3 phase load calculation

[mike1061]

This is for a 2 story building with a basement, in Chicago. The 1st floor is to be a bakery and the 2nd floor art studio/office. The basement will be storage for the 1st floor.

Did I do a good job?
Thanks
Mike

View attachment load calc 2.txt

 

[david luchini]

Why are you multiplying by 1.732?

 

[augie47]

I see a red flag. You state your voltage is 240 volt, 3 phase 4 wire. That would normally come from a delta system and you would hsve a "high" leg which would be of not use for your 120 volt loads and possibly could not be used on some of your single phase 240 volt loads depending on their having neutral connections.
Is the supply a 240/120 delta or 208Y/120 ??

 

[mike1061]

Why are you multiplying by 1.732?

That is what I thought I was supposed to do.
Thanks For the reply.
Mike

 

[mike1061]

It is 240, Delta, with a high leg.
Thanks for the reply.
Mike

I see a red flag. You state your voltage is 240 volt, 3 phase 4 wire. That would normally come from a delta system and you would hsve a "high" leg which would be of not use for your 120 volt loads and possibly could not be used on some of your single phase 240 volt loads depending on their having neutral connections.
Is the supply a 240/120 delta or 208Y/120 ??

 

[mike1061]

And I fully understand about not using the high leg for 120/240 loads with a neutral wire.
It's the load calculation I don't understand.
Thanks
Mike

I see a red flag. You state your voltage is 240 volt, 3 phase 4 wire. That would normally come from a delta system and you would hsve a "high" leg which would be of not use for your 120 volt loads and possibly could not be used on some of your single phase 240 volt loads depending on their having neutral connections.
Is the supply a 240/120 delta or 208Y/120 ??

 

[augie47]

If you could take full advantage of the 3 phase you would be diving by the 1.732 for a load of approximately 115 amps.
Since you might not be able to use the high leg on some equipment, the safe calculation would be based on 240 volt.
Even then, assuming your math is correct, you are looking at a 200 amp service.

 

[Little Bill]

That is what I thought I was supposed to do.
Thanks For the reply.
Mike

You need to divide by 1.732 instead of multiply.

Or you can multilply the voltage x 1.732 then divide that into your power.
ie; 47468/(240x1.732)

 

[mike1061]

OK, thanks alot. I really appreciate it.
Mike

 

[texie]

OK, thanks alot. I really appreciate it.
Mike

The point, I think, Augie was trying to get you to realize is that you have a high leg in your case that you don't have much load on (none if you don't use the right breakers) it so you can't assume the load is balanced. Thus you can't just divide by 1.732 as this assumes balanced loading. For example, if you had a 208/120Y service, your load would only be about 135 amps. But in your case most (maybe all) will be on 2 phases so your load is closer to 200 amp.

 

[mike1061]

Ok, I see. I didn't realize that was what he meant, but I did get the fact I needed to use 200 amps.
I also changed the multiply to divide.
Thanks
Mike

The point, I think, Augie was trying to get you to realize is that you have a high leg in your case that you don't have much load on (none if you don't use the right breakers) it so you can't assume the load is balanced. Thus you can't just divide by 1.732 as this assumes balanced loading. For example, if you had a 208/120Y service, your load would only be about 135 amps. But in your case most (maybe all) will be on 2 phases so your load is closer to 200 amp.

 

[Smart $]

The point, I think, Augie was trying to get you to realize is that you have a high leg in your case that you don't have much load on (none if you don't use the right breakers) it so you can't assume the load is balanced. Thus you can't just divide by 1.732 as this assumes balanced loading. For example, if you had a 208/120Y service, your load would only be about 135 amps. But in your case most (maybe all) will be on 2 phases so your load is closer to 200 amp.

Ok, I see. I didn't realize that was what he meant, but I did get the fact I needed to use 200 amps.
I also changed the multiply to divide.
Thanks
Mike

I have to wonder why this is even going to be a 3? service?

 

[texie]

I have to wonder why this is even going to be a 3? service?

I had the same thought, especially a 240/120 4 wire at that. 120/240 single phase or 208Y/120 would be much more appropriate. But you know how it goes, there is problably some facts we don't know about.

 

[mike1061]

That's what building has. Most buildings I've run into are 120/240 not 120/208.
It's always bothered me, you see the whole panel with every third space empty.
Isn't that very in-efficiant?
Thanks
Mike

 

[Smart $]

That's what building has. Most buildings I've run into are 120/240 not 120/208.
It's always bothered me, you see the whole panel with every third space empty.
Isn't that very in-efficiant?
Thanks
Mike

So you are replacing an existing service that is 240/120 3? 4W...???

If you are replacing the service, there is no set rule that you have to stick with the same voltage configuration... up until the POCO says that's all they will provide. Have you asked???

If POCO says you're stuck, there's nothing that says you have to maintain 3? after the service disconnect, is there? Many installations of 240/120V 3? 4W systems actually install both a 3? panel (when they actually have 3? loads) and a 1? panel, so every third breaker space isn't empty. In your case, you could simply tap the service disconnect with a 3-wire feeder (L1-A, L2-C, and N) to a 1? panel... unless you are looking at a service entrance MCB panel. Just giving you an option.

 

[mike1061]

OK, I'll call Edison and see what they say about changing to 120/208.

I have done several jobs with 1 or more single phase panels, but it seems to me that it's still in-efficient. Isn't it? I mean all you have done is tap 2 of the service conductors, so things are still not balanced, right? There for, Edison still has to generate electricity for the third leg that nobody uses, right?
Thanks
Mike

 

[Smart $]

OK, I'll call Edison and see what they say about changing to 120/208.

Do you really want 120/208? Is that 208/120V 3? 4W, or 120/208 1? 3W? Why not just 120/240V 1? 3W?

I have done several jobs with 1 or more single phase panels, but it seems to me that it's still in-efficient. Isn't it? I mean all you have done is tap 2 of the service conductors, so things are still not balanced, right? There for, Edison still has to generate electricity for the third leg that nobody uses, right?
Thanks
Mike

Not exactly. When they know what the unbalance is, they assign their phases so as to best balance distribution. They connect single phase services to different distribution phases accordingly all the time. You have to remember this one customer is not the only one connected to the distribution line.

IMO, if you tell the POCO you (or the customer) wants 120/240V 1? 3W, and they say you get 240/120V 3? 4W, you have no obligation to use the high leg.

 

[augie47]

As noted..if you have 240 volt equipment be careful asking for a 208Y/120 service. Some of the equipment you listed may do poorly on 208. If you are building a new service you could most likely eliminate the high leg entirely, but since it is there you might as well use it where you can. One day they may want to add a piece of 3 phase equipment which in some cases is more efficient (motors).
If you do utilize the high leg on single phase loads, watch 240.85 and. as Texie noted, use the right breakers (no slash rated)

 

[mike1061]

The reason for three phase is, that is what's there and they might want to get 3 phase equipment in the future. The first plan was to use 3 phase mixers, but the last one had the 1 phase that I used in the calculation.
From my experiance, people say the 1 phase mixers don't work nearly as well as the 3 phase.

Thanks
Mike