unused 208V leg on commercial bldg.

[iwire]

Larry are you not the guy that would rather drop a sub panel in every other room but you want to nickle and dime a service? :grin:

Just kidding around.


For my own personal pleasure I would have to install a 3 phase panel when there is a three phase service, I could not sleep to do otherwise.

Let me ask you this.

A 200 amp service panel was destroyed by water damage but the rest of the service is fine.

If you knew the service calcs required no more then 100 amps but the existing service drop, meter and conductors were rated for 200 amps would you save a few bucks and install a 100 amp panel or would you provide a 200 amp panel so the customer has as much capacity as the service conductors will allow?

Well replacing a 3 phase panel with a single phase panel reduces the capacity by one third.

 

[micromind]

I'd put the 3 phase board in. I'd also let the owner know why I'm spending slightly more money now, opposed to potentially alot more later.

To me, a good part of being a true electrician, rather than just a guy trying to get through another day, is to give the customer the best possible installation I can. This includes forseeing reasonable additions and modifications to the property. If I communicate all this to the owner, I stand a very good chance of being chosen for additional work.

 

[mwysinger]

The way the service is set up now is this: There is a very large cabinet with the fused disconnect in it with a trough connected to the side with the feeders in it. As of now, there are only taps made to the feeders in the trough, and the previous elect. only used single phase in to a 120/240 panel. There were, however, several conduits coming from the trough to other remote disconnects for old package a/c's, which have long since been removed. The high leg feeder is still in the trough, but it is not used at present. All I wanted to do was to repull the feeders from the disco. to the trough, as the old 4/0's look like they were hit with a grinder, and there is bare copper showing through in a couple of places, and install a replacement 200A MB panel inside. He is currently using a 100A main lug panel only, so his only protection is a 300A disconnect, which also has a broken door latch. How 'bout them apples?!:-?

 

[peter d]

Well replacing a 3 phase panel with a single phase panel reduces the capacity by one third.

That's not quite correct. It would reduce the available KVA by a factor of 1.732.

Let's take a 200 amp 3 phase service.

200A * 208 V * 1.732 = 72,051 VA

Now convert it to single phase:

200 A * 208 V = 41,600 VA

Or 30,451 VA less at single phase. That's a reduction of almost half the capacity at 3 phase, actually 42.3% less.



Let's look at another example at 480 volts.

200 A * 480 V * 1.732 = 166,272 VA

Single phase:

200 A * 480 V = 96,000 VA.

Or 70,272 VA less, again a reduction of 42.3 %.


Or, to put it another way, a single phase service will give you 57.7% of a 3-phase service at the same amperage.

 

[Rich Elec.]

There's no need to remove the fuse. In fact, I doubt you could do that because there's more than likely some 2-pole breakers that utilize that 'high leg" of the system. Removing the fuse would disconnect on phase of the power to those circuits.

Could I have an example of a 2-pole load that would utilize one 120 volt leg, and one 208 "high leg."

Thanks.
Rich.

 

[JohnJ0906]

You still get 240v between any 2 legs of the 3. The "high leg" is 208 to ground/neutral, but ANY 2 of the 3 legs is 240v.

 

[480sparky]

Could I have an example of a 2-pole load that would utilize one 120 volt leg, and one 208 "high leg."

Thanks.
Rich.

What John said... he beat me to it.

 

[LarryFine]

Could I have an example of a 2-pole load that would utilize one 120 volt leg, and one 208 "high leg."

Sure: any 240v, line-to-line load that does not require a neutral: appliances, motors, transformers, etc.

You can use any two lines of a high-leg system as long as the high-leg conductor is marked orange anywhere it's accessible.

 

[LarryFine]

If you knew the service calcs required no more then 100 amps but the existing service drop, meter and conductors were rated for 200 amps would you save a few bucks and install a 100 amp panel or would you provide a 200 amp panel so the customer has as much capacity as the service conductors will allow?

I would indeed install 200a equipment.

However, as I said earlier, this is a new installation I did, and I installed a 200a 1-ph panel and a 125a 3-ph panel. The total cost was still less, and each panel is utilized in the way it was designed.

In fact, in the delicatessen we did about 3 years ago, there was also an existing open-Delta service, 400a, with mast-mounted CT's, feeding two 3-p fused disco's, a 200a and a 125a, via a trough.

