The Siren Board

I'd rather bump this topic than start a new one, but I'm still confused on a few phase things.

1. This one is more of a clarification, but a 3 phase siren can run off 1, 2, or 3 transformers, given that they are able to produce power, right? And are pretty much all single phase siren setups run off of 1 transformer?

Well, it depends on the transformer. They make single transformers that are actually three transformers in one can. The majority of three phase power is derived from connecting 2 or 3 single phase transformers in Wye or Delta.

2. In terms of wires going into the siren, how many are needed to provide power for a 3 phase siren and a single phase siren?

Well, it depends on the service. You have three phase 3 wire (no ground), 3 phase 4 wire (3 hots & a neutral), and three phase corner ground, which has two insulated wires and the third phase is carried in the bare messenger. Keep in mind that the neutral is usually brought in through the messenger wire, so for a 3 phase 4 wire service you will have three insulated wires in the service drop and the neutral connection will be made on the bare messenger.

Single phase comes in 120 only (one wire and messenger), 240 only (no neutral), and 240/120 (2 wires and a neutral messenger)

3. Since my area is filled with Tempests, are T-128 and T-135s offered in both single and 3 phase varieties or they all 3 phase? Same question with 2001s as well. The ones around are seen with both one transformer and 2 transformers. Also, I believe all P-50s are 3 phase as well, am I right?

All DC sirens are single phase. They can run off a three phase service since two legs of three phase 208/230 is single phase. Most of the time they just tie back the unused leg when they replace a three phase siren with a DC. All P-50s are three phase, no exceptions.

4. I thought that in order to have 480V, you would need 3 transformers, however, I'm seeing this P-50 run off of 2 transformers, yet have a very fast windup. What am I missing here?

You can have 480 three phase from two transformers via an open delta transformer bank connected for 480. Delta banks tend to run at a higher voltage than wye banks (I've seen 490 volts on a 480 delta before). That explains the rapid windup. Delta is awesome, it makes sirens run like a bat out of hell.

So when you just use two out of three phase legs for single phase, do you have to have a neutral between the two or do you just use the two legs?

I'll leave the other ones to people more knowledgeable than me, but will address this one:

3. Since my area is filled with Tempests, are T-128 and T-135s offered in both single and 3 phase varieties or they all 3 phase? Same question with 2001s as well. The ones around are seen with both one transformer and 2 transformers.

Single-phase. Phase doesn't matter to the sirens themselves; the motors are all DC. If it has batteries, then the siren runs off of the batteries during operation and a set of AC trickle-chargers replenishes them afterward. In the case of an AC-only 2001, a single phase of AC mains is stepped down and rectified to 48 volts DC and sent to the motors.

Andys Live WX wrote:So when you just use two out of three phase legs for single phase, do you have to have a neutral between the two or do you just use the two legs?

Depends on if you need 120 instead of 208 or 230. Whelens use only 120 volts to charge the batteries, and the same can be said for some DC only mechanical sirens. If it has a rectifier it needs 208-230.

I always bring a neutral into my disconnects and out the weatherhead, even if I don't use it for 120. Reason being the neutral provides a ground path back to the power source. Back when 3 phase 3 wire services were still common you wouldn't know a phase had went to ground until another phase grounded out also, creating a phase to phase short and tripping the breaker or blowing the fuses. A motor or other electrical component could be grounded and still operating fine, until you touched it and got zapped.

Andys Live WX wrote:So when you just use two out of three phase legs for single phase, do you have to have a neutral between the two or do you just use the two legs?

If you need the higher voltage, you connect between phases.

208VAC systems: Phase-neutral is 120VAC, phase-phase is 208.
480VAC systems: Phase-neutral is 277VAC, phase-phase is 480.

the stuff coming into your house is different; it's split-single-phase. Phase-neutral is 120VAC, phase-phase' is 240VAC. Appliances like dryers and ranges need the neutral wire because the controls typically run off of 120, while the heater elements get 240.

Only exception is 480 4-wire delta and 230 4 wire delta. 480 delta will give you 240 L - N on two legs, and 315 L - N on one leg. 230 4 wire delta will give you 120 L - N on two legs, and between 190-240 L - N on one leg. On both systems the leg with the high voltage L - N is known as the high leg, and is a really good way to find out if an electrician actually knows what he's doing.

If not, enjoy watching your appliances spew smoke and your toaster shoot bread through the celing on 208.

On both systems the leg with the high voltage L - N is known as the high leg, and is a really good way to find out if an electrician actually knows what he's doing.

I assume "lack of hair and eyebrows" is a good way to tell if he doesn't know what he's doing?

Or if he goes by the nickname "sparky" or "flash".