The Siren Board

FSThunderboltfan1000 wrote:Yes look at the power poles by the siren. If there are three transformers then it is regular 3-phaes if there are only one or two it is 3-phase delta.

Ok thanks! I think it is 3-phase delta.

Ok glad I could help.

Yes there are many different types of three phase. You have:

Delta
Wye
Open (or high leg) delta
Center tapped delta (includes a neutral for single phase loads)
Corner ground delta (one phase is grounded)

And then there are several different voltages that can be provided between phases (208, 240, 480, 600 [Canada], 2,400, 4,160 [the prior two being common to large industrial facilities, with voltages over that level considered distribution level voltages at utility level])

And you will need to look at the transformer wiring configuration to tell what configuration it's on, both on the primary and secondary side.

FSThunderboltfan1000 wrote:Yes look at the power poles by the siren. If there are three transformers then it is regular 3-phaes if there are only one or two it is 3-phase open delta.

If there are three transformers on the pole, it could be wye (most common) or delta. You can only tell by looking at the secondary connection on the transformers. Two transformer are are always open delta on the distribution side.

Im a Siren Addict3 wrote:

JasonC wrote:Now the question is what type of 3-phase?

There's different types of 3 phase?

Even though a few others have beaten me to the punch, I'll go ahead and post my bit as well since I already had it typed up but got distracted.

Yes there are several types of three phase, or rather there are different configurations for the transformer bank and resulting voltages for a three phase service anyway. I'm 99% sure this siren is on what's called an "open delta" service, with two transformers (usually one smaller than the other) feeding 240V to the siren, since this seems to be what pretty much all of Drumright's three phase sirens are fed from. This open delta transformer bank is usually used for smaller three phase loads, especially when there are only two overhead primary lines available to use. In addition, this is also one of two transformer arrangements that give you the infamous "high/wild leg", where one of the three power legs has a higher line-to-ground reading than the other two. In example, you will typically read around 120V line-to-ground for both A and B phases, and C phase will read somewhere in the neighborhood of 208V line-to-ground. This same principle of the wild leg also applies to what's called a "closed delta" system, which utilizes three transformers instead of two, but in the same general setup as an open delta (basically, think of this as being used for larger loads requiring 230-240V instead of 208V, or 480V instead of 460V). Last but not least is the wye system, where you have three transformers bonded together to create either 208V or 460V three phase power. As is the case with the closed delta system, this configuration is only available where there are three primary overhead lines to tap into for the transformers, and is generally used for large power services to warehouses, mills, farms, and a lot of other small industrial facilities, especially when they require higher voltage (460V).

If anyone would like to correct any mistakes I might have made or would like to elaborate further for the fun of it, please feel free to do so!

Don't forget the siren motor could be different 3 phase 3 phase Wye wound motor 9 leads dual voltage 240/480 most common or it could be Delta wound motor 6 leads dual voltage older 2t22 I have seen have this.


And then there is the listening test at single phase 2T22 sounds a lot different than a 3 phase one

murrfarms wrote:

Im a Siren Addict3 wrote:

JasonC wrote:Now the question is what type of 3-phase?

There's different types of 3 phase?

Even though a few others have beaten me to the punch, I'll go ahead and post my bit as well since I already had it typed up but got distracted.

Yes there are several types of three phase, or rather there are different configurations for the transformer bank and resulting voltages for a three phase service anyway. I'm 99% sure this siren is on what's called an "open delta" service, with two transformers (usually one smaller than the other) feeding 240V to the siren, since this seems to be what pretty much all of Drumright's three phase sirens are fed from. This open delta transformer bank is usually used for smaller three phase loads, especially when there are only two overhead primary lines available to use. In addition, this is also one of two transformer arrangements that give you the infamous "high/wild leg", where one of the three power legs has a higher line-to-ground reading than the other two. In example, you will typically read around 120V line-to-ground for both A and B phases, and C phase will read somewhere in the neighborhood of 208V line-to-ground. This same principle of the wild leg also applies to what's called a "closed delta" system, which utilizes three transformers instead of two, but in the same general setup as an open delta (basically, think of this as being used for larger loads requiring 230-240V instead of 208V, or 480V instead of 460V). Last but not least is the wye system, where you have three transformers bonded together to create either 208V or 460V three phase power. As is the case with the closed delta system, this configuration is only available where there are three primary overhead lines to tap into for the transformers, and is generally used for large power services to warehouses, mills, farms, and a lot of other small industrial facilities, especially when they require higher voltage (460V).

If anyone would like to correct any mistakes I might have made or would like to elaborate further for the fun of it, please feel free to do so!

I know we have 2 2t22A's on 240 and one on 480. What's the benefit of 480 over 240?

Smaller conductor sizing and less voltage drop. No real benefits for a single motor that size although larger commercial/industrial customers will almost always want 480v for local distribution.

So does the open Delta principle work the same for a portable diesel generator in the 10 to 20kv range? Just curious...

No, generators are either closed delta or wye.

480 is nice, until you buy a 600 volt disconnect.

IMO the cadillac of three phase is a closed delta. Perfect phase angles and higher voltage will make sirens scream. Usually a 240 delta setup will run between 240-255 volts phase to phase, and 480 delta will be around 490-500 volts.

480 wye is fine, but 208 wye sucks. Everything runs slower and hotter.

The corner grounded delta (widowmaker) is being phased out (no pun intended) but they are still quite prevalent on remote three phase installations. They have only two insulated wires in the service drop, with the bare messenger carrying the third phase which is bonded to ground at the transformer tank. Since that particular phase is referenced to ground, it will read 0 volts phase to ground, but show either 240 or 480 phase to phase. Just because it's a "grounded" phase doesn't mean it's not dangerous. If you grab it you will get lit up since you are at a different ground potential than the transformer tank. It's also known as the ghost leg or phantom leg.

There is also an open wye-wye connection, but it's not very common. Most 2 pot banks are connected wye-delta or delta-delta.

Also it is possible to have three phase power with just one transformer. They aren't very common but they are out there. You can spot them easy since they usually have three insulators on top of the tank.

If you know how to "read" the secondary side connections on the transformers it's easy to differentiate between a closed delta or wye setup. Wye banks have all the neutrals tied together, whereas a delta bank will only have 1 neutral coming off 1 transformer. If it doesn't have any neutral taps it's a 3 wire delta setup (usually 480). If it has a bare wire coming off a power leg on the transformer with a bonding jumper attached to that bushing it's a corner ground.

Another tidbit, if you look at an open delta often times they will have a big transformer and little transformer. The big transformer supplies two phases and is often center tapped for single phase loads, so it's bigger. The little transformer (kicker or lighting pot) only has to supply one phase and it's always the high leg. This how you can feed several houses and a three phase load with a two pot bank. The big pot delivers the single phase load to the houses, while the little pot and the big pot supply three phases to a three phase load. The houses will never see the high leg since they aren't connected to the "kicker".

One last thing, NEC requires that the high leg always be on B phase and flagged orange for 240 or purple for 480. However, most electrical meters will not read properly if they have the wild leg on B phase. So a standard practice is to place the wild leg on C phase, then move it to B phase on the disconnect or panel board.

Here is a three phase, 4 wire delta meter base before I wired it up. The orange wire would go on C phase, with the black wire on A phase, and the blue wire on B phase. The white wire is the neutral.



Here is an open delta bank feeding a Thunderbolt in Holliday, TX




Notice how they only have two overhead phases on the primary side? That's the beauty of an open delta. You can get three phases out of the secondary side by connecting two transformers to two primary phases and referencing the neutral.