We used the 200a to supply a 200a 1-ph MB panel, omitting the high-leg fuse, and the 125a to supply a 125a 3-ph panel. The smaller panel, a 12-space, supplies the two 3-ph RTU's and three 2-p 240v loads.

The whole idea was to use the existing disco's and everything ahead of them, avoiding having to even open the trough. I saved a bit of money for the customer, because the original plans called for a new 208Y/120v transformer bank.

Well replacing a 3 phase panel with a single phase panel reduces the capacity by one third.

Not if there are no loads that utilize the high leg. All it does is provide a panel with one third of the spaces unusable. The OP mentions that the trough already has several taps supplying unused disco's.

In my opinion, he can simply use these if and when it becomes necessary to provide 3-ph power. I'd hate to waste a 3-ph panel just in case someone adds a 3-ph load later on.

Two panels (1-ph 200a and 3-ph 125a) can cost less than one (3-ph 200a), especially when there is little or no need for the third line.

 

[iwire]

Or, to put it another way, a single phase service will give you 57.7% of a 3-phase service at the same amperage.

Thank you Mister Spock. :grin:

You do realize that 57.7% is darn close to to 66.6% or two thirds?

 

[iwire]

I Not if there are no loads that utilize the high leg. All it does is provide a panel with one third of the spaces unusable.

No Larry that is incorrect.

The panel will have less capacity regardless of what is currently in use or not, but I give you points for putting spin on it that would make a politician proud. :grin:

Again, if the service has 3 phases it is short sighted to only install a single phase panel.

 

[sawdust454]

[QUOTE= The guy who wants the work done is a car salesman/preacher,

To me this means no work without a large deposit,
Be careful

 

[LarryFine]

No Larry that is incorrect.

The panel will have less capacity regardless of what is currently in use or not, but I give you points for putting spin on it that would make a politician proud. :grin:

Again, if the service has 3 phases it is short sighted to only install a single phase panel.

Okay, no arguement that this one panel would have less overall capacity as a 1-ph panel over a 3-ph one. However, I have not suggested that 3-phase power be abandoned completely, just that it's a waste for this panel with no 3-phase loads.

 

[mwysinger]

I do see your point about going ahead and installing a 3 phase panel now, but the size I would need would be cost prohibitive over a single phase now and a small 3 phase later, as suggested by another reply. I also understand about trying to balance the load over three phases, but I really feel that for now, the customer would best be served by installing a singel phase inside and saving the high leg for future use, or even for when he has his six package a/c's put in, and then going with a sub-panel.
Thanks for all the great feedback. I have learned a lot in the few days I have been looking on this forum for ideas. You guys are really a big help.

 

[iwire]

and saving the high leg for future use, or even for when he has his six package a/c's put in, and then going with a sub-panel.

So you know more load is coming but you still want to go with less capacity today.

To each their own, I call that nickle and diming.

 

[danickstr]

the posibility of even one ac unit going in would justify the three-phase panel. Savings from 3-phase A/c is often hundreds per month, at entry levels (3ton).

Plus you have resale value increase, and the threat of 3-phase power to keep handyman hands out of the panel. Or they can melt appliances like a GC did on a panel I had installed, since every third space was conveniently available:grin:

 

[LarryFine]

So you know more load is coming but you still want to go with less capacity today.

To each their own, I call that nickle and diming.

I would install separate panels for the 1-ph and 3-ph loads even if I was going to install them both now. Does that change the discussion any?

the posibility of even one ac unit going in would justify the three-phase panel. Savings from 3-phase A/c is often hundreds per month, at entry levels (3ton).

Are you saying that 3-ph costs less per KwH? Or that 3-ph requires less Kw per HP?

Plus you have resale value increase, and the threat of 3-phase power to keep handyman hands out of the panel. Or they can melt appliances like a GC did on a panel I had installed, since every third space was conveniently available:grin:

That's among the reasons to install separate 1-ph and 3-ph panels.

 

[mwysinger]

So you know more load is coming but you still want to go with less capacity today.

To each their own, I call that nickle and diming.

I guess I finally smelled the proverbial coffee and see your point. I will price a 3-phase panel and pitch it to the customer. I do still like the idea of two panels, even if I install them now, though. Will price and consider. Thanks again.:smile:

 

[LarryFine]

Will price and consider.

Don't forget to include the difference in having and not having to open the trough in your comparison. :wink:

 

[peter d]

Thank you Mister Spock. :grin:

You do realize that 57.7% is darn close to to 66.6% or two thirds?

Close, but still not technically correct.