Electrician Talk banner
1 - 20 of 29 Posts

·
Registered
Joined
·
67 Posts
Discussion Starter · #1 ·
What does it mean when a device has this on it? Does that mean it will accept either of the two voltages?

I understand that hot to hot is the higher of the two and neutral to hot is the lower?

Also can one clarify if 120/208 means commercial writing and 120/240 means resi?

My jm decides to skip out on theory when "teaching".
 

·
Salty Member
Joined
·
31,081 Posts
You are asking some great questions and we could fill pages about it.

Lets start with this.



Notice that a motor for a supply voltage of 120 will have a name plate of 115, a 480 supply gets a 460 tagged motor.


Next thing I will mention is pay attention to detail.

In general something marked 208-230 will operate on any voltage in between. On the other hand if its was marked 208/240 it could run on either of those voltages but there will likely be different connections to make in order to select which voltage.

Others will add to your questions. :)
 

·
RIP 1959-2015
Joined
·
39,618 Posts
What does it mean when a device has this on it? Does that mean it will accept either of the two voltages?

I understand that hot to hot is the higher of the two and neutral to hot is the lower?

Also can one clarify if 120/208 means commercial writing and 120/240 means resi?

My jm decides to skip out on theory when "teaching".
120/208 is usually 3 phase.in commercial buildings.

120/240 is usually single phase in residential .

480/277 is also 3 phase in a commercial building.
 

·
Registered
Joined
·
67 Posts
Discussion Starter · #4 ·
You are asking some great questions and we could fill pages about it.

Lets start with this.



Notice that a motor for a supply voltage of 120 will have a name plate of 115, a 480 supply gets a 460 tagged motor.


Next thing I will mention is pay attention to detail.

In general something marked 208-230 will operate on any voltage in between. On the other hand if its was marked 208/240 it could run on either of those voltages but there will likely be different connections to make in order to select which voltage.

Others will add to your questions. :)
I have to say i wish your attitude on explanations were where i worked. thanks bbq for the encouragement on asking questions.
 

·
Registered
Joined
·
5,537 Posts
Just FYI, OFFICIALLY there is a convention on the order in which the numbers are presented that technically helps, although unfortunately most people don't realize this and trow them around willy nilly.

If the larger voltage is listed first, it is a 3 phase Wye service. So it would be 208Y120 or 208/120; 480Y277 or 480/277.

If the smaller voltage is listed first, it is a split-phase service, meaning a transformer winding is center tapped and grounded to derive 1/2 of the phase to phase voltage. So for residential service, it is called 120/240.

So technically, we should not call 3 phase 208 Wye "120/208V", it is supposed to be called "208Y120V" to help avoid confusion. But like I said, hardly anyone knows this and we generally know what we are talking about anyway.

The only time that becomes more important is when talking about 240V 3 phase services. There is a 3 phase 240V delta service that is occasionally offered, where one winding is center tapped as well, like a single phase service transformer. So it is called 120/240 3 phase 4 wire. Phase-to Phase it is always 240V, Phase to Neutral on the tapped winding is 120V, usually the A-C winding. So A-B, B-C and C-A are all 240V, A-N = 120V, C-N = 120V, B-N is not a valid voltage reference (it's floating) but typically measures out as 208V, so it is called "High Leg" delta.
 

·
Registered
Joined
·
67 Posts
Discussion Starter · #8 ·
Now what would be the purpose in wiring a light at 208 instead of 120? I know the amps drawn would chance as explained by my understanding of ohms law, but performance wise what difference would it make if any? I would imagine it could provide faster (motor) or brighter (lighting) capabilities?
 

·
Registered
Joined
·
1,447 Posts
Just FYI, OFFICIALLY there is a convention on the order in which the numbers are presented that technically helps, although unfortunately most people don't realize this and trow them around willy nilly.

If the larger voltage is listed first, it is a 3 phase Wye service. So it would be 208Y120 or 208/120; 480Y277 or 480/277.

If the smaller voltage is listed first, it is a split-phase service, meaning a transformer winding is center tapped and grounded to derive 1/2 of the phase to phase voltage. So for residential service, it is called 120/240.

So technically, we should not call 3 phase 208 Wye "120/208V", it is supposed to be called "208Y120V" to help avoid confusion. But like I said, hardly anyone knows this and we generally know what we are talking about anyway.
I didn't know about that thanks!
 

·
Registered
Joined
·
4,664 Posts
120/208 is usually 3 phase.in commercial buildings.

120/240 is usually single phase in residential .

480/277 is also 3 phase in a commercial building.
And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. The main service is three phase with each apartment unit being tapped off of two of the phases (and the neutral of course) with the panels connected to balance the use of the phases as much as possible.

Most residential clothes dryers are rated for 120/240 volt and work on 208Y/120 but they do take longer to dry the clothes.
 

·
Registered
Joined
·
12,167 Posts
Just FYI, OFFICIALLY there is a convention on the order in which the numbers are presented that technically helps, although unfortunately most people don't realize this and trow them around willy nilly.

If the larger voltage is listed first, it is a 3 phase Wye service. So it would be 208Y120 or 208/120; 480Y277 or 480/277.

