120v/240v Panel

Status
Not open for further replies.
A

adamscb

Senior Member
Location
USA
Occupation
EE
All,

I had a question about a panelboard I saw the other day. It said 120v/240v, and it showed two busses side-by-side with circuit breakers attached. I assume that each of these busses is 120v. How can you get 220v off of this? The 120v is single-phase, and 208v is three-phase, but I've never seen 220v before.
 
adamscb said:
All,

I had a question about a panelboard I saw the other day. It said 120v/240v, and it showed two busses side-by-side with circuit breakers attached. I assume that each of these busses is 120v. How can you get 220v off of this? The 120v is single-phase, and 208v is three-phase, but I've never seen 220v before.
Click to expand...

120/240v is single phase, 3 wire. There are two legs which are 120V to neutral, and 240V between them.
 
adamscb said:
All,

I had a question about a panelboard I saw the other day. It said 120v/240v, and it showed two busses side-by-side with circuit breakers attached. I assume that each of these busses is 120v. How can you get 220v off of this? The 120v is single-phase, and 208v is three-phase, but I've never seen 220v before.
Click to expand...
120/240v 1ph3w is a nominal voltage which also could be 115/230 or even as low as 110/220.
What it can't be 120/220 or 115/240 or 110/230 or 120/230 or 110/240.. The LV will be half of the HV. Since the 120/240 is nominal the voltages could even end up being 118/236.
As a member of this forum I find it interesting that you question the use of a 2p breaker.
 
That makes sense. The reason I ask this, is because I'm designing the receptacle and other low-voltage equipment layout for a room in the plant I work in. I'm thinking that if I design everything for 240v, then I can feed more equipment from the panel, because 240v has less current than 120v. However, I guess the trade-off is that two-pole breakers take up more space in a panel than one-pole breakers. Every choice has its ups and downs.
 
templdl said:
As a member of this forum I find it interesting that you question the use of a 2p breaker.
Click to expand...

Considering I'm just out of school and learning on the job, that was a legit question. I am not questioning the use of anything.
 
adamscb said:
That makes sense. The reason I ask this, is because I'm designing the receptacle and other low-voltage equipment layout for a room in the plant I work in. I'm thinking that if I design everything for 240v, then I can feed more equipment from the panel, because 240v has less current than 120v. However, I guess the trade-off is that two-pole breakers take up more space in a panel than one-pole breakers. Every choice has its ups and downs.
Click to expand...

Your total kVA will be the same if the equipment has the same wattage at 120V or 240V.
 
adamscb said:
Considering I'm just out of school and learning on the job, that was a legit question. I am not questioning the use of anything.
Click to expand...
Thanks for the clarification as somethings we take this knowedge for granted. I have found it helpful to draw a sketch of a panel with a 2p main breaker the feeds 2 vertical bus and either a single grounded neutral bar to the side for a service entrance panel.
The common pant will have 2 rows of breakers orientated horizontally with the line end of each breaker pointed toward the center and the load ends outward. The breakers directly opposite one another will be fed from the same vertical bus with the ones directly above an below the other bus.. Thus ever other breaker will alternate being feed from one or the other bus.
In doing this each single pole breaker that is lcasted above or beli
 
Last edited:
adamscb said:
Considering I'm just out of school and learning on the job, that was a legit question. I am not questioning the use of anything.
Click to expand...

Yes, it was a legit question. You are new at this power business and there is much to learn. More than you can imagine, frankly. In my opinion, you are to be commended for for asking questions like this. Some years down the road you will be the guy with "all the answers" that others will come to. Until then, keep learning and plugging away.
 
Sorry, my post was in complete as well as other errors.

