Is this imbalance kosher?

[Wilber100]

Hi,

I'm new to the forum and am registered as a consumer. I am a Metrologist and I have used this forum as a source of knowledge for years now. I love it. I couldn't find the answer to my specific issue this time, so here I am. Please excuse my limited understanding of the NEC and the basics of a three phase power system.

So, a customer sends in a plating power pack for calibration which is really no more than a 100 A / 20 Vdc power supply with a timer. I look at the unit and the first thing I see is a 30 A, 3 phase, 4 prong, twist lock plug on it. We don't have that service in our building so I can't calibrate it. I started to wonder, why the heck would a PS like this need 3 phase? I look a little closer and make a gruesome discovery. The owner of the PS has wired the plug so that only one phase is being used. The device is truly a 480 V single phase PS. He is apparently plugging this into a 3 phase service, but using ony one leg. I don't know if the power service the customer has is wye or delta or if it even matters.

My concerns are potential problems with creating an imbalane in the electrical service, if there are any code issues with this, or any other issues.


Thanks to anyone who can expound on this.

 

[charlie b]

I am sure you hear the question all the time, so I will answer it for you, and for the benefit of our membership.

• A ?meteorologist? deals with the science of weather.
• A ?metrologist? deals with the science of measurement.

In answer to your observations,

• The utility?s supply being wye or delta does not matter.
• If a building has a 3-phase service, and if someone turns on a light or plugs in a computer, that load will appear on only one phase, and will create an imbalance between the three phases. But the load is insignificantly small, and the overall distribution of loads on the three phases will give a generally balanced condition.

The load imbalance that you are describing will not be a concern. That said, the fact that someone is modifying power supply components in ways that the manufacturer did not intend can certainly create a safety concern. But it is not a code issue, in that the code does not deal with manufactured equipment.

 

[Wilber100]

Thanks Charlie.
You are right. I can't tell if it's going to rain or not, but if you need something measured, I'm youre guy.

So I have one more question.
To accomodate a wider range of customer workload, i.e. various line voltage (actually phase) requirements, I would like your opinion.
Would I have a 480/3 phase drop installed with a 3 phase receptacle, and do what this customer has done (wire the plug with only one leg) when I have an instrument that is single phase, or have a 3 phase AND a single phase receptacle installed?

 

[charlie b]

I think that having the utility install two services, one that is single phase and the other that is three phase, is likely to be overkill for your business. But I could not be certain, without doing a more in depth review of your building and of the available utility options. However, I think there is an easier, and cheaper, alternative. I think you can purchase an electronic power conversion device that takes single phase power as an input and gives you three phase power as an output. This is outside my area of expertise, so perhaps someone else can offer some information. For example, I do not know whether this is something that you could simply plug into a wall receptacle, or whether you would need an electrician to install the system.

 

[xformer]

Sounds Like a job for a Rotary phase converter...

 

[Besoeker]

Hi,

I'm new to the forum and am registered as a consumer. I am a Metrologist and I have used this forum as a source of knowledge for years now. I love it. I couldn't find the answer to my specific issue this time, so here I am. Please excuse my limited understanding of the NEC and the basics of a three phase power system.

So, a customer sends in a plating power pack for calibration which is really no more than a 100 A / 20 Vdc power supply with a timer. I look at the unit and the first thing I see is a 30 A, 3 phase, 4 prong, twist lock plug on it. We don't have that service in our building so I can't calibrate it. I started to wonder, why the heck would a PS like this need 3 phase? I look a little closer and make a gruesome discovery. The owner of the PS has wired the plug so that only one phase is being used. The device is truly a 480 V single phase PS. He is apparently plugging this into a 3 phase service, but using ony one leg. I don't know if the power service the customer has is wye or delta or if it even matters.

My concerns are potential problems with creating an imbalane in the electrical service, if there are any code issues with this, or any other issues.


Thanks to anyone who can expound on this.

A few points in no particular order...
I'm a Brit and I can't comment on your code issues.
The DC output is 2kW. I don't think such a load on just one phase would ordinarily be a problem.
If the power supply has a rectifier as the input then the ripple on the DC is hugely different between single phase and three phase.

Single phase:



Three phase:



It has significant implications for component ratings....

 

[jim dungar]

The owner of the PS has wired the plug so that only one phase is being used. The device is truly a 480 V single phase PS.

If the device is "truly a ... single phase" unit, then there is no need to be discussing three phase at all.

The only question is: can you use 2 hot legs from a 4-wire plug?

 

[xformer]

IMHO... This would be allowed as long as the voltage rating and the ampere rating of the Cap and Receptacle were not exceeded... And as long as 210.24 was not violated.

 

[sparkyrick]

If the device is "truly a ... single phase" unit, then there is no need to be discussing three phase at all.

The only question is: can you use 2 hot legs from a 4-wire plug?

I see this all the time. Shops will install 3P4W receptacles through their shop, then install 3P4W plugs on single phase equipment.

 

[Besoeker]

The only question is: can you use 2 hot legs from a 4-wire plug?

That ignores the question of whether the unit was designed to operate on single phase.

 

[jim dungar]

That ignores the question of whether the unit was designed to operate on single phase.

Go ahead call the OP a liar.
You really should learn to read all of a post.

The device is truly a 480 V single phase PS.

 

[Besoeker]

I am sure you hear the question all the time, so I will answer it for you, and for the benefit of our membership.
A ?meteorologist? deals with the science of weather.
A ?metrologist? deals with the science of measurement.

The implicit assumption is just a tad patronising don't you think?

 

[Besoeker]

Go ahead call the OP a liar.
You really should learn to read all of a post.

OK. I missed that.
Humble apologies.
And I didn't call anyone a liar.
Perhaps you can reciprocate by apologising for that incorrect assertion.