I can't seem to get a accurate answer on what the difference is. For example:Today I opened a 250v plug it had three power feeders but no neutral. I ran 277v for my lights which carry a neutral. 220v for a dryer which had two 110v power feeders w/no neutral and my water heater has 208, what do I run for that? My problem is that i have done this for 2 years and for my first year i was terrified to ask questions, which held me back. If you can help please do so. As you see I am very confused on the differences.
difference between voltage. (ex: 208/220/240/277)
- Thread starter geoff1
- Start date
- Status
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Here are common types of voltages.
120/240 single phase
120/208 three phase
120/240 three phase
277/480 three phase
In my list, the first number (in blue) is the voltage from hot to neutral.
The second number (red) is the voltage from hot - to - hot on the different phases.
Some loads use all three phases, and no neutral. Some use a hot and a neutral, it depends on the load.
120/240 single phase
120/208 three phase
120/240 three phase
277/480 three phase
In my list, the first number (in blue) is the voltage from hot to neutral.
The second number (red) is the voltage from hot - to - hot on the different phases.
Some loads use all three phases, and no neutral. Some use a hot and a neutral, it depends on the load.
JohnJ0906
Senior Member
- Location
- Baltimore, MD
Geoff, don't be afraid to ask questions. How else can you learn? This site is a great resourse. Also, you can go to the public library and see what books they have-I did this a lot when I was new to the trade.
ibew441dc
Senior Member
geoff11
George gave you a good list of common electrical systems, and I'm sure there still just as confusing
It sounds like your still very new to the trade . The beginning years can be very exciting but also very confusing. Don't get discouraged though your in a great place on this forum. Your sure to learn something here .
It will take time to fully grasp the fundamentals, I would recommend trade school, apprenticeship, self study and this forum.
Mike Holt offers many valuable tools to get you started.
welcome to the forum
ibew441dc
George gave you a good list of common electrical systems, and I'm sure there still just as confusing
It sounds like your still very new to the trade . The beginning years can be very exciting but also very confusing. Don't get discouraged though your in a great place on this forum. Your sure to learn something here
.It will take time to fully grasp the fundamentals, I would recommend trade school, apprenticeship, self study and this forum.
Mike Holt offers many valuable tools to get you started.
welcome to the forum
ibew441dc
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
georgestolz said:
- Location
- New Jersey
- Occupation
- Journeyman Electrician
geoff1 said:
There isn't a one size fits all answer. For example in a dwelling you may have 30 amp/240 volt circuit for a hot water heater which will not have a neutral in the circuit. But the 30 amp/240 volt electric dryer circuit would have a neutral connection since the dryer light would operate on 120 volts.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Stepping away from commercial for a moment (where an engineer generally makes all the decisions) to residential (where the electrician frequently makes the decisions), here's how the decision-making process tends to work on that level.
A homeowner wants a hot tub in their backyard. They walk in, three days after you've started roughing the house and tell you. You send them to the hot-tub vendor to pick a model. They do and despite all odds, return with the specs on the model they want.
They should know the appliance they want first. Then, we can wire accordingly.
This hot tub requires 120/240V single phase, and the nameplate calls for a 30 amp circuit. When it calls for "120/240V" that means that inside the appliance, it uses both line-to-neutral and line-to-line loads, or it would simply say "240V" or "120V". Typically, the lights and stuff inside will use 120V, while the heating elements will use 240V.
We look at the voltage that will be serving the house - 120/240 single phase, and know that we can pull two hot conductors, a neutral, (and an equipment grounding conductor) and give the appliance the voltage it needs.
Then we can turn our attention to the amps involved, which determine our size of wire. Distance also affects our decision here - long distances typically need a size or two bigger.
So, when an engineer starts the process of designing the electrical for a much bigger building, it probably follows the same general idea. There is an appliance which must be chosen according to the voltages available on the site, and then the wire size is chosen based on nameplate ratings and distance.
A homeowner wants a hot tub in their backyard. They walk in, three days after you've started roughing the house and tell you. You send them to the hot-tub vendor to pick a model. They do and despite all odds, return with the specs on the model they want.
They should know the appliance they want first. Then, we can wire accordingly.
This hot tub requires 120/240V single phase, and the nameplate calls for a 30 amp circuit. When it calls for "120/240V" that means that inside the appliance, it uses both line-to-neutral and line-to-line loads, or it would simply say "240V" or "120V". Typically, the lights and stuff inside will use 120V, while the heating elements will use 240V.
We look at the voltage that will be serving the house - 120/240 single phase, and know that we can pull two hot conductors, a neutral, (and an equipment grounding conductor) and give the appliance the voltage it needs.
Then we can turn our attention to the amps involved, which determine our size of wire. Distance also affects our decision here - long distances typically need a size or two bigger.
So, when an engineer starts the process of designing the electrical for a much bigger building, it probably follows the same general idea. There is an appliance which must be chosen according to the voltages available on the site, and then the wire size is chosen based on nameplate ratings and distance.
NoVA Comms Power
Senior Member
- Location
- Alexandria, VA
Another decent source of easy-to-understand info -- especially for receptacles -- is at the Cooper Wiring devices site.geoff1 said:
http://64.239.63.88/catalog/
Scroll down to "Technical References" and then "Wiring Diagrams"
The diagrams there clearly illustrate the voltage relationships between the conductors as well as the physical layout of the connectors themselves.