If the smaller voltage is listed first, it is a split-phase service, meaning a transformer winding is center tapped and grounded to derive 1/2 of the phase to phase voltage. So for residential service, it is called 120/240.

So technically, we should not call 3 phase 208 Wye "120/208V", it is supposed to be called "208Y120V" to help avoid confusion. But like I said, hardly anyone knows this and we generally know what we are talking about anyway.

The only time that becomes more important is when talking about 240V 3 phase services. There is a 3 phase 240V delta service that is occasionally offered, where one winding is center tapped as well, like a single phase service transformer. So it is called 120/240 3 phase 4 wire. Phase-to Phase it is always 240V, Phase to Neutral on the tapped winding is 120V, usually the A-C winding. So A-B, B-C and C-A are all 240V, A-N = 120V, C-N = 120V, C-N is not a valid voltage reference (it's floating) but typically measures out as 208V, so it is called "High Leg" delta.
In the case where a 208Y120 transformer feeds two ungrounded and one grounded conductor to multiple services, how would you correctly write the voltage that feeds the single-phase panel?
 

·
Registered
Joined
·
1,447 Posts
And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. The main service is three phase with each apartment unit being tapped off of two of the phases (and the neutral of course) with the panels connected to balance the use of the phases as much as possible.

Most residential clothes dryers are rated for 120/240 volt and work on 208Y/120 but they do take longer to dry the clothes.
I have worked in many apartment building like that. They seem to bring it in for 3ph motor loads.
 

·
Registered
Joined
·
7,881 Posts
Also can one clarify if 120/208 means commercial writing and 120/240 means resi? .
Simple explanation:

120/208 3 phase is a more modern system called Wye. It has 120V to ground on all 3 legs and 208 volts between any of them.


120/240 3 phase is an older system called Delta. It has 2 legs @ 120V to ground and one leg @ 208 V to ground with 240 between any of the hot legs.

Ask someone else how this works :laughing: I'm just a mechanic.

And, 120/240 single phase is 120V to ground on both legs and 240 between them.


Generally speaking, most resi has a single phase system and most commercial has a 3 phase system.

Large commercial buildings will have 277/480 3 phase systems coming in. That has 277V to ground and 480 between legs. AC and mechanical loads will be 480V. It allows smaller wires to operate larger loads. Lighting will be 277Volts, one hot, one neutral. Same principal here, more lights on a circuit.

In the equipment rooms there will be transformers to take the 480 down to 120/208 to feed separate panels for the receptacle and incandescent lighting loads.
 

·
Salty Member
Joined
·
31,081 Posts
And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. .
It is here too, Harry just did not mention it.

We also have entire residental neighborhoods with 208 volt services.
 

·
Banned
Joined
·
16,967 Posts
And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. The main service is three phase with each apartment unit being tapped off of two of the phases (and the neutral of course) with the panels connected to balance the use of the phases as much as possible.

Most residential clothes dryers are rated for 120/240 volt and work on 208Y/120 but they do take longer to dry the clothes.
I can't believe you left out your dissertation about SCE's distribution system. :rolleyes:
 

·
Registered
Joined
·
781 Posts
mxslick said:
And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. The main service is three phase with each apartment unit being tapped off of two of the phases (and the neutral of course) with the panels connected to balance the use of the phases as much as possible.

Most residential clothes dryers are rated for 120/240 volt and work on 208Y/120 but they do take longer to dry the clothes.
We do a lot of assisted living complexes and senior residences, we had one older gentlemen complain to us (not knowing that he had a 120/208 service) that he was only getting 208 volts at his range, an then told us it was due to "poor craftsmanship" Man that was good for a laugh haha
 

·
Registered
Joined
·
11,762 Posts
Just FYI, OFFICIALLY there is a convention on the order in which the numbers are presented that technically helps, although unfortunately most people don't realize this and trow them around willy nilly.

If the larger voltage is listed first, it is a 3 phase Wye service. So it would be 208Y120 or 208/120; 480Y277 or 480/277.

If the smaller voltage is listed first, it is a split-phase service, meaning a transformer winding is center tapped and grounded to derive 1/2 of the phase to phase voltage. So for residential service, it is called 120/240.

So technically, we should not call 3 phase 208 Wye "120/208V", it is supposed to be called "208Y120V" to help avoid confusion. But like I said, hardly anyone knows this and we generally know what we are talking about anyway.

The only time that becomes more important is when talking about 240V 3 phase services. There is a 3 phase 240V delta service that is occasionally offered, where one winding is center tapped as well, like a single phase service transformer. So it is called 120/240 3 phase 4 wire. Phase-to Phase it is always 240V, Phase to Neutral on the tapped winding is 120V, usually the A-C winding. So A-B, B-C and C-A are all 240V, A-N = 120V, C-N = 120V, B-N is not a valid voltage reference (it's floating) but typically measures out as 208V, so it is called "High Leg" delta.
Regarding the order of the numbering Ive always listed the smaller voltage first, it makes more sense for me.
 
1 - 20 of 29 Posts
Top