I'm installing the wiring for a septic system on a commercial complex and am curious about some things on the print.

There are six pumps and two blowers in this system. Why would this system use three phase when all the pumps and motors are single-phase?

The main disconnect is showing three-phase and single-phase, but with only one neutral. Is this correct?

Thanks
Dave

Tiger:

Two possibilities come to mind:

One, the mfg. makes a system with larger pumps which require 3 phase power, but uses the same controller with smaller single phase systems.

Two, it is an attempt to provide a balanced load to the system's supply at least as far as the pumps are concerned.

As for the disconnect, perhaps the motors are all 208-240v and can operate phase-to-phase and the control system itself requires 120 volts. (Thus the single neutral.) Again, seems to be a move to avoid multiple inventory on disconnects.

Do you have a link to the mfg.?

Just looking at your question from another continent:

The idea of a 3-phase system is that with a balanced load on the 3 phases current on the (always) one and only neutral is going to zero.

3 phase (120°) is sort of an actual standard service in some parts of Europe even for the smallest apartment.

But if there is no three phase consumer in the installation you will be free to switch to single phase or balance it between two 180° single phases or whatever you want.

So where does the guy come from who did the wiring scheme?

Hi Dave,
It would seem that the designer wants the pumps and blowers connected in a Star (Wye) topography, hence the Neutral.
The Neutral in this configuration will only carry the Out of Balance current.
Which if done like this will be in the order of a few Amperes, if that.

The link for this manufacturer is www.aquarobicinternational.com

The unit I'm wiring is the one with two fiberglass tanks and a constructed wetland.

The motors are single-phase 240 volt, and the controls are 120 volt.

Dave

This is just my 2 cents but when you do your work or your bid make sure about your wiring methods. In some applications you might need a Class I Div. 1 wiring.

Good point Caper. We needed seal offs on the raceways feeding the lift pumps down in the honey pot.

Good point. I think I'm looking at three options here.

The manufacturer provides a pvc box inside the tanks with terminal strips. The pumps have power cords with plugs. If I can get manufacturer's instructions to cut the plugs and use their pvc box that may be a good option,

Explosionproof outlets, or

run the cords outside the tanks to std. exterior outlets.

Thanks
Dave

Found this on the bottom of the linked page:


So it seems that all units in the 15k-85k gals. cap. range will use the same std. panel, and perhaps if the unit Dave's installing is near the bottom end of that range the pumps will be single phase, but the input power requirement will be three phase as Trumpy noted.

I would guess that the larger unit's pumps would be three phase.

May I just simply ask (still looking from Europe) how one provides
3 phase, 230/460 volt, 60 Hz., 3 hot wires plus a neutral and a ground.
with additional 115V for the alarming?

A small link to a wiring scheme of the transformer would be sufficient to imagine what strange things you're doing over there.

Thanks Wolfgang

Wolfgang, we do things a little diffeent here.

Our "220" volt circuits are created by using two 110 legs that are 'out of time' with each other; this contrasts to your use of a 220 leg with a neutral wire.

In our 208 three phase set-ups, we have three legs that are each only 120 to ground, plus a neutral. The 120 circuits are simply drawing from just one leg.

Where the actual three phase power measures out at 240, the individual legs will likely measure out as 120, 120, and 208 volts respectively. In that case, you must be vcareful as to which leg you take your 120 from!

@ renosteinke:
Thanks for the answer. I have already seen those schemes with transformers tapped in the midst of one leg. So I have no problem with the details given for the small installation in this thread, assuming the 2 hot wires are at 180° of a single phase transformer (or single leg):


but I wondered how does one provide 460V, 230 V and 115 V at the same time out of one transformer in three phases:

As all voltages are linked here by factor 2 and not 1.73, what is three phase here? Or is a second transformer involved?
Thnaks for your patience.

The "230, 460" portion will be 230 or 460 volt. The motors come with 9 leads, and the windings can be connected either in series or in parallel.

The "115" portion could be taken from the same transformer for the 230 volt system, however the "460" volt version would require the control voltage to be taken from another source.
I don't understand why they would want a "neutral" to be run with the 460 volt system, as this would provide 277 volt power.

The actual 3Ø system voltages are nominally rated as:
120/208 Wye
120/240 Delta
277/480 Wye
and although they are becoming less common, there are still some 240 and 480 delta systems out there that provide no "neutral" at all.

Now I got it, thanks a lot. Doesn't sound very "harmonized" yet.

The designer made an error on the plan. L1 and L2 are 230-volt single-phase, and L3 is 115-volt single phase. There is no 3-phase circuit. In two emails the guy still hasn't told me the amperage requirements for the two circuits.

This is like receiving a machine arrive in 15 parts with no installation instructions other than a print with who-knows-how-many errors in it.

I think this guy enjoys travel with all expenses paid by the customer.

Dave

I got some cut sheets for the pumps today, so maybe I'm being impatient. I'm still trying to find out if it's OK for the 230-volt pumps to run at 250-volts, or if I need to drop the voltage with a transformer.

Dave

Tiger, NEMA standards typically allow for + or - 10% of the rated voltage for motors. So running "230" motors on 250 volts actual should be fine.