Last edited:
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
That is true. We generally don?t get to the detail of sizing branch circuit conductors until the second half of the project. That is when we will work with the mechanical and plumbing engineers to find out what size components (vent fans, condensing units, circulating water pumps, etc.) they are planning to install. Often, we will have to call the vendors, or look for on-line information, in order to pin down the manufacturer?s recommended overcurrent protection and branch circuit sizing. This is the point at which we need to verify that the mechanical engineers are not specifying equipment that requires a voltage that will not be present in the building.georgestolz said:
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
The voltage itself, e.g. 250, 277, 220, 240, 208, etc. is inconsequential because it is possible to derive any voltage you want, simply by utilizing the proper transformation (transformer). The transformer connection will dictate whether a neutral is available for use from the system. The way voltage is stated becomes very important, 120/208Y is single phase, three wire , open wye service, where 208Y/120v is a three phase, 4 wire service. Also, 120/240V is a single phase, three wire system, where 240/120V is a three phase, high leg delta system. Refer to Jim Dungar's post.
A word of caution, there are so many people that incorrectly state voltages that it is necessary to determine the number of phases and wires. If not explicitly stated or obvious, then you better ask.
For a full listing of standard USA voltages refer to ANSI/IEEE C84.1.
A word of caution, there are so many people that incorrectly state voltages that it is necessary to determine the number of phases and wires. If not explicitly stated or obvious, then you better ask.
For a full listing of standard USA voltages refer to ANSI/IEEE C84.1.
I think the answer has been covered thoroughly but I still feel the compulsion to add "my 2 cents".
A single phase load can be connected to 2 ungrounded phase conductors or to an ungrounded phase wire and a neutral. . Does the load ?know? the difference ? . The load only ?knows? the voltage. . If the load runs at 120volts, if you supply it with 120v with 2 ungrounded phase conductors or supply it with one ungrounded phase wire and a neutral, it?ll work either way.
Compare these:
120/208v wye supply
single phase 120v load
You connect to one of the ungrounded phase conductors and to the grounded neutral center point of the wye and run your load at 120v.
120/240v center tapped delta supply
single phase 120v load
You connect to one of the ungrounded phase conductors and to the grounded neutral center tap of one of the delta transformer coils and run your load at 120v.
120/240v center tapped single phase (usually residential)
single phase 120v load
You connect to one of the ungrounded phase conductors and to the grounded neutral center tap of the single transformer coil and run your load at 120v.
120v 3phase corner grounded delta supply (I?ve never actually seen one of these)
single phase 120v load
You connect to one of the ungrounded phase conductors and to the grounded phase conductor and run your load at 120v.
Four different supply configurations all can supply the same 120v single phase and all have proper grounding. . The load doesn?t ?know? which supply its hooked up to. . If you give it the proper voltage and ground one of the current carrying conductors, if the manufacturer wants that, or use 2 ungrounded phases if the manufacturer wants that, then a single phase load doesn?t ?know? or care what the transformer configuration is.
As far as the 125volt and 250volt markings go. . That?s not the required supply voltage. . It?s the maximum rated voltage. . 125volt equipment used to be supplied by 110volts if you go back about 100 years. . 125volt equipment used to be supplied by 115volts if you go back about 50 years. . 125volt equipment is supplied by 120volts today. . You can usually figure out how old a persons teacher is by listening when they talk about general use plug voltage. . If they say 120v, then their teacher is young. . If they say 115v, then their teacher is old. . If they say 110v, then their teacher is ancient.
There is no transformer configuration preference for single phase loads. . But you can get the 120v out of a number of common sources. . Use a residential 120/240v single phase transformer supply, use a 120/208v 3phase wye transformer supply, use a 120/240v 3phase center tapped delta transformer supply. . Match the voltage and the grounding requirements and determine if the transformer can handle the load, and if the supply conductors are rated for the increased current.
David
geoff1 said:
A single phase load can be connected to 2 ungrounded phase conductors or to an ungrounded phase wire and a neutral. . Does the load ?know? the difference ? . The load only ?knows? the voltage. . If the load runs at 120volts, if you supply it with 120v with 2 ungrounded phase conductors or supply it with one ungrounded phase wire and a neutral, it?ll work either way.
Compare these:
120/208v wye supply
single phase 120v load
You connect to one of the ungrounded phase conductors and to the grounded neutral center point of the wye and run your load at 120v.
120/240v center tapped delta supply
single phase 120v load
You connect to one of the ungrounded phase conductors and to the grounded neutral center tap of one of the delta transformer coils and run your load at 120v.
120/240v center tapped single phase (usually residential)
single phase 120v load
You connect to one of the ungrounded phase conductors and to the grounded neutral center tap of the single transformer coil and run your load at 120v.
120v 3phase corner grounded delta supply (I?ve never actually seen one of these)
single phase 120v load
You connect to one of the ungrounded phase conductors and to the grounded phase conductor and run your load at 120v.
Four different supply configurations all can supply the same 120v single phase and all have proper grounding. . The load doesn?t ?know? which supply its hooked up to. . If you give it the proper voltage and ground one of the current carrying conductors, if the manufacturer wants that, or use 2 ungrounded phases if the manufacturer wants that, then a single phase load doesn?t ?know? or care what the transformer configuration is.
As far as the 125volt and 250volt markings go. . That?s not the required supply voltage. . It?s the maximum rated voltage. . 125volt equipment used to be supplied by 110volts if you go back about 100 years. . 125volt equipment used to be supplied by 115volts if you go back about 50 years. . 125volt equipment is supplied by 120volts today. . You can usually figure out how old a persons teacher is by listening when they talk about general use plug voltage. . If they say 120v, then their teacher is young. . If they say 115v, then their teacher is old. . If they say 110v, then their teacher is ancient.
There is no transformer configuration preference for single phase loads. . But you can get the 120v out of a number of common sources. . Use a residential 120/240v single phase transformer supply, use a 120/208v 3phase wye transformer supply, use a 120/240v 3phase center tapped delta transformer supply. . Match the voltage and the grounding requirements and determine if the transformer can handle the load, and if the supply conductors are rated for the increased current.
David
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