me to death for passing along an assembly that i don't have a full understanding of. Im unable to reverse engineer every piece of equipment that i sell an adapter for.

It was explained to me that, say you have a single phase 250V conveyor system that also has a heater for production of some sort. This setup either will run the conveyor of the heater but not both. A better example would be a commercial pizza oven. I just don't have a firm mental grip on how one hot leg of the 250V equipment supplied like this is just ok with becoming the neutral.

I have even had an appliance service tech who was fixing my clothes dryer run half of my dryer on a extension cord to make sure the element was heating and then checked to see if the drum was rotating properly. I asked him how this is and he just said his boss showed him how and that it just WORKS!!!

If anybody can give any real technical feedback on how this operates, I would really appreciate your time and knowledge. :)
 
Nycedreemz said:
I have had quite a few customers ask for a plug adapter with this setup. A 125V plug to a 250V connector.

( Example ) L5-20P (Single phase 125V line) to L6-20R (Single phase 250V load). Now i know to do this in reverse is a major no no. The person only needs to run half of the 250V load to do what they need to do. I have had plenty order this set up and have been pleased with its performance.
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jumper said:
I is confused.
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I is confused to.
 
Many (but certainly not all) switchmode power supplies are equally happy seeing 120vac or 240vac on their input terminals. Those supplies are referred to as auto-ranging; think laptop power supplies. Some VFDs and servo drives are capable of being powered with a lower voltage so as to be programmed and set up, but will not be able to spin a motor on the lower supply voltage. Heating elements don't care about reduced voltage; they will just run cooler.

On the other hand, there are many devices - some power supplies, contactors, relays, etc... - that will be VERY happy running on half voltage, and will quickly become damaged. Without knowing WHAT is connected to your adapter, you have no idea as to the suitability of running from a reduced voltage.

As to how things are connected, an L5-20 (properly wired, of course) supplies one HOT, one NEUTRAL, and one GROUND. 120vac is derived from the H-N connection.

An L6-20 supplies two HOTS, and one GROUND. 240vac (or 208vac, if supplied from two phases of a three phase wye-connected supply) is derived from the H-H connection.

Bottom line is, if your customer's equipment doesn't mind running on reduced voltage, I don't see a problem with your adapter. As you said though, going the other way (being able to supply a lower voltage receptacle from a higher voltage source) is a big no-no.


SceneryDriver
 
As others have said, whether or not this adapter will work as desired is entirely dependent on the equipment being supplied. Using the example of your dryer, the tech was able to test it with a 120V extension cord because residential dryers in the US are supplied by 120/240V, not straight 240V. The drum motor, blower fan and electronic controls (if any) are all 120V loads fed from L1 (typically, although it could be L2) and neutral. These loads are usually identical for gas and electric dryers, and a gas dryer plugs into a regular 120V, 15 amp receptacle.

Typically, the heating elements will be the only 240V load in a residential dryer (there may be exceptions to this, but I'm not aware of any). Since they're just resistance heaters, they can be tested with 120V -- they just won't get as hot as if they were supplied by 240V.

If your customers are using your adapter for this type of situation, it should be fine. If, on the other hand, one of them uses your adapter to supply, say, a 240V motor (maybe for a 240V compressor), I don't see that ending well.
 
jumper said:
I is confused, you built what kind of adapter?

Short and sweet, what voltages to what pin outs?
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Here it is short and sweet Three wire 12 Gu. Adapter

L5-20P, Black (Hot), White (Neutral), Green (Ground) (125Vac max), to an L6-20R With X (Hot), Y (Hot), And G (Ground) (250Vac max)

What I do is take the Hot from the L5-20P and terminate to the X (Hot) blade of the L6-20R, The neutral (white) is then terminated to the Y (2nd Hot), and then the ground (G) is terminated to (G) on both. This is now an adapter that is powering a 250V appliance, equipment etc. with 125V only.

I was just curious about the neutral being tapped on what is normally a hot path on the 250V side of this assembly. I know that this works but, I was just looking for a higher educated breakdown of how the equipment now takes a normally "hot path" and is just fine operating as the "return path" when using this style of adapter.:thumbsup:
 
Nycedreemz said:
I was just curious about the neutral being tapped on what is normally a hot path on the 250V side of this assembly. I know that this works but, I was just looking for a higher educated breakdown of how the equipment now takes a normally "hot path" and is just fine operating as the "return path" when using this style of adapter.:thumbsup:
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The powered equipment, whatever it is, only cares about the difference in potential between its two power wires. The power supply could be floating, with no reference to ground at all and the equipment wouldn't care. I have worked overseas in Hong Kong pretty extensively, and over there, the H-N voltage is 240v. Devices that need two hot phases in this country (the U.S) run just fine on the 240v-to-neutral supplied over there (assuming of course there's no problem with the 50Hz supply frequency). Granted, there are other reasons why some equipment might need a ground reference, but it's a difference in voltage potential that actually powers things.

It might help if you actually tell us what the widget actually is that your customer is trying to power. We can probably give you a better answer then.


SceneryDriver
 
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SceneryDriver said:
The powered equipment, whatever it is, only cares about the difference in potential between its two power wires. The power supply could be floating, with no reference to ground at all and the equipment wouldn't care. I have worked overseas in Hong Kong pretty extensively, and over there, the H-N voltage is 240v. Devices that need two hot phases in this country (the U.S) run just fine on the 240v-to-neutral supplied over there (assuming of course there's no problem with the 50Hz supply frequency). Granted, there are other reasons why some equipment might need a ground reference, but it's a difference in voltage potential that actually powers things.

It might help if you actually tell us what the widget actually is that your customer is trying to power. We can probably give you a better answer then.


SceneryDriver
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Right on, I don't dive any deeper into questioning what my customers are powering with the adapters I assemble. If they give me a breakdown of what they have going on, I do my best to give them the most efficient solution that i know. UL has told me a number of times that, it is the responsibility of the consumer to know what they need for any custom made electrical assembly that is ordered. As long as what i provide does not or does not have the potential to place anybody in harms way. In terms of Voltages, Amperages, Operating frequencies and so on, its the consumers responsibility to make sure that what they order from me will properly operate their equipment.
 
Without knowing what is being supplied, it is pretty hard to tell you what is happening. Apparently there is loads that can accept either input voltage, maybe with or without performance issues. If it is resistive load, applying half voltage yields only a quarter of total wattage output - not half. If there are motors involved and they are directly connected to incoming line voltage, it probably is not going to work very well unless they are oversized for the driven load, or possibly shaded pole motors driving a fan or pump will work - but at a lesser capacity.
 
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