Sorry, my post was in complete as well as other errors.

templdl said:
Thanks for the clarification as somethings we take this knowedge for granted.
Click to expand...
Thanks for the clarification as somethings we take this knowedge for granted. I have found it helpful to draw a sketch of a panel with a 2p main breaker the feeds 2 vertical bus and either a single grounded neutral bar to the side for a service entrance panel.
The common panel will have 2 rows of breakers orientated horizontally with the line end of each breaker pointed toward the center and the load ends outward. The breakers directly opposite one another will be fed from the same vertical bus with the ones directly above an below the other bus.. Thus ever other breaker will alternate being feed from one or the other bus.
In doing this each single pole breaker that is located directly above or below will have a voltage difference of 240v but 120 to neutral.
Should you have 2 pole spaces available right next to one another allowing for you to snap is a 2 pole breaker, that breaker will connect to both vertical busses and providing 240v between the 2 load terminals.
 
adamscb said:
That makes sense. The reason I ask this, is because I'm designing the receptacle and other low-voltage equipment layout for a room in the plant I work in. I'm thinking that if I design everything for 240v, then I can feed more equipment from the panel, because 240v has less current than 120v. However, I guess the trade-off is that two-pole breakers take up more space in a panel than one-pole breakers. Every choice has its ups and downs.
Click to expand...
Whether you wire a receptacle 120V or 240V (not the same type receptacle, BTW) depends on what type of loads you intend to plug into it. Rarely if ever do you have a choice.
 
adamscb said:
That makes sense. The reason I ask this, is because I'm designing the receptacle and other low-voltage equipment layout for a room in the plant I work in. I'm thinking that if I design everything for 240v, then I can feed more equipment from the panel, because 240v has less current than 120v. However, I guess the trade-off is that two-pole breakers take up more space in a panel than one-pole breakers. Every choice has its ups and downs.
Click to expand...

You may need to look at the equipment you intend to run and base decisions off of what it requires.

Not trying to put you down, but why is someone as green as you are the one designing this - or do you have someone to look over your shoulder?
You did do right thing looking for extra help regardless.
 
ggunn said:
Whether you wire a receptacle 120V or 240V (not the same type receptacle, BTW) depends on what type of loads you intend to plug into it. Rarely if ever do you have a choice.
Click to expand...

I understand what you are saying, but with a panelboard (not a receptacle) do I have a choice between 120v or 240v?

kwired said:
You may need to look at the equipment you intend to run and base decisions off of what it requires.

Not trying to put you down, but why is someone as green as you are the one designing this - or do you have someone to look over your shoulder?
You did do right thing looking for extra help regardless.
Click to expand...

There's a senior EE with whom I work with who's double-checking everything.
 
Last edited:
adamscb said:


I understand what you are saying, but with a panelboard (not a receptacle) do I have a choice between 120v or 240v?
Click to expand...
Your load(s) need whatever they are designed for. You need to supply them accordingly. Some loads will have a choice though. Some loads could be something other then 120 or 240.
 
adamscb said:


I understand what you are saying, but with a panelboard (not a receptacle) do I have a choice between 120v or 240v?
Click to expand...

Of course. A single pole breaker gives you 120V hot to neutral and a double pole breaker gives you 240V hot to hot.
 
templdl said:
As a member of this forum I find it interesting that you question the use of a 2p breaker.
Click to expand...

I do very little residential work. Using a 2P breaker is considered 208V single-phase, not 240V. 240V sounds weird to me.
 
adamscb said:
That makes sense. The reason I ask this, is because I'm designing the receptacle and other low-voltage equipment layout for a room in the plant I work in. I'm thinking that if I design everything for 240v, then I can feed more equipment from the panel, because 240v has less current than 120v. However, I guess the trade-off is that two-pole breakers take up more space in a panel than one-pole breakers. Every choice has its ups and downs.
Click to expand...

You can't really feed more equipment but you can use less wire in doing so, because two poles on the different phases can share a neutral. It's called a multi-wire branch circuit and you can search the code for definitions and rules related to it.

It's really important that the two poles come from the separate busbars in the panel or else you can overload the neutral wire. A normal panelboard is arranged so that a full-sized 2-pole breaker connects one pole to each busbar. In some older panelboards it's possible to install them wrong, most newer panelboards its not so easy.

Don't confuse tandem breakers with proper 2-pole breakers, they are not the same thing.
 
Status
Not open for further replies.
Top